Borders' Dictionary of Health Physics

Mach number
Ratio of gas to acoustic velocity; indicator of compressibility.
(AM-1993)

Macrophage
Large phagocytes; specifically, histiocytes.
(HPJ 60)

Macrophyte
Plants that can be seen with the unaided eye.
(NCRP 76)

Macroscopic cross section
Cross section per unit volume of a given material for a specified process.
(IEC 50-393-1993)

Macrosomatic
Having the sense of smell strongly are acutely developed.
(ICRP 49)

Magnet
The laminated steel structure of an accelerator in which the magnetic flux circulates.
(NBS 55)

Magnetic bottle
A magnetic field used to confine or contain a plasma in controlled fusion (thermonuclear) experiments. (See controlled thermonuclear reaction, plasma.)
(USAEC-1974)

Magnetic dipole
A current flowing in an infinitesimally small loop. When the current is oscillating, the dipole becomes an elementary radiating magnetic dipole.
(NCRP 67)

Magnetic dipole strength
A vector, the magnitude of which is equal to the product of the current flowing in a loop and the area of the current loop, and whose direction is perpendicular to the plane of the loop and obeys the righthand rule. Magnetic dipole moment is expressed in units of ampere square meter (A m²).
(NCRP 67)

Magnetic field strength
A field vector, H, that is equal to the product of the magnetic fluxz density and the reciprocal of the permeability. Magnetic filed strength is expressed in units of ampere per meter (A/m).
(NCRP 67)

Magnetic flux density
A vector field quantity, B, that results in a force, F, that acts on a moving charge or charges. When B is vector multiplied by velocity, v, at which an infinitesimal unit test charge, q, is moving, the result is the force which acts on the test charge divided by q.

(NCRP 67)

Magnetic mirror
A magnetic field used in controlled fusion experiments to reflect charged particles back into the central region of a magnetic bottle. (See controlled thermonuclear reaction.)
(USAEC-1974)

Magnetic Resonance Imaging (MRI)
An imaging technique based on the magnetic properties of biological molecules. These images provide detailed anatomical views for diagnostic purposes.
(NCRP 125)

Magnetic susceptibility
The ratio of the magnetization at a point in a medium to the magnetic field strength at that point.
(NCRP 67)

Magnetization (magnetic polarization)
The difference between the magnetic flux density in a medium and the magnetic flux density in a vacuum for the same magnetic field strength, all divided by the permeability of vacuum. Magnetization is expressed in units of ampere per meter (A/m).
(NCRP 67)

Magnification
Enlargement of the visual image recorded on an x-ray receptor by means of the divergence of x rays from a small source.
(NCRP 66)

Magnification imaging
An imaging procedure carried out with magnification usually produced by purposeful introduction of distance between the subject and the image receptor.
(NCRP 102)

Main
A duct or pipe connecting two or more branches to the exhauster or air-cleaning equipment.
(ANSI Z9.2-1971)

Maintenance bypass
Approved action or a device which renders inoperable one or more parts of safety system for the purpose of maintenance, test, or repair.
(IEC 50-393-1993)

Major decommissioning activity
For a nuclear power reactor facility, any activity that results in permanent removal of major radioactive components, permanently modifies the structure of the containment, or results in dismantling components for shipment containing greater than class C waste in accordance with Sec. 61.55 of this chapter.
(10CFR50.2)

Major radioactive components
For a nuclear power reactor facility, the reactor vessel and internals, steam generators, pressurizers, large bore reactor coolant system piping, and other large components that are radioactive to a comparable degree.
(10CFR50.2)

Make-up air
Outside air supplied to the building.
(ANSI Z9.2-1971)

Man-rem
See person-rem.
(BEIR III)

Man-rems
See person-rems.
(BEIR I)

Management
Storage, packaging, or treatment of radioactive waste.
(10CFR110.2)

Management
The chief executive officer or that person's delegate or delegates.
(10CFR35.2)

Manhattan project
The War Department program during World War II that produced the first atomic bombs. The term originated in the code-name, "Manhattan Engineer District", which was used to conceal the nature of the secret work underway. The Atomic Energy Commission, a civilian agency, succeeded the military unit Jan. 1, 1947.
(USAEC-1974)

Manipulator
A hand-operated or hand-controlled device for remotely handling an object in an environment which is too hazardous to permit direct access.
(ANSI N1.1-1976)

Manipulators
Mechanical devices used for safe handling of radioactive materials. Frequently they are remotely operated from behind a protective shield. (See hot cell.)
(USAEC-1974)

Manometer
A device used to measure pressure differences
(AM-1993)

Manufacturer
Any person engaged in the business of manufacturing, assembling or importing x-ray equipment.
(ANSI N537-1976)

Manufacturer certified instrument
An instrument that has been certified and warranted by the manufacturer as meeting the requirements of this standard.
(ANSI N42.17A-1989)

Manufacturer certified instrument
An instrument that has been certified and warranted by the manufacturer as meeting the requirements of this standard.
(ANSI N42.17C-1989)

Manufacturing license
A license pursuant to Appendix M of part 52 of this chapter to manufacture a nuclear power reactor(s) to be operated at sites not identified in the license application.
(10CFR170.3)

Manufacturing run
A normal quantity of any item built on a single job order. This is also referred to as an economic quantity.
(ANSI N42.17A-1989)

Marginal zone
This zone is recognizable soon after the formation of the ventricular one; it is a cell-sparse layer composed of the outer most cytoplasmic parts of the ventricular cells. It contains no primary cell type of its own and the nuclei of the ventricular cells do not enter it.
(ICRP 49)

Marine insurer
The marine insurer or underwriter provides financial protection to the shipper or carrier for nonnuclear events that involve the vessel and cargo. Coverage is available for property damage and loss as well as liability. Policies written by the marine insurer typically have a nuclear exclusion clause.
(ANSI N14.24-1985)

Marine surveyor
The marine surveyor often acts on behalf of the marine insurer and performs a number of functions related to the safety of the vessel and cargo. These functions involve not only determining suitability of the barge and towing vessel for the cargo being carried but also include evaluating numerous operations for the loading, carriage, and unloading of the cargo. The surveyor plays a key role, marine terminal operator. In major ports, there are numerous terminals for the loading and unloading of commodities. Such terminals are generally operated by private concerns, although the ownership may be public or private. Marine terminals are frequently operationally specific, such as break-bulk cargo or containerized cargo. Some terminals are designated facilities of particular hazard for hazardous material handling purposes.
(ANSI N14.24-1985)

Martin's diameter
Length of the horizontal line bisecting particle cross section into equal areas
(AM-1993)

Mass
The quantity of matter in a body. Often used as a synonym for weight, which, strictly speaking, is the force exerted by a body under the influence of gravity. (See atomic mass unit, atomic weight.)
(USAEC-1974)

Mass
The material equivalent of energy - different from weight in that it neither increases nor decreases with gravitational force.
Critical Mass - The minimum mass of fissile material which can be made critical with a specified geometrical arrangement and material composition.
Relativistic mass - The increased mass associated with a particle when its velocity is increased. The increase in mass becomes appreciable only at velocities approaching the velocity of light, 3 x 10¹⁰ cm/sec.
(RHH)

Mass (equivalent) diameter
Diameter of a sphere composed of the particle bulk material with no voids that has the same mass as the particle in question
(AM-1993)

Mass (or volume) contamination
Contamination that is found throughout the mass (or volume) of the material or property, e.g., radioactive activation products produced within a material by irradiation.
(10CFR834.2)

Mass attenuation coefficient
The mass attenuation coefficient, µ/r, of a material for uncharged ionizing particles is the quotient of dN/N by rdl, where dN/N is the fraction of particles that experience interactions in traversing a distance dl in a material of density r,

Unit: m² kg^-1.
µ is called the total linear attenuation coefficient. For neutrons, µ is sometimes given the symbol S, and is called the macroscopic cross section. The mass attenuation coefficient is the product of s and N_A/M, where N_A is the Avogadro Constant, and M is the molar mass of the target element,

(ICRU 44)

Mass attenuation coefficient
The mass attenuation coefficient, µ/r, of a material for indirectly ionizing particles of specified energy is the quotient of dN/N by rdl, where dN/N is the fraction of particles that experience interactions while traversing a distance dl in a medium of density r.

According to this definition the number N(x) of neutrons which have not undergone an interaction after traveling a distance x is:

where N(0) is the number of neutrons at x = 0. The inverse of m is the mean free path of the neutrons in the material.
The quantity µ is frequently called the macroscopic cross section of the material with regard to neutrons of the specified energy; sometimes the symbol S is used instead of µ.
(ICRU 26)

Mass attenuation coefficient (µ/r)
For a material and for uncharged ionizing particles, quotient of total linear attenuation coefficient µ by density r.

(IEC 50-393-1993)

Mass attenuation coefficient (µ/r)
The mass attenuation coefficient of a material for uncharged ionizing particles is the quotient dN/N by rdl, where dN/N is the fraction of particles that experience interactions in transversing a distance dl in a material of density r.

(ICRU 33)

Mass attenuation coefficient (µ/r)
The mass attenuation coefficient of a material for indirectly ionizing particles is the quotient dN/N by rdl, where dN/N is the fraction of particles that experience interactions in transversing a distance dl in a material of density r.

(ICRU 19)

Mass attenuation coefficient (µ/r)
The mass attenuation coefficient of a material for indirectly ionizing particles is the quotient of dN by the product of r, N and dl where N is the number of particles incident normally upon a layer of thickness dl and r, and dN is the number of particles that experience interactions in this layer.

(NBS 92)

Mass coefficient of reactivity
The partial derivative of reactivity with respect to the mass of a given substance in a specified location.
(ANSI N1.1-1976)

Mass defect
Of a nucleus, the difference between the sum of the masses of the constituent nucleons and the mass of the nucleus.
(ANSI N1.1-1976)

Mass defect
The difference between the atomic mass and the mass number of a nuclide. (See packing fraction.)
(USAEC-1974)

Mass defect
Difference between the mass of the nucleus as a whole and the sum of the component nucleon masses.
(RHH)

Mass energy absorption coefficient
The mass energy absorption coefficient, µ_en/r of a material for uncharged ionizing particles is the product of the mass energy transfer coefficient, µ_tr/r, and (1 - g) where g is the fraction of the energy of secondary charged particles that is lost to bremsstrahlung in the material,

Unit: m² kg^-1
(ICRU 44)

Mass energy absorption coefficient
The mass energy absorption coefficient (µ_en/r) of a material for indirectly ionizing particles is µ_K/r (1-G) where G is the proportion of the energy of secondary charged particles that is lost to bremsstrahlung in the material.
(NBS 92)

Mass energy absorption coefficient (µ_en/r)
For a material and for uncharged ionizing particles, product of the mass energy transfer coefficient and (1 - g), where g is the fraction of the energy of secondary charged particles that is lost to bremsstrahlung in the material.

(IEC 50-393-1993)

Mass energy absorption coefficient (µ_en/r)
The mass energy absorption coefficient of a material for uncharged particles is the product of the mass energy transfer coefficient, µ_tr/r, and (1-g), where g is the fraction of the energy of secondary charged particles that is lost to bremsstrahlung in the material.

(ICRP 51)

Mass energy absorption coefficient (µ_en/r)
The mass energy absorption coefficient of a material for indireclty ionizing particles of specified energy is the product of the mass energy transfer coefficient for that energy and (1-g), where g is the fraction of the energy of secondary charged particles that is lost to bremsstrahlung in the material.

(ICRU 19)

Mass energy absorption coefficient (µ_en/r)
The mass energy absorption coefficient of a material for indirectly ionizing particles is µ_k/r (1-G), where G is the fraction of the energy of secondary charged particles that is lost to bremsstrahlung in the material.
(ICRU 10f)

Mass energy relation
The name sometimes given to the equation E = mc².
(RHH)

Mass energy transfer coefficient
The mass energy transfer coefficient, µ_tr/r, of a material for uncharged ionizing particles is the quotient of dE_tr/EN by rdl, where E is the energy of each particle (excluding rest energy), N is the number of particles, and dE_tr/EN is the fraction of incident particle energy that is transferred to kinetic energy of charged particles by interactions in traversing a distance dl in the material of density r.

Unit: m² kg^-1
(ICRU 44)

Mass energy transfer coefficient
The mass energy transfer coefficient of a material for uncharged ionizing particles is the quotient dE_tr/EN by rdl, where E is the energy of each particle (excluding rest energy), N is the number of particles, and dE_tr/EN is the fraction of incident particles energy that is transferred to kinetic energy of charged particles by interactions in transversing a distance dl in material of density r.

(ICRP 51)

Mass energy transfer coefficient
The mass energy transfer coefficient of a material, µ_tr/r, for indirectly ionizing particles of specified energy is the quotient dE_tr/E by rdl where dE_tr/E is the fraction of the incident particle energy (excluding rest energies) that is transferred to kinetic energy of charged particles by interactions in traversing a distance dl in a medium of density r.

(ICRU 26)

Mass energy transfer coefficient (µ_tr/r)
For a material and for uncharged ionizing particles, quotient of dEtr/EN by rdl, where E is the energy of each particle, excluding rest energy, N is the number of particles, and dE_tr/EN is the fraction of the energy of all incident particles that is transformed to kinetic energy of charged particles by interactions in traversing a distance dl in the material of density r.

(IEC 50-393-1993)

Mass energy transfer coefficient (µ_k/r)
The mass energy transfer coefficient (µ_k/r) of a material for indirectly ionizing particle is the quotient dE_k by the product of E, r and dl when E is the sum of energies (excluding rest energies) of the indirectly ionizing particle incident normally upon a layer of thickness dl and density r, and dE_k is the sum of the kinetic energies of all charged particles liberated in this layer.

(NBS 92)

Mass measurement process
A series of operations using various devices and procedures to produce a statement of the mass of an object.
(ANSI N15.18-1988)

Mass Median Aerodynamic Diameter (MMAD)
The aerodynamic diameter of a particle having median mass, i.e., the masses of particles above and below this value are equal.
(NCRP 125)

Mass Median Diameter (MMD)
The particle diameter for which there is an equal mass particles above and below this size.
(NCRP 125)

Mass median size
Size with an equal mass of particles above and below this value (See also median size.)
(AM-1993)

Mass number
The number of nucleons in the nucleus.
(ANSI N1.1-1976)

Mass number
[Symbol A] The sum of the neutrons and protons in a nucleus. It is the nearest whole number to an atom's atomic weight. For instance, the mass number of uranium-235 is 235.
(USAEC-1974)

Mass number (A)
Number of nucleons contained in an atomic nucleus.
(IEC 50-393-1993)

Mass numbers
The number of nucleons (protons and neutrons) in the nucleus of an atom. (Symbol: A).
(RHH)

Mass per unit area
Quantity equal to the product of the mass per unit volume, density, of a material and the thickness of the same material.
(IEC 50-393-1993)

Mass scattering power
The mass scattering power, T/r, of a material for charged particles is the quotient of d² by r dl, where d² is the increase in the mean square angle of scattering of a charged particle traversing a distance dl in a material of density r.

Unit: radian² m² kg^-1.
(ICRU 44)

Mass spectrograph, mass spectrometer
Two related devices for detecting and analyzing isotopes. They separate nuclei that have different charge to-mass ratios by passing the nuclei through electrical and magnetic fields. (See isotope separation.)
(USAEC-1974)

Mass spectrometer
Apparatus intended to analyze a substance or reaction products in terms of relative abundances of its components, separating the components by their mass to charge ratios.
(IEC 50-394-1993)

Mass standard
An object that serves as a reference for the introduction of the International System of Units (SI) into the mass measurement process. Mass values are assigned to test objects by comparison with the known mass of mass standards. Synonym: reference standards.
(ANSI N15.18-1988)

Mass stopping power
The mass stopping power (S/r) of a material for charged particles is the quotient dE_s by the product of dl and r, where dE_s is the average energy lost by a charged particle of specified energy in traversing a path length dl, and r is the density of the medium.

Note: dE_s denotes energy lost due to ionization, electronic excitation and radiation. For some purposes it is desirable to consider stopping power with the exclusion of bremsstrahlung losses. In this case S/r must be multiplied by an appropriate factor that is less than unity.
(NBS 92)

Mass stopping power
The mass stopping power (S/r) of a material for charged particles is the quotient of dE_s, by the product dl and r, where dE_s is the average energy lost by a charged particle of specified energy in traversing a path length dl, and r is the density of the medium.

(ICRU 10f)

Mass Stopping Power [Sr(Er)]
Ratio of the average energy lost by a charged particle in traversing a distance in a material to the density of the material.
(NCRP 125)

Mass Transfer Coefficient
Proportionality factor for mass transfer due to mass concentration gradient of the gas.
(NCRP 125)

Mass-energy equation
(mass-energy equivalence) (mass-energy relation)
The statement developed by Albert Einstein, German born American physicist, that "the mass of a body is a measure of its energy content," as an extension of his 1905 Special Theory of Relativity. The statement was subsequently verified experimentally by measurements of mass and energy in nuclear reactions. The equation, usually given as: E = mc², shows that when the energy of a body changes by an amount, E, (no matter what form the energy takes) the mass, m, of the body will change by an amount equal to E/c². (The factor c², the square of the speed of light in a vacuum, may be regarded as the conversion factor relating units of mass and energy.) This equation predicted the possibility of releasing enormous amounts of energy (in the atomic bomb) by the conversion of mass to energy. It is also called the Einstein equation.
(USAEC-1974)

Mast Cell
Cells of the subepithelial source of the globule leukocytes that contain substances (e.g. histamine) which mediate allergic reactions.
(NCRP 125)

Material
Special nuclear material.
(10CFR74.4)

Material access area
Any location which contains special nuclear material, within a vault or a building, the roof, walls, and floor of which constitute a physical barrier.
(10CFR74.4)

Material access area
Any location which contains special nuclear material, within a vault or a building, the roof, walls, and floor of which each constitute a physical barrier.
(10CFR73.2)

Material balance
The determination of an inventory difference (ID).
(10CFR74.4)

Material buckling
Quantity, , providing a measure of the multiplying properties of a medium as a function of the materials and their disposition.

(IEC 50-393-1993)

Material control test
A comparison of a preestablished alarm threshold with the results of a process difference or process yield performed on a unit process.
(10CFR74.4)

Material in process
Any special nuclear material possessed by the licensee except in unopened receipts, sealed sources, measured waste discards, and ultimate product maintained under tamper-safing.
(10CFR74.4)

Materials license
A byproduct material license issued pursuant to part 30 of this chapter, or a source material license issued pursuant to part 40 of this chapter, or a special nuclear material license issued pursuant to part 70 of this chapter, or a license for the storage of spent fuel issued pursuant to part 72 of this chapter.
(10CFR170.3)

Materials License
A license, certificate, approval, registration, or other form of permission issued by the NRC pursuant to the regulations in 10 CFR parts 30, 32 through 36, 39, 40, 61, 70, 71 and 72.
(10CFR171.5)

Matrix material
A material that is free of radionuclides, that has the same or closely similar properties as the material to be measured by NDA, and that can be mixed with uranium and plutonium compounds to prepare calibration material.
(ANSI N15.35-1983)

Matter
The substance of which a physical object is composed. All materials in the universe have the same inner nature, that is, they are composed of atoms, arranged in different (and often complex) ways; the specific atoms and the specific arrangements identify the various materials. (See atom, element.)
(USAEC-1974)

MAWP
Maximum allowable working pressure permitted by ASME Code requirements.
(ANSI N14.1-1990)

Maximal credible accident
The worst accident in a reactor or nuclear-energy installation that, by agreement, need be taken into account in deriving protective measures.
(BEIR III)

Maximal credible accident
The worst accident in a reactor or nuclear-energy installation that, by agreement, need be taken into account in deriving protective measures.
(RHH)

Maximal permissible dose equivalent (abbr. MPD)
The greatest dose equivalent that a person or specified part shall be allowed to receive in a given period.
(BEIR III)

Maximally exposed individual
An individual whose location and habits tend to maximize his or her radiation dose from a particular source, resulting in a dose higher than that received by other individuals in the general population.
(NCRP 93)

Maximum absorbed dose (maximum tissue dose)
The highest value of absorbed dose within a single beam or combination of beams.
(ICRU 30)

Maximum absorbed dose (maximum tissue dose)
The highest value of absorbed dose within a single beam or combination of beams.
(ICRU 24)

Maximum acceptable irradiation rate (of a detector)
Highest dose rate or fluence rate of particles at which the detector operates within specifications.
(IEC 50-394-1993)

Maximum contaminant level goals (MCLG's)
An enforceable standard under the Safe Drinking Water Act, set as close to the MCLG as feasible taking into consideration cost, availability of treatment technologies, and other practical considerations.
(RRM)

Maximum contaminant levels (MCL's)
A non-enforceable health goal under the Safe Drinking Water Act, set a levels which would result in no known or anticipated adverse health effects and allow an adequate margin of safety.
(RRM)

Maximum credible accident
A hypothetical accident used for safe design of a reactor or radiochemical plant which is that sequence of plausible events that releases the largest amount of radioactivity outside the containment.
(ANSI N1.1-1976)

Maximum credible accident
The most serious reactor accident that can reasonably be imagined from any adverse combination of equipment malfunction, operating errors, and other foreseeable causes. The term is used to analyze the safety characteristics of a reactor. Reactors are designed to be safe even if a maximum credible accident should occur.
(USAEC-1974)

Maximum credible accident
The worst accident in a reactor or nuclear energy installation that, by agreement, need be taken into account in deriving protective measures.
(BEIR I)

Maximum exposed individual (maximum individual)
The individual whose location and habits tend to maximize his radiation dose, resulting in a dose higher than that received by other individuals in the general population.
(NCRP 81)

Maximum normal operating pressure
The maximum gauge pressure that would develop in the containment system in a period of one year under the heat test specified in §71.71(c)(1), in the absence of venting, external cooling by an ancillary system, or operational controls during transport.
(10CFR71.4)

Maximum permissible annual dose (MPAD)
The annual maximum occupational-radiation-dose limit recommended by the ICRP for the body or part of the body.
(ANSI N343-1978)

Maximum permissible body burden
The quantity of activity of a specific radioactive material that may be present in a worker's body continually for a working lifetime and result in the maximum permissible dose.
(NCRP 65)

Maximum permissible concentration
An accepted upper limit for the concentration of a specific radionuclide in air or water, such that occupational exposure for the working life time of an individual to the MPC values would not result in radiation doses exceeding the standards recommended by competent authorities.
(NCRP 75)

Maximum permissible concentration (MPC)
The concentration of a radionuclide in air or water that would lead to an amount of the radionuclide in the critical organ that would just deliver the maximum permissible dose rate to that organ. A phrase used when the conventional system of units is employed. It corresponds to the Derived Reference Air Concentration (DRAC).
(NCRP 118)

Maximum permissible concentration (MPC)
The concentration of air (MPC_a) or water (MPC_w) that would lead at equilibrium to an amount of radionuclide in the critical organ that would just deliver the maximum permissible dose to that organ. These were calculated for either 40 hrs. per week or 168 hrs. per week intakes.
(NCRP 87)

Maximum permissible concentration (MPC)
The maximum quantity per unit volume of a radioactive material in air, water, and foodstuff that is not considered an undue risk to human health.
(NCRP 62)

Maximum permissible concentration (MPC)
An accepted upper limit for the concentration of a specified radionuclide in a material taken into the body below which continuous exposure (or in the case of occupational maximum permissible concentration exposure for 40 hours per week) to the material is not considered biologically harmful.
(ANSI N43.1-1978)

Maximum permissible concentration (MPC)
An accepted upper limit for the concentration of a specified radionuclide in a material taken into the body below which continuous exposure (or in the case of occupational maximum permissible concentration, exposure for 40 hours per week) to the material will result in acceptable health risks to the specific population involved.
(ANSI N1.1-1976)

Maximum permissible concentration (MPC)
The amount of radioactive material in air, water, or food which might be expected to result in a maximum permissible dose to persons consuming them at a standard rate of intake. An obsolescent term. (See radiation protection guide, radioactivity concentration guide.)
(USAEC-1974)

Maximum permissible dose
The dose which, in the light of present knowledge, carries a negligible probability of severe somatic or genetic injuries and such that any effects that occur more frequently are limited to those of a minor nature that would be considered acceptable by the exposed individual and by competent medical authority.
(NUREG/CR 3332)

Maximum permissible dose
The dose of ionizing radiation which competent authorities have established as the maximum that can be absorbed without risk to human health.
(ERDA 76-21)

Maximum permissible dose
The maximum to dose to which the body of a person or any part thereof shall be permitted to be exposed continually or intermittently in a given period of time. The maximum doses permitted in 1 week are given in table 1.

Type of radiation	Ergs/gram in 1 week
X-rays and gamma rays	30
Beta rays and fast electrons	30
Protons	3
Slow Neutrons	3
Fast neutrons of energy not > than 20 Mev	3
Alpha rays	1.5

(NBS 55)

Maximum permissible dose (MPD)
The maximum RBE dose that the body of a person or specific parts thereof shall be permitted to receive in a stated period of time. For the radiations considered here, the RBE dose in rems may be considered numerically equal to the absorbed dose in rads and the exposure dose in roentgens numerically equal to the absorbed dose in rads.
(NBS 73)

Maximum permissible dose (MPD)
Dose of ionizing radiation that, in the light of present knowledge, is not expected to cause detectable bodily injury to a person at any time during his lifetime.
(NBS 54)

Maximum permissible dose (MPD) (maximum permissible exposure)
That dose of ionizing radiation established by competent authorities as an amount below which there is no reasonable expectation of risk to human health, and which at the same time is somewhat below the lowest level at which a definite hazard is believed to exist. An obsolescent term. (See radiation protection guide.)
(USAEC-1974)

Maximum permissible dose equivalent (H_M)
For radiation protection purposes, H_M refers to the maximum dose equivalent that radiation workers shall be allowed to receive in a stated period of time.
(NCRP 51)

Maximum permissible dose equivalent (MPD)
The largest dose equivalent received within a specified period which is permitted by a regulatory agency or other authoritative group on the assumption that receipt of such dose equivalent creates no appreciable somatic or genetic injury.
(ANSI N43.2-1977)

Maximum permissible dose equivalent (MPD)
For radiation protection purposes, maximum dose equivalents that a person shall be allowed to receive in a stated period of time. For radiation protection purposes of this report, the dose equivalent in rems may be considered numerically equal to the absorbed dose in rads and the exposure in roentgens.
(NCRP 49)

Maximum permissible dose equivalent (MPD)
The greatest dose equivalent that a person or specified part thereof shall be allowed to receive in a given period of time.
(BEIR I)

Maximum permissible dose equivalent (MPD)
The greatest dose equivalent that a person or specified part thereof shall be allowed to receive in a given period of time.
(RHH)

Maximum permissible dose equivalent (MPDE)
The amount of exposure to ionizing radiation established by authorized groups (such as the NCRP and ICRP) which carries an acceptably low probability (risk) of resulting in appreciable bodily injury to a person at any time during his lifetime.
(ANSI N43.1-1978)

Maximum permissible leakage rate
The maximum permissible leakage rates for the medium present during transport (L_N and L_A from Section 5 of this standard).
(ANSI N14.5-1987)

Maximum permissible lung burden (MPLB)
The quantity of a radionuclide deposited in the lung which, if continuously present, would result in the maximum permissible annual dose to the lung.
(ANSI N343-1978)

Maximum permissible neutron flux density
The maximum number of neutrons permitted for a given unit of time per square centimeter of body surface perpendicular to the neutron beam. The maximum permissible flux densities corresponding to the various energies are listed below.

Maximum Permissible Neutron Flux Densities
Neutron Energy (MeV)	Number of neutrons/cm²/sec
Thermal	2000
0.00001	1000
0.010	1000
0.1	200
0.5	80
1.0	60
2.0	40
3.0	30
4.0	30
5.0	30
10.0	30

(NBS 55)

Maximum permissible organ burden (MPOB)
The quantity of a radionuclide deposited in an organ which, if continuously present, would result in the maximum permissible annual dose to the organ.
(ANSI N343-1978)

Maximum permissible release rate
The radioactive content release rates that are equivalent to the appropriate package containment requirements given in Table I (R_N and R_A from Section 5).
(ANSI N14.5-1987)

Maximum service load
The maximum load that a special lifting device can lift as established by load testing. This load shall not exceed the maximum load the device is designed to support.
(ANSI N14.6-1986)

Maximum target absorbed dose (Dt,max)
The maximum target absorbed dose is the highest absorbed dose in the target area that can be regarded as "clinically meaningful". The latter term implies that at least a minimum area is irradiated to the dose level designated as "maximum". The minimum area recommended for this purpose is 2 cm², unless the whole target area is less than 4 cm², in which case a minimum area of 1 cm² should be taken to define the maximum target absorbed dose.
(ICRU 29)

Maximum use limit of filter, cartridge, or canister
The maximum concentration of a contaminant for which an air-purifying filter, cartridge, or canister is approved for use.
(ANSI Z88.2-1980)

Maximum use period
When a dosimeter is employed for several use periods, the longest of the routine use periods for which compliance with ANSI N13.15 is claimed.
(ANSI N13.15-1985)

May
The word "may" is to be understood as a permission, neither a requirement nor a recommendation.
(ANSI N545-1975)

MC&A Alarm
A situation in which there is:
(1) an out-of-location item or an item whose integrity has been violated,
(2) an indication of a flow of SSNM where there should be none, or
(3) a difference between a measured or observed amount or property of material and its corresponding predicted or property value that exceeds a threshold established to provide the detection capability required by §74.53.
(10CFR74.4)

MDL (minimum detectable level)
The threshold of detection for the device in question.
(NCRP 107)

MDL (minimum detectable level)
The threshold of detection for the device in question.
(NCRP 101)

MDMT
Minimum design metal temperature to meet ASME Code requirements.
(ANSI N14.1-1990)

Mean (or average dose equivalent)
The sum of the dose equivalent received by individuals divided by the number of individuals for which the sum is taken.
(NCRP 101)

Mean absorbed dose, D bar
The average energy per unit mass deposited in a target organ by ionizing radiation.
(MIRD)

Mean Diameter
Average diameter of the particles (sum of all diameters divided by the number of particles).
(NCRP 125)

Mean dose per unit administered activity, D/A₀
The quotient of the average dose (D) to the target organ divided by the activity (A₀) administered to the subject.
(MIRD)

Mean energy emitted per nuclear transition, D_i
The product of the number of particles (n_i) multiplied by the mean energy per particle (E_i), for type-i radiation, in suitable units. D _i is proportional to n_i E_i.
(MIRD)

Mean energy expended
The mean energy expended in a gas per ion pair formed, W, is the quotient of E by N, where N is the mean number of ion pairs formed when the initial kinetic energy E of a charged particle is completely dissipated in the gas,

Unit: J. W may be expressed in eV.
(ICRU 44)

Mean energy expended in a gas per ion pair formed (W)
The quotient E by N, where N is the mean number of ion pairs formed when the initial kinetic energy E of a charged particle is completely dissipated in the gas.
(ICRP 51)

Mean energy expended in a gas per ion pair formed (W)
The mean energy expended in a gas per ion pair formed, W, is the quotient of E by N, where N is the mean number of ion pairs formed when the initial kinetic energy, E, of a charged particle is completely dissipated in the gas:

Notes: (a) It follows from the definition that the ions produced by the bremsstrahlung or other secondary radiation emitted by the charged particles are included in N. (b) The mean number, N, of ion pairs is equal to the total liberated charge of either sign divided by the charge of the electron.
The differential value, w, of the mean energy necessary to produce an ion pair is the quotient of dE by dN, where dE is the mean energy lost by a charged particle of energy E in traversing an absorber of thickness dx, and dN is the mean number of ion pairs produced when dE is completely dissipated in the gas:

(ICRU 31)

Mean energy expended in a gas perion pair formed (W)
The quotient E by N, where N is the mean number of ion pairs formed when a directly ionizing particle of initial kinetic energy E of a charged particle is completely dissipated in the gas.

(ICRU 19)

Mean energy expended per ion pair formed (in a material) (W)
Quotient of E by N, where N is the mean number of ion pairs formed when the initial kinetic energy E of a charged particle is completely dissipated in the material.

(IEC 50-393-1993)

Mean energy imparted
The mean energy imparted, e, is the expectation value of the energy imparted. Note: e has sometimes been called the "integral dose" in the volume.
(ICRU 19)

Mean energy imparted (to matter in a volume) (e)
Expectation value of the energy imparted, to matter in a given volume.
(IEC 50-393-1993)

Mean energy per particle, E_i
The mean energy per particle of type-i radiation.
(MIRD)

Mean free path
Mean distance a molecule in a gas travels before colliding with another molecule
(AM-1993)

Mean free path
Average distance that particles of a specified type travel between interactions of a specified type in a given medium.
(IEC 50-393-1993)

Mean free path
The average distance that particles of a specified type travel before a specified type of interaction in a given medium. The mean free path may thus be specified for all interactions (i.e., total mean free path) or for particular types of interaction such as scattering, capture, or ionization.
(ANSI N1.1-1976)

Mean free path
The average distance traveled by a particle, atom, or molecule between collisions or interactions. (See collision.)
(USAEC-1974)

Mean free path
The average distance that particles of a specified type travel before a specified type (or types) of interaction in a given medium. The mean free path may be specified for all interactions (i.e., total mean free path) or for particular types of interaction such as scattering, capture, or ionization.
(RHH)

Mean free path (for a given type of interaction)
The average distance that particles of a specified type travel before a specific type of interaction takes place in a given medium. If the term mean free path is used without specifying the interaction, the term means the average distance a particel will travel before having an interaction of any sort.
(NCRP 51)

Mean free path, transport
The reciprocal of the macroscopic transport cross section.
(ANSI N1.1-1976)

Mean instrument reading
The arithmetic average of a series of readings.
(ANSI N42.17A-1989)

Mean instrument reading
The arithmetic average of a series of readings.
(ANSI N42.17B-1989)

Mean life
The average lifetime for an atomic or nuclear system in a specified state. For an exponentially decaying system, the average time for the number of atoms or nuclei in a specified state to decrease by a factor of e (2.718...).
(ANSI N1.1-1976)

Mean life
The average time during which an atom, an excited nucleus, a radionuclide or a particle exists in a particular form. (See scattering.)
(USAEC-1974)

Mean life (t)
Average radioactive lifetime of an atomic or nuclear system in a specified state.

(IEC 50-393-1993)

Mean lifetime
An average lifetime relate to the biologic or the effective half-time, or the physical half-life. Effective mean lifetime = 1.443 x effective half-time.
(MIRD)

Mean residence time
The average time that a given compound will remain in a specified state. Mean residence time, T, is related to the residence half-life, T, as:

(NCRP 62)

Mean size
Average of all sizes, i.e., the sum of all sizes divided by the number of particles
(AM-1993)

Mean target absorbed dose (D_{t, mean})
For the determination of the mean, as well as of the median and modal target absorbed dose, it is necessary to calculate the dose at each of a large number of discrete points (lattice points), uniformly distributed in the target area. The mean target absorbed dose is then calculated as the mean of the absorbed dose values in these lattice points and can be expressed by the equation:

where N is the number of lattice points, i is the column index in this lattice, j is the row index, and D_i,j is the absorbed dose at the lattice point i,j located inside the target area A_T.
(ICRU 29)

Measurement
Includes sampling and means the determination of mass, volume, quantity, composition or other property of a material where such determinations are used for special nuclear material control and accounting purposes.
(10CFR74.4)

Measurement
A value that has been assigned to a characteristic of interest as the result of an empirical determination.
(ANSI N15.54-1988)

Measurement
A value that has been assigned to a characteristic of interest.
(ANSI N15.41-1984)

Measurement assurance
The process of maintaining measurement validity within established limits.
(ANSI N15.35-1983)

Measurement control program
The procedures and activities used to ensure that a measurement process generates results of sufficient quality for their intended use.
(ANSI N15.54-1988)

Measurement control program
The procedures and activities used to ensure that a measurement process generates measurements of sufficient quality for their intended use.
(ANSI N15.41-1984)

Measurement equation
The inverse of the calibration equation, V = f^-1 (H).
(ANSI N15.19-1989)

Measurement error model
A description of the uncertainty of a measurement process. The model relates the measurement to the true value of the quantity being measured and the source of error associated with the measurement process and describes the probabilistic characteristics of the errors, usually in terms of the expected value and standard deviation.
(ANSI N15.41-1984)

Measurement model (estimated measurement equation)
The inverse of the estimated calibration equation,

(ANSI N15.19-1989)

Measurement process
All activities, procedures, and equipment used to obtain a measurement.
(ANSI N15.41-1984)

Measurement system
All of the apparatus, equipment, instruments and procedures used in performing a measurement.
(10CFR74.4)

Measurement system (of the tank)
The equipment used to sense, transmit, display, and record the data required to determine the quantity of liquid in a tank.
(ANSI N15.19-1989)

Measurement system resolution
The smallest incremental change that the measurement system is capable of detecting.
(ANSI N15.19-1989)

Measurements for Diagnostic Purposes
Measurements made to better define the quantity of an analyte in a sample or person following an event or positive routine sample that indicates the possibility of a significant human intake of radioactive material.
(HPS N13.30-1996)

Measuring and test equipment (M&TE)
Devices or systems used to calibrate, measure, gage, test, or inspect in order to control and to acquire data to verify conformance to specified requirements.
(ANSI N46.2-1978)

Mechanical Clearance Function [M(T)]
Rate of movement of particles, either phagocytized or unphagocytized, from the lung or tracheobronchial airways up the tracheobronchial tree.
(NCRP 125)

Mechanical design
Detailed design of a system which results in exact layouts, equipment specifications, shop drawings, installation details and drawings, sizing and layout of ducts, housings and equipment, and other details necessary to achieve the objectives and meet criteria established in functional design.
(ERDA 76-21)

Mechanical mobility
Aerosol parameter that indicates a particle's ability to move in a suspending medium; See mobility.
(AM-1993)

MED
Manhattan Engineer District (sometimes Manhattan Engineering District). The code name for the atomic bomb project during World War II.
(RAH)

Median
The 50th percentile demarkation for a distribution.
(TID-26608)

Median lethal dose
See lethal dose.
(USAEC-1974)

Median lethal dose (MLD)
Dose of radiation required to kill, within a specified period, 50% of the individuals in a large group of animals or organisms; also called LD₅₀.
(BEIR III)

Median lethal dose (MLD)
Dose of radiation required to kill, within a specified period, 50% of the individuals in a large group of animals or organisms; also called LD₅₀.
(BEIR I)

Median lethal dose (MLD)
Dose of radiation required to kill, within a specified period, 50% of the individuals in a large group of animals or organisms; also called LD₅₀.
(RHH)

Median lethal time (MLT, LD₅₀ time)
The time required for the death of 50% of a large population of a given species as a consequence of receiving (or attributable to) a specific absorbed dose.
(ANSI N1.1-1976)

Median size
Size with an equal number of particles above and below this value (See also mass median size.)
(AM-1993)

Median target absorbed dose (D_t,median)
The median target absorbed dose is the central value among the set of values of the absorbed dose at all lattice points in the target area, when arranged according to magnitude.
(ICRU 29)

Medical exposure
Exposure to ionizing radiation in the course of diagnostic or therapeutic procedures; includes:
1. Diagnostic radiology (e.g., x-rays)
2. Exposure to radioisotopes in nuclear medicine (e.g., iodine-131 in thyroid treatment).
3. Therapeutic radiation (e.g., cobalt treatment for cancer).
4. Dental exposure.
(BEIR III)

Medical institution
An organization in which several medical disciplines are practiced.
(10CFR35.2)

Medical Internal Radiation Dose (MIRD) Committee
A committee of the Society of Nuclear Medicine responsible for the internal dosimetry of radiopharmaceuticals used diagnostically.
(NCRP 125)

Medical physicist
As used in ICRP 44-1984: A physicist with particular training in medical applications of radiation physics.
(ICRP 44)

Medical staff
The physician available to provide the health surveillance (medical supervision) and his support personnel.
(ICRP 35)

Medical use
The intentional internal or external administration of byproduct material or the radiation therefrom to patients or human research subjects under the supervision of an authorized user as defined in 10 CFR Part 35.
(10CFR30.4)

Medium (plural, media)
The filtering material in a filter.
(ERDA 76-21)

Mega
A prefix that multiplies a basic unit by one million.
(USAEC-1974)

Mega electron volts (MeV)
Energy equal to that acquired by a particle with one electron charge in passing through a potential difference of one million volts (one MV) in a vacuum.
(NCRP 102)

Mega-electron volt (MeV)
One million electron volts, 10⁶ eV.
(RHH)

Megaton
A unit of explosive energy equivalent to that released upon detonation of 10⁶ tons of TNT.
(NCRP 94)

Megaton
A unit of explosive energy equivalent to that released upon detonation of 10⁶ tons of TNT.
(NCRP 81)

Megaton
A unit of explosive energy equivalent to that released upon detonation of 10⁶ tons of TNT.
(NCRP 75)

Megaton
A unit of explosive energy equivalent to that released upon detonation of 10⁶ tons of TNT.
(NCRP 62)

Megaton
A unit of explosive energy equivalent to that released upon detonation of 10⁶ tons of TNT.
(NCRP 45)

Megaton energy
The energy of a nuclear explosion which is equivalent to that of an explosion of one million tons (or 1000 kilotons) of TNT. (See TNT equivalent, yield.)
(USAEC-1974)

Megawatt-day per ton
A unit used for expressing the burnup of fuel in a reactor; specifically, the number of megawatt-days of heat output per metric ton of fuel in the reactor. (See burnup.)
(USAEC-1974)

Member of the public
Any individual except when that individual is receiving an occupational dose.
(10CFR20.1003)

Member of the public
An individual who is not a general employee. An individual is not a "member of the public" during any period in which the individual receives an occupational dose.
(10CFR835.2-1998)

Member of the public
An individual who is not occupationally exposed to radiation or radioactive material. An individual is not a "member of the public" during any period in which the individual receives occupational exposure.
(10CFR835.2-1993)

Member of the public (or member of the general public)
An individual other than a worker performing a work assignment related to a DOE activity. A DOE worker is considered to be a member of the public when not at work.
(10CFR834.2)

Membrane filter
A filter that is formed as a gel from a colloidal suspension; characterized by tortuous air passages
(AM-1993)

Membrane filter
One of several commercially available filter media consisting generally of very thin organic-based films having a range of selectable porosities and controlled composition. (Very thin metallic filters are also known as membrane filters.)
(ANSI N13.1-1969)

Mental retardation
Severe mental retardation implies an individual who is unable to perform simple calculations, to make simple conversation, to care for himself or herself, or was or is institutionalized. Such individuals are generally found to have an intelligence score which is less than 70 on conventional tests.
(ICRP 49)

Mesencephalon
The slighlty narrowed midportion of the developing brain that coincides with the curvature known as the cephalic flexure.
(ICRP 49)

Meson
General term applied to various very short-lived particles, with or without charge, with rest mass between that of the electron and that of the proton and which are produced in high energy nuclear reactions.
(IEC 50-393-1993)

Meson
One of a class of medium-mass, short-lived elementary particles with a mass between that of the electron and that of the proton. Examples: pi-mesons (pions) and K-mesons (kaons).
(USAEC-1974)

Meson
One of a class of medium-mass, short-lived elementary particles with a mass between that of the electron and that of the proton. Examples: pi-mesons (pions) and K-mesons (kaons).
(RHH)

Meson, pi minus
A singly-charged negative particle intermediate in mass between the proton and the electron. It undergoes an interaction with an atomic nucleus particularly near the end of its range with resulting nuclear disintegration and the liberation of high-LET radiations. A penetrating beam of pi minus mesons is of potential advantage in radiotherapy.
(ICRU 30)

Met Lab
The Metallurgical Laboratory, part of the MED.
(RAH)

Metabolic constants
Factors for the rate of transfer of radionuclides at various steps in a metabolic cycle.
(NCRP 84)

Metabolic model
A mathematical description of the behavior of ingested or inhaled radionuclides in the metabolic processes of cells, tissues, organs and organisms. It is most frequently used to describe distribution among tissues and excretion.
(NCRP 114)

Metabolic model
A mathematical description of the behavior in the metabolic processes of cells, tissues, organs and organisms. It is most frequently used to describe distribution among tissues and excretion.
(HPJ 60)

Metabolic model
A mathematical description of the metabolic processes of cells, tissues, organs and organisms. It is used here to describe distribution and translocation of radionuclides among tissues.
(FGR 11)

Metabolism
The sum of all physical and chemical processes by which living organized substance is produced and maintained and by which energy is made available for the uses of the organism.
(HPJ 60)

Metabolism
The sum of all physical and chemical processes by which living organized substance is produced and maintained and by which energy is made available for the uses of the organism.
(RHH)

Metabolite
Substances essential to the metabolism of a particular organism or to a particular metabolic process.
(HPJ 60)

Metamorphic rocks
Rocks that have been changed in their composition or texture by heat and pressure. The degree of change can be very small, such as that which occurs when shale changes into slate, or large enough to completely recrystallize the rock, as occurs in the formation of schist or gneiss.
(ENV RAD)

Metastable state
An excited nuclear state having a half-life long enough to be observed.
(RHH)

Metastasis
The transfer in the body of malignant neoplastic cells from the original or parent site to one more distant.
(RHH)

Meter
See unit of length.
(NCRP 82)

MeV
Symbol for million electron volts. See electron volt.
(NCRP 111)

MeV
A unit of energy. The energy acquired by an electron accelerated through a potential difference of one million volts.
(NCRP 78)

MeV
One million (or 10⁶) electron volts. (Also written as MeV.) (See electron volt.)
(USAEC-1974)

MgU
Megagram of uranium, the SI equivalent of MTU.
(NCRP 81)

Micro
A prefix that divides a basic unit by one million.
(USAEC-1974)

Microcurie
That amount of radioactive material which disintegrates at the rate of 37 thousand atoms per second.
(10CFR30.4)

Microcurie
See curie.
(HPJ 60)

Microcurie (µc)
One-millionth of a curie (3.700 x 10⁴ disintegrations per second).
(NBS 73)

Microcurie (µc)
One-millionth of a curie (3.700 x 10⁴ disintegrations per second).
(NBS 66)

Microcurie (µc)
One-millionth of a curie (3.700 x 10⁴ disintegrations per second).
(NBS 54)

Microcurie (µCi)
A one millionth part of a curie or 3.7 x 10⁴ nuclear transformations per second.
(NCRP 65)

Microcurie (µCi)
The millionth part of a curie, 3.7 x 10⁴ disintegrations per second.
(NCRP 48)

Microform
A process for reproducing printed matter in a much reduced size.
(NCRP 114)

Micrometer (symbol: µm)
Unit of length = 10^-6 m.
(BEIR III)

Micromicro
See pico.
(USAEC-1974)

Micron
Unit of length equal to 10^-6 meters. (Symbol: µ).
(BEIR I)

Micron
Unit of length equal to 10^-6 meters. (Symbol: µ).
(RHH)

Micronize
A process by which coarse powders are mechanically reduced to a particle size suitable for redispersion as an aerosol from a solvent or propellant
(AM-1993)

Microparticles
Particles with sizes of the order of micrometers
(AM-1993)

Microscopic cross section
Cross section per target nucleus, atom, or molecule.
(IEC 50-393-1993)

Microscopic cross section
A microscopic cross section, s, i.e. an interaction probability per atom and unit fluence, is defined as:

where r is the density of the material, M is the molar mass of the medium, and N_A is the Avogadro constant.
(ICRU 26)

Microspheres
Microscopic spheres labeled with bound photon-emitting radionuclides.
(ANSI/HPS N13.45-1998)

Microwave
An electromagnetic wave having a wavelength of approximately 1 meter to 1 millimeter corresponding to frequencies of about 300 to 300,000 megacycles per second.
(RHH)

Midline absorbed dose
The absorbed dose calculated or measured for a point in tissue and at the "midline" or "center" of the biological specimen, i.e., for the point lying equidistant from the exterior points on the specimen. The designation is for dosimetric purposes and implies no particular biological significance for the midline location.
(NCRP 66)

Midline absorbed dose (kerma)
The absorbed dose (kerma) calculated or measured for a point in tissue and at the "midline" or "center" of the biological specimen (animal), i.e., for the point lying equidistant from the exterior points on the specimen. The designation is for dosimetric purposes and implies no particular biological significance for the midline location.
(ICRU 30)

Migration area
Sum of the slowing-down area from fission energy to thermal energy and the diffusion area for thermal neutrons.
(IEC 50-393-1993)

Migration area
The sum of the slowing-down from fission to thermal energy and the diffusion area for thermal neutrons.
(ANSI N1.1-1976)

Migration length
Square root of the migration area.
(IEC 50-393-1993)

Migration length
The square root of the migration area.
(ANSI N1.1-1976)

Mil
Unit of length equal to one-thousandth of an inch.
(RHH)

Mildew
A visible fungal growth on surfaces
(AM-1993)

Milli
A prefix that divides a basic unit by one thousand.
(USAEC-1974)

Milliampere (mA)
One thousandth of an ampere, a unit of electric current.
(NCRP 68)

Milliampere (mA)
One thousandth of an ampere, a unit of electric current density.
(NCRP 66)

Milliampere-second (mAs)
The numerical product of the milliamperage multiplied by the exposure time in seconds.
(NCRP 68)

Milliampere-second (mAs)
The numerical product of the milliamperage multiplied by the exposure time in seconds.
(NCRP 66)

Milliampere-seconds (mAs)
The product of x-ray tube current in milliamperes and operating time in seconds.
(NCRP 48)

Millicurie
That amount of radioactive material which disintegrates at the rate of 37 million atoms per second.
(10CFR30.4)

Millicurie (mc)
One-thousandth of a curie (3.700 x 10⁷ disintegrations per second).
(NBS 73)

Millicurie (mc)
One-thousandth of a curie (3.700 x 10⁷ disintegrations per second).
(NBS 66)

Millicurie (mc)
One-thousandth of a curie (3.700 x 10⁷ disintegrations per second).
(NBS 54)

Millicurie (mCi)
The thousandth part of the curie, 3.7 x 10⁷ disintegrations per second.
(NCRP 48)

Millicurie (mCi)
One-thousandth of a curie.
(NCRP 49)

Million electron volt (MeV)
1 million electron volts.
(NBS 63)

Million electron volts (MeV)
1,000,000 eV.
(NCRP 65)

Million electron volts (MeV)
Energy equal to that acquired by a particle with one electronic charge in passing through a potential difference of one million volts (one Mv).
(NBS 73)

Million electron volts (MeV)
Energy equal to that acquired by a particle with one electronic charge in passing through a potential difference of one million volts (one Mv).
(NBS 54)

Million electron volts (MeV)
A unit of energy equal to 1,000 kev.
(NBS 55)

Million eletron volts (MeV)
Energy equal to that acquired by a particle with one electronic charge in being accelerated through a potential difference of one million volts (one MV).
(NCRP 49)

Millirad (mrad)
The thousandth part of a rad.
(NCRP 48)

Millirad (mrad)
One-thousandth of a rad.
(NBS 73)

Millirad (mrad)
One-thousandth of a rad.
(NBS 66)

Millirad (mrad)
One-thousandth of a rad (0.001 rad).
(NBS 54)

Millirem (mrem)
One-thousandth of a rem.
(HPJ 60)

Millirem (mrem)
One-thousandth of a rem.
(NBS 66)

Milliroentgen
A submultiple of the roentgen equal to one one-thousandth (1/1000th) of a roentgen.
(HPJ 60)

Milliroentgen (mr)
A one-thousandth part of a roentgen.
(NCRP 65)

Milliroentgen (mr)
One-thousandth of a roentgen.
(NCRP 49)

Milliroentgen (mr)
The thousandth part of the roentgen.
(NCRP 48)

Milliroentgen (mr)
One-thousandth of a roentgen.
(NBS 73)

Milliroentgen (mr)
One-thousandth of a roentgen.
(NBS 66)

Milliroentgen (mr)
One-thousandth of a roentgen (0.001 r).
(NBS 54)

Milliwatt
One-thousandth of a watt (10^-3 watt).
(NBS 55)

Minimum detectable quantity (of a radiation measuring assembly)
Quantity, for example activity, which will give a mean indication that in the presence of a specified background there is a 95% probability that such an indication will not be produced by specified background alone.
(IEC 50-394-1993)

Minimum bioassay program
A limited bioassay program designed to sample only a few most-exposed workers to confirm that safe routine operations are maintained, or to monitor levels of exposure below 0.1 ALI y^-1. It may consist of only confirmatory bioassays.
(ANSI/HPS N13.22-1995)

Minimum detectable activity (MDA)
That activity giving an indication corresponding to 4.65 times the standard deviation of the indication given by a specific background, divided by the appropriate conversion factor to result in units of activity.
(ANSI N42.17B-1989)

Minimum detectable amount
The smallest amount of a radionuclide in a sample that will be detected with b probability of non-detection (Type II error) while accepting an a probability of erroneously detecting that radionuclide in an appropriate blank sample (Type I error.) For this standard, the a and b probabilities are both set at 0.05.
(ANSI N13.30-1989D)

Minimum detectable amount
A term used to indicate the ability of a particular radioanalytical method to discern between the radioactivity associated with the radionuclide content of the sample of interest and background radiation with a particular degree of statistical confidence.
(NCRP 87)

Minimum Detectable Amount (MDA)
The smallest amount (activity or mass) of an analyte in a sample that will be detected with a probability b of non-detection (Type II error) while accepting a probability a of erroneously deciding that a positive (non-zero) quantity of analyte is present in an appropriate blank sample (Type I error).
(HPS N13.30-1996)

Minimum detectable amount (MDA)
The smallest amount (activity or mass) of an analyte in a sample that will be detected with a probability beta of non-detection (Type II error) when the decision level for detection accepts a probability alpha of erroneously deciding that a positive (non-zero) quantity of analyte is present in an appropriate blank sample (Type I error). For this standard, alpha and beta probabilities are both set at 0.05.
(ANSI/HPS N13.22-1995)

Minimum Detectable Concentration (MDC)
The MDA expressed in units of concentration.
(HPS N13.30-1996)

Minimum induction period
The period of time between radiation exposure and the detection of the first excess case of thyroid cancer following radiation exposure (sometimes called latent period).
(NCRP 80)

Minimum target absorbed dose (D_{t, min})
The minimum target absorbed dose is the lowest absorbed dose in the target area. No area limit is recommended when reporting minimum target absorbed dose.
(ICRU 29)

Minimum Testing Level (MTL)
The amount of radioactive material that the service laboratory should be able to measure for participation in the performance testing program, assuming the sample(s) are free of interference from other radionuclides unless specifically addressed. The MTLs should not be construed as being the appropriate MDA required for a specific internal dosimetry program, but rather an acceptable minimum testing level for radiobioassay service laboratories based on good measurement practice.
(HPS N13.30-1996)

Ministerial change
A change that is made, after ascertaining the applicable requirements, by persons in authority in conformance with the requirements and without making a discretionary judgment about whether those requirements should apply in the case at hand.
(10CFR35.2)

Minor
An individual less than 18 years of age.
(10CFR20.1003)

Minor
An individual less than 18 years of age.
(10CFR835.2-1993)

Minute volume
That amount of air moving through the lung per minute; the product of the breathing rate times the volume of air per breath.
(BEIR IV)

Minute volume or ventilation rate
The volume of air expired per minute. It is the product of the tidal volume and the breathing frequency.
(NCRP 76)

MIRD
Medical Internal Radiation Dose; a committee of the Society of Nuclear Medicine.
(RAH)

MIRD
Medical Internal Radiation Dose; a committee of the Society of Nuclear Medicine.
(FGR 11)

MIRD
Medical Internal Radiation Dose; a committee of the Society of Nuclear Medicine.
(NCRP 84)

Misadministration
The administration of:
(1) A radiopharmaceutical dosage greater than 30 microcuries of either sodium iodide I-125 or I-131:
   (i) Involving the wrong individual, or wrong radiopharmaceutical; or
   (ii) When both the administered dosage differs from the prescribed dosage by more than 20 percent of the prescribed dosage and the difference between the administered dosage and prescribed dosage exceeds 30 microcuries.
(2) A therapeutic radiopharmaceutical dosage, other than sodium iodide I-125 or I-131:
   (i) Involving the wrong individual, wrong radiopharmaceutical, or wrong route of administration; or
   (ii) When the administered dosage differs from the prescribed dosage by more than 20 percent of the prescribed dosage.
(3) A gamma stereotactic radiosurgery radiation dose:
   (i) Involving the wrong individual, or wrong treatment site; or
   (ii) When the calculated total administered dose differs from the total prescribed dose by more than 10 percent of the total prescribed dose.
(4) A teletherapy radiation dose:
   (i) Involving the wrong individual, wrong mode of treatment, or wrong treatment site;
   (ii) When the treatment consists of three or fewer fractions and the calculated total administered dose differs from the total prescribed dose by more than 10 percent of the total prescribed dose;
   (iii) When the calculated weekly administered dose exceeds the weekly prescribed dose by 30 percent or more of the weekly prescribed dose; or
   (iv) When the calculated total administered dose differs from the total prescribed dose by more than 20 percent of the total prescribed dose.
(5) A brachytherapy radiation dose:
   (i) Involving the wrong individual, wrong radioisotope, or wrong treatment site (excluding, for permanent implants, seeds that were implanted in the correct site but migrated outside the treatment site);
   (ii) Involving a sealed source that is leaking;
   (iii) When, for a temporary implant, one or more sealed sources are not removed upon completion of the procedure; or
   (iv) When the calculated administered dose differs from the prescribed dose by more than 20 percent of the prescribed dose.
(6) A diagnostic radiopharmaceutical dosage, other than quantities greater than 30 microcuries of either sodium iodide I-125 or I-131, both:
   (i) Involving the wrong individual, wrong radiopharmaceutical, wrong route of administration, or when the administered dosage differs from the prescribed dosage; and
   (ii) When the dose to the individual exceeds 5 rems effective dose equivalent or 50 rems dose equivalent to any individual organ.
(10CFR35.2)

Mission time (of equipment)
Interval of time during which the equipment shall perform its specified function.
(IEC 50-393-1993)

Mist
A liquid particle aerosol, typically formed by physical shearing of liquids, such as in nebulization, spraying, or bubbling.
(AM-1993)

Mist
A liquid condensation particle with sizes ranging from submicroscopic to visible or macroscopic.
(ANSI Z88.2-1980)

Mist
An aerosol composed of liquid particles.
(TID-26608)

Mist
A liquid condensation particle with sizes ranging from submicroscopic to visible or macroscopic.
(ANSI Z88.2-1969)

Mists
Suspended liquid droplets generated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state, as by splashing, foaming, and atomizing.
(ANSI Z9.2-1971)

Mixed field
Radiation field composed of more than one type of radiation.
(NCRP 112)

Mixed layer
See boundary layer.
(NCRP 76)

Mixed Low-Level Radioactive and Hazardous Waste (mixed LLW)
Waste that satisfies the definition of low-level radioactive waste (LLW) and contains hazardous waste that either (1) is listed as a hazardous waste in Subpart D of 40 CFR Part 261 or (2) causes the LLW to exhibit any of the hazardous waste characteristics identified in subpart C of 40 CFR Part 261.
(ANSI/HPS N13.45-1998)

Mixed Low-Level Radioactive and Infectious Waste (mixed LLW)
Waste that satisfies the definition of low-level radioactive waste (LLW) and contains potentially infectious or pathogenic waste.
(ANSI/HPS N13.45-1998)

Mobile nuclear medicine service
The transportation and medical use of byproduct material.
(10CFR35.2)

Mobility
Ratio of particle velocity to the force producing that velocity
(AM-1993)

Mobility
The ratio of particle terminal velocity to the force causing particle motion.
(TID-26608)

Mobility (equivalent) diameter
Diameter of a spherical particle with the same dynamic mobility as the particle in question
(AM-1993)

Mobility (of a charged particle)
Quotient of the mean velocity of a charged particle in the direction of an electric field by the magnitude of the field strength, in a specified medium.
(IEC 50-394-1993)

Modal target absorbed dose (D_{t, modal})
The modal target absorbed dose is the absorbed dose that occurs most frequently at lattice points in the target area. Its value may be influenced by the choice of method for its calculation (e.g., spacing of lattice points). Exceptionally, in a particular patient, more than one modal target absorbed dose may be found.
(ICRU 29)

Mode
Value occurring most often in a distribution of values; peak value of a distribution
(AM-1993)

Mode (cavity or transmission line)
An electromagnetic field pattern within a cavity or transmission line that is determined by the geometrical configuration of the structure and the wavelength of the electromagnetic wave within the structure.
(NCRP 67)

Model
A mathematical abstraction of an ecological or biological system, sometimes including specific numerical values for the parameters of the system.
(NCRP 123I)

Model
A term that is used to designate the total set of assumed conditions, spatial, structural and kinetic, for which an absorbed dose calculation is to be made. In particular, an animal model refers to some other species (usually mammalian) in which measurements are made. A mathematical model can be a diagram in which regions of interest and the transfer rates between pairs of these regions are indicated and the equations, usually differential or integral equations, that describe such a system in formal terms. If a mathematical model is to be fitted to numerical data, it must be sufficiently simple to be compatible with the data. For physical model, See phantom.
(NCRP 83)

Model
A mathematical abstraction of an ecological or biological system, sometimes including specific numerical values for the parameters of the system.
(NCRP 76)

Model
A physical or mathematical representation of reality.
(NUREG/CR 3332)

Model
A mathematical abstraction of an ecological or biological system, sometimes including specific numerical values for the parameters of the system.
(ICRP 29)

Model
Descriptive term or number to identify a specific sealed source design.
(ANSI N542-1977)

Model identification coefficients
Factors used for converting the distribution of activity of cumulated activity in a compartmental model to the distribution by organs.
(NCRP 83)

Model overkill
The inappropriate applications of complex models for problems that can be adequately addresses using simpler approaches.
(NCRP 123I)

Model overkill
The inappropriate applications of complex models for problems that can be adequately addresses using simpler approaches.
(NCRP 76)

Model prediction
The result or dependent variable produced by a model calculation.
(NCRP 123I)

Model prediction
The result or dependent variable produced by a model calculation.
(NCRP 76)

Model prediction
The result or dependent variable produced by a model calculation.
(NUREG/CR 3332)

Model run
That number of a specific type of instrument from first manufacture to the first design change (or any design change to the subsequent design change) that will change the ability of the instrument to meet the required test parameters.
(ANSI N42.17C-1989)

Model structure
The conceptual design, mathematical equations and set of algorithms that control the results or predictions produced from a given set of input data or assumptions.
(NCRP 123I)

Model structure
The conceptual design, mathematical equations and set of algorithms that control the results or predictions produced from a given set of input data or assumptions.
(NCRP 76)

Model structure
The conceptual design, mathematical equations, and set of algorithms that control the results or predictions produced from a given set of input.
(NUREG/CR 3332)

Model validation
Documentation of the discrepancy (or agreement) between model predictions and actual events through comparison of predicted values with accurately measured field data obtained over the range of conditions representing the extent of the intended application of the model.
(NCRP 123I)

Model validation
Documentation of the discrepancy (or agreement) between model predictions and actual events through the comparison of predicted values with accurately measured field data obtained over the range of conditions representing the extent of intended application of the model.
(NCRP 76)

Model validation
Documentation of the difference between model predictions and actual events through comparison of predicted values with measured field data obtained over the range of conditions representing the extent of intended application of the model.
(NUREG/CR 3332)

Model verification
An indication of whether or not a computer code accurately mimics a given model.
(NUREG/CR 3332)

Modeling
A mathematical representation that is intended to predict the amount of radioactivity released to an unrestricted area from a given set of input data or assumptions.
(ANSI/HPS N13.45-1998)

Moderately uniform exposure
The irradiation is moderately uniform if the ratio of maximum dose to minimum dose is between 1.10 and 1.30, i.e., 1.10 < D_max/D_min <1.30.
(ICRU 30)

Moderating ratio
Of a moderator, the ratio of the slowing-down power to the thermal macroscopic absorption cross section.
(ANSI N1.1-1976)

Moderation
Process by which neutron energy is reduced through scattering collisions without appreciable capture.
(IEC 50-393-1993)

Moderation
Of a moderator, the ratio of the slowing-down power to the thermal macroscopic absorption cross section.
(ANSI N1.1-1976)

Moderator
Material used to reduce, by scattering collisions and without appreciable capture, the kinetic energy of neutrons.
(IEC 50-393-1993)

Moderator
Material used to moderate or slow down neutrons from the high energies at which they are released.
(NCRP 81)

Moderator
Material used to moderate or slow down neutrons from the high energies at which they are released.
(NCRP 62)

Moderator
A material used to reduce neutron energy by scattering without appreciable capture.
(ANSI N1.1-1976)

Moderator
A material, such as ordinary water, heavy water or graphite, used in a reactor to slow down high-velocity neutrons, thus increasing the likelihood of further fission. (See absorber, thermal neutrons.)
(USAEC-1974)

Moderator
Material used to moderate, i.e., slow down, neutrons. Neutrons lose energy by scattering collisions with the nuclei of the moderator.
(NCRP 38)

Moderator
Material used to moderate or slow down neutrons from the high energies at which they are released.
(RHH)

Moderator
Material used in a nuclear reactor to moderate, i.e., slow down, neutrons from the high energies at which they are released. Neutrons lose energy by scattering collisions with nuclei of the moderator.
(NBS 63)

Moderator control
Control of a reactor by an adjustment of the properties, position or quantity of the moderator in such a way as to change the reactivity.
(IEC 50-393-1993)

Modifying factor
A numerical factor used to modify calculation of Equivalent Dose to account for variation of the LET and radiation effects with tissue type and exposure.
(RRM)

Modular calibration materials
The units or containers (modules) that contain well-characterized material that may be either matrix only or a homogeneous mixture of matrix and nuclear material in varying proportions. These modules are arranged or dispersed in a larger container in different arrangements to simulate different, nonhomogeneous (radial or axial) configurations. NDA calibration material A material used to calibrate NDA that satisfies the following criteria:
(1) It is similar to the materials to be assayed in all properties that affect the assay
(2) The mass of uranium or plutonium isotopes is known as a result of independent assay traceable to reference materials.
(ANSI N15.35-1983)

Modulation transfer function (MTF)
The modulus of the generally complex optical transfer function, expressed as a function of spatial frequency.
(ICRU 54)

Modulation transfer function (MTF)
A mathematical entity that expresses the relative response of an imaging system or system component to sinusoidal inputs as a function of varying spatial frequency, which is often expressed in lines per millimeter (lp/mm). The reference value most commonly used is that for zero frequency. The MTF can be thought of as a measure of spatial resolution of the detector system.
(NCRP 102)

Modulation transfer function (MTF)
May be used to describe in the spatial-frequency domain the unsharpness produced by a system. It is the ratio of the output depth of modulation to the input depth of modulation, expressed as a function of spatial frquency and normalized to zero spatial frequency. It is also identical with the modulus of the Fourier transform of the point spread function of the system, normalized to zero spatial frequency.
(NCRP 66)

Module
Removable plug-in-unit generally with a front panel, and designed to be introduced into a crate.
(IEC 50-394-1993)

Modulo 2 counting
By using a binary counter with only two states, the parity (even or odd) of a count is obtained. This technique can be of interest for sorting out events (such as afterpulses or coincidences) which, by their very nature, occur in pairs and therefore do not affect the measured parity.
(ICRU 52)

Moisture content
The volumetric fraction of the ground water medium "occupied by liquid water".
(NCRP 76)

Mold
A visible fungal growth on surfaces
(AM-1993)

Mole
See unit of amount of substance.
(NCRP 82)

Mole (mol)
SI unit of amount of substance, equal to the amount of substance of a system which contains as many elementary entities as there are atoms in 0,012 kilogram of carbon 12.
(IEC 50-393-1993)

Molecular Diffusion
The spreading out of molecules or ions in a fluid, in a direction tending to result in uniform concentrations in all portions of the system.
(NCRP 125)

Molecular diffusion
The transfer of mass between adjacent layers of fluid in laminar flow.
(RRM)

Molecular diffusion
The spreading out of molecules or ions in a fluid, in a directions tending to result in uniform concentrations in all portions of the system.
(NCRP 76)

Molecular weight
The sum of the atomic weights of all the atoms in a molecule.
(RHH)

Molecule
A group of atoms held together by chemical forces. The atoms in the molecule may be identical, as in H2, S2, and S8, or different, as in H2O and CO2. A molecule is the smallest unit of matter which can exist by itself and retain all its chemical properties.
(USAEC-1974)

Molecule
Smallest quantity of a compound which can exist by itself and retain all properties of the original substance.
(RHH)

Molten salt breeder reactor (MSBR)
See liquid metal fast breeder reactor.
(NCRP 62)

Molten salt reactor
A fused-salt reactor.
(USAEC-1974)

Momentum
The product of the mass of a body and its velocity; MKSA units, kg-m/sec.
(RHH)

Monitor
To determine the level of ionizing radiation or radioactive contamination in a given region. Also, a device used for this purpose.
(NCRP 105)

Monitor
An instrument that provides a continual measurement of on or more parameters and generates a signal to record or transmit that measurement.
(ANSI N42.17B-1989)

Monitor
Instrument or device for determining, periodically or continually, the expsoure rate in an area (area monitoring) or to a person (personnel monitoring), or for determining radioactive contamination.
(NCRP 48)

Monitor
An instrument that measures the level of ionizing radiation in an area. (See radiation detection instrument, radiation monitoring.)
(USAEC-1974)

Monitor
(1) To measure an airborne radioactive constituent or the gross content of radioactive material continuously or at a frequency which permits an evaluation of the concentration over an interval of time.
(2) The instrumentation or device used in monitoring.
(ANSI N13.1-1969)

Monitor, personnel
See personnel monitor.
(NCRP 107)

Monitor, personnel
See personnel monitor.
(NCRP 102)

Monitor, radiation
A radiation-measuring assembly provided with devices intended to draw attention to an event or situation which might result in overexposure to the radiation. The assembly may include indicating and/or recording instruments.
(NCRP 51)

Monitor, radiation
A radiation detector whose purpose is to measure the level of ionizing radiation (or quantity of radioactive material) and possibly give warning when it exceeds a prescribed amount. It may also give quantitative information on dose or dose rate. The term is frequently prefixed with a word indicating the purpose of the monitor, such as: area monitor, air particulate monitor.
(ANSI N1.1-1976)

Monitored retrievable storage installation or MRS
A complex designed, constructed, and operated by DOE for the receipt, transfer, handling, packaging, possession, safeguarding, and storage of spent nuclear fuel aged for at least one year and solidified high-level radioactive waste resulting from civilian nuclear activities, pending shipment to a HLW repository or other disposal.
(10CFR72.3)

Monitoring
Determining (either by modeling, sampling and empirical analysis, or real time direct reading instruments) the amount of radiation or radioactive material present at a particular location or in a medium such as air, ash, or waste.
(ANSI/HPS N13.45-1998)

Monitoring
Observing and making measurements to provide data to evaluate the performance and characteristics of the disposal site.
(10CFR61.2)

Monitoring
The measurement of radiation levels, airborne radioactivity concentrations, radioactive contamination levels, quantities of radioactive material, or individual doses and the use of the results of these measurements to evaluate radiological hazards or potential and actual doses resulting from exposures to ionizing radiation.
(10CFR835.2-1998)

Monitoring
Measurement of radioactivity for reasons related to the estimation or control of exposure to radiation or radioactive materials. The term includes the interpretation of measurement results.
(ANSI/HPS N13.22-1995)

Monitoring
Means provided to indicate continuously the state or condition of a system, sub-system, equipment or assembly.
(IEC 50-393-1993)

Monitoring
Continuous or periodic determination of the amount of radiation or radioactivity present in a given area or in a volume of effluent.
(NCRP 118)

Monitoring
Actions intended to detect and quantify radiological conditions.
(10CFR835.2-1993)

Monitoring
The measurement of radiation or activity for reasons related to the estimation or control of exposure to radiation or radioactive material. The term includes the interpretation of the measurements.
Individual - The making and interpreting of measurements by equipment carried on the person of workers, or measurements made of the activity in their bodies or in excreta or body fluids, where such measurements are intended to provide an estimate of the dose equivalent or committed dose equivalent to tissues of the body, or of the intake of radioactive material to the body of of the content of radioactivity in the body.
In or of the workplace - Monitoring intended to provide information about the environment of the worker and about the operations he performs.
Operational - Monitoring specifically related to certain operations.
Routine - Monitoring carried out at times that are independent of the particular phase of the operations then in hand, often at prescribed intervals, and intended to ascertain whether any change has taken place calling for reassessment of the operating conditions.
Special - Monitoring initiated for limited period in order to elucidate a specific problem or when an abnormal or suspected abnormal situation exists.
(ICRP 35)

Monitoring
Measurements of radiation in pusuit of a program of protection.
(ICRP 36)

Monitoring
Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination present in an occupied region.
Area Monitoring - Routine monitoring of the radiation level or contamination of a particular area, building, room or equipment. Some laboratories or operations distinguish between routine monitoring and survey activities.
Personnel Monitoring - Monitoring any part of an individual, his breath, or excretions, or any part of his clothing.
(RHH)

Monitoring
The measurement of radiation or radioactivity for reasons related to the assessment or control of exposure to radiation or radioactive material.
(ICRP 7)

Monitoring
Periodic or continuous determination of the exposure rate in an area (are monitoring) or the exposure received by a person (personnel monitoring) or the measurement of contamination levels.
(NBS 73)

Monitoring
Periodic or continuous determination of the dose rate in an occupied region or of the dose received by a person.
(NBS 54)

Monitoring (radiation monitoring, radiation protection monitoring)
The measurement of radiation levels, concentrations, surface area concentrations or quantities of radioactive material and the use of the results of these measurements to evaluate potential exposure and doses.
(10CFR20.1003)

Monitoring program
A monitoring program will need to specify the type and frequency of measurements, procedures for measurements or for sampling and subsequent laboratory analysis, statistical test procedures, methods of data handling, interpretation and recording. The network of sampling locations must be carefully chosen with regard to the source and pathways of exposure. The final part of the monitoring program may involve computation of dose equivalents to individuals or populations or it may merely require comparison of measurements with appropriate derived and authorized limits.
(ICRP 43)

Monitoring system
Any system, required under the monitoring sections in applicable subparts, used to sample and condition (if applicable), to analyze, and to provide a record of emissions or process parameters.
(40CFR61.02)

Monitoring, personal
The measurement of activity in the whole body, in a region of the body, in material eliminated from the body or in air for reasons related to the estimation of intake of radioactive material. The term monitoring includes interpretation of the measurements.
Routine monitoring: Monitoring carried out at regular intervals during normal operations.
Special monitoring: Monitoring carried out in actual or suspected abnormal conditions.
Operational monitoring: Monitoring related to ceratin operations.
Confirmatory monitoring: Monitoring carried out in situations where workers are most unlikely to be exposed to significant intakes, in order to demonstrate satisfactory conditions.
(ICRP 54)

Monitoring, radiation (radiation protection)
The continuing collection and assessment of the pertinent information to determine the adequacy of radiation protection practices and to alert to potentially significant changes in conditions or protection performance.
(ANSI N1.1-1976)

Monoclonal antibodies
Monospecific antibodies produced by a single dose of B-cells.
(HPJ 60)

Monodisperse
Composed of particles with a single size or a small range of sizes
(AM-1993)

Monodisperse
Particles falling within a very narrow range of sizes so as to behave identically as far as deposition in the lung.
(ENV RAD)

Monodisperse Aerosol
Aerosol composed of particles having a single size or a very small range of sizes.
(NCRP 125)

Monodisperse aerosol
An aerosol containing particles of nearly the same size, generally applied to aerosols having relative standard deviations of size < 0.1.
(TID-26608)

Monoenergetic
Posessing a single energy. This term is sometimes used to characterize a radiation field in which the particles or photons have various energies within a narrowly limited band.
(NCRP 51)

Monoenergetic radiation
Ionizing radiation consisting of photons with practically the same energy, or corpuscles of one type having nearly the same kinetic energy.
(IEC 50-393-1993)

Monosomy
The absence of one chromosome from the complement of an otherwise diploid cell.
(BEIR V)

Monte carlo calculation
The evaluation of a probability distribution by means of random sampling.
(BEIR V)

Monte carlo method
The use of a computer-determined random number scheme for selecting the value of a variable such as the angle of scatter to use in a given calculation. The use of the Monte Carlo method for determining absorbed fractions is described by Snyder et al. (1974).
(NCRP 83)

Monte carlo method
A method permitting the solution by means of a computer of problems of physics, such as those of neutron transport, by determining the history of a large number of elementary events by the application of the mathematical theory of random variables.
(RHH)

Morbidity
1. The condition of being diseased.
2. The incidence, or prevalence, of illness in any sample.
(BEIR III)

Morbidity
1. The condition of being diseased.
2. The ratio of sick to well persons in a community.
(BEIR I)

Mortality (rate)
The rate to which people die from disease, e.g., a specific type of cancer, often expressed as number of deaths per 100,000 per year.
(BEIR V)

Mosaic semiconductor detector
Semiconductor detector consisting of several individual detectors connected in parallel into a mosaic structure in order to increase the sensitive area.
(IEC 50-394-1993)

Mossbauer effect
Recoil free nuclear emission and resonant absorption of gamma radiation.
(IEC 50-393-1993)

Mounting frame
The structure to which a filter unit is clamped and sealed.
(ERDA 76-21)

Mouthpiece
That portion of a respirator which is held in the wearer's mouth and is connected to an air purifying device or respirable gas source, or both. It is designed to make a gas-tight or particle-tight fit with the mouth.
(ANSI Z88.2-1980)

Movement control center
An operations center which is remote from transport activity and which maintains periodic position information on the movement of strategic special nuclear material, receives reports of attempted attacks or thefts, provides a means for reporting these and other problems to appropriate agencies and can request and coordinate appropriate aid.
(10CFR73.2)

MPC
Maximum Permissible Concentration; replaced by the DAC for the concentration limit in air, and no longer used for the concentrations in water.
(FGR 11)

MPC
Maximum permissible concentration. These concentrations are set by the National Committee on Radiation Protection. They are recommended maximum average concentrations of radionuclides to which a worker may be exposed, assuming that he works 8 hours per day, 5 days a week, and 50 weeks a year.
(ANSI Z88.2-1969)

MPCa
Maximum permissible concentration. These concentrations are set by the National Committee on Radiation Protection. They are recommended maximum average concentrations of radionuclides to which a worker may be exposed, assuming that he works 8 hours per day, 5 days a week, and 50 weeks a year.
(ANSI Z88.2-1980)

MSBR
Molten Salt Breeder Reactor
(NCRP 62)

MTU
Metric tons of uranium equivalent, as applied to mass of reactor fuel.
(NCRP 81)

MTU
Metric tons of uranium equivalent, as applied to mass of reactor fuel.
(NCRP 75)

MTU
Metric tons of uranium.
(NCRP 62)

Mu-meson
See muon.
(USAEC-1974)

Mucociliary Clearance Velocity (Mucous Flow Rates)
Time rate of movement for particles up the mucus escalator of the tracheobronchial airways.
(NCRP 125)

Mucociliary pathway
Those portions of the respiratory tract lined with cilia that propel materials to the mouth.
(NCRP 84)

Mucocilliary blanket
The layer of mucus lining the generations of the lung above the pulmonary region and responsible for transporting deposited materials out of the lung and into the gastrointestinal (GI) tract.
(ENV RAD)

Mucocilliary pathway
Those portions of the respiratory tract lined with cilia that propel materials toward the mouth.
(FGR 11)

Mucous cells
Columnar epithelial cell of extrathoracic and bronchial airways with mucous secretary granules in cytoplasm.
(ICRP 66)

Mucous Escalator
Mucus flow moving up the tracheobronchial airways due to ciliary action.
(NCRP 125)

Mucus Cells Or Mucus Glands
Cells or glands secreting a viscid fluid consisting of mucin, inorganic salts, and water that are present in the bronchi.
(NCRP 125)

Multigroup model
Model which divides the neutron population into a finite number of energy groups with each group being assigned a single effective energy.
(IEC 50-393-1993)

Multigroup model
A model which divides a neutron population into a finite number of neutron energy groups.
(ANSI N1.1-1976)

Multigroup theory
A theory of neutron transport using the multigroup model.
(ANSI N1.1-1976)

Multijunction semiconductor detector
Semiconductor detector in which a combination of several PN junctions is used.
(IEC 50-394-1993)

Multilateral approval
Approval by both the appropriate competent authority of the country of origin and of each country through or into which the shipment is to be transported. This definition does not imply approval from countries over which radioactive materials are carried in aircraft, if there is no scheduled stop in that country.
(49CFR173.403)

Multimodal
More than one transport mode. This term indicates that there are several transport methods required to achieve a complete shipment from shipper to receiver.
(ANSI N14.24-1985)

Multiple dosimetry
The practice of using more than one dosimeter on an individual's body to obtain information regarding radiation exposure. (Also known as "multiple badge dosimetry" or "multibadging.")
(HPS N13.41-1997)

Multiple source
A multiple source is comprised of two or more sealed sources securely incorporated in a housing or equipment so as to give rise to a radiation field suitable for special purposes. In practice, a multiple source may also be referred to as a source array or a source assembly and the individual sources therein as source elements.
(ICRU 18)

Multiplication (subcritical)
Ratio of the total number of neutrons resulting from fission and a source, which exist in equilibrium in a subcritical assembly, to the total number of neutrons which would exist in the assembly due to the source in the absence of fission.
(IEC 50-393-1993)

Multiplication factor
Ratio of the total number of neutrons produced during a time interval, excluding neutrons produced by sources whose strengths are not a function of fission rate, to the total number of neutrons lost by absorption and leakage during the same interval.
(IEC 50-393-1993)

Multiplication factor (k)
The ratio of the total number of neutrons produced during a time interval (excluding neutrons produced by sources whose strengths are not a function of fission rate) to the total number of neutrons lost by absorption and leakage during the same time interval. When the quantity is evaluated for an infinite medium or for an infinite repeating lattice, it is referred to as the infinite multiplication factor (k_¥), and when the quantity is evaluated for a finite medium, it is referred to as the effective multiplication factor (k_eff.)
(ANSI N1.1-1976)

Multiplication factor (or constant)
[Symbol k] The ratio of the number of neutrons present in a reactor in any one neutron generation to that in the immediately preceding generation. Criticality is achieved when this ratio is equal to one. The "infinite" multiplication factor is the ratio in a theoretical system from which there is no leakage, that is, a reactor of infinite size; for an actual reactor (from which leakage does occur), the term effective multiplication factor, which is the ratio based on neutrons available after leakage, is commonly used. (See generation time, leakage, neutron, reactivity.)
(USAEC-1974)

Multiplication factor, subcritical
In a subcritical assembly containing a neutron source, the equilibrium ratio of the total number of neutrons resulting from fission and the source to the total number of neutrons which would exist in the assembly due to the source alone.
(ANSI N1.1-1976)

Multiplication, neutron
The production by a neutron of other neutrons in a medium containing fissionable material.
(ANSI N1.1-1976)

Multiplicative interaction model
A model in which independent risk factors interact so the combined risk is the product of the relative risk due to each factor alone.
(BEIR IV)

Multiplicative interaction model (MIM)
The assumption that the relative risk (the relative excess risk plus one) resulting from the exposure to two risk factors is the product of the relative risks from the two factors taken separately.
(BEIR V)

Multiplying medium
Medium inside which fission chain reactions can take place.
(IEC 50-393-1993)

Multiplying medium
A medium in which a neutron-induced fission chain reaction can take place.
(ANSI N1.1-1976)

Muon
A secondary cosmic particle with a mass about 215 times that of the electron. Positive and negative muons exist.
(NCRP 94)

Muon
(Contraction of mu-meson.) An elementary particle, classed as a lepton (not as a meson), with 207 times the mass of an electron. It may have a single positive or negative charge. (See lepton, meson.)
(USAEC-1974)

Muon (µ)
Elementary short-lived charged particle, having a rest mass approximately 207 times that of the electron, spin 1/2, and life time of 2.2 (s.
(IEC 50-393-1993)

Muon or mu meson
A cosmic particle with a mass of 215 times that of the electron. Positive and negative muons exist.
(NCRP 45)

Mushroom cloud
See atomic cloud.
(USAEC-1974)

Mutation
The alteration of existing genes or chromosomes to create in their place new variants or alleles of these genes or chromosomes; it involves some change in the sequence of nucleotides within a particular region of DNA.
(HPJ 60)

Mutation
Change in the germ plasm of an individual; this change may be transmitted to subsequent generations.
(NCRP 48)

Mutation
A permanent transmissible change in the characteristics of an offspring from those of its parents.
(USAEC-1974)

Mutation
Alteration of the usual hereditary pattern, usually sudden.
(RHH)

MWe
Megawatts electrical.
(NCRP 81)

MWe
Megawatts electrical.
(NCRP 75)

MWe
Megawatts electrical.
(NCRP 62)

MWt
Megawatts thermal.
(NCRP 81)

MWt
Megawatts thermal.
(NCRP 75)

MWt
Megawatts thermal.
(NCRP 62)

Mycelium
A mass of fungal hyphae.
(AM-1993)

Mycotoxin
A toxic chemical produced by fungi.
(AM-1993)

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