Distribution of 241Am in offspring from BALB/c mice injected with 241Am at 14 days of gestation: relation to calcium and iron metabolism and comparison with distribution of 241Am after injection of adults

Pregnant mice were given intravenous injections of 241Am citrate at 14 days of gestation. The fetal skeleton had a higher or similar uptake of 241Am per gram of fresh tissue than the liver. In comparison, the liver in adults concentrated 5 to 20 times more 241Am per gram of fresh tissue than the bones. Measurement of changes in calcium and iron content and concentration with time, showed that in the developing mice intensive calcification of bones determined the uptake of 241Am. The 241Am uptake was related to the calcium concentration of the fetal bones, which was greater at 14 days of gestation in the anterior bones, the mandibles and calvaria, than in the ribs and femurs. Transfer of 241Am to pups via milk resulted in further accumulation of 241Am in the skeleton and liver. The incorporation in the skeleton persisted after weaning and contributed to the lifetime body burden. The 241Am concentration decreased rapidly with time after injection in relation to the growth of the organs. Radiation dose rates and cumulative radiation doses were calculated for liver and bones of contaminated offspring.     

Competence of alpha spectrometry analysis algorithms used to resolve the 241Am and 243Am alpha peak overlap.

Five alpha spectrometry analysis algorithms were evaluated for their ability to resolve the 241Am and 243Am peak overlap present under typical low-level counting conditions. The major factors affecting the performance of the algorithms were identified using design-of-experiment combined with statistical analysis of the results. The study showed that the accuracy of the 241Am/243Am ratios calculated by the algorithms depends greatly on the degree of peak deformation and tailing. Despite the improved data quality obtained using an algorithm that may include peak addition and tail estimation, the accurate determination of 241Am by alpha spectrometry relies primarily on reduction of peak overlap rather than on algorithm selection.     

Spectrometry and dosimetric evaluation of the gamma-ray emissions of 241Am

New, detailed measurements have been made of the photon spectrum of the radionuclide ²⁴¹Am. Observations, recorded for a 95% confidence level over local background, provide affirmation of a number of lines previously considered to be of equivocal existence. A number of hitherto unreported emissions are similarly observed. Peak areas, expressed as a percentage of that for the 59.54 keV emission, have been ascribed to all lines of the detailed spectrum. This leads to an estimated increase in the value of exposure calculated from the measured fluence spectrum, relative to that from the 59.54 keV line, of (3.1 ± 0.8)%, taking into account all emissions beyond the predominating 59.54 keV gamma-ray emission.     

Biosorption of 241Am by Rhizopus arrihizus: preliminary investigation and evaluation.

The biosorption of 241Am from solution by a fungus-Rhizopus Arrihizus (R. arrihizus), and the effect of experimental conditions on the adsorption were investigated. The preliminary results showed that the biosorption of 241Am by R. arrihizus is very efficient. An average of more than 99% of the total 241Am was removed by R. arrihizus of 1.3 g/l (dry weight) from 241Am solutions of 5.6-111 MBq/l (44.3-877.2 microg/l) (C0), with adsorption capacities (W) of 4.2-79.4 MBq/g biomass (dry weight) (33.2-627.5 microg/g). The biosorption equilibrium was achieved within 1 h and the optimum pH ranged from 1 to 3. No significant differences in 241Am biosorption were observed at 10-45 degrees C, or in solutions containing Au3+ or Ag+, even 2,000 times above 241Am concentration. The relationship between concentrations and adsorption capacities of 241Am indicated that the 241Am biosorption by R. arrihizus obeys the Freundlich adsorption equation.     

Determination of 241Am in sediments by direct counting of low-energy photons

A method is described for the non-destructive measurement of ²⁴¹Am in sediments. The procedure involves direct counting of the 59.6-keV γ-ray emission of ²⁴¹Am. The dependence of self-absorption of this low-energy γ-ray on sample density is accounted for by a simple technique utilizing direct γ-ray transmission measurements on the sample and efficiency calibration standard. Measurements on five sediment and soil reference materials show that the technique provides a detection limit of about 1 mBq/g for a 2.5 × 10⁵s count. The utility of the technique in environmental studies is illustrated through results of ²⁴¹Am measurements on a ²¹⁰Pb-dated Lake Ontario sediment core.     

Adsorption of 241Am and 226Ra from natural water by wood charcoal.

The adsorption of (241)Am and (226)Ra from natural water by a granulated wood charcoal was investigated as a function of the solution pH, in the range 4-10, and of the water flow, in the range 3.5-42 cm(3)/min. The percentage adsorption of (241)Am (fairly constant at >80% for all pHs) was greater than that of (226)Ra (which increased with increasing pH from approximately 40% up to >80%). The results are explained by considering the different species of each radionuclide present at the pH values of the solution at the end of the adsorbent column, and the pH of the point of zero charge of the adsorbent. At pH 6, the elimination of (241)Am from natural water was independent of the water flow, while the elimination of (226)Ra declined linearly as the flow rate was increased.     

Standardization of 241Am by digital coincidence counting,liquid scintillation counting and defined solid angle counting

The nuclide ²⁴¹Am decays by alpha emission to ²³⁷Np. Most of the decays (84.6%) populate the excited level of ²³⁷Np with energy of 59.54 keV. Digital coincidence counting was applied to standardize a solution of ²⁴¹Am by alpha–gamma coincidence counting with efficiency extrapolation. Electronic discrimination was implemented with a pressurized proportional counter and the results were compared with two other independent techniques: Liquid scintillation counting using the logical sum of double coincidences in a TDCR array and defined solid angle counting taking into account activity inhomogeneity in the active deposit. The results show consistency between the three methods within a limit of a 0.3%. An ampoule of this solution will be sent to the International Reference System (SIR) during 2009. Uncertainties were analysed and compared in detail for the three applied methods.     

Determination of 51Cr and 241Am X-ray and gamma-ray emission probabilities per decay

In this paper results of X-ray and gamma-ray emission probabilities per decay of ⁵¹Cr and ²⁴¹Am are presented. The measurements were carried out by means of HPGe planar and REGe spectrometers. The activity of ⁵¹Cr and ²⁴¹Am samples was determined in a 4πβ?γ coincidence counting system. The HPGe spectrometers were calibrated in a well defined geometry by means of ⁵⁴Mn, ⁵⁵Fe, ⁵⁷Co, ¹³³Ba, ¹⁵²Eu, ^166mHo and ²⁴¹Am sources, previously standardized in a 4πβ?γ coincidence system. The MCNP Monte Carlo code was used for simulation of the REGe spectrometer calibration curve, for the selected geometry, and compared with the experimental curve. The experimental results were compared with data from literature.     

Determination of disintegration rates and gamma-ray emission probabilities of 65Zn and 241Am.

Radioactive solutions of (65)Zn and (241)Am were standardized within the frame of the CCRI (II)/BIPM key comparisons carried out recently in 2003. The activity concentrations (in Bqg(-1)) were determined using the 4pi(proportional counter)-gamma coincidence counting method with efficiency extrapolation. Liquid scintillation methods were also used for (241)Am activity determination. The 1115.5 keV of (65)Zn and the 26.35 and 59.54 keV of (241)Am gamma-ray emission probabilities were determined as 0.4971, 0.0206 and 0.3587, respectively, using a planar germanium detector. The associated relative uncertainties were 0.33%, 1.56% and 0.47%, respectively.     

Athletic Menstrual Cycle Irregularity: Endocrine Response to Exercise and Training

In brief: Studies over the last five years show a relatively high incidence of menstrual cycle irregularity in athletes. We have attempted to analyze and report on the survey literature on athletic menstrual irregularity. The evidence shows that chronic exercise stimulates marked changes in the menstrual cycle and that profound increments can occur in the availability of sex hormones during exercise. However, it is not understood how exercise stimulates changes in the cycle. Researchers now must synthesize the exercise-induced effects on hormone concentrations.     

Response of Megakaryocytes of the ‘August’ Rat to X-irradiation

Summary

Methods of evaluating the numbers of megakaryocytes of the ‘August’ rat are described. As a result of these studies, it is concluded that irradiation causes a block in cell-divisions in the stem-cell preceding the megakaryoblast, and results in a fall in numbers of megakaryocytes, and consequently of platelets. A similar conclusion was reached by Zajicek and Zeuthen (1956). Megakaryocyte numbers are readily reduced by x-rays, a dose of 80 r effecting a reduction of 50 per cent within 7 days of irradiation. Studies on partially shielded animals demonstrated a pronounced megakaryocyte hyperplasia in the shielded sites. Recovery in the irradiated areas was found to commence earlier than after whole-body radiation. These results throw some light on the mechanisms by which platelet levels are maintained after partial-body irradiation.     

Decay data evaluation project (DDEP): Updated evaluations of the 233Th and 241Am decay characteristics

The results of new decay data evaluations are presented for ²³³Th (β^?) decay to nuclear levels in ²³³Pa and ²⁴¹Am (α) decay to nuclear levels in ²³⁷Np. These evaluated data have been obtained within the Decay Data Evaluation Project using information published up to 2009.     

Testing of methyleneiminodiacetic-catechol and other aromatic chelating agents for decorporation of 238Pu and 241Am in rats

The removal of 238Pu and 241Am by five chelating agents prepared in China was compared in pilot experiments with removal by Ca-DTPA and LICAM(C). The most promising substance is quinamic acid (a methyliminodiacetic polyquinoline derivative, code name 811 or 703-73), especially in combination with Ca-DTPA. However, the best over-all reduction of both 238Pu and 241Am in all the organs studied was achieved by Ca-DTPA-administered at a ten-fold human equivalent dosage.     

Tumorigenic target cell regions in bone marrow studied by localized dosimetry of 239 Pu, 241 Am and 233 U in the mouse femur

Purpose : To study the temporal change in microdistribution of plutonium-239, americium-241 and uranium-233 in the mouse distal femur and to compare and combine calculated radiation doses with those obtained previously for the femoral shaft. Also, to relate doses to relative risks of osteosarcoma and acute myeloid leukaemia. Materials and methods : Computer-based image analysis of neutron-induced and α -track autoradiographs of sections of mouse femora was used to quantify the microdistribution of 239 Pu, 241 Am and 233 U from 1 to 448 days after intraperitoneal injection. Localized dose-rates and cumulative doses over this period were calculated for different regions of the marrow spaces in trabecular bone. The results were then combined with previous data for doses to the cortical marrow of the femoral shaft. A morphometric analysis of the distal femur was carried out. Results : Initial deposition on endosteal surfaces and dose-rates near to the trabecular surfaces at 1 day were two to four times greater than corresponding results for cortical bone. Burial was most rapid for 233 U, about twice the rate in cortical bone. As in cortical bone, subsequent uptake into the marrow was seen for 239 Pu and 241 Am but not 233 U. Cumulative doses to 448 days for different regions of trabecular marrow were greater than corresponding values for cortical marrow for each radionuclide. Combined doses reflected the greater overall volume of cortical marrow. Conclusions : Cumulative radiation doses to the 10 μ m thick band of marrow adjacent to all endosteal surfaces were in the ratio of ~7:3:1 for 239 Pu: 241 Am: 233 U. This ratio is not inconsistent with observed incidences of osteosarcoma induction by the three nuclides. Analysis of doses to different depths of marrow, however, showed that although ratios were probably not significantly different to that for a 10 μ m depth, better correlations with osteosarcomagenic risk were obtained with 20-40 μ m depths. For acute myeloid leukaemia, the closest relationship between relative risk and doses was obtained by considering only the central 5-10% of marrow, which gave a dose ratio of ~12:11:1 for 239 Pu: 241 Am: 233 U respectively.     

Tumorigenic target cell regions in bone marrow studied by localized dosimetry of 239Pu, 241Am and 233U in the mouse femur

PURPOSE: To study the temporal change in microdistribution of plutonium-239, americium-241 and uranium-233 in the mouse distal femur and to compare and combine calculated radiation doses with those obtained previously for the femoral shaft. Also, to relate doses to relative risks of osteosarcoma and acute myeloid leukaemia. MATERIALS AND METHODS: Computer-based image analysis of neutron-induced and alpha-track autoradiographs of sections of mouse femora was used to quantify the microdistribution of (239)Pu, (241)Am and (233)U from 1 to 448 days after intraperitoneal injection. Localized dose-rates and cumulative doses over this period were calculated for different regions of the marrow spaces in trabecular bone. The results were then combined with previous data for doses to the cortical marrow of the femoral shaft. A morphometric analysis of the distal femur was carried out. RESULTS: Initial deposition on endosteal surfaces and dose-rates near to the trabecular surfaces at 1 day were two to four times greater than corresponding results for cortical bone. Burial was most rapid for (233)U, about twice the rate in cortical bone. As in cortical bone, subsequent uptake into the marrow was seen for (239)Pu and (241)Am but not (233)U. Cumulative doses to 448 days for different regions of trabecular marrow were greater than corresponding values for cortical marrow for each radionuclide. Combined doses reflected the greater overall volume of cortical marrow. CONCLUSIONS: Cumulative radiation doses to the 10 microm thick band of marrow adjacent to all endosteal surfaces were in the ratio of approximately 7:3:1 for (239)Pu:(241)Am:(233)U. This ratio is not inconsistent with observed incidences of osteosarcoma induction by the three nuclides. Analysis of doses to different depths of marrow, however, showed that although ratios were probably not significantly different to that for a 10 microm depth, better correlations with osteosarcomagenic risk were obtained with 20-40 microm depths. For acute myeloid leukaemia, the closest relationship between relative risk and doses was obtained by considering only the central 5-10% of marrow, which gave a dose ratio of approximately 12:11:1 for (239)Pu:(241)Am:(233)U respectively.     

Microdistribution and localized dosimetry of the alpha-emitting radionuclides 239Pu, 241Am and 233U in mouse femoral shaft

PURPOSE: To analyse the temporal change in microdistribution of 239Pu, 241Am and 233U in mouse femur and to compare the calculated radiation doses with regions of the bone marrow thought to contain target cells for osteosarcoma and leukaemia with relative risk for those diseases. MATERIALS AND METHODS: Neutron-induced and alpha-track autoradiographs were prepared from femora of the CBA/H mouse that had been injected with 40 kBq kg(-1) radionuclide between 1 and 448 days previously. Computer-based image analysis of the autoradiographs was performed and dosimetric methods applied to obtain radiation dose-rates to different regions of the marrow cavity. RESULTS: Initially each radionuclide deposited on endosteal and periosteal bone surfaces; 241Am was additionally deposited on vascular canal surfaces. Redistribution resulted in 233U being incorporated into bone, while 239Pu and 241Am showed transfer into both bone volume and marrow. Accumulation in the central marrow peaked at 112-224 days post-injection, but subsequently was cleared by 448 days. Cumulative doses to both osteosarcomagenic and myeloid leukaemogenic target cell regions showed the trend 239Pu > 241Am > 233U. CONCLUSIONS: Calculation of cumulative doses to a 10-microm layer of marrow adjacent to bone surfaces appears to be a suitable predictor for risk of osteosarcoma. Risks of myeloid leukaemia in the mouse are better predicted by considering the central marrow as the target region rather than average dose to all marrow.     

Direct and bystander effects in human blood lymphocytes exposed to 241Am alpha particles and the relative biological effectiveness using chromosomal aberration and micronucleus assay

Abstract

Purpose: It is important to understand the significance of alpha (α) radiation-induced bystander effects (RIBE) and its relative biological effectiveness (RBE); this is because the phenomenon is not universal and the mechanism is unclear and because the RBE is widely varying and projected to be very high.

Materials and methods: Isolated lymphocytes from healthy volunteers (n?=?10) were exposed to either low fluence α-particles (²⁴¹Am), γ-rays (⁶⁰Co), or X-rays (225 kVp and 6?MV). Co-culture methodology was employed to investigate bystander effects (BEs). Chromosomal aberrations (CA) and micronucleus (MN) formation were used to study the BE and calculated RBE.

Results: Lymphocytes directly exposed to the types of radiation used showed a dose-dependent increase in the frequency of CA and MN; dose independent increases in the frequency of these chromosomal damages in co-cultured bystander cells, implies that all three types of radiation-induced a BE. The calculated RBE at the level of 5% induced aberrations varied between 9 and 20.

Conclusion: The magnitude of low fluence α-particle induced RIBE is higher than in low LET (linear energy transfer) radiation. The RBE also varies depending upon the endpoints used and adds up to targeted effects. Since the endpoint of CA is considered as an important and early marker of risk prediction, the RIBE and RBE using CA as a marker are relevant for radiation protection purposes.     

Determination of 241Am in sediments by isotope dilution high resolution inductively coupled plasma mass spectrometry (ID HR ICP-MS).

Trace levels (pg kg(-1)) of 241Am in sediments were determined by isotope dilution high resolution inductively coupled plasma mass spectrometry (ID HR ICP-MS) using a microconcentric nebulizer. 241Am was isolated from major elements like Ca and Fe by different selective precipitations. In further steps. Am was first separated from other transuranic elements and purified by anion exchange and extraction chromatography prior to the mass spectrometric measurements. The ID HR ICP-MS results are compared with isotope dilution alpha spectrometry.