A widely applied technical measure of nuclear safeguards and nonproliferation for the nondestructive verification and mass-assay of items containing separated plutonium is passive neutron multiplicity counting. The primary source of time correlated passive neutrons is the spontaneous fission of Pu, where the ²⁴⁰Pu is usually the dominant isotope with ²³⁸Pu and ²⁴²Pu also contributing to a degree depending on the grade or burnup of the material. Consequently, knowledge of the ²⁴⁰Pu spontaneous fission rate, expressed as fission per gram per second, and the associated uncertainty is key in interpreting measurement data absolutely. The ²⁴⁰Pu spontaneous fission rate derives (and vice versa) from the ²⁴⁰Pu spontaneous fission half-life. In this work we review and reevaluate the available experimental data on the spontaneous fission (SF) half-life of the Pu isotopes ²³⁸Pu, ²⁴⁰Pu and ²⁴²Pu. The SF half-lives are used to compute the corresponding specific SF rates which are the traditional nuclear data parameters needed for analytical applications, especially the nondestructive assay of plutonium for safety, security and safeguards.

From 7 measurements we recommend a SF half-life of (4.745 ± 0.083) × 10¹⁰ y for ²³⁸Pu corresponding to a specific SF rate of (1171 ± 20) fis ⋅ s^-1 ⋅ g^-1.

There are 16 absolute experimental determinations of ²⁴⁰Pu half-life. Based on this evaluation, we find that the weighted mean of the 16 half-life determinations is (1.1608 ± 0.0091) × 10¹¹ y corresponding to a specific SF rate of (474.7 ± 3.7) fis ⋅ s⁻¹ ⋅ g⁻¹, where the relative uncertainty of about 0.78% is the external standard error.

From 8 measurements we recommend a SF half-life of (6.766 ± 0.037) × 10¹⁰ y for ²⁴²Pu corresponding to a specific SF rate of (807.7 ± 4.4) fis ⋅ s⁻¹ ⋅ g⁻¹. Finally, we conclude that there is a need for more experiments on all three plutonium nuclides using new techniques that have emerged in recent years.

一种广泛应用的核保障和防扩散技术措施，用于对含有分离钚的物品进行无损核查和质量分析，是被动中子多重计数。与时间相关的被动中子的主要来源是 Pu 的自发裂变，其中²⁴⁰ Pu 通常是主要同位素，²³⁸ Pu 和²⁴² Pu 的贡献程度也取决于材料的等级或燃耗。因此，了解²⁴⁰ Pu 自发裂变率（表示为每秒每克裂变）以及相关的不确定性是绝对解释测量数据的关键。在^240个从普自发裂变率导出（反之亦然）²⁴⁰ Pu 自发裂变半衰期。在这项工作中，我们审查并重新评估了关于 Pu 同位素²³⁸ Pu、²⁴⁰ Pu 和²⁴² Pu的自发裂变 (SF) 半衰期的可用实验数据。SF 半衰期用于计算相应的特定 SF 率，这是分析应用所需的传统核数据参数，尤其是用于安全、安保和保障的钚无损分析。

从 7 次测量中，我们建议²³⁸ Pu的 SF 半衰期为 (4.745 ± 0.083) × 10 ¹⁰ y，对应于 (1171 ± 20) fis ⋅ s ^-1 ⋅ g ^-1的特定 SF 率。

²⁴⁰ Pu 半衰期有 16 个绝对实验测定值。基于此评估，我们发现 16 个半衰期测定的加权平均值为 (1.1608 ± 0.0091) × 10 ¹¹ y，对应于 (474.7 ± 3.7) fis ⋅ s ^-1 ⋅ g ^-1的特定 SF 率，其中约 0.78% 的相对不确定度是外部标准误差。

从 8 次测量中，我们建议²⁴² Pu的 SF 半衰期为 (6.766 ± 0.037) × 10 ¹⁰ y，对应于 (807.7 ± 4.4) fis ⋅ s ^-1 ⋅ g ^-1的特定 SF 率。最后，我们得出结论，需要使用近年来出现的新技术对所有三种钚核素进行更多实验。