Comparison of the NIST and ENEA Air Kerma Standards

A comparison was made between the National Institute of Standards and Technology (NIST) and Ente per le Nuove Tecnologie l’Energia e l’Ambiente (ENEA) air kerma standards for medium energy x rays and ⁶⁰Co gamma rays. The comparison took place at ENEA in June 1994. Two different transfer chambers from NIST were used for the comparison. The measurements were made at radiation qualities similar to those used at the Bureau International des Poids et Mesures (BIPM) (generating voltages of 100 kV, 135 kV, 180 kV and 250 kV, respectively) and with ⁶⁰Co gamma radiation. The transfer chamber calibration factors obtained at the NIST and at the ENEA agreed with one another to 0.03 % for ⁶⁰Co gamma radiation and between 0.1 % to 0.8 % for the medium energy x-ray beam codes.     

Comparison of the NIST and PTB Air-Kerma Standards for Low-Energy X-Rays

A comparison has been made of the air-kerma standards for low-energy x rays at the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB). The comparison involved a series of measurements at the PTB and the NIST using the air-kerma standards and two NIST reference-class transfer ionization chamber standards. Results are presented for the reference radiation beam qualities in the range from 25 kV to 50 kV for low energy x rays, including the techniques used for mammography dose traceability. The tungsten generated reference radiation qualities, between 25 kV and 50 kV used for this comparison, are new to NIST; therefore this comparison will serve as the preliminary comparison for NIST and a verification of the primary standard correction factors. The mammography comparison will repeat two previously unpublished comparisons between PTB and NIST. The results show the standards to be in reasonable agreement within the standard uncertainty of the comparison of about 0.4 %.     

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%。     

Comparison of the NIST and NPL Air Kerma Standards Used for X-Ray Measurements Between 10 kV and 80 kV

A direct comparison was made between the air kerma primary standards used for the measurements of low-energy x rays at the National Institute of Standards and Technology (NIST) and the National Physical Laboratory (NPL). The comparison was conducted at the NPL using NPL reference radiation qualities between 10 kV and 80 kV. The results show the primary air-kerma standards to agree within 0.6 % of their values for beam qualities up to 80 kV.     

Comparison of the NIST and BIPM Standards for Air Kerma in Medium-Energy X-Rays

A comparison has been made of the air-kerma standards for medium-energy x-rays of the National Institute of Standards and Technology (NIST) and the Bureau International des Poids et Mesures (BIPM). The comparison involved a series of measurements at the BIPM and the NIST using the air-kerma standards and three NIST reference-class transfer ionization chamber standards. Reference beam qualities in the range from 100 kV to 250 kV were used. The results show the standards to be in reasonable agreement within the combined standard uncertainty of the comparison of 0.37 %, although a significant trend with radiation quality is observed and the possible sources discussed.     

防护水平X射线电离室的校准及不确定度分析

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)。     

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.     

Comparison of the NIST and BIPM Medium-Energy X-Ray Air-Kerma Measurements

The air-kerma standards used for the measurement of medium-energy x rays were compared at the National Institute of Standards and Technology (NIST) and at the Bureau International des Poids et Mesures (BIPM). The comparison involved a series of measurements at the BIPM and the NIST using the air-kerma standards and two NIST reference-class transfer ionization standards. Reference beam qualities in the range from 60 kV to 300 kV were used. The results show the standards to be in agreement within the combined standard uncertainty of the comparison of 0.35 %.     

自制球形空腔电离室的性能测试

为建立和完善250～600 kV段X射线空气比释动能基准,自主研制了一系列石墨空腔电离室作为基准电离室,以球形空腔电离室为例,在参考辐射场上对其性能进行了相关测试,包括电离室的饱和特性、重复性以及漏电情况.结果显示电离室的工作电压为600V,重复性好于0.1％,漏电流值小于30fA,本套电离室的性能符合相关要求.     

Comparison of the NIST and BIPM Air-Kerma Standards for Measurements in the Low-Energy X-Ray Range

A direct comparison was made between the air-kerma standards used for the measurement of low-energy x rays at the National Institute of Standards and Technology (NIST) and the Bureau International des Poids et Mesures (BIPM). The comparison was carried out at the BIPM using the BIPM reference beam qualities in the range from 10 kV to 100 kV. The results show the standards to be in agreement to around 0.5 % at reference beam qualities up to 50 kV and at 100 kV. The result at the 80 kV beam quality is less favorable, with agreement at the 1 % level.     

~(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%。     

NIST Gas Hydrate Research Database and Web Dissemination Channel

To facilitate advances in application of technologies pertaining to gas hydrates, a freely available data resource containing experimentally derived information about those materials was developed. This work was performed by the Thermodynamic Research Center (TRC) paralleling a highly successful database of thermodynamic and transport properties of molecular pure compounds and their mixtures. Population of the gas-hydrates database required development of guided data capture (GDC) software designed to convert experimental data and metadata into a well organized electronic format, as well as a relational database schema to accommodate all types of numerical and metadata within the scope of the project. To guarantee utility for the broad gas hydrate research community, TRC worked closely with the Committee on Data for Science and Technology (CODATA) task group for Data on Natural Gas Hydrates, an international data sharing effort, in developing a gas hydrate markup language (GHML). The fruits of these efforts are disseminated through the NIST Sandard Reference Data Program [1] as the Clathrate Hydrate Physical Property Database (SRD #156). A web-based interface for this database, as well as scientific results from the Mallik 2002 Gas Hydrate Production Research Well Program [2], is deployed at http://gashydrates.nist.gov.     

对向测量皮托管的国际比对

为验证现场烟道流量测量使用的对向测量S型皮托管、球形三维皮托管和棱形三维皮托管校准系数的一致性,中国计量科学研究院(NIM)主导开展了包括美国国家标准与技术研究院(NIST)和韩国标准科学研究院(KRISS)参加的皮托管校准比对。比对结果表明:S型皮托管在不同实验室间比对结果吻合度相对较差,不适合作为比对标准器;球形三维皮托管在不同实验室间比对结果吻合度高于棱形三维皮托管,流速校准系数差异对测量轴向流速的影响高于偏航角参考位置偏差与俯仰角校准系数差异造成的影响;皮托管的偏航角参考位置偏差和俯仰角校准系数差异造成的轴向流速差异在0.03%~0.9%,由于流速校准系数差异造成的轴向流速差异在1.9%~12.2%。     

用于放疗量传的照射量、空气比释动能和水吸收剂量量值体系比较

用照射量和空气比释动能校准的电离室进行剂量测量时,依据IAEA TRS 277报告,需要经历四级量值转换过程,不确定度也较大,但目前仍是国内使用的量值体系.我国正在建立60Co γ射线以及高能光子下的水吸收剂量基准装置并进行国际比对,之后将拥有水吸收剂量的量值复现的能力.在60Co γ射线参考辐射场和加速器高能X射线辐射场下,使用NE2571和NE2570/1A、PTW TW30013和PTW UNIDOS两套电离室剂量仪,分别按照277和398报告的要求计算并比较2种方法计算出的水吸收剂量值,从而验证了277报告和398报告的一致性.     

Comparison of absolute spectral irradiance responsivity measurement techniques using wavelength-tunable lasers

Independent methods for measuring the absolute spectral irradiance responsivity of detectors have been compared between the calibration facilities at two national metrology institutes, the Helsinki University of Technology (TKK), Finland, and the National Institute of Standards and Technology (NIST). The emphasis is on the comparison of two different techniques for generating a uniform irradiance at a reference plane using wavelength-tunable lasers. At TKK's Laser Scanning Facility (LSF) the irradiance is generated by raster scanning a single collimated laser beam, while at the NIST facility for Spectral Irradiance and Radiance Responsivity Calibrations with Uniform Sources (SIRCUS), lasers are introduced into integrating spheres to generate a uniform irradiance at a reference plane. The laser-based irradiance responsivity results are compared to a traditional lamp-monochromator-based irradiance responsivity calibration obtained at the NIST Spectral Comparator Facility (SCF). A narrowband filter radiometer with a 24 nm bandwidth and an effective band-center wavelength of 801 nm was used as the artifact. The results of the comparison between the different facilities, reported for the first time in the near-infrared wavelength range, demonstrate agreement at the uncertainty level of less than 0.1%. This result has significant implications in radiation thermometry and in photometry as well as in radiometry.     

Changes in the U.S. Primary Standards for the Air Kerma From Gamma-Ray Beams

Monte Carlo photon-electron transport calculations have been done to derive new wall corrections for the six NBS-NIST standard graphite-wall, air-ionization cavity chambers that serve as the U.S. national primary standard for air kerma (and exposure) for gamma rays from ⁶⁰Co, ¹³⁷Cs, and ¹⁹²Ir sources. The data developed for and from these calculations have also been used to refine a number of other factors affecting the standards. The largest changes are due to the new wall corrections, and the total changes are +0.87 % to +1.11 % (depending on the chamber) for ⁶⁰Co beams, +0.64 % to +1.07 % (depending on the chamber) for ¹³⁷Cs beams, and −0.06 % for the single chamber used in the measurement of the standardized ¹⁹²Ir source. The primary standards for air kerma will be adjusted in the near future to reflect the changes in factors described in this work.     

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。     

Calibration of a pyroelectric detector at 10.6 microm with the National Institute of Standards and Technology high-accuracy cryogenic radiometer

The National Institute of Standards and Technology (NIST) is establishing an infrared detector calibration facility to improve radiometric standards at infrared wavelengths. The absolute response of the cryogenic bolometer that serves as the transfer standard for this facility is being linked to the NIST high- accuracy cryogenic radiometer (HACR) at a few laser wavelengths. At the 10.6-microm CO(2) laser line, this link is being established through a pyroelectric detector that has been calibrated against the HACR. We describe the apparatus, methods, and uncertainties for the calibration of this pyroelectric detector.     

低能X射线空气比释动能国际关键比对

为促进我国在低能X射线空气比释动能计量领域内的量值统一并达到国际等效,中国计量科学研究院(NIM)于2018年采用平板自由空气基准电离室复现低能X射线空气比释动能,并通过传递电离室Radcal-RC6M在国际计量局(BIPM)低能X射线辐射场中开展了间接比对,其比对结果在合成标准不确定度为0.37%范围内与国际计量局等效一致,该比对结果已纳入国际计量局的关键比对数据库(KCDB)。     

An Examination of New Paradigms for Spline Approximations

Lavery splines are examined in the univariate and bivariate cases. In both instances relaxation based algorithms for approximate calculation of Lavery splines are proposed. Following previous work Gilsinn, et al. [7] addressing the bivariate case, a rotationally invariant functional is assumed. The version of bivariate splines proposed in this paper also aims at irregularly spaced data and uses Hseih-Clough-Tocher elements based on the triangulated irregular network (TIN) concept. In this paper, the univariate case, however, is investigated in greater detail so as to further the understanding of the bivariate case.