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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%。 相似文献
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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。 相似文献
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防护水平电离室剂量计是辐射防护的主要计量器具,需要在窄谱参考辐射质下进行检定和校准。利用EGSnrc软件模拟了参考辐射质X射线能谱,分析得到的能谱分辨率和平均能量与ISO 4037-1推荐值的最大偏差分别为7.1%和1.04%,均满足规范要求。依托60~250kV X射线空气比释动能国家基准装置,在窄谱系列参考辐射质下完成了距离X光机1m处参考点的空气比释动能量值复现;然后通过替代法对两个传递电离室进行校准并完成量值传递;最后利用传递电离室复现的2.25m处的空气比释动能率对PTW-32002球形电离室进行校准,获得相应的校准因子,校准因子相对扩展不确定度为2.2%(k=2)。 相似文献
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为建立高注量率同步辐射X射线计量领域相关的国家标准,对同步辐射X射线能量标定方法进行研究。在北京同步辐射装置上选择6、10和20keV三个能量点进行实验,得到的传递探测器校准因子与辐射能量的关系曲线近似直线,变化趋势呈线性递减;在20keV能量点,不同直径光阑条件下进行的标定实验验证了传递探测器的校准因子与光源照射到基准电离室与传递探测器的光子通量有关。在上海光源上进行10~70keV能量标定实验,得到传递探测器的校准因子拟合曲线;10~20keV能量段的变化趋势与在北京同步辐射装置得到的校准因子变化趋势一致,30~70keV能量段的校准因子随着能量的增加而平稳缓慢增大。对各个能量点标定产生的A类不确定度进行评定,为后续建立国家计量标准同步辐射X射线空气比释动能量值传递体系提供了技术数据。 相似文献
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为建立基于圆饼电离室系统的~(60)Coγ射线空气比释动能基准装置,对辐射场及场中电离室的相关物理参量进行了蒙特卡洛模拟研究。通过BEAMnrc程序建立辐照器模型计算测量点处能谱和注量分布,使用EGSnrc计算圆饼电离室在辐射场中各物理参量。~(60)Coγ射线空气比释动能绝对测量装置通过蒙特卡洛模拟得到的相关物理参数合成不确定度为0.20%,该结果与澳大利亚计量院同结构电离室的结果在不确定度范围内一致,与国家基准球-圆柱形电离室及球形电离室相比在不确定范围内符合。 相似文献
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K荧光因为拥有良好的单能性而被用于刻度校准仪器仪表.K荧光产额与单能性直接关系着刻度的准确性.利用RC6M电离室,测量锆(Zr)、硫酸铯(Cs2SO4)、钨(W)3种材料分别作为辐射体时的电离电流,计算得出其空气比释动能,进而求出K荧光辐射场在60cm处的光子注量.结果显示,计算得出的光子注量率在107~109m-2·s-1的量级.分析了K荧光X射线光子注量的不确定度的来源,最终计算得出当用Zr作为辐射体时,光子注量的相对扩展不确定度为5.78%,当用Cs2S04作为辐射体材料时,光子注量的相对扩展不确定度为1.08%,当用W作为辐射体材料时,光子注量的相对扩展不确定度为1.34%. 相似文献
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Free-air ionisation chambers are widely used at standards laboratories as primary standards for absolute measurements of air kerma in X-ray fields. The area of the diaphragm aperture of a free-air ionisation chambers is an important factor for absolute measurements because it defines the size of the X-ray beam incident on the free-air chamber. In this study, correction factors for the contribution of X rays transmitted through the diaphragm of a free-air ionisation chamber and those scattered from the surface of the diaphragm aperture are obtained by Monte Carlo simulation for two different sized free-air ionisation chambers and for various diaphragm aperture sizes, X-ray energies and source-to-chamber distances. 相似文献
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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. 相似文献
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《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1988,272(3):866-870
The dosimetry of a nearly-monoenergetic 6–7 MeV photon source developed at the National Bureau of Standards (NBS) for radiation protection instrument calibration has been carried out by NaI(Tl) scintillation spectrometry. This approach uses calculated 3 in. × 3 in. NaI(Tl) detector-response functions that have been shown to be reasonably accurate up to 20 MeV. A least-squares fit of the appropriate response functions to a selected region of the pulse-height distribution determines the primary 6–7 MeV photon fluence. The uncertainty in the fluence determination is based on the χ2 of the fit, the statistics of the data, and the uncertainty in the response functions. The air kerma delivery due to the primary photons at a reference point in the photon field was calculated from the primary photon fluence. The uncertainty in the determination of air kerma delivery for primary photons was less than 5% (1 std. dev.). The primary high-energy photon contribution to the detector response was subtracted from the data and the remaining distribution due to lower-energy photons was evaluated by spectrum unfolding analyses. The spectrum-unfolded results indicate that a contribution of approximately 12% of the total air kerma was mostly from a continuous distribution of photons extending up to 4.5 MeV. 相似文献