National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD, USA.
Analyst. 2017 Oct 9;142(20):3822-3829. doi: 10.1039/c7an01308f.
The accuracy of low-level hydrogen measurements with prompt gamma-ray activation analysis (PGAA) depends on identifying and accounting for all background H signals, including interfering signals. At the cold-neutron (CN)PGAA facility at the NIST Center for Neutron Research, the sources of background H signals were investigated in the context of titanium-based matrices containing low-levels of H (<300 mg H per kg Ti) with the measurements of prepared standards (mixtures of polyvinyl chloride and titanium oxide) and Ti alloy (Ti6Al4V) samples. The sensitivity ratio, defined as the ratio of the H signal to the Ti signal per unit mass ratio of H in Ti, was determined (1) with the measurements of prepared standards and (2) based on partial gamma-ray production cross sections and full-energy detection efficiencies. The resulting calibrations from these two approaches agreed within experimental uncertainty. A series of Ti alloy NIST Standard Reference Materials (SRMs) previously certified for the H content (SRMs 2452, 2453, 2453a, 2454) were used as test cases, with the mass fractions determined based on the sensitivity ratios derived from method 1 and method 2, respectively. The results agreed with the certified values within experimental uncertainties, validating the analysis performed on the new instrument with newly-prepared standards at low H mass fractions (method 1), and with the standard-independent analysis (method 2). Various sample mounting improvements were made to lower the background H signal. Spectral interferences near the H peak were identified as potential sources of bias and as a limiting factor in the detection limit of H in Ti alloy samples.
利用瞬发伽马射线活化分析（PGAA）进行低水平氢测量的准确性取决于识别和考虑所有背景 H 信号，包括干扰信号。在 NIST 中子研究中心的冷中子（CN）PGAA 设施中，针对含低水平 H（<300mgH/kgTi）的钛基基质，研究了背景 H 信号的来源，测量了制备标准（聚氯乙烯和二氧化钛混合物）和 Ti 合金（Ti6Al4V）样品。定义为单位质量比 Ti 中的 H 的 H 信号与 Ti 信号的灵敏度比，通过以下两种方法确定：（1）通过制备标准的测量，（2）基于部分伽马射线产生截面和全能量检测效率。这两种方法的校准结果在实验不确定度内一致。先前针对 H 含量（SRM 2452、2453、2453a、2454）进行认证的一系列 Ti 合金 NIST 标准参考材料（SRM）被用作测试案例，质量分数分别基于方法 1 和方法 2 得出的灵敏度比确定。结果在实验不确定度内与认证值一致，验证了在新仪器上使用新制备的低 H 质量分数标准（方法 1）和独立于标准的分析（方法 2）进行的分析。对各种样品安装进行了改进，以降低背景 H 信号。在 H 峰附近发现了光谱干扰，这些干扰被认为是产生偏差的潜在来源，也是 Ti 合金样品中 H 检测限的限制因素。
