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1.
Utilizing Pu isotopic standards characterized by the Institute for Nuclear Materials and Measurement (IRMM), New Brunswick Laboratory (NBL) measured the γ-ray branching ratios of the 148.567-keV 241Pu, the 152.72-keV 238Pu, the 159.995-keV 241Pu and the 160.28-keV 240Pu γ-rays. The study reported here includes the measurement of four IRMM standards, utilizing three different detectors for a total of 16 spectra, finding branching ratios of (1.863 ± 0.008) × 10 −6, (9.230 ± 0.068) × 10 −6, (6.321 ± 0.040) × 10 −8 and (4.065 ± 0.017) × 10 −6, γ/disintegration, respectively. 相似文献
2.
Four types of light weight concrete (LWC) commonly used in Hong Kong, namely, autoclave aerated concrete (plus lime), autoclave aerated concrete (plus Pulverized Fuel Ash or PFA), concrete with synthetic aggregate ‘Leca’ and concrete with polystyrene bean as aggregate were measured for their 226Ra, 232Th and 40K contents using high-resolution gamma spectrometry. All the radionuclide contents except those for the PFA autoclave aerated concrete were below the world averages of building materials. The Ra-equivalents for these four LWC were 49.6, 249, 122 and 44.2 Bq kg −1, respectively, and were much smaller than a recommended limit of 370 Bq kg −1 for construction materials for dwellings. The gamma-dose rate for an indoor environment with partition walls built with LWC was estimated to be about 20 × 10 −8 Gy h −1, which corresponded to a reduction in the effective dose of about 0.25 mSv y −1 when compared to that obtained for an indoor environment built with normal concrete (NC) only. The Rn exhalation rates from the three lowest Ra-equivalent LWC were calculated as 0.509, 1.28, and 0.335 mBq m −2 s −1, respectively, which corresponded to a reduction in the indoor Rn concentration of around 14 Bq m −3 and reduction in the tracheobronchial dose reaching 1 mSv y −1 by using the James lung-dosimetry model, when compared to the case of NC. 相似文献
3.
As per TG-43 dose calculation formalism, it is essential to obtain various dosimetric parameters such as the air-kerma strength, dose rate constant, radial dose function, and anisotropy function, as they account for accurate determination of dose rate distribution around brachytherapy sources. Most of the available reported Monte Carlo simulations were performed in liquid water phantoms with a bounded region of 30-cm diameter. In this context, an attempt was made to report the dosimetric parameters for various commercially available pulsed-dose rate (PDR) and high-dose rate (HDR) sources under unbounded phantom conditions, as the data may be used as input to treatment planning systems (TPSs) for quality control assistance. The air-kerma strength per unit activity, S k/A, was computed for various Iridium-192 ( 192Ir) sources in dry air medium. The air-kerma strength and dose rate constant for old PDR is (9.77 ± 0.03) 10 −8 U/Bq and 1.124 ± 0.001 cGyh −1U −1; for new PDR, the values are (9.96 ± 0.03) 10 −8 U/Bq and 1.124 ± 0.001 cGyh −1U −1; for old MHDR, the values are (9.80 ± 0.01) 10 −8 U/Bq and 1.115 ± 0.001 cGyh −1U −1; for new MHDR, (9.80 ± 0.01) 10 −8 U/Bq and 1.112 ± 0.001cGyh −1U −1; for old VHDR, the values are (10.32 ± 0.01) 10 −8 U/Bq and 1.035 ± 0.002 cGyh −1U −1; for new VHDR, the values are (10.34 ± 0.02) 10 −8 U/Bq and 1.096 ± 0.001 cGyh −1U −1. The computed radial dose function values and anisotropy function values are also in good agreement with available data. 相似文献
4.
A procedure, adaptable to large-scale remote operation, was developed to purify no-carrier-added (NCA) 47Sc from irradiated Ti targets. Methods based on extraction chromatography and cation-exchange chromatography were compared. Results of this comparison led to the development of an optimized procedure based on cation-exchange with Dowex AG 50W-X4 and 47Sc elution with HCl/HF. This method gave 90–97% overall 47Sc recovery, with a Ti separation factor greater than 2.4×10 −5, and specific activities ≥0.9 GBq μg −1. Use of the 47Sc product, for labeling monoclonal antibodies, resulted in consistent labeling yields of ≥90%. 相似文献
5.
The relationship between the radiation absorbed dose and the NMR longitudinal and transversal relaxation rates, R1 and R2, respectively, of a ceric sulphate dosimeter was examined. By adding copper sulphate, the R1 and R2 dose-responses were found to be linear up to 60 kGy with dose sensitivities of 13×10 −6 and 15×10 −6 s −1 Gy −1, respectively. There is thus the potential for a three-dimensional ceric dosimeter for high dose applications, provided a suitable gelling substance is used. 相似文献
6.
During the routine isotope production schedule at the Australian National Medical Cyclotron thick copper plates, electroplated with enriched target materials, are bombarded with 30 MeV protons with an average beam current of 200 μA. As a result an intense high-energy, prompt neutron flux of the order of 1.72 × 10 13 neutrons·cm −2·2 −1 is generated in the immediate vicinity of the target. The stray fast neutrons were moderated using a water-filled PVC bucket placed on the target station. A maximum thermal neutron flux of 3.88 × 10 9 neutrons·cm −2·s −1 was measured in the bucket using cobalt activation discs. The thermal neutrons from this irradiation facility has been used for the neutron activation analysis of trace elements in archaeological artefacts. It has also been planned to utilize the fast neutron flux by varying the geometry of the water moderator in order to estimate oxygen concentration in high-temperature superconductors and aluminium and silicon in ceramics. 相似文献
7.
The development of analytical procedures for the measurement of ultra-low levels of 236U in marine samples using high-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) and accelerator mass spectrometry (AMS) techniques are discussed and results are presented for IAEA reference materials—marine sediments (IAEA-135, 306, 384 and 385), marine biota (IAEA-134 and 414) and seawater (IAEA-381), collected in areas affected by nuclear reprocessing plants and nuclear weapons tests. The obtained minimum detection limit of the 236U/ 238U atom ratio was 1×10 −8 for AMS and 1×10 −6 for HR-ICPMS. 相似文献
8.
The purpose of this study was to investigate effects of normal brain iron on proton diffusion and its quantification by diffusion MRI. The studies were undertaken in 24 cases ages ranging from 15 to 74 years (mean=45 years) with normal iron deposition in the globus pallidus to characterize the appearances on diffusion imaging with differing b values and on apparent diffusion coefficient (ADC) maps. Diffusion MRI was obtained by the spin-echo echo-planar imaging sequence ( n=20 patients) or by the gradient-echo diffusion sequence, PSIF ( n=4). In the PSIF sequence, pixel lens calculations were performed. In the echo-planar sequence, ADC value calculations were performed by using Stejskal–Tanner formula and by direct reading from automatically generated ADC maps. ADC values obtained from the normal appearing parenchyma were used as controls. Twenty patients with acute cerebral infarction were included for comparison of ADC values with those of iron deposition. The mean ADC value in the normal cerebral parenchyma was 0.85±0.11×10 −3 mm 2/s. In the globus pallidus, mean ADC value was 48±0.12×10 −3 mm 2/s. That of regions with acute infarction was 0.34±0.11×10 −3 mm 2/s. On b=0 or 50, b=500 and b=1000 s/mm 2 images of the echo-planar diffusion imaging globus pallidus appeared hypointense compared to surrounding parenchymal structures. Low signal and low pixel values were evident on the PSIF imaging. This study indicates that, on diffusion MRI, normal iron deposition reveals prominent low signal on all the images of the echo-planar diffusion imaging sequence with differing b values, as well as on the gradient-echo diffusion, PSIF sequence. Low signal on ADC maps and low ADC values are evident. These represent characteristic diffusion MRI features of normal iron deposition in the brain, reflecting susceptibility effects. 相似文献
9.
The effects of pH and Sr 2+ solution concentration on diffusion and sorption of Sr 2+ in compacted bentonite (ρ b=1000±30 kg/m 3) were studied using an “in-diffusion” method at an ionic strength of 0.1 M NaClO 4. The results (distribution coefficients, Kd, apparent and effective diffusion coefficients, Da and De) derived from the capillary method are in good agreement with the literature data obtained for similar bentonite dry densities and fit Fick's second law very well. The results suggest that the diffusion of Sr 2+ in compacted bentonite decreases slightly with increasing pH values and also increases slightly with increasing Sr 2+ solution concentration. The distribution coefficients are weakly dependent on the solution concentrations and show a slight increase with increasing pH values. The average effective diffusion coefficient of Sr 2+ in compacted bentonite is (1.2±0.2)×10 −9 m 2/s, surface diffusion effects are found for the diffusion of Sr 2+ in compacted bentonite. 相似文献
10.
Using a high-resolution gamma-spectrometer system, the activity concentrations of 7Be, 137Cs, 40K and 226Ra were determined in the pine needles. Activity concentrations of the concerned radionuclides in the needle samples were as follows: 7Be, 24.6±2.40 to 210±7.21 Bq kg −1, 40K, 23.5±12.4 to 287±15.6 Bq kg −1, 226Ra, 0.44±0.12 to 12.3±2.18 Bq kg −1, and 137Cs, 0.61±0.30 to 2.29±0.38 Bq kg −1. It is found that the frequency distributions obtained for 7Be and 137Cs can be fitted to a normal distribution, and for 40K and 226Ra can be fitted to a log-normal distribution. 相似文献
11.
In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities ρ i of the LR 115 detector to 222Rn and its alpha-emitting short-lived progeny, 218Po and 214Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by 222Rn, 218Po and 214Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 μm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor Fp, which is defined in the present work as ( F1+ F3) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny ( 218Po+ 214Po) to the concentration of radon gas ( 222Rn). In particular, we have found Fp=(ρ/ρ itC0)−1, where ρ (track/m 2) is the total track density on the detector, ρ i=0.288×10 −2 m, t is the exposure time and C0 (Bq/m 3) is the concentration of 222Rn. If C0 is known (e.g. from a separate measurement), we can obtain Fp. The proxy equilibrium factor Fp is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor. 相似文献
12.
We have previously shown that the accumulation of fluorine-18-labeled fluoromisonidazole ([ 18F]FMISO) is inversely correlated to tissue oxygenation, allowing the quantification of porcine liver tissue hypoxia in vivo. We determined the activity from administered [ 18F]FMISO in relation to the hepatic oxygen availability and the partial pressure of oxygen in tissue (tPO 2) to define a critical oxygen delivery on a regional basis. [ 18F]FMISO was injected 2 h after onset of regional liver hypoxia due to arterial occlusion of branches of the hepatic artery in 10 domestic pigs. During the experimental procedure the fractional concentration of inspired oxygen (FiO 2) was set to 0.67 in group A ( N=5) and to 0.21 in group B ( N=5) animals. Immediately before sacrifice, the tPO 2 was determined in normal flow and flow-impaired liver segments. The standardized uptake values (SUV) for [ 18F]FMISO was calculated from 659 single tissue samples obtained 3 h after injection of approximately 10 MBq/kg body weight [ 18F]FMISO and was compared with the regional total hepatic oxygen delivery (DO 2) calculated from the regional arterial and portal venous flow (based on 141Ce- and 99mTc-microspheres measurements) and the oxygen content of the arterial and portal venous blood. In 121 tPO 2-measured liver tissue samples, the mean DO 2 was significantly decreased in occluded liver tissue samples [group A: 0.063 (0.044–0.089); group B: 0.046 (0.032–0.066)] compared to normal flow segments [group A: 0.177 (0.124–0.252); group B: 0.179 (0.128–0.25) mL· min−1· g−1; geometric mean (95% confidence limits); p < 0.01 in group A and p < 0.001 in group B]. The tPO 2 of occluded segments [group A: 5.1 (3.2–8.1); group B: 3.9 (2.4–6.2) mm Hg] was significantly decreased compared to normal flow segments [group A: 20.2 (12.6–32.5); group B: 22.4 (14.3–35.2) mm Hg; p < 0.01 in group A and p < 0.001 in group B]. Three hours after [ 18F]FMISO administration, the mean [ 18F]FMISO SUV determined in tPO 2-measured occluded segments was significantly higher [group A: 4.08 (3.12–5.34), group B: 5.43 (4.14–7.13)] compared to normal liver tissue [group A: 1.57 (1.2–2.06), group B: 1.5 (1.16–1.93); p < 0.001 for both groups]. The [ 18F]FMISO SUV allowed prediction of the tPO 2 with satisfying accuracy in hypoxic regions using the exponential regression curve { [ 18F] FMISO=1.05+6.7 (−0.117 tPO2); r2=0.75; p < 0.001}. In addition, regardless of ventilation conditions, a significant exponential relationship between the DO 2 and the [ 18F]FMISO SUV was found ( r2=0.39, p < 0.001). Our results suggest that the reduction of the oxygen delivery below the critical range of 0.1–0.11 mL· min−1· g−1 regularly causes liver tissue hypoxia. The severity of hypoxia is reflected by the [ 18F]FMISO accumulation and allows the in vivo estimation of the tPO 2 in hypoxic regions. 相似文献
13.
Marinelli (reentrant) beakers are recommended for measurement of low-activity radioactive environmental samples, in both liquid and solid phase. The preparation of Marinelli beaker standards of milk powder containing 232ThO2 at secular equilibrium with its daughter radionuclides was studied. Standards were prepared by mixing of known amounts of solid ThO2 and milk powder. The densities of the standards were 0.5–0.7 kg dm−3. Measurements of calibrated Marinelli beaker standards with HPGe detector showed that the energy dependence of the efficiency is similar to that of a point source, i.e. an almost linear dependence of log-efficiency vs. log-energy in the 200–2000 keV range, however the parabolic correlation fits better. The validity of these standards was checked by comparison with certified standard reference material IAEA-152-Milk powder containing radiocesium and radiopotassium. The results obtained were found to be in a good agreement with the published certified data. The limit of detection for the determination of radiocesium by gamma ray spectrometry under the prevailing experimental conditions is 0.03 Bq (i.e. 0.8 pCi), for samples of dairy products having lower densities of 0.7 kg dm−1. 相似文献
14.
目的 调查云南省部分地区大米和玉米放射性核素水平,充实云南地区食品放射性水平基线数据,评估其对居民产生的健康风险。 方法 依据国家标准《生物样品中放射性核素的γ能谱分析方法》《高纯锗γ能谱分析通用方法》《食品中放射性物质检验总则》《土壤中放射性核素的γ能谱分析方法》,对云南省20个县(区)大米和玉米样品进行放射性核素检测,对检测结果进行处理与分析。 结果 大米样品中 238U、 232Th、 226Ra、 40K和 137Cs活度浓度均值分别为(0.416±0.403)、(0.045±0.034)、(0.030±0.013)、(28.4±18.8)和(0.014±0.019)Bq/kg,玉米样品中 238U、 232Th、 226Ra、 40K活度浓度均值分别为(0.308±0.230)、(0.035±0.031)、(0.053±0.072)、(56.8±38.6)Bq/kg, 137Cs的活度浓度低于探测下限。 结论 云南省20个县(区)大米和玉米中 238U、 232Th、 226Ra、 40K和 137Cs的放射性水平均在国家标准正常范围内,食入后不会对居民的健康造成影响。 相似文献
15.
Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to 222Rn, measured in the presence of 220Rn. Measurements have been made by means of a widely used diffusion chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for 222Rn and 220Rn were found to be 0.470±0.022 and 0.486±0.042 m, respectively. For Monte Carlo simulations, the sensitivities to 222Rn gas were found to range from 0.618×10 –2 m (assuming that all 218Po progeny decay before deposition onto the internal walls of the diffusion chamber) to 0.405×10 –2 m (assuming that all 218Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to 220Rn gas of 0.465×10 –2 m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for 222Rn indicates that 30% of the 218Po progeny decay before deposition onto the internal walls of the diffusion chamber. 相似文献
16.
Yeast cells, Saccharomyces cerevisiae, were exposed to Sb(V) (10 −5M) and SeO 2 (10 −4M) or seleno-cystine (CySe) 2 (5 × 10 −5 M). Se, Sb, Zn and Co levels of the yeast were measured by instrumental neutron activation analysis. The results obtained show that in the absence of Se, Sb is taken up by the cells and the highest concentration of Sb in the yeast was observed during the initial 2.5 h of incubation. Both Se-compounds resulted, in general, in a minute decrease of uptake yield of Sb by the cells. This effect can be particularly observed in the presence of SeO 2. The presence of Sb in the yeast medium slightly increased the Se level only after long incubation times. Se uptake by the yeast was higher (regardless of Sb dosage) when the yeast was incubated in the medium containing (CySe) 2 (in comparison with SeO 2). The presence of Se-compounds and/or Sb caused decrease in the levels of Zn found in the cells. While SeO 2 presence resulted in minor changes of the Co level of the yeast, the combined presence of Sb and Se-compounds produced the significant enhancement of Co abundance. The similar effect was noted in the yeast incubated in a medium containing only (CySe) 2 or Sb. 相似文献
17.
Widespread use of radionuclides in medicine and industry poses the possibility of radiation accidents. We describe such an occurrence involving three industrial workers. The accident resulted from careless handling of a Cs-137 source. Evaluation of the Cs-137 whole body burden was carried out using stationary and scanning whole body counters. In addition, regional and whole body activity from contamination was assessed using an uncollimated gamma camera. This report emphasizes the value of the gamma camera for detection of radionuclide contamination in radiation accidents. 相似文献
18.
A new coincidence system, based on two thin NaI(Tl) crystals, 50×2 mm 2, with beryllium windows, 1.5 mg cm −2, positioned approximately symmetrically from the source holder (at various distances) was constructed. The electronic chains of a classical 4 πPC– γ system were utilized. A multichannel analyzer was employed for energy calibration, and an oscilloscope for visualization of the pulses. After calibration, the system was used for the standardization of an 125I solution. An energy window of 12–95 keV containing the entire spectrum (single and sum peak) was employed, and a simple demonstration of Taylor's equation [1967. X-ray–X-ray coincidence counting methods for the standardization of 125I and 197Hg. In: Standardization of Radionuclides: Proceedings of a International Atomic Energy Agency Symposium, Vienna, 1966, pp. 341–353, SM-79/65] for whole spectrum counting, was developed. The method and system were tested during the calibration of a LKB 2104 multi-gamma counter, by comparing the detection efficiency values obtained for this prepared standard solution and that utilized in the CIPM-CCRI(II) key comparison. The efficiency of the equipment was calculated as the mean of the two individual values. The result validates the method and demonstrates the accomplishment of the national traceability assurance in nuclear medicine for 125I. 相似文献
19.
High-energy electron-beam irradiation was used to remove phenol from aqueous solution. The variables that affected phenol decomposition were solute concentration, absorbed dose and total alkalinity. Experiments were conducted at large scale (480 L min −1), at solute concentrations of 10.6, 106 and 531 μmol L −1 (1, 10 and 50 mg L −1) over the pH range 5–9, and in the presence and absence of solids (3% w/w kaolin clay). Absorbed doses ranged from 0–7 kGy (0–700 krad). At low absorbed doses, catechol, hydroquinone and resorcinol were identified as the major reaction byproducts. These compounds are consistent with hydroxyl radical (OH·) addition to phenol. Subsequent ring cleavage of hydroxylated phenolic radicals and continued oxidative processes resulted in the formation of formaldehyde, acetaldehyde, glyoxal and formic acid. At high doses only trace amounts of the carbonyl derivatives were observed. Two recirculation experiments were conducted at higher phenol concentrations (≈950 μmol L −1) and it was shown that phenol was removed while the total organic carbon of the solution decreased only slightly. These results suggest that phenol was not mineralized but, rather, that irradiation resulted in the possible formation of higher molecular weight polymers. 相似文献
20.
In order to assess the radionuclide content of building materials utilized in the towns of Guarapari and Meiaipe, located in the Brazilian state Espírito Santo, 48 samples of raw materials and construction products were collected and shipped to our laboratory in Italy. Here, concentrations of background radionuclides in samples were determined by γ-ray spectroscopy with two HPGe detectors. The radium-equivalent activity concentrations in the samples varied between 14.6 (sand) and 1930 Bq kg −1 (plaster). 相似文献
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