The SNO+ experiment collected data as a low-threshold water Cherenkov detector from September 2017 to July 2019. Measurements of the 2.2-MeV s produced by neutron capture on hydrogen have been made using an Am-Be calibration source, for which a large fraction of emitted neutrons are produced simultaneously with a 4.4-MeV γ. Analysis of the delayed coincidence between the 4.4-MeV γ and the 2.2-MeV capture γ revealed a neutron detection efficiency that is centered around 50% and varies at the level of 1% across the inner region of the detector, which to our knowledge is the highest efficiency achieved among pure water Cherenkov detectors. In addition, the neutron capture time constant was measured and converted to a thermal neutron-proton capture cross section of 336.3+1.2-1.5 mb.

中文翻译：

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SNO+水相中中子-质子俘获的测量

SNO+ 实验收集了 2017 年 9 月至 2019 年 7 月作为低阈值水切伦科夫探测器的数据。 使用 Am-Be 校准源对氢中子捕获产生的 2.2-MeV s 进行了测量，其中大部分发射的中子与 4.4-MeV γ 同时产生。对 4.4-MeV γ 和 2.2-MeV 俘获 γ 之间延迟重合的分析表明，中子探测效率集中在 50% 左右，并在探测器内部区域以 1% 的水平变化，据我们所知是在纯水切伦科夫探测器中实现的最高效率。此外，测量中子俘获时间常数并将其转换为 336.3+1.2-1.5 mb 的热中子-质子俘获截面。