239 Pu中391.6 keV亚稳能级half-life的高精度测量
High precision measurement of the half-life of the 391.6 keV metastable level in 239Pu
摘要：
稀有事件物理学的材料选择需要高性能的探测器和定制的分析。在这种情况下，一种新的$β$ - $γ$检测系统，包括符合HPGe的液体闪烁体，开发的主要目的是研究超痕量铀，钍和钾的液体样品中的污染。在通过中子活化分析寻找$^{238}\textrm{U}$污染物时，由于活化产物$^{239}\textrm{Np}$衰变为相对长寿命的同分异构态$^{239}\textrm{Pu}$，因此可以对这些事件进行时间选择，从而获得强的背景抑制。研究了$^{239}\textrm{Np}$的$β^-$衰变与$^{239}\textrm{Pu}$同分异构能级在391.6 keV处去激发后的延迟事件之间符合的时间分布，对该能级的半衰期进行了精确测量。391.6 keV $^{239}\textrm{Pu}$能级的半衰期导致$190.2 \pm 0.2$ ns，从而使精度比以前的测量提高约20倍。
英文摘要：
Materials selection for rare event physics requires high performance detectors and customized analyses. In this context a novel $β$-$γ$ detection system, comprised of a liquid scintillator in coincidence with a HPGe, was developed with the main purpose of studying ultra trace contamination of uranium, thorium and potassium in liquid samples. In the search for $^{238}\textrm{U}$ contaminations through neutron activation analysis, since the activation product $^{239}\textrm{Np}$ decays to a relatively long-lived isomeric state of $^{239}\textrm{Pu}$, it is possible to perform a time selection of these events obtaining a strong background suppression. Investigating the time distribution of the coincidences between the $β^-$ decay of $^{239}\textrm{Np}$ and the delayed events following the de-excitation of the $^{239}\textrm{Pu}$ isomeric level at 391.6 keV, a precision measurement of the half-life of this level was conducted. The half-life of the 391.6 keV $^{239}\textrm{Pu}$ level resulted $190.2 \pm 0.2$ ns, thus increasing the precision by about a factor of 20 over previous measurements.
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