Mixed Fission Research Articles

A new method for quantifying 64Cu in nuclear debris samples

Quantifying 64Cu in post-detonation nuclear debris samples can provide important diagnostic information regarding the structural materials used within a nuclear device. However, this task is challenging due to the weak gamma emissions associated with the decay of 64Cu, its short half-life (12.701 h), and the presence of interfering fission product radioisotopes. Large quantities of debris sample are generally needed to accurately quantify 64Cu, which can be problematic in sample-limited scenarios where other radiometric analyses are required. Herein, we present a new method for the separation of 64Cu from solutions of mixed fission products and demonstrate the quantification of its activity through use of gas-flow proportional beta counting. The new method was validated through a series of rigorous tests and was shown to improve the detection limit of 64Cu by over two orders of magnitude, from 2.5 × 106 to 1.3 × 104 atoms/sample for 100 min measurements.

Dose reduction using Saba thyroid shield during diagnostic X-ray energy range: a phantom study

The Saba thyroid shield is a new X-ray dose reduction tool for radiosensitive organs that can reduce the X-ray dose without degrading the image quality. This study investigated its effectiveness in reducing the X-ray dose on the thyroid surface during diagnostic X-ray. This study was conducted in the lab of the Medical Physics Department at Umm-Alqura University. The experiments were performed in the year 2022. A mixed fission product phantom and a solid-state detector were used to measure the radiation dose on the thyroid surface during diagnostic X-ray using a tube voltage within 40–120 kVp. The effectiveness of the Saba thyroid shield was examined in two settings: in-field and out-of-field. Measurements were conducted for these two settings without and with the Saba thyroid shield, and the attenuation percentages were computed. Analysis of covariance was used to test the tool’s effectiveness in X-ray dose reduction. The average in- and out-of-field dose attenuation percentages using the Saba thyroid shield were 80.12 ± 0.12% and 81.13 ± 0.18%, respectively. A significant difference was shown between the measurements done without and with the Saba thyroid shield (p = 0.000) for both the in-field and out-of-field doses. The in-field and out-of-field dose reduction levels using the shield were approximately the same. This study demonstrated that the newly developed Saba thyroid shield made of copper and bismuth effectively reduces both the in-field and out-of-field radiation doses.

Alpha/beta-gated gamma–gamma spectroscopy of mixed fission products for trace analysis

Alpha/beta-gated gamma–gamma spectroscopy of mixed fission products for trace analysis

Measurement of distribution coefficients on TODGA resin and development of a group separation for mixed activation and fission product samples

Batch equilibrium experiments were performed to determine the distribution coefficients for Sc, Ir, and Ta on N,N,N′,N′ tetraoctyl-1,5-diglycolamide (TODGA) resin in various acid matrices. Distribution coefficients were determined in hydrochloric acid (Sc, Ir), nitric acid (Sc, Ta), and a mixture of nitric acid and 0.2 M hydrofluoric acid (Sc, Ir, Ta). The distribution coefficients determined through these experiments were then utilized to create a group separation method for activation products, fission products, and environmental constituents.

A deconvolution method for scintillator gamma-ray spectrum analysis based on convex optimization

A deconvolution method based on convex optimization is developed and applied to gamma-ray spectrum deconvolution of simulated complicated spectra of NaI(Tl) measurements. The gamma-ray deconvolution problem is transformed into a minimization problem with inequality constraints. Then the Lagrange dual method is applied to transform the primal Lagrange problem into the dual problem. The interior-point method is applied and the logarithm barrier function is applied to construct the Newton system for iteration search. PCG (Preconditioned Conjugate Gradient) is applied to do the inexact search of the Newton system. The proposed method is applied to deconvolution of 4 typical gamma-ray spectra: (a) characteristic gamma-ray spectrum of 137Cs; (b) characteristic gamma-ray spectrum of 60Co; (c) characteristic gamma-ray spectrum of 152Eu; (d) mixed fission products in the primary loop of PWR (Pressurized Water Reactor), including the isotopes of Kr, Xe, I and Cs. Compared with the ML-EM method, improved accuracies and high resolution can be obtained with the proposed method. Moreover, the proposed method costs about 1/3 computational time of the ML-EM method.

Rapid quantitation of uranium from mixed fission product samples

Chemical similarities between uranium(VI) and molybdenum(VI) create challenges for separation and quantitation of uranium isotopes from a mixed fission product sample. The purpose of this work was to demonstrate an improved chemical separation for the detection of 235U using gamma spectroscopy. The optimized method, which included extraction and anion exchange chromatography, demonstrated a consistent chemical yield of 74 ± 3 % for uranium. Using a fresh fission product sample the minimum detectable activity for 235U, 237U, and 238U was reduced by a factor of two. The chemical isolation of uranium was achieved in less than 4 h, with a separation factor of 1.41 × 105 from molybdenum.

Integrated separation scheme for measuring a suite of fission and activation products from a fresh mixed fission and activation product sample

Mixed fission and activation materials resulting from various nuclear processes and events contain a wide range of isotopes for analysis spanning almost the entire periodic table. This work describes the production of a complex synthetic sample containing fission products, activation products, and irradiated soil, and determines the percent chemical recovery of select isotopes through the integrated chemical separation scheme. Based on the results of this experiment, a complex synthetic sample can be prepared with low atom/fission ratios and isotopes of interest accurately and precisely measured following an integrated chemical separation method.

Timing of coalification of the upper carboniferous sediments in the upper silesia coal basin on the basis of by apatite fission track and helium dating

Streszczenie Przeprowadzono datowania za pomocą metody trakowej i helowej dla apatytów z utworów karbońskich w Górnośląskim Zagłębiu Węglowym w celu określenia ram czasowych procesów uwęglcnia. Pomierzone centralne wieki trakowe apatytów mieszczą się w przedziale od 259±11 (późny perm) do 103±6 milionów lat (wczesna kreda), a średnia długość traków waha się od 11,7±0,2 do 13,7±0,1 (im. Wszystkie wieki trakowe są młodsze od wieku stratygraficznego analizowanych próbek, wskazując znaczne zaawansowanie procesów diagcnctycznych. Próbki z zachodniej i środ- kowej części GZW mają wieki trakowe od późnego permu do środkowego/późnego triasu (259±11 do 214±10 min lat). Jcdnomodalnc rozkłady długości traków i ich średnie wartości wskazują na poje- dyncze, względnie szybkie zdarzenie postwaryscyjskicgo wychładzania do temperatury poniżej 60°C, co jest zgodne zc znaczną erozją postinwersyjną utworów gómokarbońskich po fazie asturyjskicj. W pozostałej części mczozoiku następowało wolniejsze wychładzanie. Próbki zc wschodniej i NE części GZW mają wieki trakowe od późnego triasu do wczesnej kredy (210±10 do 103±6 milionów lat). Charakteryzuje je względnie krótsza średnia długość traków i wyższe odchylenia standardowe, a także w przypadku części próbek bimodalny i/lub mieszany charakter rozkładów długości. Jest to razem wskazówką bardziej złożonej historii termicznej, z długim okresem przebywania w PAZ i możliwym drugim zdarzeniem termicznym. Wieki helowe apatytów w całym basenie są wczcs- nokredowc(144,l±l 1 do 108,1±8 milionów lat), wskazując raczej na wolne postwaryscyjskic wychła- dzanie lub możliwe mczozoicznc podgrzanie karbonu do temperatury nic większej niż 60-70°C, które spowodowało częściową dyfuzję helu i odmłodzenie wieków helowych, ale równocześnie nic spo- wodowało znaczącego zabliźniania traków na większości obszaru GZW. Jedynie w NE części GZW podgrzanie mczozoicznc mogło być nieco wyższe, do temperatury 70-85°C, powodując odmłodzenie wieków trakowych, zwłaszcza przy długim okresie przebywania w PAZ. Mczozoiczny impuls ter- miczny był przypuszczalnie spowodowany cyrkulacją gorących roztworów związaną z procesami ekstensji. Powyższe zakresy temperatur i czas ich występowania świadczą, żc uwęglenie materii organicznej w GZW nastąpiło zasadniczo z końcem okresu karbońskiego.

An independent review and prioritization of past radionuclide and chemical releases from the Los Alamos National Laboratory – implications for future dose reconstruction studies

From 1999 through 2010, a team of scientists and engineers systematically reviewed approximately eight million classified and unclassified documents at Los Alamos National Laboratory (LANL) that describe historical off-site releases of radionuclides and chemicals in order to determine the extent to which a full-scale dose reconstruction for releases is warranted and/or feasible. As a part of this effort, a relative ranking of historical airborne and waterborne radionuclide releases from LANL was established using priority index (PI) values that were calculated from estimated annual quantities released and the maximum allowable effluent concentrations according to The U.S. Nuclear Regulatory Commission (USNRC). Chemical releases were ranked based on annual usage estimates and U.S. Environmental Protection Agency (USEPA) toxicity values. PI results for airborne radionuclides indicate that early plutonium operations were of most concern between 1948 and 1961, in 1967, and again from 1970 through 1973. Airborne releases of uranium were found to be of most interest for 1968, from 1974 through 1978, and again in 1996. Mixed fission products yielded the highest PI value for 1969. Mixed activation product releases yielded the highest PI values from 1979 to 1995. For waterborne releases, results indicate that plutonium is of most concern for all years evaluated with the exception of 1956 when (90)Sr yielded the highest PI value. The prioritization of chemical releases indicate that four of the top five ranked chemicals were organic solvents that were commonly used in chemical processing and for cleaning. Trichloroethylene ranked highest, indicating highest relative potential for health effects, for both cancer and non-cancer effects. Documents also indicate that beryllium was used in significant quantities, which could have lead to residential exposures exceeding established environmental and occupational exposure limits, and warrants further consideration. In part because of the close proximity of residents to LANL, further study of historical LANL releases and the potential impact to public health is recommended for those materials with the largest priority index values; namely, plutonium, uranium, and selected chemicals.

Modeling of gamma-ray spectra to direct efficient chemical separations

A project has been undertaken at Pacific Northwest National Laboratory (PNNL) to tailor a series of efficient chemical separations to allow the rapid quantification of gamma-ray emitting isotopes in mixed fission product (MFP) samples. In support of that goal, modeling of singles and coincident gamma-ray spectra that would result from various chemical separation strategies has been performed. These simulated spectra have identified likely instances of spectral interference and have provided an estimate of the time window available for the detection of radionuclides following various chemical separation schemes. A description of results to date is presented here, demonstrating the utility of this approach for improved processing and analysis of fission product samples.

Measuring and modeling transport properties of actinide and fission product contaminants in unsaturated prairie soil

This paper presents the results of measuring and modeling the transport of actinides and fission products in unsaturated prairie soil based on the contamination from a storage tank in Alberta. In 1951, a release occurred from an underground storage tank of some 6.7 L of an acidic, aqueous solution containing an estimated 360 GBq (9.7 Ci) of dissolved mixed fission products in a 6.7 L acidic solution. The site where this occurred remained undisturbed for 50 years before soil samples were collected and analyzed for specific radionuclide content, namely Cs-137, U-238, and Sr-90. The measured diffusion coefficients (Dd) for the selected group of radionuclides were 3.0 × 10–4 cm2 s–1 (Cs-137), 1.5 × 10–5 cm2 s–1 (U-238), and 2.6 × 10–3 cm2 s–1 (Sr-90). Based on transport modeling, after a period of 250 years from the release, the Sr-90 plume would have its maximum concentration at a depth of 2.8 m, while the Cs-137 plume would have its maximum concentration at 0.5 m. It is predicted therefore, that if the three radionuclides should reach the water table depth (50 m) then they will be at a concentration lower than their clearance level values and, hence, will not pose a health hazard.Key words: transport modeling, unsaturated soil, radionuclides, diffusion coefficient, distribution coefficient, uranium, strontium, cesium.

Document Retrieval, Information Assessment, and Preliminary Prioritization of Radioactive and Non-radioactive Releases From a Large Nuclear Weapons Facility

P-772 Introduction: In the mid-1940s, the United States built numerous facilities for the production of atomic weapons. A project is underway to evaluate historical radioactive and non-radioactive use and environmental releases at one large facility to ultimately reconstruct doses received by surrounding communities. While radioactive monitoring began in the late-1940s, uses of non-radioactive materials were poorly tracked and documented until the 1970s. The purpose of this paper is to describe methods used to prioritize radioactive and non-radioactive materials based upon their potential to pose a health risk to the public. Methods: Estimates of historical uses and releases were based on an extensive review of available records. Radioactive and non-radioactive materials were evaluated separately. Both airborne and liquid-borne radionuclide releases were considered. Each airborne radionuclide was ranked by calculating a priority index (PI) based on the air volume required to dilute the annual activity released to be equal to the worst-case non-occupational Maximum Permissible Concentration (MPC). Six groups of radionuclides were evaluated: plutonium, uranium, tritium, radioactive lanthanum, mixed fission products, and mixed activation products (MAP). For liquid-borne releases, PIs (based on water volumes required to reach MPCs) were calculated for total plutonium, 238Pu, 239Pu, 89Sr, 90Sr, tritium, gross alpha, and gross beta radioactivity. Non-radioactive materials identified as being present onsite in large quantities were ranked based upon highest annual usage and USEPA toxicity factors. Ranking was based on annual usage multiplied by either the non-cancer reference dose or the inverse of the cancer potency slope factor. If both were available, the more conservative toxicity factor was used. Results: Airborne releases of plutonium and uranium were of primary concern until the early 1980s, after which MAPs were the most significant. Application of the PI approach to beryllium indicated that airborne releases of the metal also warrant high priority. Plutonium was of highest concern among liquid-borne radionuclides. Historical releases of explosives and volatile organic chemicals appear to have the greatest potential for producing off-site health effects, with methylene chloride, TNT (2,4,6-trinitrotoluene), tetrachloroethylene, chlorodifluoromethane, and trichloroethylene ranking highest. Discussion and Conclusions: Prioritization methods were used to indicate which radioactive and non-radioactive materials used in facility operations warranted highest priority in retrospective studies of public exposures. Additional data will be sought for these materials to support detailed dose reconstruction. These methods can be applied to other sites where multiple hazards are present.

Internal Dose Estimates for Workers Exposed to Plutonium by Performing In Vivo Measurements of 241Am

Individual dose estimates for workers chronically exposed to plutonium is an important task in the investigation of possible health effects from internal plutonium depositions. Systemic and total body deposition of plutonium is usually estimated from urinalysis. However, this technique used alone results in uncertainty in individual dose assessment, by about an order of magnitude. Direct in vivo measurements of 241Am content in lungs, skeleton and liver by whole-body counting allows one to improve the result of dose assessment. First of all the improvement is due to the additional qualitative information about the route of intake (sorting out subjects with contaminated wounds) and solubility of plutonium aerosol particles (estimating the lung/skeleton ratio). This paper develops an algorithm for performing quantitative estimates of individual doses for workers, using the results of in vivo measurements of 241Am by whole-body counting. The algorithm applies the new ICRP Publication 66/67 models and takes into account such parameters as the 241Pu/239Pu ratio, effective aging time of mixed fission products and actinides, particle size distribution of plutonium aerosols and some other parameters. The uncertainties in individual dose assessment due to application of these parameters were analysed. It was shown that regular in vivo measurements of 241Am in the lungs allow the detection of single intake of plutonium at a level of the order of one ALI and can be a good monitoring programme for individuals involved in operations with plutonium treated in nuclear fuel cycle.

Chromosome aberration frequencies in human lymphocytes irradiated in a phantom by a mixed beam of fission neutrons and gamma -rays

Purpose: To provide further information on the existence of a significant quadratic component of the dose-response relationship for the production of dicentrics in human lymphocytes by mixed fission neutron and gamma -ray irradiation, which has been observed previously employing the same beam under free-in-air conditions. Materials and methods: Irradiation of blood samples and dosimetry was performed at 2 cm depth in a polymethyl methacrylate (PMMA) phantom of 16 cm side-length where the PMMA material fully surrounded the blood specimen. Chromosome analysis was carried out exclusively in complete first division metaphases. Results: Dicentric yields induced by absorbed doses between 0.043 and 2.68 Gy fit a linear-quadratic model with a quadratic coefficient significantly different from zero. The distribution of dicentrics is overdispersed compared to Poisson at lower doses, but is poissonian at higher doses. Conclusion: The presence of a significant quadratic dose-response coefficient for dicentrics, both for free-in-air and phantom irradiation, is caused by the various degraded fission spectra that produce neutrons or recoil protons over a broad energy range, rather than by the gamma -ray component of the beam.

Testing hot cell shielding in the fuel conditioning facility.

A comprehensive shield test program for a hot cell complex, the Fuel Conditioning Facility at Argonne National Laboratory, has been completed with minimum radiation exposure to participants. The recently modified shielding design for two hot cells and their associated transfer paths for irradiated materials was analyzed and tested for attenuating gamma rays from mixed fission product sources. Testing was accomplished using 0.37 TBq (10 Ci) and 518 TBq (14,000 Ci) 60Co sources. Of specific concern were radiation levels around wall penetrations and the interface between transport casks and the cell floor. Detailed measurements were made for surfaces that bound the hot cells, a transfer tunnel between the two cells, and storage pits that extend below the floors of both cells. In addition to surface measurements, dose equivalent rates in adjacent corridors were determined when the larger source was exposed. Results indicate that with some administrative controls, the facility shields are adequate to meet the design criterion that limits annual dose to less than 10 mSv (1 rem) for facility workers.

An Industry Survey of Current Lower Limits of Detection for Various Radionuclides

The results of a survey to assess detection limits of various radionuclides and their associated costs is presented herein. Included among the radionuclides of interest are mixed fission products, mixed activation products, actinides and transuranics, plus tritium (3H) and 14C. The survey encompassed commercial analytical radiochemistry services and nuclear instrument suppliers in the United States. In the study, a simple soil sample was defined as the object of consideration with no requirements for any special quality control/assurance. Standard procedures and instrumentation were requested, as were standard prices/costs required for the various analyses. The minimum detectable level for most isotopes using standard procedures was on the order of 0.0037 to 0.037 Bq g-1 (0.1 to 1.0 pCi g-1). The analytical costs varied by factors of 2 to 4 over a range of 0.0037 to 0.37 Bq g-1 (0.1 to 10.0 pCi g-1). While the ability to detect below 0.0037 Bq g-1 (0.1 pCi g-1) is possible, the required detection times were considered prohibitive for a commercial laboratory.

Dose-response relationships of micronuclei in human lymphocytes induced by fission neutrons and by low LET radiations

The induction of micronuclei in cytokinesis-blocked human lymphocytes of different donors has been measured after G 0 irradiation in vitro with a mixed fission neutron-γ-ray beam, 220 kV X-rays and 60Co γ-rays. The dose-response relationships for the micronucleic yeilds were linear-quadratic for both types of low LET radiations. The linear model applied for neutron-induced micronuclei over the dose range 0–0.66 Gy. At higher doses a saturation effect became apparent. For neutron-induced micronucleus yields a limiting RBE value of 12.2 was derived from the ratio of the α coefficients of neutrons and 60Co γ-rays.

Combination Protocols of Cytokine Therapy With Interleukin-3 and Granulocyte-Macrophage Colony-Stimulating Factor in a Primate Model of Radiation-Induced Marrow Aplasia

Single cytokine therapy with granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3) has been shown to be effective in decreasing the respective periods of neutropenia and thrombocytopenia following radiation- or drug-induced marrow aplasia. The combined administration of IL-3 and GM-CSF in normal primates suggested that a sequential protocol of IL-3 followed by GM-CSF would be more effective than that of GM-CSF alone in producing neutrophils (PMN). We investigated the therapeutic efficacy of two combination protocols, the sequential and coadministration of recombinant human IL-3 and GM-CSF relative to respective single cytokine therapy, and delayed GM-CSF administration in sublethally irradiated rhesus monkeys. Monkeys irradiated with 450 cGy (mixed fission neutron:gamma radiation) received either IL-3, GM-CSF, human serum albumin (HSA), or IL-3 coadministered with GM-CSF for days 1 through 21 consecutively postexposure, or IL-3 or HSA for days 1 through 7 followed by GM-CSF for days 7 through 21. All cytokines and HSA were injected subcutaneously at a total dose of 25 micrograms/kg/d, divided twice daily. Complete blood counts (CBC) and platelet (PLT) counts were monitored over 60 days postirradiation. The respiratory burst activity of the PMN was assessed flow cytometrically, by measuring hydrogen peroxide (H2O2) production. Coadministration of IL-3 and GM-CSF reduced the average 16-day period of neutropenia and antibiotic support in the control animals to 6 days (P = .006). Similarly, the average 10-day period of severe thrombocytopenia, which necessitated PLT transfusion in the control animals, was reduced to 3 days when IL-3 and GM-CSF were coadministered (P = .004). The sequential administration of IL-3 followed by GM-CSF had no greater effect on PMN production than GM-CSF alone and was less effective than IL-3 alone in reducing thrombocytopenia. PMN function was enhanced in all cytokine-treated animals.

Combination protocols of cytokine therapy with interleukin-3 and granulocyte-macrophage colony-stimulating factor in a primate model of radiation-induced marrow aplasia

Single cytokine therapy with granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-3 (IL-3) has been shown to be effective in decreasing the respective periods of neutropenia and thrombocytopenia following radiation- or drug-induced marrow aplasia. The combined administration of IL-3 and GM-CSF in normal primates suggested that a sequential protocol of IL-3 followed by GM-CSF would be more effective than that of GM-CSF alone in producing neutrophils (PMN). We investigated the therapeutic efficacy of two combination protocols, the sequential and coadministration of recombinant human IL- 3 and GM-CSF relative to respective single cytokine therapy, and delayed GM-CSF administration in sublethally irradiated rhesus monkeys. Monkeys irradiated with 450 cGy (mixed fission neutron:gamma radiation) received either IL-3, GM-CSF, human serum albumin (HSA), or IL-3 coadministered with GM-CSF for days 1 through 21 consecutively postexposure, or IL-3 or HSA for days 1 through 7 followed by GM-CSF for days 7 through 21. All cytokines and HSA were injected subcutaneously at a total dose of 25 micrograms/kg/d, divided twice daily. Complete blood counts (CBC) and platelet (PLT) counts were monitored over 60 days postirradiation. The respiratory burst activity of the PMN was assessed flow cytometrically, by measuring hydrogen peroxide (H2O2) production. Coadministration of IL-3 and GM-CSF reduced the average 16-day period of neutropenia and antibiotic support in the control animals to 6 days (P = .006). Similarly, the average 10-day period of severe thrombocytopenia, which necessitated PLT transfusion in the control animals, was reduced to 3 days when IL-3 and GM-CSF were coadministered (P = .004). The sequential administration of IL-3 followed by GM-CSF had no greater effect on PMN production than GM-CSF alone and was less effective than IL-3 alone in reducing thrombocytopenia. PMN function was enhanced in all cytokine-treated animals.

Statistical models for mixed fission track ages

In fission track analysis it is common to find that the true ages of different crystal grains vary within a sample, and this may be important for geological interpretation. There are at least two well-recognized geological processes that lead to mixed ages: grains from multiple sources, and differential annealing between grains of differing composition. Data from multiple sources may be represented statistically by a finite mixture model, usually with two or three components, but data arising from the multicompositional annealing process may be better modelled as an infinite mixture. We discuss finite mixtures and two new infinite mixture models: a random effects model whose parameters describe the location and spread of the population grain ages, and a more general model encompassing both two-component mixtures and random effects. We illustrate with case studies how to use these models to estimate various features of interest such as the minimum age, the other component ages and the age dispersion.