中子源强度基准

中国计量科学研究院建立中子源强度基准的研究工作始于60年代。1972年建成并通过鉴定，1985年批准为国家基准。中子源强度基准采用锰浴法，包括锰浴池、循环系统和活化计数装置。测量范围为（5×105－5×107）中子／s，扩展不确定度为1．2％（k＝3）。中子源强度基谁是中子计量的基础，通过中子源检定，进一步对中子仪器、中子防护仪表和个人剂量计进行检定。该基准为核能核电、石油测井、钢铁、农业、医学等应用中子辐射的领域，提供了计量保证。中子源强度基准@徐沔$中国计量科学研究院@周克勤$中国计量科学研究院…     

14MeV单能中子注量率绝对测量装置

一、引言用~3H(d,n)~4He反应产生的14MeV的中子源是使用较多的一种中子源,已广泛地应用,从而迫切地要求准确测量中子场中子注量率。为此,我们于1985年建立了14MeV中子注量率的绝对测量装置,以统一中子注量率的量值。它也可作为比对用的相对测量装置。     

用锰浴法绝对定度Am-Be中子源

建立了一套循环式的硫酸锰浴装置,可以用来定度各种放射性同位素中子源的中子发射率。用这套装置定度了一个Am-Be(α,n)中子源,测得Q=(7.213±0.037)×10~6中子/秒,系统误差为±0.49％。同时得到σ_H/σ_(Mn)=0.02498±0.00014。测量中用了七种溶液浓度,N_H/N_(Mn)值的范围为34～275。对每种浓度分别用三种方法测定其N_H/N_(Mn)值,结果很好地一致。     

组织等效电离室与国外几种同类电离室在中子场中的比对

组织等效电离室是测量中子吸收剂量最方便、最有效的剂量计,因而得到广泛的应用。国际上至今还没有建立起公认的中子吸收剂量测量基准,一种测量装置的可靠性和测量结果的不确定度主要是通过各装置之间的比对来检验。为此,我们曾在国内的几处中子辐射场中将我们研制的几种IRM型组织等效电离室与FWT IC-17A电离室进行了比对性测量。同时     

中子周围剂量当量仪的校准方法与亚太比对

中子周围剂量当量(率)仪作为中子辐射水平监测的主要设备须采用适当的方法进行准确校准。亚太计量规划组织于2012年组织了该类仪器的校准比对(APMP.RI(III)-S1),比对协议规定采用放射性核素中子源的中子参考辐射场校准主导实验室提供的比对仪器,并推荐采用影锥法和距离变化法对校准结果进行散射中子修正,参比实验室将比对仪器的校准因子及其不确定度作为比对结果上报。中国计量科学研究院参加了本次比对,比对结果表明参比实验室的校准结果在不确定度范围内一致。     

国家温度副基准铟凝固点与国家基准的比对评述

铟凝固点是90国际温标(ITS-90)重要的定义固定点之一,为验证中国测试技术研究院建立保存的国家温度副基准装置复现铟凝固点热力学温度的技术水平,于2018年与中国计量科学研究院的国家温度基准装置开展铟凝固点的比对。此次比对采用标准铂电阻温度计作为传递标准。传递标准分别在副基准装置和基准装置的铟凝固点中至少3个不同温坪上进行测量,并根据ITS-90规定对测量数据进行修正,计算电阻比W,将多次测量的平均值W作为实验结果。通过归一化偏差En值对测量结果的一致性进行评判,比对结果表明铟凝固点副基准与基准在0.1 mK内相一致。     

55Fe溶液活度测量国际比对

首次用CIEMAT/NIST方法参加了BIPM(国际计量局)组织的55Fe放射性溶液活度测量国际关键比对,用该方法获得的测量结果与比对结果平均值在0.5%内一致,验证了我国放射性活度国家基准量值的国际等效性.     

2πα、2πβ粒子发射率现场校准装置的建立

基于大面积无窗流气正比计数器和多道能谱测量单元,建立了2πα、2πβ粒子发射率现场校准装置。性能测试结果表明:该装置对α平面源的坪区为700~1 500 V,坪长为800 V,坪斜为0.25%/100 V;对β平面源的坪区为1 650~2 050 V,坪长为400 V,坪斜为0.44%/100 V。使用该装置测量2πα、2πβ粒子发射率基准装置定值的标准平面源,经各项修正后,结果与基准测量结果在不确定度范围内一致。在现场校准了一批α、β标准平面源,校准结果与上一校准周期的结果在不确定度范围内一致,验证了该装置作为现场测量标准装置实现粒子发射率量值现场传递的可行性。     

633 nm激光波长基准/副基准比对

对中国计量科学研究院、中国计量测试技术研究院和长城计量测试技术研究所的633 nm127I2饱和吸收稳定激光波长基准、副基准进行了比对,这是首次进行的国内长度基准的比对.比对实验的内容包括频率稳定度测量、频差测量和相关的位移参数测量等.给出了以国际计量局BIPM C1为参考的比对结果.     

检定中子防护剂量仪表的谱中子标准辐射场

为了满足中子辐射防护剂量仪表检定和个人中子剂量计刻度的需要，我们建立了一个以Am－Be中子源为参考标准的标准中子辐射场。用于定度该场的中子周围剂量当量率，可由下式给出：式中Q是仪器定度参考点位置上的参考辐射场中子人射注量率，h”是中子注量——中子周围剂量当量转换系数，其数值由规程JJG852－93给出。在距源中心为D的参考点处，中子源直接射束导致的中子周围剂量当量率为：式中Q为参考辐射中子源的已知强度，f（）为中子源发射率各向异性修正因子，b（D）为空气对中子束的衰减修正因子。本工作在固定的源——探测器距离，…     

Absolute neutron emission rate measurement of a 252Cf source by the manganous sulfate bath method

A standard program for the absolute neutron emission rate measurement of a ²⁵²Cf source by the manganous sulfate bath method has been completed for the standardization of neutron source measurements. The MnSO₄ circulation system enables the ⁵⁶Mn activity to be measured during activation of the bath by the neutron source. The neutron capture cross section ratio of hydrogen to manganese has been determined to be 0.02506 by varying the manganese concentration in the MnSO₄ solution. From the graphical analysis of a straight line fitted to the six sets of data, the observed neutron emission rate was 2.544 × 10⁷ n/s for the ²⁵²Cf source at the reference date, January 1, 1987.     

Precise measurement of the gamma to neutron ratio of an Am-α-Be neutron source using an improved manganese bath technique

An accurate measurement of the gamma to neutron ratio for an Am-α-Be neutron source is described. The total neutron output was measured using an improved manganese bath technique and the 4.43 MeV gamma ray associated with the neutron producing reaction was measured absolutely with a NaI(Tl) detector. The experimental ratio so obtained agrees well with the theoretically computed value. It is recommended to use the experimental value of this ratio, namely 0.56±6%, as it is traceable to the primary standards.     

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)。     

光电比较仪(或高温计)系统非线性测量装置

本系统地介绍了新研制的光电比较仪（或高温计）系统非线性测量装置。新装置采用双光源单光路设计,具有独立于被测对象和不失真的特点。利用该装置对基准光电比较仪和标准光电高温计进行了系统实验,测量不确定度达到０．０１％。利用该装置测量的数据已应用于国际计量局（ＢＩＰＭ）和亚太计量规划组织（ＡＰＭＰ）主办的国际比对中。     

水量热法加速器光子水吸收剂量绝对测量与国际比对

为实现加速器光子水吸收剂量绝对测量,研制了水量热计系统,在此基础上取得国际互认并建立加速器光子水吸收剂量基准,进一步提高了我国放疗剂量量值传递能力。通过水浴与半导体制冷系统二级控温,将量热计水模体的温度漂移控制在0.5μ℃/s。利用惠斯通交流电桥测量辐射所致的热敏探针阻值变化,逐次校准热敏探针和交流电桥,实现了医用加速器光子水吸收剂量的绝对测量,合成标准不确定度为0.30%。参加了国际计量局加速器光子水吸收剂量关键比对,复现的6MV和10MV光子水吸收剂量值与比对参考值之比分别为0.9917和0.9949,在不确定度允许的范围内一致。     

Precision Neutron Polarimetry for Neutron Beta Decay

The abBA collaboration is developing a new type of field-expansion spectrometer for a measurement of the three correlation coefficients a, A, and B and the shape parameter b. The measurement of A and B requires precision neutron polarimetry. We will polarize a pulsed cold neutron beam from the SNS using a ³He neutron spin filter. The well-known polarizing cross section for n-³He has a 1/v dependence, where v is the neutron velocity, which is used to determine the absolute beam polarization through a time-of-flight (TOF) measurement. We show that by measuring the TOF dependence of A and B, the coefficients and the neutron polarization can be determined with a small loss of the statistical precision and with negligible systematic error. We conclude that it is possible to determine the neutron polarization averaged over a long run in the neutron beta decay experiment with a statistical error less than 10⁻⁴. We discuss various sources of systematic uncertainty in the measurement of A and B and conclude that the fractional systematic errors are less than 2 × 10⁻⁴.     

Standard fields of old neutron sources--parameters and traceability

Standard neutron fields of isotope neutron sources, established in the Institute of Atomic Energy, Poland, have been examined for nearly 20 y. The neutron dose equivalent and gamma dose rates were measured, applying various techniques. The neutron emission of standard neutron sources of 241Am-Be and 252Cf has been originally determined in primary standard laboratory, then checked, making use of transfer instrument calibrated in primary laboratory. The growth of neutron emission of 239Pu-Be source, used for routine calibrations, has been demonstrated. The total uncertainty of determined parameters has been discussed. The periodically repeated checks of neutron fields of standard sources with the use of transfer instrument, calibrated in primary laboratory, should provide the traceability to primary laboratory and the fields could be officially recognised.     

Key comparisons of the VNIIM and BIPM voltage standards

The results of key comparisons of the national primary standard of Russia for the unit of electrical voltage, the volt, at the Mendeleev Institute of Metrology (VNIIM) with the Josephson effect voltage standard at the BIPM are reported. For these measurements, VNIIM provided a voltage measure based on the Josephson effect with a nominal output voltage of 10 V. Measurements were made with apparatus from the BIPM voltage standard. The VNIIM voltage measure is planned for use as a transfer standard for comparison with national standards for the volt. The comparisons indicate a high degree of equivalence of the compared VNIIM and BIPM primary standards with a relative combined standard uncertainty of 2·10–10 at 10 V.     

BNCT医院中子照射器辐射场特性参数初步测量

为验证BNCT医院中子照射器的设计效果,对其辐射场的特性参数如中子能谱、中子通量密度及其空间分布、中子和γ吸收剂量率及其空间分布等进行了测量。针对该照射器的特点,建立了一套由多球谱仪、235U裂变电离室、金箔、组织等效正比计数器和热释光探测器组成的测量系统,利用蒙特卡洛计算方法优化设计探测器的结构,以提高超热能区的分辨率和甄别不同能量成分中子的能力。初步测量结果表明,该照射器的中子通量密度达到了预期设计要求。     

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 %.