【摘要】 在¹⁹⁷Au（n, 2n）¹⁹⁶Au和⁴⁵Sc（n, 2n）⁴⁴Sc^m的中子谱平均截面测量中，¹⁹⁶Au和⁴⁴Sc^m活度低、半衰期短，受其（n,γ）活化产物干扰严重。为准确测量¹⁹⁶Au和⁴⁴Sc^m,放射性活度测量装置基于反符合原理采取了以下技术措施：首先，使用液闪测量体系探测¹⁹⁸Au和⁴⁶Sc衰变发射的β^-射线，利用β^-射线反符合抑制康普顿本底；其次，使用环形NaI晶体构建便携式的反康普顿谱仪，利用反康普顿原理抑制康普顿本底。该活度测量装置利用数字谱仪将上述两套反符合系统融合为一，取得了良好实验效果。对¹⁹⁶Au和⁴⁴Sc^m的MDA分别降低到原来的16.7%和36%,在0.2 MBq ¹⁹⁸Au和⁴⁶Sc的同位素强干扰条件下，MDA分别小于0.7 Bq和0.3 Bq。更多还原

【Abstract】 In the spectral mean cross section measurements of ¹⁹⁷Au（n, 2 n）¹⁹⁶Au and ⁴⁵Sc（n, 2 n）⁴⁴Sc^m, the activation products ¹⁹⁶Au and ⁴⁴Sc^m have low activity and shorter half-life, but the activation products ¹⁹⁸Au and ⁴⁶Sc from neutron capture reactions of ¹⁹⁷Au（n, g） and ⁴⁵Sc（n, g） have strong activity and longer half-life, which results in poor signal-to-noise ratio of gamma-ray characteristic peaks, and increases the measuring uncertainty of ¹⁹⁶Au and ⁴⁴Sc^m activity. In order to accurately measure ¹⁹⁶Au and ⁴⁴Sc^m, a radioactive activity measuring device based on anti-coincidence principle was developed. The main techniques used were as follows: Firstly, liquid flash measurement system has been used to detect the beta-ray emitted by the decay of ¹⁹⁸Au and ⁴⁶Sc, basing on the anti-coincidence principle, the beta-ray would be used to suppress Compton background caused by gamma-rays emitted by the two nuclides above; Secondly, a portable anti-Compton spectrometer has been constructed using a ring sodium iodide crystal, and the Compton background caused by the decay of ¹⁹⁸Au and ⁴⁶Sc has been further suppressed by the anti-Compton principle. Thirdly, a thin layer of lead shield has been placed between the radioactive source distributed evenly in the liquid scintillation and a well-shaped high purity germanium（HPGe） crystal to absorb the X-rays emitted by the decay of the ¹⁹⁶Au, as results, the coincidence between the X-rays and the characteristic gamma-rays emitted by ¹⁹⁶Au in the HPGe crystal reduces significantly, and the detection efficiency of this measurement device for ¹⁹⁶Au increases too. By using the digital spectrometer, the liquid flash measurement system and the anti-Compton spectrometer integrated into one, the anti-coincidence effect could be superimposed and good experimental results were obtained. For ¹⁹⁸Au and ⁴⁶Sc, the anti-coincidence inhibition ratio is 87.1% and 86.9% respectively. The detection efficiency for ⁴⁴Sc^m is 31.3%. After increasing the shielding layer, the detection efficiency for ¹⁹⁶Au increases greatly, from 5.5% when the shielding layer is not available up to 11.9%. Under the condition of strong isotope interference(¹⁹⁸Au or ⁴⁶Sc of 0.2 MBq), the minimum detectable activity（MDA） of 24 h detecting to ¹⁹⁶Au is less than 0.7 Bq, and to ⁴⁴Sc^m is less than 0.3 Bq. Applying the double anti-coincidence measuring device established in this paper to the activity measurement of ¹⁹⁶Au and ⁴⁴Sc^m could effectively reduce the uncertainty of ¹⁹⁷Au（n, 2 n）¹⁹⁶Au and ⁴⁵Sc（n, 2 n）⁴⁴Sc^m average cross-section measurement.更多还原