WAM-C - Internal Dosimetry North 224AB 08:00 - 12:00
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WAM-C.1
08:00 A Standard for Plutonium Internal Dosimetry EH Carbaugh*, Retired CHP
Abstract: A new American National Standard for plutonium internal dosimetry is near approval. Over time, plutonium production and reprocessing has significantly decreased resulting in decontamination, decommissioning, and in some cases complete removal of plutonium facilities. Concurrent with this, the retirement of senior health physicists who specialized in plutonium internal dosimetry has also occurred, and the opportunities for cross-training of the next generation of dosimetrists have been reduced. This new standard, ANSI/HPS N13.25, Internal Dosimetry Programs for Plutonium Exposure – Basic Requirements, has been 30 years in the making, and seeks to fill a need for reference expert recommendations that can guide relative novices to plutonium internal dosimetry. Building on ANSI/HPS N13.39, this standard provides guidance on the design, administration, and operation of plutonium bioassay programs, data interpretation, intake and dose assessment, and response to intakes. Appendixes address rules of thumb, dosimetry systems, and specific bioassay methods.
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WAM-C.2
08:15 USTUR Whole-body Case 0680: 53-year Follow-up of a Manhattan Project Worker M Šefl*, U.S. Transuranium and Uranium Registries, Washington State University
; M Avtandilashvili, U.S. Transuranium and Uranium Registries, Washington State University; SY Tolmachev, U.S. Transuranium and Uranium Registries, Washington State University
Abstract: This whole-body tissue donor to the United States Transuranium and Uranium Registries (USTUR) was occupationally exposed to a mixture of plutonium compounds via chronic inhalation. This individual was one of 26 Manhattan project workers, informally known as ‘UPPU (You Pee Pu) Club’. He died 53 years post-exposure. At the time of death, 1,765 Bq of 239Pu was retained in the body, of which 39.7% was in the skeleton, 37.5% in the liver, 16.0% in the respiratory tract, and 6.8% in the remaining soft tissues. Nineteen urine, one fecal, and one blood analysis results as well as four in vivo chest measurements were available. The organ activities at the time of death and bioassay data were used to estimate the intake and radiation doses using the Taurus internal dosimetry software. ICRP recommended biokinetic models adequately described the individual’s long-term plutonium retention and excretion. The total cumulative 239Pu intake of 31,716 Bq was estimated; of which, 24,853 Bq (78.4%) were contributed by inhalation of plutonium nitrate and 6,863 Bq (21.6%) of plutonium dioxide. The committed equivalent doses to the red bone marrow, bone surface, liver, lungs, and brain were 0.71 Sv, 6.5 Sv, 8.3 Sv, 3.8 Sv, and 0.068 Sv, respectively. The committed effective dose was 1.22 Sv.
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WAM-C.3
08:30 Analysis of Long-term Retention of Plutonium in the Respiratory Tract Tissues of Four Workers: Bound Fraction vs. Scar-tissue Compartments D Poudel*, Los Alamos National Laboratory
; M Avtandilashvili, USTUR, Washington State University; JA Klumpp, Los Alamos National Laboratory; L Bertelli, Los Alamos National Laboratory; SY Tolmachev, USTUR, Washington State University; De Poudel
Abstract: Respiratory tract tissues collected from four former nuclear workers involved in various inhalation incidents were analyzed post mortem for plutonium by the United States Transuranium and Uranium Registries. Activities in the upper respiratory tract of these individuals were found to be higher than those predicted using the most recent biokinetic models described in publications of the International Commission on Radiological Protection. An assumption of ‘bound fraction’ of 0.4-4% was able to explain the data from three workers who had inhaled soluble to fairly insoluble forms of plutonium. For the fourth worker who had inhaled high-fired plutonium oxide, a more insoluble form of plutonium, a mechanism other than bound fraction was required to explain the observed retention of plutonium in the respiratory tract tissues. Literature review points to the presence of – and a significant retention of – plutonium activity in the scar tissues of the lungs. This presentation proposes a human respiratory tract model modified with the addition of scar tissue compartments to describe the long-term retention of plutonium in the respiratory tract of these individuals. The transfer rates between the compartments were determined using Markov Chain Monte Carlo analysis of the urinary excretion data, lung counts, and post-mortem measurements of the systemic and respiratory tract compartments, as available. The estimates obtained from modeling these data showed that as much as one-third of the total activity in the lung can be sequestered in scar tissues.
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WAM-C.4
08:45 Comparison of two methods to estimate skeletal plutonium concentration from limited sets of bones G Tabatadze*, U.S. Transuranium and Uranium Registries, Washington State University
; M Avtandilashvili, U.S. Transuranium and Uranium Registries, Washington State University; SY Tolmachev, U.S. Transuranium and Uranium Registries, Washington State University
Abstract: Historically, two calculation methods have been used by the United States Transuranium and Uranium Registries (USTUR) to estimate the actinide skeletal concentration: (i) arithmetic average and (ii) mass-weighted average of concentrations measured in bone samples. Preliminary comparison of skeletal concentrations, estimated for 216 partial-body USTUR cases, using these two methods indicates a statistically significant difference (p <0.05) with the bias of 15% between the estimates. The aim of this research is to determine: (1) which method of skeletal concentration estimate is more accurate for a given (collected) set of bones and (2) among the sets of bones most commonly collected for partial-body donations, which set provides more accurate estimate of the total skeletal concentration using each method. Nineteen whole-body cases with complete skeleton analyses were used to compare the estimates of the skeletal concentration based on different sets of bones with the concentration based on all measured bones from the right side of the skeleton. Out of 19 cases, 239Pu was a primary radionuclide of exposure for 17, and 238Pu for two cases. Five individuals were diagnosed with osteoporosis. Since osteoporosis significantly impacts plutonium distribution in the skeleton, 19 cases were divided in two study groups – osteoporotic (5) and non-osteoporotic (14). These cases were further sub-divided into 11 bone groups, based on a number of bones (2 to 8) and their frequency of collection at autopsies. These groups represent different balance of cortical- and trabecular-bone-rich bone samples. To compare the two methods, for each bone group, the arithmetic (Ca) and weighted (Cw) average plutonium concentrations were calculated and compared to the total skeleton concentrations (Csk). Preliminary results indicated that, for all cases and all bone groups, both Ca and Cw predict Csk within 10% of the best estimate and Cw yields slightly better estimate of the Csk for non-osteoporotic cases; however, it has a higher uncertainty.
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WAM-C.5
09:00 Latent Bone Modeling Approach to Estimate Plutonium Activity Concentration in Human Skeleton JY Zhou*, U.S. Department of Energy
; M Avtandilashvili, U.S. Transuranium & Uranium Registries, Washington State University; SY Tolmachev, U.S. Transuranium & Uranium Registries, Washington State University
Abstract: The skeleton is a major depository site for plutonium in a human body. In radiation protection, a long-term standing question is: What is the most accurate and precise way to estimate the skeleton plutonium concentration and activity from the analysis of a limited set of bones? To answer this question, a multiple linear regression was used in several studies. The key limitation of this approach is multicollinearity among independent variables since the activity concentrations from individual bones are highly correlated resulting in unstable and imprecise estimates of model coefficients. In addition, the number of individual bones allowed in a multiple linear regression model is limited, given a very small number of studied cases. Skeleton plutonium activity concentrations (Bq kg-1 of wet bone) for 19 whole-body tissue donors to the United States Transuranium and Uranium Registries (USTUR), were estimated based on post-mortem radiochemical analyses of the right side of the skeleton, where the total number of analyzed bones ranged from 72 to 89. At the USTUR, 87% of deceased Registrants are partial-body tissue donors with only 2 to 8 bones collected at autopsy. For these cases, the most commonly collected bones are rib, sternum, vertebral body, patella, clavicle, and femur middle shaft. This study applied principal components regression (PCR) by performing principal components analysis (PCA) on an analytical data set from 19 whole-body cases, followed by the selection of a set of 1 to 3 principal components as latent bones (independent variables) for a subsequent multiple linear regression modeling. Latent bone concentration (Clb) is not directly measured but is a linear combination of individually measured bone concentrations (Cbone). Latent bone concentrations, as independent variables in multiple linear regression, are uncorrelated with each other. For rib, sternum, and vertebral body, PCR analysis resulted in the first latent bone equation: Clb1 = 0.5759×Crib + 0.5755×Csternum + 0.5807×Cvert. In this case, the first latent bone alone explained 98.4% of total variance, and the skeleton plutonium concentration can be calculated as Cskel = (18.0±0.8)×Clb1 + 25.0±1.4.
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WAM-C.6
09:15 Effect of Osteoporosis on Latent Bone Models to Estimate Plutonium Activity Concentration in Human Skeleton SY Tolmachev, U.S. Transuranium & Uranium Registries, Washington State University
; M Avtandilashvili, U.S. Transuranium & Uranium Registries, Washington State University; JY Zhou*, U.S. Department of Energy
Abstract: The recently developed latent bone modeling (LBM) approach applies principal components regression (PCR) to estimate plutonium activity concentration in the human skeleton from measurements of a limited set of bone samples. The analytical bone dataset contains plutonium concentrations for 90 individual bone samples from 19 whole-body donors to the United States Transuranium and Uranium Registries. These samples were divided into 6 groups by bone type: skull (11 samples), long bone end (15), long bone shaft (14), cortical bone (29), trabecular bone (18) and other bones (3). Five of 19 studied individuals were diagnosed with osteoporosis. This study evaluated the effect of osteoporosis on LBMs for estimation of skeleton plutonium activity concentrations. For each bone group (except for the mixed bones), the PCR was performed with and without the 5 osteoporotic cases. The PCR models were fitted for 2 to 6 bones randomly sampled from each group, and 10,000 simulations were run for a given number of sampled bones. Regression residual standard error (RSE) for the PCR simulation was used to evaluate model performance. Excluding 5 osteoporotic cases from analyses significantly improved the PCR models in terms of relative RSE reduction compared to those obtained from the analyses of all 19 cases. The average RSEs for 2 to 6 bones were reduced by 60.2±0.4% for trabecular bone, 56.1±5.1% for long bone end, 53.2±1.8% for cortical bone, 48.4±2.4% for long bone shaft, and 22.4±1.9% for skull. Therefore, separate models should be used for non-osteoporotic and osteoporotic individuals when possible. The RSEs of PCR models for non-osteoporotic individuals were 1.9±0.4 for long bone end (epiphysis), 2.5±0.1 for trabecular bone, 2.8±0.1 for cortical bone, 2.8±0.2 for long bone shaft (diaphysis), and 4.2±0.1 for skull. The non-osteoporotic PCR model, accounting for all bone types, was developed by selecting 3 ‘best’ bones with the lowest RSE in each of 5 bone groups. When the analytical dataset for 14 non-osteoporotic cases was reduced from 90 to 18 bones (15 ‘best’ bones plus 3 others), a further improvement of the PCR model fit was achieved with RSE of 1.4±0.4. Due to the limited number of cases, the model to estimate plutonium concentration for osteoporotic individuals was not proposed.
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WAM-C.7
09:30 Uncertainty Evaluation of Skeleton Plutonium Activity Concentration Estimated from a Latent Bone Model JY Zhou*, U.S. Department of Energy
; M Avtandilashvili, U.S. Transuranium & Uranium Registries, Washington State University; SY Tolmachev, U.S. Transuranium & Uranium Registries, Washington State University
Abstract: The recently proposed latent bone model (LBM) for non-osteoporotic individuals applies principal components regression (PCR) to estimate plutonium activity concentration in the human skeleton from measurements of a limited set of bone samples. This study developed a Monte Carlo method to evaluate uncertainty in LBM estimates of skeleton plutonium activity concentration (Cskel) using PCR analysis. For this study, the analytical bone dataset was prepared using plutonium concentrations in 18 preselected ‘best’ bone samples from 14 non-osteoporotic whole-body donors to the United States Transuranium and Uranium Registries. The tissue donors’ age ranged from 52 to 87 years and the Cskel ranged from 0.9 to 42.0 Bq kg-1 of wet weight. The bone set contained 3 samples from each of 6 bone types: skull, long bone end (epiphysis), long bone shaft (diaphysis), cortical bone, trabecular bone, and other bones. The PCRs were used to fit LBMs for 2 to 6 randomly sampled bones, and 10,000 simulations were run for a given number of bone samples. The simulation results indicated that the residuals of plutonium concentrations were normally distributed for each of 14 studied cases. The standard deviation of the residuals (SD) of normal distributions were used to determine the uncertainties associated with the estimated Cskel. Linear regression was used to derive a relationship between SD and Cskel for each number of sampled bones. The linear regression equations for 2 and 6 sampled bones were: SD = 0.061×Cskel + 0.846 (r2 = 0.573, p = 0.0011) and SD = 0.024×Cskel + 0.446 (r2 = 0.398, p = 0.0098), respectively. The higher uncertainties were associated with a lower Cskel and a smaller number of sampled bones. As Cskel increased, the estimated relative standard deviations (SD/Cskel) decreased from 100% to 8% for 2 bones and from 52% to 3% for 6 bones.
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WAM-C.8
09:45 Latent Bone Modeling Approach to Select Best Combination of Bones for Estimating Plutonium Activity Concentration in Human Skeleton SY Tolmachev*, U.S. Transuranium & Uranium Registries, Washington State University
; M Avtandilashvili, U.S. Transuranium & Uranium Registries, Washington State University; JY Zhou, U.S. Department of Energy
Abstract: The United States Transuranium and Uranium Registries (USTUR) holds data and bone samples from 290 partial-body tissue donors. Bone samples collected at autopsy were radiochemically analyzed to estimate skeleton activity concentrations of plutonium, americium, and uranium. At the USTUR, the most commonly collected bone samples are rib, sternum, vertebral body, patella, clavicle, and femur middle shaft. Among these, patella, rib, and vertebral body are bones whose collection at autopsy is the easiest. This study applied the recently developed latent bone modeling (LBM) approach to select the best combination of sample bones for estimating the skeleton plutonium activity concentration (Cskel). The analytical bone dataset contained plutonium concentrations for the 6 most commonly collected bones from 14 non-osteoporotic USTUR whole-body tissue donors with known Cskel. The LBM models were built for all possible combinations from these 6 bones. The LMB model residual standard error (RSE) was used to determine the best combination of bones. For two bones (15 combinations), RSEs ranged from 1.096 to 4.888 with the best combination being patella and clavicle; for 3 bones (20 combinations), RSEs ranged from 0.853 to 2.557 with the best combination being patella, clavicle, and rib; for 4 bones (15 combinations), RSEs ranged from 0.792 to 2.073 with the best combination being patella, clavicle, rib, and femur middle shaft; for 5 bones (6 combinations), RSEs ranged from 0.970 to 1.382 with the best combination being patella, clavicle, rib, femur middle shaft, and sternum. The LBM RSE for the 3 easy-to-collect bones (patella, rib, and vertebral body) was 1.522. The LBM RSEs for the two bone combinations of these 3 bones were 1.366 for patella and rib, 2.018 for patella and vertebral body, 2.499 for rib and vertebral body. It is worth noting that the patella and rib combination had smaller RSE (1.366) than that of patella, rib and vertebral body (1.522), although, in general, a smaller RSE is associated with a larger number of bones in the LBM.
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WAM-C.9
10:30 Visualizations of Temporal and Tissue Variations in Activity and Dose from Intakes of Radionuclides DW Jokisch*, Francis Marion University
; AB Barker, Francis Marion University
Abstract: Computational internal dosimetry involves modeling the time-dependent distribution of radioactive material in various tissues and the calculation of energy deposition to target regions of interest. It is helpful to view the variations in activity and dose with time and location, as it provides insight on the impact of biokinetic modeling parameters and energy absorption quantities. Plotting of the activities and doses versus time has long been a useful tool for visualizing these relationships. The following visualizations have been produced providing new ways for viewing such data. Animated, “racing” bar charts of activity highlight the most important source regions and how they change with time. Heatmaps of activity and dose have been created using scalable vector graphic images of source and target regions in the human body. Such heatmaps provide insight into the location of activity and energy absorption and, if animated, provides viewers with a visual representation of material moving through the body with respect to time. Treemaps (rectangular alternatives to pie charts) have been created which show the relative contribution to committed effective dose for various target tissues and members of a decay chain. The benefits of the visualizations are: (1) they provide experts with valuable tools for confirming the modeling and calculations are functioning as intended; and (2) they provide viewers with meaningful insights as to how radioactive material moves through the body with respect to time and the relative importance of different tissues for intakes of varying radioactive materials.
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WAM-C.10
10:45 Dose coefficients for the embryo/fetus for a comprehensive set of radionuclides SO Schwahn, ORNL Center for Radiation Protection Knowledge
; CE Samuels*, ORNL Center for Radiation Protection Knowledge; RW Leggett, ORNL Center for Radiation Protection Knowledge
Abstract: Twenty years ago, the International Commission on Radiological Protection (ICRP) issued Publication 88, “Doses to the embryo and fetus from intakes of radionuclides by the mother.” Its authors performed meticulous research on biokinetics of 31 elements to determine appropriate effective dose coefficients for offspring following acute inhalation or ingestion of 74 radionuclides by the mother (approximately 400 cases considering two intake modes and multiple physiochemical forms of many of the radionuclides). The Center for Radiation Protection Knowledge (CRPK) at Oak Ridge National Laboratory explored the relationships of these dose coefficients with the concurrent dose to the mother’s uterus. These relationships were used to develop effective dose coefficients for the embryo and fetus, based on derived doses to the mother’s uterus, for the remaining radionuclides addressed in ICRP Publication 107 with half-lives of 10 minutes or more. The CRPK also expanded the scope of effective dose coefficients for radionuclides addressed in Publication 88 to include estimates for additional intake modes and chemical forms. The end result is a comprehensive compilation of conservative prenatal effective dose coefficients for 888 radionuclides, including those most likely to be encountered by a pregnant worker.
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WAM-C.11
11:00 Testing decision level (DL) and minimum detectable amount (MDA) for Hanford in vivo counting systems BL Rosenberg*, HMIS/NV5
; TP Lynch; CL Antonio
Abstract: Testing the decision level (DL) and minimum detectable amount (MDA) of a radionuclide for a direct bioassay (in vivo) counting system is a requirement for in vivo monitoring programs across the DOE complex. Bottle manikin absorption (BOMAB) and torso phantoms are used in conjunction with point sources to facilitate the testing. This paper describes a method of testing the DL and MDA values of in vivo counting systems with equipment commonly used by in vivo programs. This method is cost effective and minimizes waste since the radiological sources used can have broad ranges for decay activities. The results from the testing indicated that the current DL and MDA values are valid for the equipment and methods used at the Hanford in vivo counting facility.
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WAM-C.12
11:15 S-Values for Brain Subregion and Lacrimal Gland Sources to Support Radionuclide and Radiopharmaceutical Dosimetry in the Mesh-Type ICRP Reference Phantoms BN President*, University of Florida
; JL Brown, University of Florida; CM Correa Alfonso, University of Florida; SJ Domal, University of Florida; WE Bolch, University of Florida
Abstract: Dose assessment in radiopharmaceutical therapy (RPT) relies on the calculation of S-values from radionuclide sources of agent localization. To correctly estimate radiation dose to specific substructures in the brain during RPT, a realistic multi-region model of the brain is essential. Currently, the ICRP adult reference phantoms include a single homogeneous brain model and lack tissue regions for the lacrimal glands. This work focused on implementing an existing UF multi-region brain model within the cranial vault of ICRP mesh-based phantoms to perform S-values calculation to support neuroimaging studies. Additionally, models of the lacrimal glands were inserted within the ocular regions of the skull to support off-target dosimetry of protein-specific membrane antigen therapy agents. The ICRP reference phantoms and the UF multi-region brain model was derived from two separate individuals, and thus the 3D shape of the brain models and the ICRP cranial vaults differed. A contour-based deformable image registration was performed between the brain sub-regions and the ICRP phantoms skull. Further enhancements included the incorporation of the tear films and lacrimal glands. Finally, the enhanced ICRP phantoms were tetrahedralized using TETGEN software to perform Monte Carlo (MC) simulations using the MC transport code PHITS. Computed S-values were obtained in which the tear film, lacrimal gland, salivary glands, and brain subregions were considered as potential source regions. Radionuclide S-values are presented for the ICRP reference adult male and female in which a new multi-region brain model has been implemented to include 43 different brain substructures. The resulting data are provided to support the dosimetry of a wide variety of neuroimaging agents. Comparisons are made between the previously stylized multi-region brain models reported in MIRD Pamphlet No. 15. The incorporation of the multi-region brain and accompanying internal structures in the ICRP reference phantoms will now allow for more accurate dose assessments for both diagnostic neuroimaging studies, and RPT treatments. Future work will include the incorporation of multi-region brain models within the ICRP pediatric phantom series, as well as cellular level models of organs and tissues to support RPT using alpha-particle emitters.
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WAM-C.13
11:30 Incidence of the Pseudo Pelger-Huet Mutation In Radium Dial Painters Reflects Effectiveness of Regulation RE Goans*, MJW Corporation
Abstract: The Pelger-Huet cell (PH) has been recently described as a radiation-induced biomarker in circulating neutrophils. The PH cell, described by Pelger (1928) and Huet (1931), is a bi-lobed neutrophil characterized by a thin chromatin bridge. In humans, PH derives from an autosomal dominant mutation on the long arm of chromosome 1, 1q42.12. Since the cell is derived from mutations in the red marrow and has a long half-life (> 15 y), it appears to be a useful biomarker for retrospective dosimetry. In a collaborative effort with the US Transuranium and Uranium Registry (USTUR), it has been possible to examine peripheral blood slides from a cohort of 166 former radium dial painters. The radium dial painters are a well-described group of predominantly young women who incidentally ingested 226Ra and 228Ra, as they painted luminescent watch dials in the first half of the twentieth century. Our cohort contained 107 dial painters, 22 dial handlers, 19 radium chemists, and other personnel dealing with radium. Members of the cohort had ingestion of 226Ra and 228Ra at an early age (average age 20.6 ± 5.4 y; range 13-40 y) during the years 1914-1955. Exposure duration ranged from 1-1,820 weeks with red marrow dose 1.5-6,750 mGy. PHA expressed as a percentage of total neutrophils in this cohort rises in a sigmoidal fashion over five decades of red marrow dose. Six subjects eventually developed malignancies: five osteosarcomas and one mastoid cell neoplasm. Many dial-painting facilities began to prohibit brush tipping in the period 1925-1927. When the data are plotted as a function of date of entry into the workforce, the PH percentage for dates after 1927 is 81% of that prior to 1927, reflective of the occupational regulations prohibiting brush tipping that were put in place.
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WAM-C.14
11:45 Should (alpha,n) Neutrons Be Considered in Internal Dosimetry? NE Hertel*, Georgia Institute of Technology
; K Griffin, Georgia Institute of Technology; C Samuels, ORNL Center for Radiation Protection Knowledge; D. Jokisch, Francis Marion University; KF Eckerman, ORNL Center for Radiation Protection Knowledge
Abstract: Specific absorbed fractions (SAFs) for spontaneous fission (SF) neutrons are provided by the International Commission on Radiological Protection (ICRP) in their Publication 133 for 28 radionuclides that have spontaneous fission in their branching ratios. The ICRP SAFs are defined for radiations emitted directly in the decay of radionuclides and include the absorbed energy deposited by secondary particles. Alpha-emitting radionuclides can generate secondary neutrons if the alpha particle energy exceeds the the (α,n) reaction threshold. The absorbed energy due to neutrons from (α,n) reactions would be included in the SAF value for the alpha emission.
Previously we reported computations of (α,n) yields for two radionuclides which decay via both SF and alpha emission, Pu-238 and Pu-240. The (α,n) yield in elemental compositions corresponding to bone, liver and lung were generated using the SOURCES-4C code. For both radionuclides over 10 times more neutrons are emitted via (α,n) reactions than by SF on a unit activity basis. To further investigate the impact of including (α,n) neutrons in internal dosimetry, we computed the Pu-238 alpha SAF to include the (α,n) neutrons for adrenals<-liver using the male ICRP reference phantoms and the SOURCES-4C spectrum as a source term in MCNP 6.2. Any dose due to the secondary (α,n) neutrons would be added to the alpha particle SAF (zero for this source-target configuration) by scaling the (α,n) dose contribution by the alpha decay rate in the liver. Our preliminary computations yielded an alpha SAF of 2.13E-09 per kg based on (α,n) reactions in the liver compared to 0.0692 per kg for the SF neutron emissions in the liver. However, when the doses in the target organs are computed, the SAF for spontaneous fission neutrons is multiplied by the SF neutron emission rate of 1.9E-09 per decay, while the alpha SAF is multiplied by a decay fraction of approximately 1. Thus the adrenals doses are impacted more by the inclusion of the (α,n) neutrons in the alpha particle SAF than by SF neutron emission in the liver. Application of our findings to other source-target configurations are more complicated and will be discussed. As an example, the alpha SAFs for the blood as the source without any consideration of (α,n) secondaries yields nonzero SAFs for every organ and may make the addressing of (α,n) reactions in internal dosimetry merely an academic study.
REFERENCES
1. W.E. Bolch et al., The ICRP Computational Framework for Internal Dose Assessment for Reference Adults: Specific Absorbed Fractions, International Commission on Radiological Protection Publication 133 (2016).
2. W.B. Wilson et al., SOURCES 4C: A Code for Calculating (α,n), Spontaneous Fission, and Delayed Neutron Sources and Spectra, Los Alamos National Laboratory, LA-UR-02-1839 (2002).
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