Nuclear Disintegration and Inner-Shell Atomic Processes in Heavy Elements

原子中的电子与原子核之间的高阶相互作用可以影响原子核的跃迁和衰变。这些效应包括通过电子桥机制（EBM）的γ射线发射、电子跃迁的核激发（NEET）和逆内转换。该项目的目标是建立核原子光谱学。为了实现这一目标，我们开展了以下几个方面的工作：1）发展核-原子光谱实验技术; 2）研究^ U、^ Th等的原子过程与低能核跃迁之间的相互作用<235><229>; 3）积累由核跃迁引起的内壳层原子过程的基础数据<229m><229m>。进行了以下实验：a）由宽型Ge探测器（由基金提供）和Si带电粒子探测器组成的测量系统的构建，用于α-γ和X-γ符合测量。B）多参数数据采集的电子设备和软件的准备。c）测量^ Th和^ U的α-γ符合谱<229><233>。d）测量<229m>由纯^ U提取的^ Th<233>的光子。我们试图<229m>从用冷却光电倍增管测量的光子强度的时间依赖性中提取^ Th的衰变。（<229m>5）对^ Th的α衰变的观测<229m>：在^ Th（γ，n）^ Th产生的α谱中，我们观测到一个半衰期很短的衰变组分，约为14小时<229><230><229>。该成分可能归因于^ Th的衰变<229m>。我们正在计划对不同化学形式的Th进行类似的测量。

Higher-order interactions between electrons in an atom and its nucleus can affect the nuclear transition and disintegration. Such effects involve γ-ray emission via electronic bridge mechanism (EBM), nuclear excitation by electron transition (NEET), and inverse internal conversion. The goal of this project is to establish nuclear-atomic spectroscopy. We took up the following sub-themes to reach the goal :1) Development of experimental techniques for nuclear-atomic spectroscopy.2) Investigation of interactions between atomic processes and low energy nuclear transitions in ^<235>U, ^<229>Th, and so on.3) Accumulation of fundamental data on inner-shell atomic processes caused by nuclear transitions.The nucleus ^<229m>Th is the best candidate to study EBM, because the extremely low excitation energy of 3.5eV cannot be released by emission of an internal conversion electron. In the period of this fund, therefore, we focused on the decay properties of ^<229m>Th. The following experiments were carried out :a) Construction of a measuring system composed of a broad-type Ge detector (supplied by the funds) and a Si charged-particle detector for α-γ and X-γ coincidence measurements.b) Preparation of electronics and software for multi-parameter data taking.c) Measurements of α-γ coincidence spectra for ^<229>Th and ^<233>U.d) Measurements of photons from ^<229m>Th prepared by milking pure ^<233>U.We tried to extract the decay of ^<229m>Th from the time dependence of the intensity of photons measured with a cooled photomultiplier. At present, there is no evidence of having detected the decay photons from ^<229m>Th.e) Observation of the α-decay of ^<229m>Th.We observed a decay component with a short half-life of about 14h in the α spectrum of ^<229>Th produced by ^<230>Th (γ, n)^<229>Th. This component may be attributed to the decay of ^<229m>Th. We are planing similar measurements for different chemical forms of Th.