Appendix C
Glossary and Acronyms
Σ  Risk cross section. 
absolute risk (AR)  The rate of disease among a population. 
absorbed dose (D)  The fundamental dose quantity is absorbed dose, D, defined as the quotient of by dm, where is the mean energy imparted by ionizing radiation to matter of mass dm; thus 
Unit: J kg^{−1}. 

The special name for the unit of absorbed dose is gray (Gy). A formerly used (nonSI) unit is rad. 1 Gy = 1 J/kg = 100 rad. 1 rad = 0.01 J/kg. In radiation protection and epidemiology, absorbed dose averaged over organs and tissues is used.  
activity (A)  Variation dN of number of nuclei N in a particular energy state, in a sample of a radionuclide, due to spontaneous nuclear transitions from this state during an infinitesimal time interval, divided by its duration dt. thus: 
A = dN/dt. Unit: s^{−1}. 

The special name for the unit of activity is becquerel (Bq). A formerly used (nonSI) unit is curie (Ci). 1 Bq = 1 s^{−1} = 2.7 × 10^{−11} Ci. 1 Ci = 3.7 × 10^{10} Bq.  
additive effect  When two agents do not interact, the combined effect is equal to the sum of the effects of the two agents acting alone. 
AML  Acute myeloid leukemia. 
apoptosis  Programmed cell death. The cell death is characterized by a distinctive fragmentation of DNA that is regulated by cellular functions. 
artificial radioactivity  Manmade radioactivity produced by fission, fusion, particle bombardment, or electromagnetic irradiation. 
attributable risk (AR)  The estimated rate of a disease (such as lung cancer) that could, in theory, be prevented if all exposures to a particular causative agent (such as radon) were eliminated. 
AU  Astronomical unit. 
background radiation  The radiation to which a member of the population is exposed from natural sources, composed of terrestrial radiation due to naturally occurring radionuclides in the soil and building material, cosmic radiation originating in outer space, and naturally occurring radionuclides in the human body. 
baseline rate of cancer  The annual cancer incidence observed in a population in the absence of the specific agent being studied; the baseline rate includes cancers from a number of other causes, such as smoking and occupational exposures to chemicals. 
becquerel (Bq)  SI unit of activity. 1 Bq = 1 s^{−1} = 2.7 × 10^{−11} Ci. 
BEIR  Biological Effects of Ionizing Radiation. Refers to the reports by the National Research Council’s Committee on Biological Effects of Ionizing Radiation and its successor committees. The most recent of these reports is BEIR VII, published in 2006. 
beta particle  An electron or positron emitted from a nucleus during radioactive decay. 
bias  Factors that influence the outcome of data collection, such as causing certain measurements to have a greater chance of being included than others. 
Boltzmann transport equation  Describes the trajectory and interactions of particles traversing a medium. So called because of its similarity to the expression obtained by Boltzmann in connection with the kinetic theory of gases. 
BRYNTRN  Computational model of baryon transport. 
cancer  A malignant tumor of potentially unlimited growth, capable of invading surrounding tissue or spreading to other parts of the body by metastasis. 
carcinogen  An agent that can cause cancer. Ionizing radiation is a physical carcinogen; there are also chemical and biological carcinogens; biological carcinogens may be extrinsic (e.g., viruses) or intrinsic (genetic defects). 
carcinoma  A malignant tumor (cancer) of epithelial origin. 
casecontrol study  An epidemiologic study in which people with disease and a similarly composed control group are compared in terms of exposures to a putative causative agent. 
cell culture  The growing of cells in vitro (in a glass or plastic container, or in suspension) in such a manner that the cells are no longer organized into tissues. 
CME  Coronal mass ejection. 
CNS  Central nervous system. 
cohort study  An epidemiologic study in which groups of people (the cohort) are identified with respect to the presence or absence of exposure to a diseasecausing agent, and in which the outcomes of disease rates are compared; also called a followup study. 
collective effective dose  For a specified group of individuals: the sum of individual effective doses from a specified source within a specified time period. Unit: j/kg; special name used for unit: personSv. 
competing risks  Causes other than the agent under study that contribute to the mortality rate. The mortality rate from these other causes is not included in the risk of dying from the factor under study. 
confidence interval (CI)  An interval estimate of an unknown parameter, such as a risk. A 95 percent confidence interval, as an example, is constructed from a procedure that is theoretically successful in capturing the parameter of interest in 95 percent of its applications. Confidence limits are the end points of a confidence interval. 
constant relative risk (CRR)  A risk model which assumes that the ratio of the risk at a specific dose and the risk in the absence of the dose remains constant after a certain time. 
coronal mass ejections  Large regions of plasma ejected outward from the Sun by an electromagnetic process in the solar atmosphere. 
curie (Ci)  Former special unit of radioactivity. 1 Ci = 3.7 × 10^{10} Bq. 
DDREF (dose and dose rate effectiveness factor)  A judged factor by which the radiation effect, per unit of dose, caused by a given high or moderate dose of radiation received at high dose rates is reduced when doses are low or are received at low dose rates. 
deletion  Type of mutation in which sections of DNA are removed; term can refer to the removal of a single base or many bases. 
detriment  The total harm to an exposed group (and its descendants) as a consequence of exposure of the group to radiation. The principal components of detriment are probability of fatal cancer attributable to radiation, weighted probability of nonfatal cancer attributable to radiation, weighted probability of severe heritable effects, and length of life lost from any harm induced. 
detrimentadjusted risk  The probability of the occurrence of cancer or heritable effect, adjusted to allow for the different components of detriment to express the severity of the consequences. 
DNA  Deoxyribonucleic acid; the genetic material of cells. 
doseeffect (doseresponse) model  A mathematical formulation and description of the way that the effect (or biological response) depends on the dose. 
dose equivalent  The dose equivalent, H, at a point is given by 
H=QD, 

where D is the absorbed dose and Q is the quality factor at that point. The unit of dose equivalent is joules per kilogram (J kg^{1}), and its special name is the sievert (Sv).  
This quantity is used by the ICRU (see ICRU) in the definition of operational quantities, including ambient dose equivalent and personal dose equivalent, applied in radiation monitoring.  
dose range  Definitions of low, medium, and high doses vary widely in the literature. For the purposes of this report, dose ranges are defined as follows: Low dose: 0 to 100 mGy (mSv). Medium dose: in excess of 100 mGy up to a maximum of 1 Gy. High dose: in excess of 1 Gy up to the very high total doses used in radiation therapy (on the order of 20 to 60 Gy). 
dose rate  The absorbed dose delivered per unit time. 
dose rate effectiveness factor (DREF)  The factor by which the effect per unit dose caused by a specific type of radiation changes at low doses or low dose rates (protracted or fractionated delivery of dose) as compared to high doses delivered at high (or acute) dose rates. 
dosimetric model  A method for estimating risk based on the use of physical models for doses to target cells and the use of results from epidemiologic studies of exposures to humans from other types of radiation. 
EB  Empirical Bayes. 
ecological fallacy  The fact that two populations differ in many factors other than the one being evaluated and that one or more of these other factors may be the underlying reason for any difference noted in their morbidity or mortality experience. 
ecologic study  A method of epidemiologic study in which rates of health effects outcome based on population rather than individual data are related to the measure of population radiation exposure. 
effective dose  As defined by the ICRP (see ICRP): the sum of the equivalent doses H_{T} in all specified tissues and organs T of the body of a reference person, each weighted by W_{T}, the tissue weighting factor after sexaveraging of the equivalent doses. 
where Unit: J kg^{−1}. 
The special name for the unit of effective dose is sievert (Sv). Effective dose is used to set exposure limits for radiation protection of stochastic effects and for implementing the optimization principle (ALARA, or “as low as reasonably achievable”) in radiation protection. The quantity enables the summation of doses from internal emitters and external radiation fields in order to provide a single numerical value.  
electron volt (eV)  A special unit of energy: 1 eV = 1.6 × 10^{−19} J = 1.6 × 10^{−12} erg; 1 eV is equivalent to the energy gained by an electron in passing through a potential difference of 1 V; 1 keV = 1,000 eV; 1 MeV = 1,000,000 eV. 
empirical model  Derived from measurements in populations, as opposed to a theoretical model. 
EPA  Environmental Protection Agency. 
epidemiology  The study of the determinants of the frequency of disease in humans. The two main types of epidemiologic studies of chronic disease are cohort (or followup) studies and casecontrol studies. 
equivalent dose  The equivalent dose in an organ or tissue. H_{T}, defined by 
where
and w_{R} is the radiation weighting factor for radiation R. The sum is performed over all types of radiations involved. Unit: J kg^{−1}. 

The special name for the unit of equivalent dose is sievert (Sv). 1 Sv = 1 J/kg = 100 rem. 1 rem = 0.01 Sv (“rem” was the formerly used special name for equivalent dose). 

ESP  Emission of solar protons. 
etiology  The science or description of cause(s) of disease. 
EVA  Extravehicular activity. 
excess absolute risk (EAR)  The rate of disease in an exposed population minus the rate of disease in an unexposed population. Also termed “attributable risk” or “risk difference.” 
excess relative risk (ERR)  The rate of disease in an exposed population divided by the rate of disease in an unexposed population minus 1.0. 
exposure (E)  The condition of having contact with a physical or chemical agent. 
fibrosis  Damage to normal tissue that results in the formation of excess fibrous connective tissue in an organ or tissue. 
fractionation  The delivery of a given dose of radiation as several smaller doses separated by intervals of time. 
galactic cosmic ray (GCR)  Very energetic charged particles that have their origin inside our Galaxy and have speeds approaching the speed of light, propagating in the rarefied plasmas of space. 
gamma radiation  Also gamma rays; shortwavelength electromagnetic radiation originating from the decay of radioactive nuclei, from bremsstrahlung, and from cosmic sources. 
GCR  Galactic cosmic ray. 
geometric mean  The geometric mean of a set of positive numbers is the exponential of the arithmetic mean of their logarithms. The geometric mean of a lognormal distribution is the exponential of the mean of the associated normal distribution. 
geometric standard deviation (GSD)  The geometric standard deviation of a lognormal distribution is the exponential of the standard deviation of the associated normal distribution. 
germ cells  Reproductive cells such as the sperm and egg and their progenitor cells. 
GMIR  Global merged interaction regions. 
GOES  Geostationary operational environmental satellite. 
gray (Gy)  Special name of the SI unit for absorbed dose (see unit of dose). 1 Gy = 1 J/kg = 100 rads. 
halflife, biological  Time required to eliminate half of an incorporated amount of any substance from a body by metabolic processes of elimination; it is approximately the same for both stable and radioactive isotopes of a particular element. 
halflife, radioactive  Period of time that it takes for the amount of a radioactive substance to decrease by half by decay. 
heliosphere  A vast, spheroidal cavity, approximately 200 times the mean SunEarth distance, created in the interstellar gas by the outflowing solar wind. 
highLET radiation  Heavy, charged particles, such as protons or alphaparticles or heavier ions (such as are encountered in galactic cosmic radiation), that produce ionizing events densely spaced on a molecular scale (e.g., L > 10 keV/μm). Neutrons are also considered as highLET radiation because the charged particles released in neutron interactions with matter are highLET particles. 
HMF  Heliospheric magnetic field. 
HRP  Human Research Program (NASA). 
HZE  High atomic number (Z) and energy (E). 
HZETRN  High charge and energy transport code. 
ICRP (International Commission on Radiological Protection)  An independent international organization that provides recommendations and guidance on protection against ionizing radiation. 
ICRU (International Commission on Radiation Units and Measurements)  An independent international organization that provides recommendations and guidance on radiation quantities, units, and measurements for all applications of ionizing radiation. 
incidence  Also, incidence rate; the rate of occurrence of a disease within a specified period of time, often expressed as a number of cases per 100,000 individuals per year. 
in utero  In the womb: i.e., before birth. 
inverse doserate effect  An effect in which, for a given exposure, the probability of effect per unit dose increases as the dose rate is lowered. 
in vitro  Cell culture conditions in glass or plastic containers. 
in vivo  In the living organism. 
ionizing radiation  Particles or electromagnetic radiation sufficiently energetic to dislodge electrons from an atom or molecule, thereby creating an ion pair. Ionizing radiation includes x and gamma radiation, electrons (beta radiation), alpha particles (helium nuclei), and heavier charged atomic nuclei. Neutrons ionize indirectly by first interacting with components of atomic nuclei. 
ISS  International Space Station. 
kerma  The kerma (kinetic energy released in matter) for ionizing uncharged particles (photons, neutrons) is the quotient of the mean sum of the initial kinetic energies of all charged particles liberated in a unit mass of a material by the uncharged particles incident on that mass. Unit: J kg^{−1}. 
The special name for the unit of kerma is gray (Gy). If all of the kinetic energy is absorbed “locally,” the kerma is approximately equal to the absorbed dose.  
latent period  The period of time between exposure and expression of the disease. After exposure to a dose of radiation, there typically is a delay of several years (the latent period) before any cancer is observed. 
LET  The linear energy transfer (LET) for charged particles of a given type and energy in a given material is the quotient of the mean energy lost by the charged particles due to electronic interactions in traversing a unit track length. The unit often used for LET is keV μm^{−1}. 
life table  Shows the number of persons of a given number born or living at a specified age who live to attain successive higher ages, together with the numbers who die in each interval. 
linear model or relationship (also linear doseeffect relationship)  The linear model is a special case of the linearquadratic model, with the quadratic coefficient equal to zero; the linear model expresses the effect (e.g., cancer or mutation) as proportional to the dose (linear function of the dose). 
linearquadratic model  Also, linearquadratic doseeffect relationship; expresses the effect (e.g., cancer) as the sum of two components, one proportional to the dose (linear term) and one proportional to the square of the dose (quadratic term). The linear term predominates at low doses; the quadratic term, at high doses. 
LNT model  Linear nothreshold dose response for which any dose greater than zero has a finite probability of producing an effect (e.g., mutation or cancer). The probability is calculated either from the slope of a linear model or from the limiting slope, as the dose approaches zero, of a linearquadratic model. 
lognormal distribution  When the logarithms of a randomly distributed quantity have a normal (Gaussian) distribution. 
lowLET radiation  X rays and gamma rays, charged particles, such as electrons or highenergy protons that produce low ionization density (e.g., L < 10 keV/μm). 
LSS  Life span study. Longterm study of health effects in the Hiroshima and Nagasaki atomic bomb survivors. 
mechanistic basis  An explanation derived from a knowledge of the individual stages leading to an effect. 
metaanalysis  An analysis of epidemiologic data from several studies based on data included in publications. 
MLE  Maximum likelihood estimate. 
model  A schematic description of a system, theory, or phenomenon that accounts for its known or inferred properties and that may be used for further study of its characteristics. 
Monte Carlo calculation  The method for evaluation of a probability distribution by means of random sampling. 
mortality (rate)  The frequency at which people die from a disease (e.g., a specific cancer), often expressed as the number of deaths per 100,000 population per year. 
MSL RAD  Mars Science Laboratory Radiation Assessment Detector. 
multiplicative effects  The combined effect of two agents is equal to the product of the effects of the two agents acting alone. 
natural radioactivity  The property of radioactivity exhibited by more than 50 naturally occurring radionuclides. 
NCRP (National Council on Radiation Protection and Measurements)  U.S. Council commissioned to formulate and disseminate information, guidance, and recommendations on radiation protection and measurements. 
NEO  NearEarth object. 
neoplasm  Any new and abnormal growth, such as a tumor; neoplastic disease refers to any disease that forms tumors, whether malignant or benign. 
NIH  National Institutes of Health (U.S.). 
nonstochastic  A description of effects whose severity is a function of dose; for these, a threshold may occur; some examples of somatic effects believed to be nonstochastic are cataract induction, nonmalignant damage to the skin, hematological deficiencies, and impairment of fertility. 
normal distribution  The socalled bellshaped curve of randomly distributed quantities; also referred to as a “Gaussian distribution.” 
NS  Neversmoker. 
NSRL  NASA Space Radiation Laboratory. 
NTE  Nontargeted effect. Biological response occurring in unirradiated cells as a result of radiation exposure in other cells. Generally taken to include bystander responses, in which biological changes are seen in unirradiated cells communicating with irradiated (“targeted”) cells, and genomic instability in progeny of irradiated cells. 
odds ratio (OR)  The odds of being exposed among diseased persons divided by the odds of being exposed among nondiseased persons. 
oncogene  An overexpressed or mutated version of a normal gene that can, in a dominant fashion, release a cell from normal restraints controlling its proliferation and convert it into a tumor cell, by itself or in combination with other cellular changes. (This should be contrasted to a tumor suppressor gene whose product acts to suppress malignant transformation of cells and operates in a recessive manner, where in classical terms, both alleles must be lost or mutated to stop or curtail the supply of the growth suppressor gene product.) 
PEL  Permissible exposure limit. 
phenotype  The genetically and environmentally determined physical appearance of an organism. 
photon  An electromagnetic quantum whose energy (Eph) equals the product of the Planck constant (h) and its frequency (v). With the convenient units eV and s, and with the wavelength λ in μm: E_{ph} = 4.136 10^{−15} v = 1.24/λ. 
plasma  A gas in which a significant number of the atoms and molecules have lost one or more electrons and in which, therefore, electromagnetic effects are important. 
pooled analysis  An analysis of epidemiologic data from several studies based on original data from the studies. 
PRA  Probabilistic risk assessment. 
prevalence  The number of cases of a disease in existence at a given time per unit of population, usually 100,000 persons. 
probability of causation  A number that expresses the probability that a given cancer, in a specific tissue, has been caused by a previous exposure to a carcinogenic agent, such as radiation. 
projection model  A mathematical model that simultaneously describes the excess cancer risk at different levels of some factor such as dose, time after exposure, or baseline level of risk, in terms of a parametric function of that factor. It becomes a projection model when data in a particular range of observations are used to assign values to the parameters in order to estimate (or project) excess risk for factor values outside that range. 
promoter  An agent that is not by itself carcinogenic but which can amplify the effect of a true carcinogen by increasing the probability of latestage cellular changes needed to complete the carcinogenic process. 
proportional mortality ratio  The ratio of the percentage of a specific cause of death among all deaths in the population being studied divided by the comparable percentage in a standard population. 
protraction  The spreading out of a radiation dose over time by continuous delivery at a lower dose rate. 
QMSFRG  Quantum multiple scattering fragmentation. 
quadraticdose model  A model that assumes that the excess risk is proportional to the square of the dose. 
quality factor (Q)  A LETdependent factor by which the absorbed dose is multiplied to obtain (for radiation protection purposes) the dose equivalent. The currently used values of Q were chosen by the ICRP on the basis of published RBE (see relative biologic effectiveness) values for a range of radiation and biological end points. Absorbed dose in Gy x Q dose equivalent in Sv. 
quality factor (QF)  A track structuredependent factor, for use in NASA’s proposed model, by which the absorbed dose is multiplied to scale the cancer risk coefficients for lowLET radiation so as to apply to space radiation. The proposed values of QF are chosen in the 2011 NASA report on the basis of an empirical relationship and available data on RBE values for HZE particles for a range of biological end points. 
rad  The formerly used special name for the unit of absorbed dose, now replaced by the SI unit Gy (see unit of dose). 1 rad = 0.01 Gy = 100 erg/g. 
radiation weighting factor  w_{R}, used by the ICRP to weight absorbed dose of an organ or tissue to obtain equivalent dose for the organ or tissue. 
radioactivity  The property of nuclide decay in which particles or gamma radiations are usually emitted. 
radiogenic  Caused by radiation. 
radioisotope  A radioactive atomic species of an element with the same atomic number and usually identical chemical properties. 
radionuclide  A radioactive species of an atom characterized by the constitution of its nucleus. 
random errors  Errors that vary in a nonreproducible way around a limiting mean. These errors can be treated statistically by use of the laws of probability. 
REIC  Risk of exposureinduced cancer. 
REID  Risk of exposureinduced death. The difference in a causespecific death rate for exposed and unexposed populations of a given sex and a given age at exposure, as an additional cause of death introduced into a population. 
relative biological effectiveness (RBE)  The ratio D_{ref}/D, where D is the absorbed dose of a specified radiation and D_{ref} is the absorbed dose of a sparsely ionizing reference radiation (gamma rays or X rays) that produces the same level of effect. When the magnitude of the dose D is not specified, the RBE is meant to be the lowdose limit of the ratio D_{ref}/D (this lowdose RBE equals the lowdose effectiveness [initial slope] of the specified radiation to that of the reference radiation). 
relative risk (RR)  The rate of disease in an exposed population divided by the rate of disease in an unexposed population. Also termed “rate ratio.” 
rem  (rad equivalent man). A special unit of dose equivalent, now replaced by the SI unit sievert (see unit of dose). 1 rem = 0.01 Sv. 
RERF  Radiation Effects Research Foundation (Japan). 
risk  A chance of injury, loss, or detriment. A measure of the deleterious effects that may be expected as the result of an action or inaction. 
risk assessment  The process by which the risks associated with an action or inaction are identified and quantified. 
risk coefficient  The increase in the annual incidence or mortality rate per unit dose: (1) absolute risk coefficient is the increase of the incidence or mortality rate per unit dose; (2) relative risk coefficient is the fractional increase above the baseline incidence or mortality rate per unit dose. 
risk estimate  The increment of the incidence or mortality rate projected to occur in a specified exposed population per unit dose for a specified exposure regime and expression period. 
SEP  Solar energetic particle. 
SI units  Units of the International System of Units as defined by the General Conference of Weights and Measures in 1960. They are the base units, such as meter (m), kilogram (kg), second (s), and their combinations, which have special names (e.g., the unit of energy, 1 J = 1 kg m^{2}/s^{2}, or absorbed dose, 1 Gy = 1 J/kg. (See unit of dose.) 
sievert (Sv)  Special name of the SI unit of dose equivalent, equivalent dose, and effective dose (see unit of dose). 1 Sv = 1 J/kg = 100 rem. 
solar cycle  A periodic change of the Sun’s activity with a period of approximately 11 years; typically, consists of 7 years of solar maximum and 4 years of solar minimum. 
solar particle event  Very energetic process from the Sun produced both by solar flares and by shocks driven by fast coronal mass ejections; occurs when very strong magnetic fields in the solar photosphere reach a critical instability. 
solid cancers  All malignant neoplasms other than those of the lymphatic and hematopoietic tissue. 
somatic cells  Nonreproductive cells. 
SPE  Solar particle event. 
specific activity  Activity of a given nuclide per unit mass of a compound, element, or radioactive nuclide. 
specific energy (z)  The energy per unit mass actually deposited in a microscopic volume in a single energy deposition event or at a given absorbed dose. This is a stochastic quantity as opposed to its average, the absorbed dose, D. The mean energy imparted by ionizing radiation to a medium per unit mass. Unit: 1 Gy = 1 J/kg. 
standardized mortality ratio (SMR)  The ratio (multiplied by 100) of the mortality rate from a disease in the population being studied divided by the comparable rate in a standard population. The ratio is similar to a relative risk times 100. 
stochastic  Effects whose probability of occurrence in an exposed population (rather than severity in an affected individual) depends on dose; stochastic effects are commonly regarded as having no threshold; hereditary effects are stochastic; some somatic effects, especially cancers, are regarded as being stochastic. 
STS  Space Transportation System. 
suppressor gene  A gene that can suppress another gene such as an oncogene. Changes in suppressor genes can lead to expression by genes such as oncogenes. 
synergistic effect  Increased effectiveness results from an interaction between two agents, so that the total effect is greater than the sum of the effects of the two agents acting alone. 
systemic errors  Errors that are reproducible and tend to bias a result in one direction. Their causes can be assigned, at least in principle, and they can have constant and variable components. Generally, these errors cannot be treated statistically. 
target cells  Cells in a tissue that have been determined to be the key cells in which changes occur in order to produce an end point such as cancer. 
TE  Targeted effect; occurrence of biological responses in irradiated cells (in contrast to NTE; see above). 
threshold hypothesis  The assumption that no radiation injury occurs below a specified dose. 
transformed cells  Tissue culture cells changed from growing in an orderly pattern exhibiting contact inhibition to growing in a pattern more like that of cancer cells. 
transport  The term used in the study of energetic particles (GCR, SEP, etc.) to describe quantitatively the motion of the particles and their interaction with matter. Generally, transport calculations use an equation (see Boltzmann transport equation) that depends on the medium (e.g., shielding material, structural material, human body, interplanetary space) and particles being studied. 
turbulence  The essentially random fluctuations that often occur in a largescale fluid. 
u  Atomic mass unit. Kinetic energies are often expressed in units of MeV per atomic mass unit (u), MeV/u, because particles with identical E then have the same β. 
uncertainty  The range of values within which the true value is estimated to lie. It is a best estimate of possible inaccuracy due to both random and systemic errors. 
units of dose  Dosimetric units. Unit conversion factors: Gray (SI): 1 Gy = 1 J/kg = 100 rad: used for absorbed dose and kerma. Sievert (SI): 1 Sv = 1 J/kg = 100 rem: used for equivalent dose, effective dose, and dose equivalent. Rem: 1 rem = 0.01 Sv. 
UNSCEAR  United Nations Scientific Committee on the Effects of Atomic Radiation; publishes periodic reports on sources and effects of ionizing radiation. 
variability  The variation of a property or a quantity among members of a population. Such variation is inherent in nature and is often assumed to be random; it can then be represented by a frequency distribution. 
weighted dose (d)  The dose to the atomic bomb survivors, roughly adjusted to account for the increased effectiveness of the small neutron absorbed dose contribution. The weighted dose equals the gammaray absorbed dose to a specified organ plus the neutron absorbed dose multiplied by a weighting factor that has usually been set equal to 10 in the analyses by RERF (see RERF). 
x radiation  Also x rays; penetrating electromagnetic radiation, usually produced by bombarding a metallic target with fast electrons in a high vacuum. 
This page intentionally left blank.