γ射线空气比释动能测量不确定度分析

基于空气比释动能测量的Bragg-Gray空腔理论,通过采用石墨空腔电离室对γ射线空气比释动能率进行测量,建立了测量数学模型,考虑到空气比释动能测量过程中的各影响量及其修正,采用实验测量或蒙卡模拟计算的方法得到各修正因子并分析不确定度,得到γ射线空气比释动能测量的扩展不确定度约为0.5%,其中主要是由壁效应修正和平均电离功的不确定度贡献,因此有必要开展相应的研究,以提高空气比释动能的测量水平。     

医用X辐射源空气比释动能率的测得值的不确定度评定

对医用X辐射源空气比释动能率的测得值的不确定度评定,建立不确定度模型,分析和计算各分量的相对标准不确定度,得出空气比释动能率的合成标准不确定度及其扩展不确定度。     

高剂量率近距离192Ir治疗源的井型电离室仪器的校准

针对后装治疗用192Ir放射源的参考空气比释动能率的量值急需进行溯源。参考国际通例,由指型电离室(PTW-30013)在60Co γ射线和250kV X射线下的空气比释动能校准因子推导得出192Ir γ射线的空气比释动能校准因子,从而测定192Ir放射源参考空气比释动能率标准值,进而完成对井型电离室的参考空气比释动能率校准。通过不确定度评定得出:192Ir放射源的参考空气比释动能率的不确定度为3.6%,井型电离室校准因子的不确定度为3.8%。     

空气比释动能率测量不确定度评定

文章主要论述工业X射线探伤机空气比释动能率测量不确定度的评定，并详细分析了空气比释动能率不确定度的来源、标准不确定度分量的评定及自由度的计算等。     

中能X射线空气比释动能基准不确定度分析

根据空气比释动能复现公式建立数学模型,介绍了中能X射线100-250 kV空气比释动能基准测量不确定度的评定方法,分析了空气比释动不确定度的来源.依次对物理常数、有效测量体积、距离定位、电离电流、温度气压以及修正因子不确定度进行了分析.最终得到测量中能X射线空气比释动能的相对合成标准不确定度为0.22％,其中不确定度来源中最大的2个量分别为电离功和修正因子.     

60C0γ射线空气比释动能量值国内比对

中国计量科学研究院作为主导实验室,组织了全国15个实验室参加的60Coγ射线空气比释动能量值比对.比对结果表明各参比实验室测量的比对点处空气比释动能率在0.6%以内吻合,核验比对给出的传递标准空气比释动能校准因子在0.8%以内吻合.     

最小额定空气比释动能率与诊断剂量仪

ＪＪＧ744 -97“医用诊断Ｘ射线辐射源”检定规程检定条件一节中 ,提出了用于本规程的诊断剂量仪的一些技术要求 ,如能响、基本误差、重复性、校准因子的不确定度、年稳定性等 ,并明确为带电离室型剂量仪 ,并以积分测量法检测间歇工作方式工作的Ｘ光机 ,对标准的要求比ＪＪＧ744 -91更加明确。在实际检定过程中 ,我们发现有个问题不容忽视 ,那就是最小额定空气比释动能率 ,什么是最小额定空气比释动能率呢 ?即满足仪器所有技术指标所能测定的最小空气比释动能率。通常 ,对于普通型的Ｘ光机 ,在规定的检定条件下其输出空气比释动能率在 2 0…     

空气比释动能与照射量比较

空气比释动能和照射量都可以用于校准剂量计 ,但仔细研究空气比释动能和照射量基准的原理、定义、建立以及校准和转换为水吸收剂量的计算 ,表明无论从理论上还是实践上空气比释动能都比照射量更为方便 ,而且可能引入的不确定度更小 ,因而更优越。     

医用诊断X辐射源辐射输出的空气比释动能率测量不确定度评定

文章对检定“医用诊断X辐射源”辐射输出的空气比释动能率的测量结果不确定度进行了详细的分析和评定 ,评定的方法符合JJG10 5 9- 1999和JJF10 33- 2 0 0 1技术规范的要求。     

X射线探伤机空气比释动能率测量不确定度评定

基于X射线探伤机空气比释动能率测量的数学模型，对其测量不确定度进行了评定。     

Kerma rate effects on thermoluminescent response of CVD diamond

The thermoluminescence (TL) response of chemical vapour deposition diamond is studied after X-irradiation (45 kV) at room temperature for various air kerma rates ranging from 0.7 to 100 Gy.min(-1). For a given air kerma, the TL signal as a function of air kerma rate exhibits large variations and is higher for low air kerma rates than for higher ones. In order to explain these results, the simplest energy-level scheme has been considered, that is, with only one electron trap and one recombination centre. Kinetic equations are numerically solved. Calculations are made for various electron-hole generation rates and show that the trap filling as a function of electron-hole generation rate follows, actually, the same evolution as the one of experimental TL response. The kerma rate effect on TL response is explained by the competitivity between the recombination and the trapping processes during irradiation.     

Calibration of a 7.6 cm x 7.6 cm (3 inch x 3 inch) sodium iodide gamma ray spectrometer for air kerma rate

An experimental procedure is described for converting a gamma ray spectral measurement from a 7.6 cm x 7.6 cm (3 inch x 3 inch) sodium iodide (NaI) detector to air kerma rate. The calibration procedure involves measuring the energy deposited in the detector using 10 radioactive sources of known activity covering an energy range from 60 keV to 1,836 keV. For each of the 10 sources, gamma ray spectra were measured with the source at different angles to the detector axis. The total energy deposited in the detector for the ten sources was confirmed by Monte Carlo calculations. The spectra measured at different angles were combined to produce a spectrum that would represent a homogeneous semi-infinite source of radiation. The resultant spectrum was then subdivided into 10 energy regions. Based on the known air kerma rates due to the sources, a calibration coefficient was calculated for each of the 10 energy regions. These calibration coefficients could then be used to convert the energy deposited in the 10 regions of an unknown spectrum to air kerma rate. The calibration procedure was confirmed by comparing the results from the detector with those from calibrated collimated beams of 137Cs and 60Co. A comparison of measurements using a calibrated pressurised ionisation chamber with those from a similar Nal spectrometer in Finland provided additional confirmation of the calibration procedure.     

~(137)Cs γ射线空气比释动能基准石墨空腔电离室的研制

根据Bragg-Gray理论研制了圆柱形石墨空腔电离室,用于~(137)Cs空气比释动能基准的建立。通过理论计算灵敏体积内部电场分布,优化了电离室壁和收集极之间接地保护的结构设计,在此基础上,对研制的电离室的饱和曲线、本底电流以及稳定性等电学性能进行了测试,其结果表明完全达到设计要求。对电离室的各项修正因子进行了理论计算和实验测量,实现了~(137)Cs空气比释动能的量值复现,其合成标准不确定度为0.25%。     

X射线环境辐射监测仪器校准方法的研究

环境辐射监测仪表作为微弱放射性监测计量器具,它的量值溯源是一个急需解决的问题。由于环境辐射剂量率低且电离信号微弱,故通常采用大体积电离室或者充压电离室进行测量。依托60~250kV X射线空气比释动能基准电离室,在完成重过滤窄谱X射线辐射质空气比释动能绝对测量的基础上,通过逐级替代法完成大体积环境辐射监测仪器的校准。测量结果不确定度为5.6%(k=2),实现环境水平X射线空气比释动能测量量值溯源,为国内环境辐射监测仪器在低剂量率水平的性能评价提供计量保障。     

Interaction of a moist capillary-porous solid with a hot gas flow

An experimental investigation of the temperature distribution in the boundary layer of air above a capillary-porous solid from which a liquid is evaporating is described. An analysis of the experimental results confirms Lykov's hypothesis of the presence of a bulk evaporation source in the boundary layer of air above a capillary-porous solid. This source increases the rate of heat and mass transfer from the solid to the air flow.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 3, pp. 463–469, September, 1969.     

Determination of conversion factors from air kerma to operational dose equivalent quantities for low-energy X-ray spectra

The conversion coefficients from air kerma to ICRU operational dose equivalent quantities for STUK's realisation of the X-radiation qualities N-15 to N-60 of the ISO narrow (N) spectrum series were determined by utilising X-ray spectrum measurements. The pulse-height spectra were measured using a planar high-purity germanium spectrometer and unfolded to fluence spectra using Monte Carlo generated data of the spectrometer response. To verify the measuring and unfolding method, the first and second half-value layers and the air kerma rate were calculated from the fluence spectra and compared with the values measured using an ionisation chamber. For each radiation quality, the spectrum was characterised by the parameters given in ISO 4037-1. The conversion coefficients from the air kerma to the ICRU operational quantities H(p)(10), H(p)(0.07), H'(0.07) and H(*)(10) were calculated using monoenergetic conversion coefficients at zero angle of incidence. The results are discussed with respect to ISO 4037-4, and compared with published results for low-energy X-ray spectra.     

测量物体转动惯量的新方法研究

利用刚体绕定轴转动的动能定理,在建立了单轴气浮台绕定轴转动的转动惯量与时间关系的基础上,提出了一种基于单轴气浮台利用能量衰减测量物体转动惯量的新方法。通过理论推导得出了测量物体转动惯量的实验计算式,并进行了实验验证,实验测量结果与理论计算结果的相对误差均在±0.5%以内。     

高速铁路气动噪声的数值分析及分布特征研究

以京沪线为研究背景,建立用于数值计算的简化的车辆-桥梁模型,基于宽频带噪声源法和声类比理论,利用Fluent软件分别研究了列车在高架桥上高速行驶时的近场气动噪声的声源强度特性和远场气动噪声的空间分布特性。研究结果表明：沿桥梁纵向气动噪声强度在车尾变截面处最大,车头变截面处次之;沿桥梁横向气动噪声强度随着离桥梁横向距离的增加而减小,且减小的幅度越来越小;沿桥梁垂向气动噪声在距离轨道顶面高度1.2 m处的强度最大。