Improved Determination of the Neutron Lifetime
Improved Determination of the Neutron Lifetime
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DOI：
10.1103/physrevlett.111.222501
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发表时间：
2013-11-27
影响因子：
8.6
通讯作者：
Wietfeldt, F. E.
中科院分区：
文献类型：
--
作者：
Yue, A. T.;Dewey, M. S.;Wietfeldt, F. E.
使用束法对中子寿命的最精确测定是在2005年完成的，并报告了tau(n) = 886.3 +/- 1.2 [stat] +/- 3.2 [system]) s的结果。主要的不确定性归因于中子束的绝对通量测定（2.7 s）。通量是用中子监测器测量的，该监测器计算了在薄的、特征良好的锂-6沉积物中吸收的中子诱导带电粒子。根据沉积物的面密度、探测器的立体角和评估的核数据文件ENDF/B-VI Li-6(n,t)(4) He热中子截面计算监测器的探测效率。在目前的工作中，我们用第二个全吸收中子探测器来测量中子寿命测量中使用的相同监测器的探测效率。这种直接的方法不依赖于Li-6(n, t)(4)；他的横截面或任何其他核数据。检测效率与2005年使用的值一致，但测量精度为0.057%，不确定度提高了五倍。我们通过辅助测量验证了中子监测器的时间稳定性，使我们能够将测量到的中子监测器效率应用于2005年实验的寿命结果。更新后的生存期为tau n = d887: 7 +/- 1.2 stat +/- 1:9 [(system]) s。
The most precise determination of the neutron lifetime using the beam method was completed in 2005 and reported a result of tau(n) = 886.3 +/- 1.2 [stat] +/- 3.2 [syst]) s. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was measured with a neutron monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized Li-6 deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the evaluated nuclear data file, ENDF/B-VI Li-6(n,t)(4) He thermal neutron cross section. In the current work, we measure the detection efficiency of the same monitor used in the neutron lifetime measurement with a second, totally absorbing neutron detector. This direct approach does not rely on the Li-6(n, t)(4); He cross section or any other nuclear data. The detection efficiency is consistent with the value used in 2005 but is measured with a precision of 0.057%, which represents a fivefold improvement in the uncertainty. We verify the temporal stability of the neutron monitor through ancillary measurements, allowing us to apply the measured neutron monitor efficiency to the lifetime result from the 2005 experiment. The updated lifetime is tau n = d887: 7 +/- 1.2 stat +/- 1: 9[(syst]) s.