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Neutron quality factor

Description: Both the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP) have recommended that the radiation quality weighting factor for neutrons (Q{sub n}, or the corresponding new modifying factor, w{sub R}) be increased by a value of two for most radiation protection practices. This means an increase in the recommended value for Q{sub n} from a nominal value of 10 to a nominal value of 20. This increase may be interpreted to mean that the biological effectiveness of neutrons is two times greater than previously thought. A decision to increase the value of Q{sub n} will have a major impact on the regulations and radiation protection programs of Federal agencies responsible for the protection of radiation workers. Therefore, the purposes of this report are: (1) to examine the general concept of {open_quotes}quality factor{close_quotes} (Q) in radiation protection and the rationale for the selection of specific values of Q{sub n}; and (2) to make such recommendations to the Federal agencies, as appropriate. This report is not intended to be an exhaustive review of the scientific literature on the biological effects of neutrons, with the aim of defending a particular value for Q{sub n}. Rather, the working group examined the technical issues surrounding the current recommendations of scientific advisory bodies on this matter, with the aim of determining if these recommendations should be adopted by the Federal agencies. Ultimately, the group concluded that there was no compelling basis for a change in Q{sub n}. The report was prepared by Federal scientists working under the auspices of the Science Panel of the Committee on Interagency Radiation Research and Policy Coordination (CIRRPC).
Date: June 1, 1995
Partner: UNT Libraries Government Documents Department

Persistence of gamma-H2AX and 53BP1 foci in proliferating and nonproliferating human mammary epithelial cells after exposure to gamma-rays or iron ions

Description: To investigate {gamma}-H2AX (phosphorylated histone H2AX) and 53BP1 (tumour protein 53 binding protein No. 1) foci formation and removal in proliferating and non-proliferating human mammary epithelial cells (HMEC) after exposure to sparsely and densely ionizing radiation under different cell culture conditions. HMEC cells were grown either as monolayers (2D) or in extracellular matrix to allow the formation of acinar structures in vitro (3D). Foci numbers were quantified by image analysis at various time points after exposure. Our results reveal that in non-proliferating cells under 2D and 3D cell culture conditions, iron-ion induced {gamma}-H2AX foci were still present at 72 h after exposure, although 53BP1 foci returned to control levels at 48 h. In contrast in proliferating HMEC, both {gamma}-H2AX and 53BP1 foci decreased to control levels during the 24-48 h time interval after irradiation under 2D conditions. Foci numbers decreased faster after {gamma}-ray irradiation and returned to control levels by 12 h regardless of marker, cell proliferation status, and cell culture condition. Conclusions: The disappearance of radiation induced {gamma}-H2AX and 53BP1 foci in HMEC have different dynamics that depend on radiation quality and proliferation status. Notably, the general patterns do not depend on the cell culture condition (2D versus 3D). We speculate that the persistent {gamma}-H2AX foci in iron-ion irradiated non-proliferating cells could be due to limited availability of double strand break (DSB) repair pathways in G0/G1-phase, or that repair of complex DSB requires replication or chromatin remodeling.
Date: December 22, 2010
Creator: Groesser, Torsten; Chang, Hang; Fontenay, Gerald; Chen, James; Costes, Sylvain V.; Barcellos-Hoff, Mary Helen et al.
Partner: UNT Libraries Government Documents Department

Analysis of Flow Cytometry DNA Damage Response Protein Activation Kinetics Following X-rays and High Energy Iron Nuclei Exposure

Description: We developed a mathematical method to analyze flow cytometry data to describe the kinetics of {gamma}H2AX and pATF2 phosphorylations ensuing various qualities of low dose radiation in normal human fibroblast cells. Previously reported flow cytometry kinetic results for these DSB repair phospho-proteins revealed that distributions of intensity were highly skewed, severely limiting the detection of differences in the very low dose range. Distributional analysis reveals significant differences between control and low dose samples when distributions are compared using the Kolmogorov-Smirnov test. Radiation quality differences are found in the distribution shapes and when a nonlinear model is used to relate dose and time to the decay of the mean ratio of phosphoprotein intensities of irradiated samples to controls. We analyzed cell cycle phase and radiation quality dependent characteristic repair times and residual phospho-protein levels with these methods. Characteristic repair times for {gamma}H2AX were higher following Fe nuclei as compared to X-rays in G1 cells (4.5 {+-} 0.46 h vs 3.26 {+-} 0.76 h, respectively), and in S/G2 cells (5.51 {+-} 2.94 h vs 2.87 {+-} 0.45 h, respectively). The RBE in G1 cells for Fe nuclei relative to X-rays for {gamma}H2AX was 2.05 {+-} 0.61 and 5.02 {+-} 3.47, at 2 h and 24-h postirradiation, respectively. For pATF2, a saturation effect is observed with reduced expression at high doses, especially for Fe nuclei, with much slower characteristic repair times (>7 h) compared to X-rays. RBEs for pATF2 were 0.66 {+-} 0.13 and 1.66 {+-} 0.46 at 2 h and 24 h, respectively. Significant differences in {gamma}H2AX and pATF2 levels comparing irradiated samples to control were noted even at the lowest dose analyzed (0.05 Gy) using these methods of analysis. These results reveal that mathematical models can be applied to flow cytometry data to uncover important and subtle differences following exposure to ...
Date: December 15, 2010
Creator: Association, Universities Space Research; Chappell, Lori J.; Whalen, Mary K.; Gurai, Sheena; Ponomarev, Artem; Cucinotta, Francis A. et al.
Partner: UNT Libraries Government Documents Department

Development of Real-Time Measurement of Effective Dose for High Dose Rate Neutron Fields

Description: Studies of the effects of low doses of ionizing radiation require sources of radiation which are well characterized in terms of the dose and the quality of the radiation. One of the best measures of the quality of neutron irradiation is the dose mean lineal energy. At very low dose rates this can be determined by measuring individual energy deposition events, and calculating the dose mean of the event size. However, at the dose rates that are normally required for biology experiments, the individual events can not be separated by radiation detectors. However, the total energy deposited in a specified time interval can be measured. This total energy has a random variation which depends on the size of the individual events, so the dose mean lineal energy can be calculated from the variance of repeated measurements of the energy deposited in a fixed time. We have developed a specialized charge integration circuit for the measurement of the charge produced in a small ion chamber in typical neutron irradiation experiments. We have also developed 4.3 mm diameter ion chambers with both tissue equivalent and carbon walls for the purpose of measuring dose mean lineal energy due to all radiations and due to all radiations except neutrons, respectively. By adjusting the gas pressure in the ion chamber, it can be made to simulate tissue volumes from a few nanometers to a few millimeters in diameter. The charge is integrated for 0.1 seconds, and the resulting pulse height is recorded by a multi channel analyzer. The system has been used in a variety of photon and neutron radiation fields, and measured values of dose and dose mean lineal energy are consistent with values extrapolated from measurements made by other techniques at much lower dose rates. It is expected that this technique will prove ...
Date: August 29, 2003
Creator: Braby, L. A.; Reece, W. D. & Hsu, W. H.
Partner: UNT Libraries Government Documents Department

Biology relevant to space radiation

Description: The biological effects of the radiations to which mankind on earth are exposed are becoming known with an increasing degree of detail. This knowledge is the basis of the estimates of risk that, in turn, fosters a comprehensive and evolving radiation protection system. The substantial body of information has been, and is being, applied to questions about the biological effects of radiation is space and the associated risk estimates. The purpose of this paper is not to recount all the biological effect of radiation but to concentrate on those that may occur as a result from exposure to the radiations encountered in space. In general, the biological effects of radiation in space are the same as those on earth. However, the evidence that the effects on certain tissues by the heaviest-charged particles can be interpreted on the basis of our knowledge about other high-LET radiation is equivocal. This specific question will be discussed in greater detail later. It is important to point out the that there are only limited data about the effects on humans of two components of the radiations in space, namely protons and heavy ions. Thus predictions of effects on space crews are based on experimental systems exposed on earth at rates and fluences that are higher than those in space and one the effects of gamma or x rays with estimates of the equivalent doses using quality factors.
Date: August 1996
Creator: Fry, R. J. M.
Partner: UNT Libraries Government Documents Department

Adaptive response against spontaneous neoplastic transformation induced by low dose ionizing radiation

Description: This project is being conducted to ascertain the shape of the dose response curve for neoplastic transformation in vitro over the dose range 0.0 to 10 cGy, and to determine how this depends on radiation quality and dose fractionation. Preliminary data already have indicated that at a dose of 1 cGy the induced transformation frequency is less than the spontaneous transformation frequency. The results will be compared with animal and human epidemiological data on the induction of cancer by low doses of radiation. This will hopefully allow for a more informed estimation of the risk of cancer induction at low doses.
Date: June 1, 2001
Creator: Redpath, J. Leslie
Partner: UNT Libraries Government Documents Department

Adaptive response against spontaneous neoplastic transformation induced by low dose ionizing radiation

Description: This project is being conducted to ascertain the shape of the dose response curve for neoplastic transformation in vitro over the dose range 0.0 to 10 cGy, and how this depends on radiation quality and dose fractionation. Preliminary data already have indicated that at a dose of 1 cGy the induced transformation frequency is less than the spontaneous transformation frequency. The results will be compared with animal and human epidemiological data on the induction of cancer by low doses of radiation. This will hopefully allow for a more informed estimation of the risk of cancer induction at low doses (see Pollycove, 1998; Rossi, 1999).
Date: June 1, 2000
Creator: Redpath, J. Leslie
Partner: UNT Libraries Government Documents Department

Future research in mouse radiation genetics

Description: From thirteenth international congress of genetics; Berkeley, Ca1ifornia, USA (20 Aug 1973). The specific-locus method was used to investigate the effect of various biological and physical factors on radioinduced mutation frequency at a sample of seven gene loci of mice. The biological factors include sex, cell stage, and the interval between irradiation and fertilization. The physical factors include radiation dose, dose rate, dose fractionation, and radiation quality. It is suggested that the studies be extended to determine the effects of the various biological and physical factors on mutation frequency at low radiation dose rates in mouse spermatogonia and dictyate oocytes; investigations on the actual nature and effect of the individual mutations induced by radiation; and studies on the nature, extent, and persistence of the actual anatomical and physiologica1 damage expressed in the descendents of irradiated populations. (CH)
Date: January 1, 1972
Creator: Russell, W.L.
Partner: UNT Libraries Government Documents Department

Theory of RBE. Final report, January 1, 1967--October 31, 1998

Description: The report begins with a historical survey of research activity. Next summaries of research accomplishments in the following areas are given: (1) Radiation Dose Distribution; (2) The 1-Hit Detector: Action Cross Sections; (3) Many Hit Detectors; (4) Biological Cells; (5) Implications for Radiation Protection; and (6) Implications for Radiation Oncology with Heavy Ion Beams.
Date: October 31, 1998
Creator: Katz, R.
Partner: UNT Libraries Government Documents Department

Overview of CSEWG shielding benchmark problems

Description: The fundamental philosophy behind the choosing of CSEWG shielding benchmarks is that the accuracy of a certain range of cross section data be adequately tested. The benchmarks, therefore, consist of measurements and calculations of these measurements. Calculations for which there are no measurements provide little information on the adequacy of the data, although they can perhaps indicate the sensitivity of results to variations in data.
Date: January 1, 1979
Creator: Maerker, R.E.
Partner: UNT Libraries Government Documents Department

Measurements of radiation quality factors using a recombination chamber

Description: The recombination chamber technique has been described in a CERN report by Sullivan and Baarli. In this method, one uses the fact that a high pressure ion chamber operated at a voltage beneath its plateau will measure a greater response to radiation of low LET than to radiation of high LET in fields of equivalent absorbed dose rate. This report describes a calibration procedure and results obtained in accelerator radiation fields. 8 references, 6 figures. (ACR)
Date: March 1, 1984
Creator: Cossairt, J.D.; Grobe, D.W. & Gerardi, M.A.
Partner: UNT Libraries Government Documents Department

Spatiotemporal characterization of ionizing radiation induced DNA damage foci and their relation to chromatin organization

Description: DNA damage sensing proteins have been shown to localize to the sites of DSB within seconds to minutes following ionizing radiation (IR) exposure, resulting in the formation of microscopically visible nuclear domains referred to as radiation-induced foci (RIF). This review characterizes the spatio-temporal properties of RIF at physiological doses, minutes to hours following exposure to ionizing radiation, and it proposes a model describing RIF formation and resolution as a function of radiation quality and nuclear densities. Discussion is limited to RIF formed by three interrelated proteins ATM (Ataxia telangiectasia mutated), 53BP1 (p53 binding protein 1) and ?H2AX (phosphorylated variant histone H2AX). Early post-IR, we propose that RIF mark chromatin reorganization, leading to a local nuclear scaffold rigid enough to keep broken DNA from diffusing away, but open enough to allow the repair machinery. We review data indicating clear kinetic and physical differences between RIF emerging from dense and uncondensed regions of the nucleus. At later time post-IR, we propose that persistent RIF observed days following exposure to ionizing radiation are nuclear ?scars? marking permanent disruption of the chromatin architecture. When DNA damage is resolved, such chromatin modifications should not necessarily lead to growth arrest and it has been shown that persistent RIF can replicate during mitosis. Thus, heritable persistent RIF spanning over tens of Mbp may affect the transcriptome of a large progeny of cells. This opens the door for a non DNA mutation-based mechanism of radiation-induced phenotypes.
Date: September 15, 2009
Creator: Costes, Sylvain V; Chiolo, Irene; Pluth, Janice M.; Barcellos-Hoff, Mary Helen & Jakob, Burkhard
Partner: UNT Libraries Government Documents Department

Radiation quality of beams of negative pions

Description: As a negative pion stops in tissue, it attaches itself to an adjacent atom to form a mesonic atom. Subsequently, the wave function of the pion interacts with that of the nucleus and the pion is absorbed. Because the energy associated with the rest mass of the pion is greater than the separation energy of the nuclear particles, the nucleus disintegrates (pion star). In tissue, approximately 40 MeV goes into overcoming the binding energies; 20 MeV goes into kinetic energy of charged particles; 80 MeV goes into kinetic energy of neutrons. In cases where biological studies are performed with beams of negative pions, as much as 20% of the total absorbed dose in the treatment volume and about 50% of the high-LET dose (> 100 keV/..mu..m) can result from neutrons. The degree of biological response and the variation of that response throughout the treatment volume can be altered by the neutron dose.
Date: January 1, 1981
Creator: Dicello, J.F. & Brenner, D.J.
Partner: UNT Libraries Government Documents Department

Personnel neutron dosimetry

Description: This edited transcript of a presentation on personnel neutron discusses the accuracy of present dosimetry practices, requirements, calibration, dosemeter types, quality factors, operational problems, and dosimetry for a criticality accident. 32 figs. (ACR)
Date: April 1, 1982
Creator: Hankins, D.
Partner: UNT Libraries Government Documents Department

Role of repair processes in neoplastic transformation induced by ionizing radiation in C3H/10T1/2 cells

Description: The paper discusses the mechanisms underlying the induction and modulation of neoplastic transformation by the type and mode of radiation delivery. Those features of transformation in vitro characteristic of induction by ionizing radiation are described. 33 references, 10 figures. (ACR)
Date: January 1, 1984
Creator: Hill, C.K.; Elkind, M.M. & Han, A.
Partner: UNT Libraries Government Documents Department

Radiation characterization, and exposure rate measurements from cartridge, 105-mm, APFSDS-T, XM774

Description: In response to a recommendation from the Joint Technical Coordinating Group for Munitions Effectiveness, Working Group on Depleted Uranium Munitions, the Department of the Army contracted with Pacific Northwest Laboratory (PNL) to investigate the health physics problems associated with the assembly, storage, and use of 105-mm, APFSDS-T, XM774 ammunition. Each round of this ammunition contains a penetrator rod of 3.4 kg of depleted uranium (DU), which is classified as a radioactive source material. The study carried out by PNL included laboratory and field analyses and an assessment of current health physics practices. The data sought included: the characteristics of radiation emitted from a penetrator and an assembled projectile; a comparison of film and thermoluminescent dosimeters; a comparison of radiation detection instruments; and the exposure rates from a single XM774 round, a loaded storage container, a standard pallet, and a loaded tank.
Date: November 1, 1979
Creator: Bartlett, W.T.; Gilchrist, R.L.; Endres, G.W.R. & Baer, J.L.
Partner: UNT Libraries Government Documents Department

Investigation of the microdosimetric characteristics of broad, therapeutic beams of negative pions at LAMPF

Description: Preclinical human studies with negative pions are presently being conducted at the Clinton P. Anderson Meson Physics Facility (LAMPF) of the Los Alamos Scientific Laboratory. Presently, the proton current at LAMPF is 300 ..mu..A, average, and the instantaneous pion rate at the biomedical channel is about 2.4 x 10/sup 7/ pions/sec, cm/sup 2/. This corresponds to a dose rate of about 6 rad/min in a 1 liter volume. Conventional microdosimetric techniques are not applicable at these event-rates because of detector damage, gas breakdown, pileup and deadtime effects, and saturation of the electronics. A new microdosimetric system developed at LAMPF in order to overcome these problems is described. Treatment fields as large as 17 x 17 cm/sup 2/ and as deep as 10 cm have been developed. The radiation quality of such pion beams is changing rapidly throughout the treatment volume. For this reason, microdosimetric data have been obtained for a broad, therapeutic beam (10 cm deep, 1 liter volume) as part of a continuing program to characterize those aspects of the radiation quality which produce changes in the biological response. Microdosimetric data have been obtained at several positions along the central axis of the beam in the peak region. The characteristics of the broad, pion beams are discussed and are compared with those of a narrow pion beam, with neutron data, and with data for broad, heavy-ion beams. An attempt is made to calculate broad beam distributions from data for narrow beams for purposes of treatment planning, and the results are compared with the measured spectra.
Date: January 1, 1978
Creator: Dicello, J.F. & Zaider, M.
Partner: UNT Libraries Government Documents Department

Cataract production in mice by heavy charged particles

Description: The cataractogenic effects of heavy charged particles have been evaluated in mice in relation to dose and ionization density (LET/sub infinity/). The study was undertaken due to the high potential for eye exposures to HZE particles among SPS personnel working in outer space. This has made it imperative that the relative biological effectiveness (RBE) in relation to LET/sub infinity/ for various particles be defined so that appropriate quality factors (Q) could be assigned for estimation of risk. Although mice and men differ in susceptibility to radiation-induced cataracts, the results from this project should assist in defining appropriate quality factors in relation to LET/sub infinity/, particle mass, charge, or velocity. Evaluation of results indicated that : (1) low single doses (5 to 20 rad) of iron (/sup 56/Fe) or argon (/sup 40/Ar) particles are cataractogenic at 11 to 18 months after irradiation; (2) onset and density of the opacification are dose related; (3) cataract density (grade) at 9, 11, 13, and 16 months after irradiation shows partial LET/sub infinity/-dependence; and (4) the severity of cataracts is reduced significantly when 417 rad of /sup 60/Co gamma radiation is given in 24 weekly 17 rad fractions compared to giving this radiation as a single dose, but cataract severity is not reduced by fractionation of /sup 12/C doses over 24 weeks.
Date: March 1, 1981
Creator: Ainsworth, E.H.; Jose, J.; Yang, V.V. & Barker, M.E.
Partner: UNT Libraries Government Documents Department

Mechanisms of Low Dose Radiation-induced T helper Cell Function

Description: Exposure to radiation above levels normally encountered on Earth can occur during wartime, accidents such as those at Three Mile Island and Chernobyl, and detonation of “dirty bombs” by terrorists. Relatively high levels of radiation exposure can also occur in certain occupations (low-level waste sites, nuclear power plants, nuclear medicine facilities, airline industry, and space agencies). Depression or dysfunction of the highly radiosensitive cells of the immune system can lead to serious consequences, including increased risk for infections, cancer, hypersensitivity reactions, poor wound healing, and other pathologies. The focus of this research was on the T helper (Th) subset of lymphocytes that secrete cytokines (proteins), and thus control many actions and interactions of other cell types that make up what is collectively known as the immune system. The Department of Energy (DOE) Low Dose Radiation Program is concerned with mechanisms altered by exposure to high energy photons (x- and gamma-rays), protons and electrons. This study compared, for the first time, the low-dose effects of two of these radiation forms, photons and protons, on the response of Th cells, as well as other cell types with which they communicate. The research provided insights regarding gene expression patterns and capacity to secrete potent immunostimulatory and immunosuppressive cytokines, some of which are implicated in pathophysiological processes. Furthermore, the photon versus proton comparison was important not only to healthy individuals who may be exposed, but also to patients undergoing radiotherapy, since many medical centers in the United States, as well as worldwide, are now building proton accelerators. The overall hypothesis of this study was that whole-body exposure to low-dose photons (gamma-rays) will alter CD4+ Th cell function. We further proposed that exposure to low-dose proton radiation will induce a different pattern of gene and functional changes compared to photons. Over the course of this ...
Date: October 31, 2008
Creator: Gridley, Daila S.
Partner: UNT Libraries Government Documents Department

Phenomenological models

Description: The biological effects of ionizing radiation exposure are the result of a complex sequence of physical, chemical, biochemical, and physiological interactions. One way to begin a search for an understanding of health effects of radiation is through the development of phenomenological models of the response. Many models have been presented and tested in the slowly evolving process of characterizing cellular response. A range of models covering different endpoints and phenomena has developed in parallel. Many of these models employ similar assumptions about some underlying processes while differing about the nature of others. An attempt is made to organize many of the models into groups with similar features and to compare the consequences of those features with the actual experimental observations. It is assumed that by showing that some assumptions are inconsistent with experimental observations, the job of devising and testing mechanistic models can be simplified. 43 refs., 13 figs.
Date: September 1, 1990
Creator: Braby, L.A.
Partner: UNT Libraries Government Documents Department

Stochastic basis for curve shape, RBE and temporal dependence

Description: This paper uses biophysical-microdosimetric quantities, measured in a physical surrogate or phantom cell, to explain the shape of absorbed dose-quantal cell response curves, the role of radiation quality and the influence of dose rate. Responses expected are explored first in simple autonomous cell systems, followed by increasingly-complex systems. Complications seen with increasingly-complex systems appear to be confined largely to the higher dose and dose rate ranges.
Date: August 10, 1982
Creator: Bond, V.P.
Partner: UNT Libraries Government Documents Department

Effect of radiation quality and repair processes on the incidence of neoplastic transformation in vitro. [X radiation, mice]

Description: Studies of the effect of radiation dose fractionation on survival of mammalian cells show that x-ray dose fractionation results in a substantial increase in net survival due to the rapid repair of sublethal damage. For high LET radiations, however, the magnitude of any net survival increase is appreciably less and may be essentially absent. Thus the capacity of cells to repair sublethal damage is an important factor in considering the effect of fractionation radiation exposure in the potential of surviving cells to produce cancer. The carcinogenic potential of dose fractionation has been studied in animals and in recent years it has been extensively studied in vitro. Using mouse embryo derived C3H/10T1/2 cells we have demonstrated that x-ray dose fractionation results in appreciable repair of cumulative damage related to transformation, i.e., subtransformation damage. Considerably less reduction in neoplastic transformation is observed after fission-spectrum neutron dose fractionation. This paper presents new information demonstrating that reduction in neoplastic transformation following dose fractionation is a result of repair of subtransformation damage, rather than repair of sublethal damage.
Date: January 1, 1979
Creator: Han, A. & Elkind, M. M.
Partner: UNT Libraries Government Documents Department

Influence of dose, dose rate, and radiation quality on radiation carcinogenesis and life shortening in RFM and BALB/C mice. [Gamma radiation, fission neutrons]

Description: The effects produced by /sup 137/Cs gamma rays delivered at a high (45 rads/min) or intermediate (8.2 rads/day) dose rate and the effect of fission neutrons at a high (25 rads/min) and low (1 rad/day) rate in a population of nearly 30,000 RFM and 11,000 BALB/c mice have been studied. Gamma ray doses ranged from 10 to 400 rads with the RFM's and from 50-400 rads with the BALB/c's, while neutron doses ranged from 5 to 200 rads with both strains. The present paper will present an overview of these data and the general findings while subsequent publications will present detailed analyses of each aspect. A variety of neoplasms were sensitive to induction after radiation exposure, including tumors of both reticular tissue origin (leukemia, lymphoma, etc.) and solid tumors. For the RFM, thymic lymphomas were the dominant reticular tissue neoplasm while the majority of solid tumors were either lung adenomas or fit into the broad category of endocrine related tumors, including ovarian, pituitary, harderian, and uterine tumors. The BALB/c was much less sensitive to induction of reticular tissue neoplasms. The tumors that were most sensitive to induction included malignant lung carcinomas, mammary adenocarcinomas and ovarian tumors. In general for both life shortening and tumor induction after gamma ray exposures, when the low to intermediate dose range was sufficiently defined, linearity could be rejected and a dose squared or linear-dose squared relationship adequately fit the data. For neutron exposures, on the other hand, linear relationships were the general finding. The RBE for neutrons varied with tumor type and total dose level. For gamma ray irradiation, the intermediate dose rate resulted in a decreased effectiveness in all cases, while for neutron exposures the dose rate relationships were more complex.
Date: January 1, 1978
Creator: Ullrich, R.L. & Storer, J.B.
Partner: UNT Libraries Government Documents Department