The present evaluation of currently known nine nuclides of A=231: (²³¹Rn, ²³³Fr, ²³¹Ra, ²³¹Ac, ²³¹Th, ²³¹Pa, ²³¹U, ²³¹Np and ²³¹Pu) represents an update and revision of previous A=231 evaluation by 2013Br04. All the known decay and reaction data are evaluated, with recommended properties given in the Adopted Levels, Gammas datasets, for gamma-ray energies, photon branching ratios, level half-lives, spins, parities, transition probabilities, and configuration assignments. For ²³¹Rn, only an identification of the nuclide has been made without an experimental determination of its half-life. For ²³¹Fr, no excited states are known. About 30 levels in ²³¹Ra up to 1774 keV excitation are known only from β⁻ decay of ²³¹Fr with level half-lives determined for five excited states. For ²³¹Ac, excited states up to 3122 keV are known from β⁻ decay, (t,α), and fragmentary information for high-spin levels from two heavy-ion reaction studies, with lifetimes of excited states measured for five levels. Extensive structure and rotational band information for ²³¹Th is available for a large number of levels up to 1714 keV from β⁻ and α decays, (n,γ) thermal and resonance, single-particle transfer reactions (d,p), (d,t) and (³He,α), with limited data for high-spin levels from one secondary reference, and half-lives available for five excited states. Very detailed structure data are available for ²³¹Pa up to 2139 keV from β⁻, ε and α decays, (α,t), (d,d′) and high-spin data from heavy-ion Coulomb excitation and (p,2nγ) reaction, with level half-lives known for 34 excited states, mostly deduced by evaluators from transition probabilities determined in Coulomb excitation. Only eight excited states are known in ²³¹U up to 1268 keV from ε and α decays, with no data for half-lives of excited states. For ²³¹Np and ²³¹Pu, only the ground-state is known from α decays, with a tentative level at 324 keV in ²³¹Pu. Measurements of nuclear rms charge radius and isotope shifts for ²³¹Ra have been made by 2018Ly01, and that for rms charge radius for ²³¹Fr by 2014Bu06.

²³⁵U is a well known nuclide for nuclear structure and reactor applications. There have been a large number of studies of its alpha decay to levels in ²³¹Th, including some recent ones such as 2018Ma03 and 2017Le03, yet evaluators' analysis of the decay scheme suggests that, while α-particle transitions are well established, but several issues still remain about intricacies of gamma-ray and conversion electron spectroscopy which need to be resolved through dedicated experiments for a complete understanding of the decay scheme characteristics, although, this sort of research project would seem a challenging spectroscopic problem. As commented in individual datasets for other decays, important spectral information is lacking for most of the decay schemes, with almost no information available for some of these, resulting in many incomplete decay schemes in A=231 mass chain.

目前已知的 A=231 的九种核素的当前评估：（²³¹ Rn、²³³ Fr、²³¹ Ra、²³¹ Ac、²³¹ Th、²³¹ Pa、²³¹ U、²³¹ Np 和²³¹ Pu）代表了对先前 A= 的更新和修订2013Br04 之前的 231 次评估。评估所有已知的衰变和反应数据，并在采用的能级、伽马数据集中给出推荐的属性，用于伽马射线能量、光子分支比、能级半衰期、自旋、奇偶校验、跃迁概率和配置分配。对于²³¹Rn，仅对核素进行了鉴定，而没有对其半衰期进行实验测定。对于²³¹ Fr，没有已知的激发态。^在231 Ra 到 1774 keV 激发中大约 30 个能级仅从^{231 Fr 的}β ^-衰变已知，其中能级半衰期确定为五个激发态。对于^{231 Ac，从}β ^-衰变 (t, α ) 和来自两个重离子反应研究的高自旋能级的零碎信息已知高达 3122 keV的激发态，并测量了五个能级的激发态寿命。²³¹的广泛结构和旋转带信息Th 可用于从β ^-和α衰变、(n, γ ) 热和共振、单粒子转移反应 (d,p)、(d,t) 和 ( ³ He, α )，来自一个二级参考的高自旋能级数据有限，并且可用于五个激发态的半衰期。非常详细的结构数据可用于²³¹ Pa 至 2139 keV，来自β ^-、ε和α衰变、( α ,t)、(d,d') 以及来自重离子库仑激发和 (p,2n) 的高自旋数据γ) 反应，已知 34 种激发态的水平半衰期，主要由评估者从库仑激发中确定的跃迁概率推导出来。^在231 U 到 1268 keV 的ε和α衰变中，仅已知 8 个激发态，没有激发态半衰期的数据。对于²³¹ Np 和²³¹ Pu，仅从α衰变已知基态，在²³¹ Pu中的暂定水平为 324 keV 。到 2018 年 Ly01 已经测量了²³¹ Ra的核 rms 电荷半径和同位素位移，到 2014 年 Bu06 测量了²³¹ Fr 的 rms 电荷半径。

²³⁵ U 是用于核结构和反应堆应用的众所周知的核素。已经有大量关于其 α 衰变到²³¹ Th 水平的研究，包括最近的一些研究，例如 2018Ma03 和 2017Le03，但评估人员对衰变方案的分析表明，虽然α- 粒子跃迁已经确立，但是关于伽马射线和转换电子能谱的复杂性仍然存在一些问题，需要通过专门的实验来解决，以便全面了解衰变方案的特征，尽管这种研究项目似乎是一个具有挑战性的光谱问题。正如在其他衰变的单个数据集中所评论的那样，大多数衰变方案都缺乏重要的光谱信息，其中一些几乎没有可用的信息，导致 A=231 质量链中的许多不完整衰变方案。