Ratio of the probability that the data set (image data, g) would occur from a specified hypothesis H1 to the probability that it would occur from the alternative hypothesis, H2.
(ICRU 54)
li (t)
Fractional rate of particle transport of material towards regional lymph nodes from region i at time t after an acute intake.
(ICRP 66)
Label
See tracer, isotopic.
(USAEC-1974)
Labeled compound
A compound consisting, in part, of labeled molecules; by observation of radioactivity or isotopic composition, this compound or its fragments may be followed through physical, chemical, or biologic processes.
(BEIR III)
Labeled compound
A compound consisting, in part, of labeled molecules; by observation of radioactivity or isotopic composition, this compound or its fragments may be followed through physical, chemical, or biologic processes.
(BEIR I)
Labeled compound
A compound consisting, in part, of labeled molecules; by observation of radioactivity or isotopic composition, this compound or its fragments may be followed through physical, chemical, or biologic processes.
(RHH)
Labeled molecule
A molecule containing one or more atoms distinguished by non-natural isotopic composition (with radioactive or stable isotopes).
(RHH)
Labeling (radiochemistry)
The incorporation of a tracer, radioactive or stable, into a molecular species or macroscopic sample for purposes of detection.
(ANSI N1.1-1976)
Laboratory certified instrument
An instrument or specific type of instrument that has been certified by a third party accredited testing laboratory as meeting the requirements of this standard.
(ANSI N42.17C-1989)
Laboratory certified instrument
An instrument or specific type of instrument that has been certified by a third party accredited testing laboratory as meeting the requirements of this standard.
(ANSI N42.17A-1989)
Laboratory standard
A standard used to test the accuracy of analytical procedures or measurement equipment.
(NCRP 114)
Laboratory standard
In this report, a 226Ra solution prepared from an NBS certified source and used to deliver a known amount or known rate of production of 222Rn.
(NCRP 97)
Lacunae
Tiny spaces within mammalian bone which house the osteocytes. They are formed during the process of bone formation as osteoblasts surround themselves with calcified matrix and are renamed osteocytes. Lacunae in human bone are approximately prolate spheroids 24 mm long and 8 mm in diameter and occupy about 2% of bone volume. These figures correspond to 25,000 lacunae/mm³.
(ICRP 20)
Lag time
The time between the occurrence of the primary ionizing event and the occurrence of the count.
(RHH)
li(t)
Overall instantaneous rate of clearance of material from region i at time t after an acute intake.
(ICRP 66)
Lamellar tearing
A condition that may occur following the welding of thick rolled carbon steel plates to each other, particularly at T-joints, where an internal delamination occurs in the base metal between flattened inclusions that are perpendicular to shrinkage stresses.
(ANSI N14.6-1986)
Lamina dissecans
A cell-sparse layer between the Purkinje and inner granular layers of the cerebellum seen at the five-layer stage; it has been recognized only in primates (and possibly in the blue whale). The lamina dissecans appears at about the 20th week of development and disappears some 12 weeks later. Its function is unknown.
(ICRP 49)
Lamina propria
A layer of reticular and collagenous connective tissue and elastic fibers, containing lymphoid cells and macrophages, and delimited from the epithelium by the basement membrane.
(ICRP 66)
Laminar flow
Gas flow with a smooth, nonturbulent pattern of streamlines, with no streamline looping back on itself: usually occurs at very low Reynolds numbers.
(AM-1993)
Land carrier
A land carrier is a railroad or truck operator or a series of such organizations that perform the overland portion of a multimodal shipment of radioactive material. The land carrier typically provides routine transportation services as compared to a rigging company (or heavy hauler), which uses specialized equipment to move large objects relatively short distances as part of its loading or unloading function. (See Rigging company.)
(ANSI N14.24-1985)
Land disposal facility
The land, buildings, and equipment which is intended to be used for the disposal of radioactive wastes into the subsurface of the land. For purposes of this chapter, a geologic repository as defined in Part 60 is not considered a land disposal facility.
(10CFR61.2)
Langerhans cells
Dendritic cells in the epidermis containing rod or racket-shaped so--called Birbeck granules. The cells have surface receptors for immunoglobulin (Fc) and complement (C3). The cells are derived from bone marrow stem cells and are involved in antigen processing.
(ICRP 59)
Lanthanide series
The series of elements beginning with lanthanum, Element No. 57, and continuing through lutetium, Element No. 71, which together occupy one position in the Periodic Table of the elements. These are the "rare earths", which all have chemical properties similar to lanthanum. They also are called the "lanthanides". (See rare earths.)
(USAEC-1974)
Large area (macro) transfer factor
The factor describing the scaling of information between the input and output of an imaging system. It is concerned with changes in the signal over a large area, c.f., spatial detail transfer characteristic.
(ICRU 54)
Larynx
Organ structure of the muscle and cartilage at the upper end of the human trachea containing the vocal cords.
(NCRP 125)
Laser
Light amplification by the stimulated emission of radiation. The laser region is the portion of the spectrum which includes ultra-violet, visible light and infrared.
(RHH)
Late somatic effects
Radiation effects that may occur in individuals a considerable time after exposure to radiation; these include mutagenic effects and carcinogenic effects.
(NCRP 105)
Latency time
Time which elapses between the arrival of a particle at the detector and the moment when the pulse characteristic quantity reaches the threshold of response of the circuit associated with the detector.
(IEC 50-394-1993)
Latent energy (of a radioactive aerosol)
Total energy released per volume unit of the radioactive aerosols under a full decay of the daughter products of the emanations contained in these aerosols.
(IEC 50-393-1993)
Latent period
The period of time between exposure and expression of the disease. After exposure to a dose of radiation, there is a delay of several years (the latent period) before any cancers are seen.
(BEIR V)
Latent period
Period or state of seeming inactivity between time of exposure of tissue to an injurious agent and an observed response. Also time to response or induction period.
(NCRP 98)
Latent period
The period of time between exposure and expression of the disease. After exposure to a dose of radiation, there is a delay of several years (the latent period) before any cancers are seen.
(BEIR IV)
Latent period
Period of seeming inactivity between time of exposure of tissue to injurious agent and response.
(BEIR III)
Latent period
The period between the time of the exposure to an agent and the beginning of the response.
(ANSI N1.1-1976)
Latent period
The period or state of seeming inactivity between the time of exposure of tissue to an injurious agent and response.
(BEIR I)
Latent period
Period of seeming inactivity between time of exposure of tissue to injurious agent and response.
(RHH)
Lattice
An orderly array or pattern of nuclear fuel elements and moderator in a reactor or critical assembly. Also, the arrangement of atoms in a crystal. (See geometry.)
(USAEC-1974)
Lattice reactor
An array of fuel and other materials arranged according to a regular pattern.
(ANSI N1.1-1976)
Lattice, active
A region containing a regularly repeating spatial distribution of fissile material and, usually, other material, in which a fission chain reaction can occur.
(ANSI N1.1-1976)
Lavage
Washing out of an organ (i.e., stomach, intestinal tract, sinuses or lung).
(NCRP 125)
Law, 1/v
The inverse dependence of some neutron cross sections on the relative speeds of the neutron and nucleus. This dependence is observed for slow neutron absorption cross sections when there are no nearby resonance levels.
(ANSI N1.1-1976)
Lay-barge radiography
Industrial radiography performed on any water vessel used for laying pipe.
(10CFR34.3)
LD50
See dose, median lethal.
(ANSI N1.1-1976)
LD50
See dose, median lethal.
(BEIR I)
LD50
Dose of ionizing radiation required to kill 50 percent of the animals in a given group. A time limit of 30 days is usually applied. (LD50/30).
(NBS 63)
LD50 (radiation dose)
Dose of radiation required to kill, within a specified period, 50 percent of the individuals in the population.
(NCRP 98)
LD50 (radiation dose)
See median lethal dose.
(BEIR III)
LD50 time
See median lethal time.
(ANSI N1.1-1976)
Leach
Dissolve soluble material by the action of percolating liquid.
(NCRP 118)
Leachate
The solution or product obtained by leaching.
(NCRP 118)
Lead equivalence
The thickness of lead affording the same attenuation, under specified conditions, as the material in question.
(NCRP 49)
Lead equivalent
The thickness of lead affording the same attenuation, under specified conditions, as the material in question.
(NCRP 102)
Lead equivalent
The thickness of lead affording the same attenuation, under specified conditions, as the material in question.
(RHH)
Lead equivalent
The thickness of lead affording the same attenuation, under specified conditions, as the material in question.
(NBS 73)
Lead equivalent
Thickness of lead affording the same reduction in dose rate as the material in question, under specified conditions.
(NBS 54)
Lead-in guides
Mechanical provisions for the alignment of two members of the hoisting system where the control of the alignment between these members is difficult because of the lack of precision available in the positioning mechanism or because of the difficulty of observing accurately the relative positions of the two members to be mated.
(ANSI N14.6-1986)
Leak
Any opening through a containment system that permits the escape of the contents. NOTE: It is considered conservative to assume that slurries and powders behave as a liquid and aerosols behave as gases. (The predicted leakage rate will be greater than the actual leakage rate.)
(ANSI N14.5-1987)
Leakage
In nuclear engineering, the escape of neutrons from a reactor core. Leakage lowers a reactor's reactivity. (See neutron economy.)
(USAEC-1974)
Leakage (direct) radiation
All radiation coming from the source except the useful beam.
(NBS 54)
Leakage (in a reactor)
Escape of radiation through a shield, especially by holes or cracks through the shield.
(IEC 50-393-1993)
Leakage (reactor theory)
The net loss of neutron from a region of a reactor by escape across the boundaries of the region.
(ANSI N1.1-1976)
Leakage (shielding)
Escape of radiation through a shield, especially by way of holes or cracks.
(ANSI N1.1-1976)
Leakage current
Total detector current flowing at the operating bias in the absence of radiation.
(IEC 50-394-1993)
Leakage factor, fast
The probability that a neutron will leak from a specified system while it is a fast neutron.
(ANSI N1.1-1976)
Leakage factor, intermediate
The probability that a neutron will leak from a specified system while it is an intermediate neutron.
(ANSI N1.1-1976)
Leakage radiation
See radiation.
(NCRP 49)
Leakage radiation
See radiation.
(NCRP 102)
Leakage radiation
All radiation, except the useful beam, coming form within the accelerator components, e.g., that radiation that is attenuated by a collimator, diaphragm, or source shielding.
(NCRP 51)
Leakage radiation
Radiation other than the useful beam emitted from the x-ray tube assembly.
(ANSI N537-1976)
Leakage radiation
All radiation coming from the source except the useful beam.
(NBS 73)
Leakage radiation
All radiation coming from the accelerator outside the limits of the useful beam.
(NBS 55)
Leakage technique factors
These are specific technique factors (associated with specific source assemblies) which are used in measuring leakage radiation. They are defined as follows:
(1) For diagnostic source assemblies (qv) (a) for capacitor energy storage equipment, the maximum rated kV and the maximum rated number of exposures in an hour at the maximum rated kV with the mAs being the greater of 10 mAs or the minimum mAs (allows greatest exposure in an hour) available. (b) for field emission equipment rated for pulsed operation, the maximum rated number of pulses in an hour at the maximum kVp. (c) for all other types of equipment, the maximum rated kVp and the maximum rated continuous tube current for the maximum kVp.
(2) For therapeutic source assemblies (qv) for x-ray production at tube potentials below 500 kV, the maximum rated continuous tube current for the maximum kV.
(3) For therapeutic source assemblies for x-ray production at tube potentials of 500 kV and above and for gamma source assemblies, see therapeutic source assemblies.
(NCRP 102)
Leaktight
A leakage rate less than or equal to 1 x 10-7 std cm³/s, at an upstream pressure of 1 atm abs and a downstream pressure of 0.01 atm abs or less, irrespective of the form of the radioactive contents. 1 x 10-7 std cm³/s is equal to 4.09 x 1012 gram-mols/s of dry air or helium and is equivalent to a helium leakage rate, under the same conditions, of 1.96 x 10-7 cm³/s. Note: Leak paths with leakage rates of 10-7 std cm³/s are small and clog easily with liquids or minute particles. Although such small leaks can be detected, they are rarely found in practice.
(ANSI N14.5-1987)
Leaktightness
The condition of a system, unit, or component where leakage through its pressure boundary is less than a specified maximum value at a specified pressure differential across the pressure boundary.
(ERDA 76-21)
Leaky aquifer
An aquifer which consists of at least two permeable units separated by a less permeable layer which partially separates the water in each unit, but allows for a certain amount of leakage between units.
(NCRP 76)
Lens of the eye
A tissue of concern from a dosimetric and regulatory point of view because of the potential for radiation-induced cataracts. The lens of the eye is assumed to be located at a depth of 300 mg cm-2.
(HPS N13.41-1997)
Lens of the eye dose equivalent
The external exposure of the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 cm.
(10CFR835.2-1993)
Lepton
One of a class of light elementary particles (having small mass). Specifically, an electron, a positron, a neutrino, an antineutrino, a muon, or an antimuon.
(USAEC-1974)
Lepton
One of a class of light elementary particles (having small mass). Specifically, an electron, a positron, a neutrino, an antineutrino, a muon, or an antimuon.
(RHH)
Lesion
A hurt, wound or local degeneration.
(RHH)
LET
The energy lost by a charged particle passing through a substance per unit length of path; related concepts are mass, atomic, molecular and relative stopping power. Also know as linear energy transfer.
(ENV RAD)
LET
See linear energy transfer.
(ANSI N1.1-1976)
Lethal damage
Damage which, unless modified or repaired, results in the death of a cell. Note that even in the case of a single exposure, the physiological conditions during the irradiation or the metabolic events that follow may influence the degree of effect expressed by a cell. In the instance of cell survival, for example, and in the simplest case of exponential inactivation, the survival curve may become less steep (or more steep) depending upon the repair (or enhancement) of potentially lethal damage during or after exposure.
(ICRU 30)
Lethal dose
A dose of ionizing radiation sufficient to cause death. Median lethal dose (MLD or LD-50) is the dose required to kill within a specified period of time (usually 30 days) half of the individuals in a large group of organisms similarly exposed. The LD-50/30 for man is about 400-450 roentgens. (See biological dose, roentgen, survival curve, threshold dose.)
(USAEC-1974)
Lethargy
Of a neutron, the natural logarithm of the ratio of a reference energy to the neutron energy.
(ANSI N1.1-1976)
Lethargy (of a neutron)
Natural logarithm of the ratio of a reference energy to the energy of a neutron.
(IEC 50-393-1993)
Leukemia
A form of cancer in the blood. Any of several diseases of the hemopoietic system characterized by uncontrolled leukocyte proliferation.
(RRM)
Leukemia
A disease in which there is a great over production of white blood cells, or a relative over production of immature white cells, and great enlargement of the spleen. The disease is variable, at times running a more chronic course in adults than in children. It is almost always fatal. It can be produced in some animals by long-continued exposure to low doses of ionizing radiation.
(RHH)
Leukemia
Disease of blood-forming organs, usually with greatly increased production of white blood cells; these cells are invasive, and body deterioration may be either chronic (slow) or acute (rapid).
(NBS 63)
Leukocyte
White blood corpuscle.
(NBS 63)
Level meter
Measuring assembly, including an ionizing radiation source and a radiation meter, intended to measure or to indicate the level in a container of liquid or granular substances, even when direct access to that level is not possible.
(IEC 50-394-1993)
Level width
(1) The range of energies around a given excitation energy at which an excited state of a nucleus may exist.
(2) The uncertainty in the energy of the excited state of a nucleus corresponding to the uncertainty in the time existence (i.e., the mean life) of the excited state.
(ANSI N1.1-1976)
Level width, partial
A quantity assigned to each mode of decay when the decay of a resonance level can proceed in several different ways. Each partial level width is proportional to the probability of the corresponding mode of decay, and their sum is equal to the total resonance width.
(ANSI N1.1-1976)
License
A general or specific export or import license issued pursuant to this part.
(10CFR110.2)
License
A license issued under the regulations in part 30 through 36, 39, 40, 50, 60, 61, 70, or 72 of this chapter.
(10CFR20.1003)
License
A license issued under the regulations in Part 61 of this chapter.
(10CFR61.2)
License
A license for by-product material issued pursuant to the regulations in this part and Parts 31 through 36 and 39 of this chapter.
(10CFR30.4)
License
A license issued under the regulations in parts 30 through 36, 39, 40, 60, 61, 70, or 72 of this chapter, including licenses to operate a production or utilization facility pursuant to part 50 of this chapter. Licensee means the holder of such a license.
(10CFR19.3)
License
Except where otherwise specified, means a license issued pursuant to the regulations in this part.
(10CFR40.4)
License
A license issued pursuant to part 70 of this chapter.
(10CFR74.4)
License
Except where otherwise specified, means a license issued pursuant to the regulations in this part.
(10CFR70.4)
License
A license issued under the regulations in part 30 through 35, 39, 40, 50, 60, 61, 70, or part 72 of this chapter.
(10CFR20.3)
Licensed material
Source material, special nuclear material, or byproduct material received, possessed, used, transferred or disposed of under a general or specific license issued by the Commission.
(10CFR20.1003)
Licensed Material
By-product, source, or special nuclear material received, possessed, used, or transferred under a general or specific license issued by the Commission pursuant to the regulations in this chapter.
(10CFR71.4)
Licensed material
Byproduct, source, or special nuclear material received, processed, used, or transferred under a license issued by the Commission under the regulations in this chapter.
(10CFR39.2)
Licensed material
Source material, special nuclear material, or by-product material received, possessed, used, or transferred under a general or specific license issued by the Commission pursuant to the regulations in this chapter.
(10CFR20.3)
Licensed material
Source material, special nuclear material, or byproduct material received, possessed, used or transferred under a general or special license issued by the Atomic Energy Commission or a state.
(USAEC-1974)
Licensee
The holder of a license.
(10CFR20.1003)
Licensee
An individual licensed operator or senior operator.
(10CFR55.4)
Licensee
A person authorized by a specific or a general license to export or import nuclear equipment or material pursuant to this part.
(10CFR110.2)
Licensee
The holder of such a license.
(10CFR61.2)
Licensee
The holder of such a license.
(10CFR20.3)
Life table
A table showing the number of persons who, of a given number born or living at a specified age, live to attain successive higher ages, together with the numbers who die in each age interval.
(BEIR V)
Life-span study (LSS)
Life-span study of the Japanese atomic-bomb survivors; the sample consists of 120,000 persons, of whom, 82,000 were exposed to the bombs, mostly at low doses.
(BEIR IV)
Life-span study (LSS)
Life-span study of the Japanese atomic-bomb survivors; the sample consists of 120,000 persons, of whom, 82,000 were exposed to the bombs, mostly at low doses.
(BEIR III)
Lifetime
See mean life.
(ANSI N1.1-1976)
Lifetime risk
The lifetime probability of dying of a specific disease.
(NCRP 98)
Lifetime risk
The lifetime probability of dying from a specific disease.
(BEIR IV)
Lifetime risk
Exposure-induced risks reported as a function of the distribution of age in a population.
(RRM)
Lifetime risk ratio
The ratio of the lifetime risk (Re) of an exposed person to the lifetime risk of an unexposed person (R0). This number minus 1 is the proportional increased risk associated with exposure (Re - R0).
(BEIR IV)
Light guide
Optical device which is intended to transmit light without significant loss and may be placed between a scintillator and a photomultiplier tube.
(IEC 50-394-1993)
Light hydrogen
Ordinary hydrogen.
(USAEC-1974)
Light scattering
Change in the direction of light radiation due to reflection, diffraction, and refraction from a particle.
(AM-1993)
Light sensitivity (of a photomultiplier)
Quotient of a photomultiplier anode current by an incident light flux.
(IEC 50-394-1993)
Light sensitivity nonuniformity (of a photomultiplier)
Variation of the light sensitivity over the photocathode surface.
(IEC 50-394-1993)
Light water
Ordinary water (H2O), as distinguished from heavy water (D2O).
(USAEC-1974)
Likelihood ratio (L)
Ratio of the probability that the data set (image data, g) would occur from a specified hypothesis H1 to the probability that it would occur from the alternative hypothesis, H2.
(ICRU 54)
Limited occupancy area
Area in which the radiation level may be so high that a person, in a day's work, might receive radiation exceeding the permissible dose.
(NCRP 48)
Limited quantity of radioactive material
A quantity of radioactive material not exceeding the material package limits specified in §173.423 and which conform with requirements specified in §173.421.
(49CFR173.403)
Limiting Vvalue
A dose quantity of interest for which limits have been established to control radiation exposures. Examples of limiting values may include regulatory limits, ALARA (As Low As Reasonably Achievable) goals, administrative limits, Planned Special Exposure limits, or others.
(HPS N13.41-1997)
Limits (dose limits)
The permissible upper bounds of radiation doses.
(10CFR20.1003)
Linac
Short for linear accelerator.
(USAEC-1974)
Line power switch
A device for making and breaking the connections to the electrical supply.
(ANSI N537-1976)
Line spread function
The radiant exposure distribution in the image of an infinitely narrow and infinitely long slit (line source) of unit radiant energy per unit length (ICRU, 1986).
(ICRU 54)
Line spread function (LSF)
A one-dimensional representation of a two-dimensional intensity distribution of a point image. The LSF is a measure of the ability of a system to form images of extended objects.
(NCRP 66)
Lineal energy
Lineal energy is defined by ICRU as
where e is the energy imparted to the matter in a volume of interest by an energy deposition event and l is the mean chord length in that volume.
(ICRP 60)
Lineal energy
The lineal energy, y, is the quotient of e by l where e is the energy imparted to the matter in a volume of interest by an energy deposition event and l is the mean chord length in that volume,
Unit: J m-1. y may be expressed in eV m-1, or some convenient sub-multiple or multiple, such as keV µm-1. For a convex region of volume, V, and surface area, a, the mean chord length, l, equals 4V/a.
(ICRU 44)
Lineal energy (y)
Quotient of e by , where e is the energy imparted to the matter in a volume of interest by an energy deposition event and is the mean chord length in that volume.
(IEC 50-393-1993)
Lineal energy (y)
The quotient e by l, where e is the energy imparted to the matter in a volume of interest by a single energy deposition event and l is the mean chord length in that volume.
(ICRU 36)
Lineal energy (y)
The stochastic quantity lineal energy, y, is the quotient e by d, where e is the energy imparted to the matter in a volume during an energy deposition event and d is the mean chord length in the volume of interest.
(ICRU 26)
Lineal energy (y)
The stochastic quantity lineal energy, y, is the quotient e by d, where e is the energy imparted to the matter in a volume during an energy deposition event and d is the mean chord length in the volume of interest.
(ICRU 19)
Linear (L) model
Also, linear dose-effect relationship; expresses the effect (e.g., mutation or cancer) as a direct (linear) function of dose.
(BEIR V)
Linear (L) model
Also, linear dose response relationship; expresses the incidence of (e.g., mutation or cancer) as a direct (linear) function of dose.
(NCRP 98)
Linear accelerator
A particular type of high voltage x-ray machine.
(NCRP 48)
Linear accelerator
A long straight tube (or series of tubes) in which charged particles (ordinarily electrons or protons) gain in energy by the action of oscillating electromagnetic fields. (See accelerator.)
(USAEC-1974)
Linear accelerator
A device for accelerating charged particles. It employs alternate electrodes and gaps arranged in a straight line, so proportioned that when potentials are varied in the proper amplitude and frequency, particles passing through the waveguide receive successive increments of energy.
(RHH)
Linear collision stopping power
That part of the total linear stopping power due to all events other than energy transfer to bremsstrahlung.
(IEC 50-393-1993)
Linear collision stopping power
The quotient dE by dl where dl is the distance traversed by the particle and dE is the energy loss due to collisions.
(ICRU 30)
Linear detector
Radiation detector in which the output signal is a linear function of a quantity related to the incident radiation, generally the energy being lost in the sensitive volume of the detector.
(IEC 50-394-1993)
Linear dose model
This model postulates that the excess risk is linearly proportional to the dose.
(BEIR IV)
Linear energy transfer
The linear energy transfer or restricted collision stopping power, LD, of a material for charged particles is the quotient of dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl due to those collisions with electrons in which the energy loss is less than D,
Unit: J m-1. LD may also be expressed in keV µm-1. When D is larger than the maximum delta-ray energy, LD is called L¥, which is identical to collision stopping power, Scol.
(ICRU 44)
Linear energy transfer
The average energy locally imparted to a medium by a charged particle of specified energy per unit of distance traversed. Note: (1) The term "locally imparted" may refer to a maximum distance from the track or to a maximum value of discrete energy loss by the particle beyond which losses are no longer considered as local. In either case, the limits chosen should be specified; (2) The concept of LET is different from that of stopping power. The former refers to energy imparted within a limited volume, the latter to the loss of energy from the particle regardless of where this energy is absorbed.
(ANSI N1.1-1976)
Linear energy transfer (LD)
The linear energy transfer or restricted linear collision stopping power, LD, of a material for charged particles is the quotient dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl due to those collisions with electrons in which the energy is less than D.
(ICRP 51)
Linear energy transfer (LD)
The linear energy transfer or restricted linear collision stopping power, LD, of a material for charged particles is the quotient dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl due to those collisions with electrons in which the energy is less than D.
(ICRU 33)
Linear energy transfer (LD)
The quotient dE by dl, where dl is the distance traversed by a particle and dE is the average energy loss in dl due to those collisions with energy transfers less than some specified value of D, i.e.
(ICRU 30)
Linear energy transfer (LD), LET
For a material and for charged particles, quotient of dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl due to those collisions with electrons in which the energy loss is less than a chosen value D.
(IEC 50-393-1993)
Linear energy transfer (L)
Is the quotient of dE by dl, where dE is the energy lost by a charged particle in traversing a distance dl due to those collisions with electrons in which the energy loss is less than D.
(NCRP 93)
Linear energy transfer (L)
The linear energy transfer (L) of charged particles in a medium is the quotient dEL by dl where dEL is the average energy locally imparted to the medium by a charged particle of specified energy in traversing a distance dl.
(NBS 92)
Linear energy transfer (L)
The linear energy transfer (L) of charged particles in a medium is the quotient dEL by dl where dEL is the average energy locally imparted to the medium by a charged particle of specified energy in traversing a distance dl.
(ICRU 10f)
Linear energy transfer (L)
The linear energy transfer (L) of charged particles in a medium is the quotient dEL by dl where dEL is the average energy locally imparted to the medium by a charged particle of specified energy in traversing a distance dl.
(ICRU 10b)
Linear Energy Transfer (LET)
Energy lost by a charged particle, due to collisions with electrons, in traversing a distance through matter.
(NCRP 125)
Linear energy transfer (LET)
Average amount of energy lost per unit track length.
Low LET - Radiation characteristic of light charged particles such as electrons produced by X-rays and gamma rays where the distance between ionizing events is large on the scale of a cellular nucleus.
High LET - Radiation characteristic of heavy charged particles such as protons and alpha particles where the distance between ionizing events is small on the scale of a cellular nucleus.
(BEIR V)
Linear energy transfer (LET)
Average amount of energy lost per unit of particle track length and expressed in keV µm-1.
(NCRP 98)
Linear energy transfer (LET)
Average amount of energy lost per unit track length.
Low LET - Radiation characteristic of electrons, X-rays and gamma rays; the distance between ionizing events is large on the scale of a cellular nucleus.
High LET - Radiation characteristic of protons and fast neutrons; the distance between ionizing events is small on the scale of a cellular nucleus. Average LET is specified to even out the effect of a particle that is slowing down near the end of its path and to allow for the fact that secondary particles are not all of the same energy.
(BEIR IV)
Linear energy transfer (LET)
A measure of the ability of biological material to absorb ionizing radiation; the radiation energy lost per unit length of path through a biological material. In general, the higher the LET value, the greater the relative biological effectiveness of the radiation in that material.
(NCRP 65)
Linear energy transfer (LET)
Average amount of energy lost per unit track length.
Low LET - Radiation characteristic of electrons, X-rays and gamma rays; the distance between ionizing events is large on the scale of a cellular nucleus.
High LET - Radiation characteristic of protons and fast neutrons; the distance between ionizing events is small on the scale of a cellular nucleus. Average LET is specified to even out the effect of a particle that is slowing down near the end of its path and to allow for the fact that secondary particles are not all of the same energy.
(BEIR III)
Linear energy transfer (LET)
The average energy lost by a directly ionizing particle per unit distance of its travel in a medium. As here employed the term is to denote LET¥, i.e., the entire energy loss of charged particles (e.g., delta rays) which are not considered separately.
(NCRP 62)
Linear energy transfer (LET)
The average energy lost by a directly ionizing particle per unit distance of its travel in a medium.
(NCRP 51)
Linear energy transfer (LET)
The average amount of energy lost per unit of particle spur-track length.
(BEIR I)
Linear energy transfer (LET)
The average energy lost by a directly ionizing particle per unit distance of its travel in a medium. As here employed the term is to denote LET¥, i.e., the entire energy loss of charged particles (e.g., delta rays) which are not considered separately.
(NCRP 38)
Linear energy transfer (LET)
The linear rate of loss of energy (locally absorbed) by an ionizing particle traversing a material medium.
(NBS 63)
Linear energy transfer or restricted linear collision stopping power
The linear energy transfer or restricted linear collision stopping power, LD, of charged particles in a medium is the quotient of dE by dl, where dl is the distance traversed by the particle and dE is the energy loss due to collisions with energy transfers less than some specified value D.
(ICRU 19)
Linear hypothesis
The hypothesis that excess risk is proportional to dose.
(BEIR III)
Linear hypothesis
The assumption that a dose-effect curve derived from data in the high dose and high dose-rate ranges may be extrapolated through the low dose and low dose range to zero, implying that, theoretically, any amount of radiation will cause some damage.
(BEIR I)
Linear ion density
Number of ion pairs per unit length.
(IEC 50-393-1993)
Linear ionization (in nuclear instrumentation)
Quotient of the number of pairs each of oppositely charged ions or of a positive ion and an electron that a particle with a given kinetic energy produces along a path, by the length of the path, under specified conditions.
(IEC 50-393-1993)
Linear radiation stopping power
That part of the total linear stopping power due to energy transfer to bremsstrahlung.
(IEC 50-393-1993)
Linear shift-invariant system
An imaging system which is both linear, i.e., the magnitude of the output signal is a linear function of that of the input signal, and shift invariant, i.e., shifting the position of the input signal results only in a displacement of the output by the same amount (or a simple scaling if magnification is allowed).
(ICRU 54)
Linear-quadratic (LQ) model
The linear-quadratic dose-response relationship in which the incidence of the effect (e.g., mutation or cancer) is a combination of a linear dose term which is observed at low doses and a (dose)2 term which assumes increasing importance as the dose increases to the point where cell killing dominates.
(ICRP 59)
Linear-quadratic (LQ) model
Also, linear-quadratic dose-effect relationship; expresses the effect (e.g., mutation or cancer) as partly directly proportional to dose (linear term) and partly proportional to the square of the dose (quadratic term). The linear term will predominate at lower doses, the quadratic term at higher doses.
(BEIR V)
Linear-quadratic (LQ) model
Also, linear-quadratic dose response relationship; expresses the incidence of (e.g., mutation or cancer) as partly directly proportional to the dose (linear term) and partly proportional to the square of the dose (quadratic term). The linear term will predominate as lower doses, the quadratic term at higher doses.
(NCRP 98)
Linearity
The extent to which the instrument reading is proportional to the true quantity being measured as the intensity changes.
(NCRP 112)
Linkage
The cross-referencing of records in one file to records contained in a different file or in the same file. Linkage is accomplished by having fields within each record that point to relevant records in other files. The pointers are actually data fields that are repeated in different files. For example, the identity of the individual is repeated in the records in exposure history files and in the records in training files. Thus, the individual's identification is the linkage between these different files.
(NCRP 114)
Linked
Having or provided with a code or pointer to cross-reference a record with other records maintained in the same or a different file.
(NCRP 114)
Lipophilicity
Affinity for fat.
(NCRP 125)
Liquid counter tube
Counter tube intended to measure the activity of a liquid, typically consisting of a cylindrical tube surrounded by a coaxial cylindrical cup, which may be either fixed or removable.
(IEC 50-394-1993)
Liquid discharge
The release to the environment of soluble or insoluble material in a liquid media. The discharge generally occurs at a point, such as the end of a pipe, where it is released to any of several receptors in the environment, such as a waterway, land, sewer system, etc.
(10CFR834.2)
Liquid height
The height of liquid in the tank relative to some reference point.
(ANSI N15.19-1989)
Liquid metal fast breeder reactor (LMFBR)
A type of fast reactor using highly enriched fuel in the core, fertile material in the blanket, and a liquid metal coolant such as sodium; high energy neutrons fission the fuel in the compact core, and the excess neutrons convert fertile material into fissionable nuclides.
(NCRP 81)
Liquid metal fast breeder reactor (LMFBR)
A type of fast reactor using highly enriched fuel in the core, fertile material in the blanket, and a liquid-metal coolant such as sodium; high energy neutrons fission the fuel in the compact core, and the excess neutrons convert fertile material to fissionable nuclides.
(NCRP 62)
Liquid radioactivity meter
Radiation meter for the continuous measurement of the radioactive emission per unit volume in a given time interval in a liquid.
(IEC 50-394-1993)
Liquid scintillation solution
A solution consisting of an organic solvent (or mixture of solvents) and one or more organic scintillator solutes.
(ANSI N42.15-1980)
Liquid-wall ionization chamber
Ionization chamber intended to measure the alpha or beta activity of a liquid so situated that its surface constitutes the wall of the chamber.
(IEC 50-394-1993)
Lissencephaly
Lack of concolutional pattern in the cerebral cortex due to a defect in development.
(ICRP 49)
Lithium coated semiconductor detector
Semiconductor detector containing lithium 6 in the form of a coating on its surface to detect thermal neutrons.
(IEC 50-394-1993)
Lithium drifted semiconductor detector
Compensated semiconductor detector in which the compensated region is obtained by causing lithium ions to move through a P-type crystal under an applied electric field in such a way as to compensate the charge of the bound impurities.
(IEC 50-394-1993)
Live time
Sum of the incremental time intervals during which the analyzer is sensitive to input signals.
(IEC 50-394-1993)
LNET
Lymphatics and lymph nodes that drain the extrathoracic region.
(ICRP 66)
LNTH
Lymphatics and lymph nodes that drain the thoracic region.
(ICRP 66)
Load factor
The ratio of average load carried by an electric power plant or system during a specific period to its peak load during that period.
(USAEC-1974)
Load line certificate
A document issued by a recognized classification society on behalf of the United States, indicating the maximum amidship draft to which a vessel may be safely loaded in the various circumstances and seasons applicable to such vessel. (See 46 CFR 42.01 for additional information concerning load lines.) This certificate is periodically renewed and serves as evidence to the USCG and the marine insurance underwriters that the vessel is in compliance with the requirements of the standards for load line certification of the American Bureau of Shipping, and Subchapter E, 46 CFR.
(ANSI N14.24-1985)
Load-bearing member
Any part in the load path of the special lifting device in which the induced stress is directly affected by the weight of the container connected to it.
(ANSI N14.6-1986)
Loading
Introduction of fuel into a nuclear reactor.
(IEC 50-393-1993)
Lobe (antenna)
A portion of the radiation pattern between adjacent minima.
(NCRP 67)
Local law enforcement agency
A local law enforcement agency (i.e., Port Authority police, state highway patrol, city police, or similar agencies) may assist or support NRC licensees in the physical protection of spent fuel when located in or traversing a heavily populated area. The use of other armed escorts is an alternative to these agencies.
(ANSI N14.24-1985)
Localization films
X-ray films made after the introduction of intracavitary or interstitial sources or applicators, to make sure of their position.
(NCRP 48)
Localization, selective (biological)
Accumulation of a particular nuclide to a significantly greater degree in certain cells of tissues.
(RHH)
Lock
In the case of vaults or vault type rooms means a three-position, manipulation resistant, dial type, built-in combination lock or combination padlock and in the case of fences, walls, and buildings means an integral door lock or padlock which provides protection equivalent to a six-tumbler cylinder lock. "Lock" in the case of a vault or vault type room also means any manipulation resistant, electromechanical device which provides the same function as a built-in combination lock or combination padlock, which can be operated remotely or by the "reading" or insertion of information, which can be uniquely characterized, and which allows operation of the device.
(10CFR73.2)
Locked
Protected by an operable lock.
(10CFR72.3)
Locus
The site occupied by a specific gene, or allele, on a particular chromosome.
(HPJ 60)
Logarithmic energy decrement
The average increase in the lethargy in a neutron collision.
(ANSI N1.1-1976)
Logging assistant
Any individual who, under the personal supervision of a logging supervisor, handles sealed sources or tracers that are not in logging tools or shipping containers or who performs surveys required by Sec. 39.67.
(10CFR39.2)
Logging supervisor
An individual who uses licensed material or provides personal supervision in the use of licensed material at a temporary jobsite and who is responsible to the licensee for assuring compliance with the requirements of the Commission's regulations and the conditions of the license.
(10CFR39.2)
Logging tool
A device used subsurface to perform well logging.
(10CFR39.2)
Lognormal distribution
If the logarithms of a set of values are distributed according to a normal distribution the values are said to have a log normal distribution, or be distributed "log-normally."
(NCRP 98)
Lognormal distribution
The distribution of a random variable whose logarithm obeys the normal or Gaussian law of probability.
(NCRP 78)
Lognormal size distribution
Particle size distribution characterized by a bell-shaped or Gaussian distribution shape when plotted on a logarithmic-size scale.
(AM-1993)
Long term stabilization
The addition of material on a uranium mill tailings pile for purpose of ensuring compliance with the requirements of 40 CFR 192.02(a) or 192.32(b)(i). These actions shall be considered complete when the Nuclear Regulatory Commission determines that the requirements of 40 CFR 192.02(a) or 192.32(b)(i) have been met.
(40CFR61.221)
Long-Lived Radionuclides
Radionuclides with half-lives too long to allow storage for radioactive decay to be practical.
(ANSI/HPS N13.45-1998)
Long-term mitigation
Mitigation by a homeowner to permanently reduce elevated radon levels in a house.
(RRM)
Loop
A closed circuit of pipe in which materials and components may be placed to test them under different conditions of temperature, irradiation, etc. If part of the loop and contents are placed in a reactor, it is called an in-pile loop.
(USAEC-1974)
Loop reactor
In a reactor, a piping system through which a fluid may flow as a part of a reactor operation of for experimental purposes. If part of an experimental loop is in the core, such a loop is usually called an in-pile loop. If the loop also contains fissionable materials, it is called an active loop (hot loop).
(ANSI N1.1-1976)
Loose surface contamination
Loose surface contamination is that amount which can be removed without removing the surface which is contaminated.
(ANSI N7.2-1963)
Loss tangent
The ratio of the imaginary part of the complex relative permittivity of a medium to its real part.
(NCRP 67)
Lost or missing licensed material
Licensed material whose location is unknown. It includes material that has been shipped but has not reached its destination and whose location cannot be readily traced in the transportation system.
(10CFR20.1003)
Lot tolerance percent defective
Expressed in percent defective, the poorest quality in an individual inspection lot that should be accepted.
(10CFR32.2)
Low dose-rate brachytherapy
In conventional brachytherapy with radium tubes, the dose rate at the point or surface where the dose is prescribed, lies between 0.4 and 2 grays per hour. It is common practice to refer to this type of treatment as low dose-rate brachytherapy.
(ICRU 38)
Low enriched uranium (LEU) fuel
Fuel in which the weight percent of U-235 in the uranium is less than 20%.
(10CFR50.2)
Low Enriched Uranium Fuel
Uranium enriched below 20 percent in the isotope uranium-235.
(10CFR171.5)
Low LET
Radiation having a low Linear Energy Transfer, for example electrons, x rays, and gamma rays. The ionization density along the radiation track is low in comparison with high LET radiations.
(ICRP 59)
Low LET
Radiation having a low energy transfer, for example, electrons, x rays, and gamma rays.
(NCRP 98)
Low population zone
The area immediately surrounding the exclusion area which contains residents, the total number and density of which are such that there is a reasonable probability that appropriate protective measures could be taken in their behalf in the event of a serious accident. These guides do not specify a permissible population density or total population within this zone because the situation may vary from case to case. Whether a specific number of people can, for example, be evacuated from a specific area, or instructed to take shelter, on a timely basis will depend on many factors such as location, number and size of highways, scope and extent of advance planning, and actual distribution of residents within the area.
(10CFR50.2)
Low population zone
The area immediately surrounding the exclusion area which contains residents, the total number and density of which are such that there is a reasonable probability that appropriate protective measures could be taken in their behalf in the event of a serious accident. These guides do not specify a permissible population density or total population within this zone because the situation may vary from case to case. Whether a specific number of people can, for example, be evacuated from a specific area, or instructed to take shelter, on a timely basis will depend on many factors such as location, number and size of highways, scope and extent of advance planning, and actual distribution of residents within the area.
(10CFR100.3)
Low population zone
An area of low population density sometimes required around a nuclear installation. The number and density of residents is of concern in providing, with reasonable probability, that effective protection measures can be taken if a serious accident should occur. (See exclusion area.)
(USAEC-1974)
Low specific activity material
Any of the following:
(1) Uranium or thorium ores and physical or chemical concentrates of those ores;
(2) Unirradiated natural or depleted uranium or unirradiated natural thorium;
(3) Tritium oxide in aqueous solutions provided the concentration does not exceed 5.0 millicuries per milliliter;
(4) Material in which the radioactivity is essentially uniformly distributed and in which the estimated average concentration per gram of contents does not exceed:
Low specific activity material (LSA)
Any of the following:
(1) Uranium and thorium ores and physical and chemical concentrates of those ores.
(2) Unirradiated natural or depleted uranium or unirradiated natural thorium.
(3) Tritium oxide in aqueous solutions provided the concentration of the contents does not exceed 5.0 millicuries per milliliter.
(4) Material in which the radioactivity is essentially uniformly distributed and in which the estimated contents does not exceed:
Low Toxicity Alpha Material
Natural uranium, depleted uranium, natural thorium; uranium-235, uranium-238, thorium-232, thorium-228 or thorium-230 when contained in ores or physical or chemical concentrates or tailings; or alpha emitters with a half-life of less than 10 days.
(10CFR71.4)
Low-enriched uranium
Uranium enriched below 20 percent in the isotope uranium-235.
(10CFR110.2)
Low-enriched uranium
Uranium enriched below 20 percent in the isotope uranium-235.
(10CFR170.3)
Low-enriched uranium
Uranium enriched below 20 percent in the isotope uranium-235.
(10CFR74.4)
Low-let
Radiation characteristic of electrons, x rays, and gamma rays.
(BEIR I)
Low-level analysis (low-level counting)
A procedure to measure the radioactive content of materials with very low levels of activity, using sensitive detecting instruments and with good shielding to eliminate the effects of background radiation and cosmic rays. (See coincidence counting, counter.)
(USAEC-1974)
Low-Level Radioactive Waste (LLW)
Radioactive waste that is not classified as high-level radioactive waste, transuranic waste, spent nuclear fuel, or uranium or thorium tailings and waste.
(ANSI/HPS N13.45-1998)
Low-level radioactive waste (LLW)
Radioactive material that:
(1) Is not high-level radioactive waste, spent nuclear fuel, or byproduct material (as defined in section 11e(2) of the Atomic Energy Act of 1954, (42 U.S.C. 2014(e)(2))); and
(2) the NRC, consistent with existing law and in accordance with paragraph (a), classifies as low-level radioactive waste.
(10CFR62.2)
Low-level waste
Low level waste is identified by 10 CFR 61 (December 1982) as "...radioactive waste not classified as high level radioactive waste, transuranic waste, spent nuclear fuel or byproduct material (uranium and thorium tailings and waste)..."
(NCRP 76)
Low-specific-activity material
Unirradiated natural or depleted UF6 or unirradiated UF6 enriched to not more than 1.0 wt% 235U.
(ANSI N14.1-1990)
Lower limit of detection
The amount of analyte material that has a 95% chance of being detected when the decision that some amount of analyte is present is made when a signal occurs at or above the decision level. It has the same meaning as minimum detectable amount (MDA), which is preferred terminology for this standard.
(ANSI N13.30-1989D)
Lower Limit of Detection (LLD)
See MDA.
(HPS N13.30-1996)
Lucas cell
A specific form of scintillation cell developed by Lucas (1957).
(NCRP 97)
Luminescence
Emission of light produced by the action of biological or chemical processes or by radiation, or any other cause except high temperature (which produces incandescence).
(USAEC-1974)
Lung class (D, W, or Y)
A classification scheme for inhaled material according to its rate of clearance from the pulmonary region of the lung.
(ICRP 56)
Lung class (D, W, or Y)
A classification scheme for inhaled material according to its rate of clearance from the pulmonary region of the lung.
(ICRP 54)
Lung class (D, W, or Y)
A classification scheme for inhaled material according to its rate of clearance from the pulmonary region of the lung.
(ICRP 30)
Lung clearance class (D, W, or Y)
A classification scheme for inhaled material according to its clearance half-time, on the order of days, weeks, or years, form the pulmonary region of the lung to the blood and the GI tract.
(FGR 11)
Lung model
Representation of the respiratory system used to make quantitative estimates of particle deposition.
(AM-1993)
Lymphatic System
Complex network of capillaries, vessels, valves, ducts and organs involved in producing, filtering, and conveying lymph and producing various blood cells.
(NCRP 125)
Lymphoblastic transformation
Transformation of lymphocytic cells into lymphoblasts upon antigenic stimulation.
(HPJ 60)
Lymphocyte
A type of white blood cell (a leucocyte) with sparse cytoplasm and round nucleus. Small lymphocytes comprise a part of the population of cells that function as a part of the immune system and are commonly used in tissue culture systems for the study of chromosomes.
(HPJ 60)
Lymphocyte
A variety of white blood cell formed in lymph glands and other lymphoid tissue. The nucleus is single and is surrounded by a thin layer of cytoplasm which is nongranular. Average life span is relatively short.
(NBS 63)
Lymphosarcoma
A sarcoma of the lymphoid tissue. This does not include Hodgkin's disease.
(BEIR V)
Lymphosarcoma
A sarcoma of the lymphoid tissue. This does not include Hodgkin's disease.
(BEIR IV)
Note: References shown in ()