We present a new analysis of the sensitivity of a water Cherenkov-based neutron multiplicity counter for nondestructive assay of trace quantities of ²⁴⁰Pu. The multiplicity counter [water-based neutron detector (WaND)] contains 1.0 m³ of water doped with 0.2% gadolinium in the form of a gadolinium salt (0.4% GdCl₃). It can be used for testing the presence of trace quantities of ²⁴⁰Pu within a sample of unknown material by observing the correlated timing behavior of neutron capture candidates in the detector. The new analysis takes advantage of the fact that the detector is comprised almost entirely of a homogeneous medium, which permits the use of a simple model to reproduce the observed neutron capture timing behavior. The results of this analysis indicate that the detector has an absolute neutron detection efficiency of 23.4 ± 1.1% and is sensitive to a ²⁴⁰Pu mass as small as 2.3 mg (at $1\sigma $ ) after a 1-h data acquisition.

中文翻译：

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使用基于切伦科夫的中子多重水探测器进行钚质量不确定性评估

我们对基于水切伦科夫的中子多重性计数器的灵敏度进行了新的分析，用于对痕量²⁴⁰ Pu进行无损检测。多重计数器 [水基中子探测器 (WaND)] 包含 1.0 m ³的水，其中掺杂了 0.2% 钆盐形式的钆 (0.4% GdCl ₃ )。可用于检测痕量²⁴⁰通过观察探测器中中子捕获候选物的相关计时行为，在未知材料样品中的 Pu。新的分析利用了探测器几乎完全由均质介质组成的事实，这允许使用简单的模型来重现观察到的中子捕获定时行为。该分析的结果表明，该检测器具有23.4±1.1％的绝对中子检测效率，并且是一个敏感^240个莆质量小至2.3毫克（在 $1\西格玛$ ) 1 小时数据采集后。