Porosity distribution by computed tomography and its importance to characterize soil clod samples

Gamma-ray computed tomography (CT) was employed to study the soil quality of clod samples used to investigate porosity (ϕ). Samples with volumes varying from 50 to 100 cm³ were collected from the soil surface. 2D CT images were obtained with millimetric resolution. Porosity distribution analyses were carried out to infer the soil clod structure. Results obtained provided a new insight on the variability of internal clod structure due to the large amount of data analyzed, information that is not provided by traditional methods used in physics applied to soil.     

A dedicated LIMS for routine gamma-ray spectrometry

We developed a Microsoft^® Access-based LIMS (Laboratory Information and Management Systems), γ-LIMS, for the management of our gamma-spectrometry laboratory, in which thousands of routine, but high-quality analyses are performed each year. This paper explains the main features of the γ-LIMS and puts special attention on the interfacing methods and solutions for using the Genie™2000 spectrometry software in conjunction with the EFFTRAN package, which serves for efficiency transfer calculations, coincidence summing corrections and a procedure for uncertainty estimation.     

137 Cs γ射线辐照对手工分血小板制品细胞因子灭活的研究

目的探讨^137Cs γ射线辐照对手工分血小板制品中细胞因子的灭活作用,明确手工分血小板制品辐照处理技术的可行性。方法手工分离血小板后,用25Gy的^137Cs γ射线照射,于照射后0、1、3、5d检测血小板制品中IL-β、IL-6、IL-8和TNF-α等细胞因子含量的变化;并分别于贮存的第0、5天分别进行pH值测定和血小板计数。结果对照组和照射组的细胞因子含量均随保存时间延长而显著增加,但对照组中细胞因子含量增加更为明显;而在同一保存时间对照组中细胞因子含量高于照射组（P〈0.05）;保存过程中,辐照组血小板计数及pH值与对照组差异无统计学意义（P〉0.05）。结论^137Cs γ射线辐照可以显著降低手工分血小板制品中细胞因子的水平。     

On the use of mercury as a means of locating background sources in ultra low-background HPGe-detector systems

In low-level gamma-ray spectrometry, it is common to measure large samples in order to obtain low detection limits for the massic activity (in mBq/kg). These samples have significant shielding effects. In order to study whether the background sources in three ultra low-background HPGe detectors were located in the detector or in the shield, Marinelli beakers filled with hyperpure mercury were measured. Although the measurements were hampered by the presence of cosmogenically produced ¹⁹⁴Hg, information regarding the major background location of ⁴⁰K, ⁶⁰Co, ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra and ²²⁸Th could be obtained.     

Efficiency transfer in the calibration of a coaxial p-type HpGe detector using the Monte Carlo method

Monte Carlo simulation was applied to the efficiency transfer exercise described in the EUROMET428 project (Appl. Radiat. Isot. 55 (2001) 493), evaluating the peak efficiencies in the energy range 60–2000 keV for a typical coaxial p-type HpGe detector and several types of source configuration: point sources located at various distances from the detector and a cylindrical box containing three matrices. The efficiency values were derived in two ways: (a) by direct calculation taking into account the physical dimensions of the detector provided by the supplier, and (b) by means of relative computation (efficiency transfer) taking also into consideration the known efficiency values for a reference point source. As expected, some significant discrepancies between the calculated and experimental values were found when a direct computation was made using the data provided by the supplier. On the contrary, the results for the peak efficiency derived by relative calculation by means of an efficiency transfer were in good agreement with the experimental values. The deviations found with this last procedure were generally below 5% for all the geometries considered, which is entirely satisfactory for the purposes of routine measurements.     

A feasibility study on gamma-ray tomography by Monte Carlo simulation for development of portable tomographic system

The electron beam X-ray tomographic scanner has been used in industrial and medical field since it was developed two decades ago. However, X-ray electron beam tomography has remained as indoor equipment because of its bulky hardware of X-ray generation devices. By replacing X-ray devices of electron beam CT with a gamma-ray source, a tomographic system can be a portable device. This paper introduces analysis and simulation results on industrial gamma-ray tomographic system with scanning geometry similar to electron beam CT. The gamma-ray tomographic system is introduced through the geometrical layout and analysis on non-uniformly distributed problem. The proposed system adopts clamp-on type device to actualize portable industrial system. MCNPx is used to generate virtual experimental data. Pulse height spectra from F8 tally of MCNPx are obtained for single channel counting data of photo-peak and gross counting. Photo-peak and gross counting data are reconstructed for the cross-sectional image of simulation phantoms by ART, Total Variation algorithm and ML-EM. Image reconstruction results from Monte Carlo simulation show that the proposed tomographic system can provide the image solution for industrial objects. Those results provide the preliminary data for the tomographic scanner, which will be developed in future work.     

Measurement of natural radioactivity in building materials of Namakkal, Tamil Nadu, India using gamma-ray spectrometry

The natural level of radioactivity in building materials is one of the major causes of external exposure to γ-rays. The primordial radionuclides in building materials are one of the sources of radiation hazard in dwellings made of these materials. By the determination of the radioactivity level in building materials, the indoor radiological hazard to human health can be assessed. This is an important precautionary measure whenever the dose rate is found to be above the recommended limits. The aim of this work was to measure the specific activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in commonly used building materials from Namakkal, Tamil Nadu, India, using gamma-ray spectrometer. The radiation hazard due to the total natural radioactivity in the studied building materials was estimated by different approaches. The concentrations of the natural radionuclides and the radium equivalent activity in studied samples were compared with the corresponding results of different countries. From the analysis, it is found that these materials may be safely used as construction materials and do not pose significant radiation hazards.     

γ源放射事故受照者呕吐开始时间与全身剂量关系

目的探讨γ源放射事故受照者呕吐开始时间与全身吸收剂量之间的关系。方法采用STATA统计软件包对39例γ源放射事故受照者资料进行回顾性分析。结果全身吸收剂量等于或大于1Gy的受照者呕吐发生率(2227)显著大于剂量在1Gy以下的受照者(112,P<0.001)。出现呕吐的受照者,呕吐开始时间(TD,以h表示)与全身吸收剂量D(Gy)之间的关系符合幂函数模型,其方程式可描述为:TD=(17.45±1.77)D-(2.21±0.30)(n=23,F=50.01,P<0.01,经校正的R2=0.8099)。受照后呕吐开始时间在2h以内的P25、P50和P75剂量分别为4.1、7.6和11Gy;呕吐开始时间大于2h的P25、P50和P75剂量分别为2.0、2.4和2.6Gy。结论在突发核或放射事件可能涉及大量患者的情形下,呕吐开始时间可作为早期分类的一个快速而实用的观察指标,但应注意其局限性。     

Adaptive response induced by low dose ionizing radiation in human cervical carcinoma cells

Adaptive response induced by low dose γ-ray irradiation in human cervical carcinoma cells was examined. Cells were exposured to low dose of γ-ray (1 cGy) followed by high doses of γ-ray irradiation (0, 1, 2, 3, 5, 7 and 9 Gy for clonogenic assay or 1.5 Gy for micronucleus assay) with various time intervals. Survival fractions of cells in both low dose-irradiated and unirradiated groups were analyzed by clonogenic assay. Survival fractions of low dose-irradiated cells was higher than that of control group irradiated only with high dose γ-ray. The increase in cell survival was maximum when low and high dose irradiation time interval was 4 hr. Frequencies of micronuclei which is an indicative of chromosome aberration were also enumerated in both low dose-irradiated and unirradiated groups. In consistent with the result obtained from survival fractions analyzed by clonogenic assay, maximum reduction in frequencies of micronuclei was observed when low dose radiation was given 4 hr prior to high dose irradiation. These results demonstrate that low dose γ-ray irradiation induced adaptive response to subsequent high dose γ-ray irradiation in human cervical carcinoma cells. Our data suggest that one of the possible mechanisms of adaptive response induced by low dose radiation is the increase in repair of DNA double strand breaks in low dose radiation-adapted cells.     

Practical problems in neutron dosimetry

The first problem discussed is the best phantom material. It is argued that tissue composition has a greater effect on dose distributions from photons than on those from neutrons. As water is normally used for photons, it should be satisfactory for neutrons, but checks are needed with high-energy neutron beams. Another serious problem is that of kerma ratios for neutrons above 20 MeV where highly discordant values have been calculated by several authors. Finally some suggestions are made about measurement of the gamma-ray component in beams of high-energy neutrons.