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1.
241Am dating of lake sediments 总被引:2,自引:0,他引:2
241Am derived from decay of fallout 241Pu is now frequently detected in analyses of lake sediments by low-background gamma assay, and offers an alternative to weapons test 137Cs in dating recent sediments at those sites where the 137Cs record has been degraded by post-depositional mobility or obliterated by Chernobyl fallout. Calculations of the in-growth of 241Am from 241Pu indicate a nominal distribution broadly similar to that of 137Cs, with the maximum 241Am activity occuring in fallout dating from 1963. Results from a number of sites suggest that 241Am is significantly less mobile in lake sediments than 137Cs, and that its distribution in cores reflects more closely the fallout record. Since further decay of existing weapons debris will increase 241Am concentrations by about 24% over the next 40 years, 241Am is likely to play an increasingly important role in assessing the validity of 210Pb dates at sites with varying sediment accumulation rates. 相似文献
2.
PurposeThe objective of this study was to evaluate the image degrading factors in quantitative 177Lu SPECT imaging when using both main gamma photopeak energies.MethodsPhantom measurements with two different vials containing various calibrated activities in air or water were performed to derive a mean calibration factor (CF) for large and small volumes of interest (VOIs). In addition, Monte Carlo simulations were utilized to investigate the effect of scatter energy window width, scatter correction method, such as effective scatter source estimation (ESSE) and triple energy window (TEW), and attenuation map on the quantification of 177Lu. Results: The measured mean CF using large and small VOIs in water was 4.50 ± 0.80 and 4.80 ± 0.72 cps MBq−1, respectively. Simulations showed a reference CF of 3.3 cps MBq−1 for the water-filled phantom considering all photons excluding scattered events. By using the attenuation map generated for 190 keV photons, the calculated CFs for 113 keV and 208 keV are 10% lower than by using the weighted mean energy of 175 keV for 177Lu. The calculated CF using the TEW correction was 17% higher than using the ESSE method for a water-filled phantom. However, our findings showed that an appropriate scatter window combination can reduce this difference between TEW and ESSE methods.ConclusionsThe present work implies that choosing a suitable width of scatter energy windows can reduce uncertainties in radioactivity quantification. It is suggested to generate the attenuation map at 113 keV and 208 keV, separately. Furthermore, using small VOIs is suggested in CF calculation. 相似文献
3.
The deposition of radiocaesium from nuclear weapons testing and the Chernobyl accident upon the Llyn Llygad Rheidol catchment in mid-Wales is described. Inventories of soil cores from the catchment support estimates of total atmospheric fallout. The mean inventory of weapons testing 137Cs in lake sediment cores is broadly similar to that in soil cores. The inventory of Chernobyl fallout in sediment cores is significantly lower and raises questions concerning the residence time of 137Cs in the catchment soils and lake waters. 137Cs and 241Am activities in a sediment core record the 1963 peak of fallout from nuclear weapons testing. The association of the peak activities of 137Cs and 241Am in the sediments with the falloot maximum is confirmed by 210Pb dating. The 210Pb dates also reveal a significant increase in sediment accumulation rates over the past 20 years. 相似文献
4.
Radionuclide concentrations in Australian terrestrial fauna, including indigenous kangaroos and lizards, as well as introduced
sheep and water buffalo, are of interest when considering doses to human receptors and doses to the biota itself. Here, concentration
ratio (CR) values for a variety of endemic and introduced Australian animals with a focus on wildlife and livestock inhabiting
open rangeland are derived and reported. The CR values are based on U- and Th-series concentration data obtained from previous
studies at mining sites and 241Am and 239/240Pu data from a former weapons testing site. Soil-to-muscle CR values of key natural-series radionuclides for grazing Australian
kangaroo and sheep are one to two orders of magnitude higher than those of grazing cattle in North and South America, and
for 210Po, 230Th, and 238U are one to two orders of magnitude higher than the ERICA tool reference values. When comparing paired kangaroo and sheep
CR values, results are linearly correlated (r = 0.81) for all tissue types. However, kidney and liver CR values for kangaroo are typically higher than those of sheep,
particularly for 210Pb, and 210Po, with values in kangaroo liver more than an order of magnitude higher than those in sheep liver. Concentration ratios for
organs are typically higher than those for muscle including those for 241Am and 239/240Pu in cooked kangaroo and rabbit samples. This study provides CR values for Australian terrestrial wildlife and livestock
and suggests higher accumulation rates for select radionuclides in semi-arid Australian conditions compared with those associated
with temperate conditions. 相似文献
5.
Jia Guogang Triulzi C. Marzano F. Nonnis Belli M. Sansone U. Vaghi M. 《Biological trace element research》1999,(1):349-357
A radioecological survey in Antarctica shows that the239+240Pu,238Pu,241Am,90Sr, and137Cs activities were detectable in nearly all the samples. The activity level of239+240Pu,241Am, and137Cs in antarctic sediments was about 5–20 times lower than in the northern Adriatic Sea sediments, but the238Pu activities were relatively high. It was interesting to note that the90Sr concentrations in all the sediments tended to be low, which could be the result of the easier exchangeable behavior of90Sr in water. High concentrations were detected in mosses and lichens and their activity levels were comparable to those in
central Italy. The radionuclide ratio analyses show that the major part of239+240Pu,241Am,90Sr, and137Cs was a result of nuclear weapon tests. The higher241Am/239+240Pu ratio was observed and it could perhaps be the result of fallout of nuclear weapon tests prior to 1962. The238Pu/239+240Pu ratio in the antarctic matrices was about seven times higher than in the Northern hemisphere and it could be inferred that
the major part of238Pu was originating from the SNAP-9A satellite accident. 相似文献
6.
The survival of Chinese hamster cells exposed to 59.5 keV 241Am gamma rays was compared with that obtained after exposure to 226Ra gamma rays. The Fricke dosimeter in conjunction with the calculational techniques of transition-zone dosimetry was employed to determine the dose rates to the cells at the petri dish/growth medium interface. The dose rates to the cells ranged from 11 to 133 cGy/h. In all cases, cell survival versus dose was best described by a simple exponential function of dose. For both radiations, graphs of D0 versus dose rate show complex but similar patterns of peaks and valleys. As the curve for 241Am is displaced toward lower dose rates compared with that for 226Ra, the relative biological effectiveness of 241Am vs 226Ra varies considerably with dose rate, ranging from 1.7 at 20 cGy/h to 1.1 at 40 cGy/h to 1.6 at 50 cGy/h. This phenomenon may be due to the LET-dependent accumulation of cells at the G2 + M interface in the cell cycle. The mean unrestricted track-average LET of 241Am (3.7 keV/microns) is 12 times higher than that for 226Ra (0.31 keV/microns) but only one-fifth that of carbon ions (18 keV/microns) for which G2 + M pile-up is observed. Application of the in vitro data derived from this study to the clinical situation, where the dose rate decreases rapidly with distance from the source, suggests that, dose for dose, 241Am will produce results little different from those obtained with 226Ra. 相似文献
7.
Summary The uptake of239Pu and241Am from different clay mineral-organic matter-sand mixtures simulating contrasting soil types was examined in growth chamber experiments. The mixtures represented various combinations of organic matter (0, 5 and 10%), kaolinite (11 type) and montomorillonite (21 type) clay minerals, each at the levels of 5, 10 and 25%, and purified quartz sand (as filler).Results indicated a marked reduction in uptake of both239Pu and241Am with increase in organic matter as well as clay content of the mixtures. The Pu Concentration Ratios (CRs) ranged from (2.5–7.0)×10–3 in the case of kaolinite-organic matter mixtures, and from (0.9–5.5)×10–3 in the case of montmorillonite-organic matter mixtures. The corresponding values of Am Concentration Ratios (CRs) obtained were (1.9–725.4)×10–3 in the case of kaolinite-organic matter mixtures, and between (0.7–3.5)×10–3 for the montmorillonite-organic matter mixtures.Reduction in the uptake of241Am with increasing clay content was more pronounced in the montmorillonite clay-organic matter mixtures as compared to that in the case of kaolinite-organic matter mixtures. While similar qualitative reduction in239Pu CRs with increasing clay content was observed, the reduction was less marked than in the case of241Am. The values for Am CRs were higher than the corresponding Pu CRs in kaolinite based mixtures whereas in the case of montmorillonite-organic matter mixtures Pu CRs exceeded the Am CRs.Increasing organic matter content and its interaction with both kaolinite and montmorillonite clay minerals were found to be equally effective in reducing the uptake of239Pu as well as241Am by plants. 相似文献
8.
V. Svoboda A. Sedlák D. Bubeníková Z. Kotašková O. Truxová 《Radiation and environmental biophysics》1985,24(3):203-209
Summary The self-renewal capacity of murine pluripotent hemopoietic stem cells (CFU-S) of vertebral bone marrow was studied under conditions of short-term and long-term internal contamination with239Pu or241Am in female mice. Measurement of the CFU-S self-renewal capacity was carried out using double transplantation assay. To evaluate the production of differentiated progeny of stem cells average erythroblast numbers/visible spleen colony and59Fe-uptake/colony were computed. The marrow cellularity/vertebra and the number of CFU-S/vertebra were decreased and affected more by239Pu than by241Am. The production of erythroblasts per a single CFU-S and the59Fe-uptake/colony were reduced, similarly the numbers of secondary spleen colonies and of secondary CFU-S in primary colonies. The above changes resulting from impaired functions of surviving CFU-S were more serious with241Am than with239Pu. The biological effects of plutonium and americium appeared independent of the phase of contamination. 相似文献
9.
A. V. Arzhannikov A. M. Batrakov A. V. Burdakov I. A. Ivanov K. I. Mekler V. V. Postupaev A. F. Rovenskikh S. V. Polosatkin V. Ya. Sazanskiĭ S. L. Sinitskiĭ Yu. S. Sulyaev 《Plasma Physics Reports》2006,32(2):94-102
In experiments on the plasma heating and confinement in the GOL-3 multimirror trap, a deuterium plasma with a density of ~1015 cm?3 and an ion temperature of 1–2 keV is confined for more than 1 ms. The plasma is heated by a relativistic electron beam. The ion temperature, which was measured by independent methods, reached 1.5–2 keV after the beginning of the beam injection. Since such a fast ion heating cannot be explained by the classical energy transfer from electrons to ions through binary collisions, a theoretical model of collective energy transfer was proposed. In order to verify this model, a new diagnostics was designed to study the dynamics of neutron emission from an individual mirror cell of the multimirror trap during electron beam injection. Intense neutron bursts predicted by this model were detected experimentally. Periodic neutron flux modulation caused by the macroscopic plasma flow along the solenoid was observed. The revealed mechanism of fast ion heating can be used to achieve fusion temperatures in the multimirror trap. 相似文献
10.
V. Volf 《Radiation and environmental biophysics》1984,23(2):141-143
Conclusion Substantial fractions of238Pu and241Am deposits were removed from the bones of growing rats by addition of Zn-DTPA to drinking water. The effect of treatment in various parts of long bones was different, obviously due to differences in the bone growth and remodelling. 相似文献
11.
Summary A method has been developed whereby the liver content of photon-emitting transuranium elements can be determined in living beagles by a combination of total-body and partial-body counting. Calibration of the system was accomplished through the photon counting of intact dogs and also of the parts of the same animals following autopsy. A determination of the calibration factors for252Cf,247Cf,243Cm,237Pu, and241Am has been made. The special case of252Cf was treated in which a significant fraction of the high energy fission gamma-ray spectrum penetrates the Pb shield employed in partial-body counting, and methods were developed which allow for this effect in the calculation of liver content. Some uniformity of response in the system was evident for all of the emitters which were considered. It is proposed that similar techniques could be applied in the determination of selected organ radioactivity in other species including man.Supported by ERDA Contract E (11-1)-119. 相似文献
12.
Solubility of airborne radioactive fuel particles from the Chernobyl reactor and implication to dose
Garger EK Sazhenyuk AD Odintzov AA Paretzke HG Roth P Tschiersch J 《Radiation and environmental biophysics》2004,43(1):43-49
Airborne particles of nuclear fuel from the Chernobyl reactor that had been collected on air filters and stored, were characterised using in vitro dissolution tests to assess effective doses after their inhalation. As solvent, the Gamble biological fluid was used to simulate lung fluid. The solubility of the measured radionuclides decreased in the order 137Cs>90Sr>>241Am239+240Pu in the simulated lung fluid. The dissolution rate constant of e.g. 239+249Pu ranged from 0.72 to 5.4×10–6 g·cm–2 d–1 and decreased (for all nuclides) with increasing particle size as predicted from theoretical considerations. Considering the inhalation dose, decreasing dose with size and increasing doses with lower solubility may partly counterbalance each other for 137Cs and 90Sr. On the other hand, for 239Pu and 241Am larger particles and associated lower solubility both change the resulting dose in the same direction towards lower values. The comparison of the experimentally determined dose coefficients with ICRP values indicates that nuclear fuel particles closely resemble type M material characteristics for 137Cs and 90Sr and type S material characteristics for 239Pu and 241Am. 相似文献
13.
The purpose of this work is to present a method for the calculation of secondary electron spectra generated by photons in water vapour in the energy region from 10 eV to 10 MeV. The cross sections below and above 1 keV have been treated separately. Examples are given for secondary electron spectra for low-energy photons, <100 eV, in which all electrons are photoelectrons, and at higher energy regions, such as for 60Co photons. The spectrum of the first generation of secondary electrons, produced by 60Co photons, which are mainly due to incoherent scattering, was fitted with a set of polynomial functions which can be used as input for electron radiation action calculations. 相似文献
14.
Effects of Naturally Occurring Aquatic Organic Fractions on 241Am Uptake by Scenedesmus obliquus (Chlorophyceae) and Aeromonas hydrophila (Pseudomonadaceae)
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Naturally occurring organics were extracted from water collected from Skinface Pond near Aiken, S.C. Organics were separated into four nominal diameter size fractions (I, >0.0183; II, 0.0183 to 0.0032; III, 0.0032 to 0.0009; IV, <0.0009 μm) by membrane ultrafiltration and introduced into Scenedesmus obliquus and Aeromonas hydrophila cultures to determine their effects on 241Am availability for uptake. Effects on 241Am uptake were determined in actively growing S. obliquus cultures after 96 h of growth and in dense cultures of nongrowing cells after 4 h. Uptake by A. hydrophila was determined after 4 and 24 h in actively growing cultures. All organic fractions stimulated S. obliquus growth, with the most pronounced effects due to larger organic fractions, whereas no apparent growth stimulation of A. hydrophila was observed for any organic fraction. For both long-term and short-term studies, cellular 241Am concentration (picocuries/cell) increased with increasing 241Am concentration for S. obliquus and A. hydrophila. Fraction IV increased 241Am uptake by both S. obliquus and A. hydrophila during 4-h incubations. During 96-h incubations fraction I was flocculated and cosedimented, with S. obliquus and A. hydrophila cells causing an apparent increase in 241Am uptake. Fractions II and III reduced apparent 241Am uptake by S. obliquus as a result of biological dilution caused by increased algal growth due to the organics. Fraction IV caused a reduction in 241Am uptake by S. obliquus not attributable to biological dilution. Organics increased 241Am uptake by A. hydrophila during 4- and 24-h incubations. A. hydrophila also caused flocculation of fraction I during 96-h incubations. 相似文献
15.
A new multi-port irradiator, designed to facilitate the study of the effects of low fluences of alpha particles on monolayer cultures, has been developed. The irradiator consists of four individual planar (241)Am alpha-particle sources that are housed inside a helium-filled Lucite chamber. Three of the radioactive sources consist of 20 MBq of (241)Am dioxide foil. The fourth source, used to produce higher dose rates, has an activity of 500 MBq. The four sources are mounted on rotating turntables parallel to their respective 1.5-microm-thick Mylar exit windows. A stainless steel honeycomb collimator is placed between the four sources and their exit windows by a cantilever attachment to the platform of an orbital shaker that moves its table in an orbit of 2 cm. Each exit window is equipped with a beam delimiter to optimize the uniformity of the beam and with a high-precision electronic shutter. Opening and closing of the shutters is controlled with a high-precision timer. Custom-designed stainless steel Mylar-bottomed culture dishes are placed on an adapter on the shutter. The alpha particles that strike the cells have a mean energy of 2.9 MeV. The corresponding LET distribution of the particles has a mean value of 132 keV/microm. Clonogenic cell survival experiments with AG1522 human fibroblasts indicate that the RBE of the alpha particles compared to (137)Cs gamma rays is about 7.6 for this biological end point. 相似文献
16.
The last few years have seen a dramatic growth in the use of 210Pb sediment dating. Despite this, considerable doubt still surrounds the nature of the processes by which 210Pb is deposited in lake sediments, and this has lead to a situation where there is a choice of dating models offering different interpretations of 210Pb data. In assessing 210Pb data it is therefore essential to first of all determine whether data is consistent with the assumptions of the dating model, and to then compare the 210Pb chronology with independent dating evidence. We have tested 210Pb data from a wide variety of sites, and our calculations indicate that the crs (constant rate of 210Pb supply) model provides a reasonably accurate chronology when the total 210Pb contents of cores from neighbouring locations are comparable. 相似文献
17.
P. Bustamante J.-L. Teyssié M. Warnau 《Journal of experimental marine biology and ecology》2006,331(2):198-207
Laboratory radiotracer experiments were performed to study the uptake, assimilation and retention of americium (241Am) and cesium (134Cs) by the common cuttlefish Sepia officinalis. Uptake and loss kinetics of the radionuclides were measured following exposure through sediments, seawater and food at different stages of the animal's life cycle. Sediment was found to be a minor uptake pathway for both radionuclides in juveniles. Following a short seawater exposure, cuttlefish accumulated 241Am and 134Cs, but only to a limited extent (whole-body CF < 2). Among the cuttlefish organs, branchial hearts and their appendages displayed the highest degree of uptake for 241Am (CF = 42 and 16, respectively), but these tissues contained low percentage of total 241Am due to their relatively small contribution to whole organism weight. The major fraction of incorporated radionuclides was associated with muscular tissues (viz. 65% and 82% of total 241Am and 134Cs, respectively). Whole-body loss of 241Am and 134Cs was relatively rapid (Tb½ = 14 and 6 days, respectively). After dietary exposure, around 60% and 30% of ingested 241Am was assimilated into the tissues of juvenile and adult cuttlefish, respectively. However, assimilated 241Am was more strongly retained in adults than in juveniles (Tb½ = 28 vs. 5 days, respectively), suggesting that different mechanisms govern 241Am elimination at both ages. Ingested 134Cs was assimilated to a similar extent in juveniles (29%) and adults (23%), but the depuration rate was four times faster in adults. Our results strongly suggest that these two radionuclides follow different excretion pathways and that the mechanisms can vary with age for a given radionuclide. 相似文献
18.
《International journal of radiation applications and instrumentation. Part B, Nuclear medicine and biology》1986,13(5):515-518
The binding of 141Ce, 239Np, 139Pu and 241Am in the liver of rats and Syrian hamsters, following injection in essentially monomeric form, was analyzed by carrier-free electrophoresis at 4–9 days and several months after radionuclide injection. In contrast to density gradient methods lysosomes can be clearly separated from other cell organelles by carrier-free electrophoresis. These, and previous results from this and other laboratories confirm that lysosomes are the main initial binding site for these four radionuclides in the livers of rats and Syrian or Chinese hamsters. Light microscopic autoradiography showed that at all the time intervals studied 241Am was more or less uniformly distributed in the liver of all three species. Thus, the changes in the electrophoretic pattern of the nuclides, observed at later time periods in hamsters, cannot be explained by gross redistribution phenomena such as accumulation in macrophages. 相似文献
19.
Salps, salp fecal pellets and other zooplankton species were analyzed for a suite of elements and natural radionuclides to assess their role in the biogeochemical cycling of nuclides in oceanic waters. The nuclide/Al ratios in organisms normalized to the same ratio in crustal rock indicated that Ca, Sr, Zn, Cu, U,210Po, and210Pb are enriched in the organisms. The concentrations of Fe, Al, Th isotopes and210Pb in salps and fecal pellets were about an order of magnitude higher than those in salps, whereas Ca, Cu, Zn, Mn and Po were higher by factors of about 2–5. Fluxes via salp defecation were higher than those which have been measured in crustacean zooplankton species, a result primarily due to the high defecation rates characteristic of salps. High nuclide levels in salp fecal pellets coupled with high defecation rates and presumed high salp biomass in many areas underscore the importance of these indiscriminate filter feeders in packaging and transporting to depth particulate-associated nuclides in surface waters. 相似文献
20.
J. Breckow A. Wenning H. Roos A. M. Kellerer 《Radiation and environmental biophysics》1988,27(4):247-259
Summary The variance-covariance method is employed at low doses and in radiation fields of low dose rates from an241Am (4 nGy/s) and a90Sr (300 nGy/s) source. The preliminary applications and results illustrate some of the potential of the method, and show that the dose average of lineal energy or energy imparted can be determined over a wide range of doses and dose rates. The dose averages obtained with the variance-covariance method in time-varying fields, for which the conventional variance method is not suitable, agree well with results obtained under the condition of constant dose rate. The results are compared to data obtained in terms of the conventional single-event measurements. The method has evident advantages, such as facility and speed of measurement. 相似文献