The nuclear half-life of ${}^{\mathrm{235m}}$U (the first metastable nuclear excited state of ²³⁵U) varies depending on chemical environments because the nucleus interacts only with outer-shell electrons in the nuclear internal conversion (IC) process due to its extremely low excitation energy at 76.737 ± 0.018 eV. Elucidating the mechanism of the half-life variation of this unique isomer would largely contribute to understanding interactions between nuclei and shell electrons. For elucidating the mechanism, we aim at measuring both half-lives and IC electron energy spectra of ${}^{\mathrm{235m}}$U in various chemical environments. In this study, we developed a retarding-field type magnetic bottle spectrometer for measuring the half-lives and energy spectra with high signal to noise ratio ($\mathrm{S}∕N$) and high energy resolution. As an evaluation of the fabricated apparatus, the collection efficiency of electrons emitted from a ${}^{\mathrm{235m}}$U sample to a channeltron electron detector was measured as a function of the strong and weak magnetic fields and the collection voltage applied to a mesh placed on the entrance of the channeltron detector. Electron collection efficiencies of almost 100% were confirmed under several conditions. Due to this high efficiency together with the low dark noise of the channeltron detector, high $\mathrm{S}∕N$ measurements have been achieved successfully. An IC-electron energy spectrum of ${}^{\mathrm{235m}}$U recorded under the most efficient condition showed an energy resolution ($\Delta E∕E$) of $\sim$2%, which is sufficiently high to observe small peak shifts and splittings in the IC-electron energy spectra of ${}^{\mathrm{235m}}$U compounds. This developed apparatus allows high precision measurements of half-lives and IC-electron energy spectra of ${}^{\mathrm{235m}}$U in various chemical environments even with small amount of ${}^{\mathrm{235m}}$U and low emission rate of IC electrons.

核的半衰期 ${}^{\mathrm{235m}}$U（²³⁵ U的第一个亚稳态核激发态 ）因化学环境而异，因为在76.737±0.018 eV的极低激发能下，核仅在核内部转换（IC）过程中与外壳电子相互作用。阐明这种独特异构体半衰期变化的机理将极大地有助于理解核与壳电子之间的相互作用。为了阐明机理，我们旨在测量半衰期和IC电子能谱。${}^{\mathrm{235m}}$在各种化学环境中的U。在这项研究中，我们开发了一种延迟场型磁瓶光谱仪，用于测量具有高信噪比的半衰期和能谱（$\mathrm{小号}∕ñ$）和高能量分辨率。作为对制成设备的评估，从电子发射器收集的电子的收集效率${}^{\mathrm{235m}}$根据强磁场和弱磁场以及施加到放置在通道加速器探测器入口处的网格上的收集电压来测量通道加速器电子探测器的U样品。在几种条件下，电子收集效率几乎达到了100％。由于这种高效率以及通道加速探测器的低暗噪声，因此$\mathrm{小号}∕ñ$测量已成功完成。的IC电子能谱${}^{\mathrm{235m}}$在最有效的条件下记录的U表示能量分辨率（$\Delta Ë∕Ë$的） $〜$2％，这足以观察到IC的IC电子能谱中的小峰移动和分裂 ${}^{\mathrm{235m}}$U化合物。这种发达的仪器可以高精度地测量半衰期和IC电子能谱${}^{\mathrm{235m}}$在各种化学环境中的U含量即使很小 ${}^{\mathrm{235m}}$U和IC电子的低发射率。