Toward an energy measurement of the internal conversion electron in the deexcitation of the 229Th isomer
Toward an energy measurement of the internal conversion electron in the deexcitation of the 229Th isomer
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229Th 异构体去激发中内转换电子的能量测量
DOI：
10.1103/physrevc.98.014317
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
and T. Schumm (*co-first authors)
中科院分区：
文献类型：
--
作者：
S. Stellmer*;Y. Shigekawa*;V. Rosecker;G. A. Kazakov;Y. Kasamatsu;Y. Yasuda;A. Shinohara;and T. Schumm (*co-first authors)
Th-229的第一激发异构态具有非常低的能量，只有几个eV，可以形成高精度原子核激光光谱学的门户。从精密光谱学中已经推导出了同分异构态的激发能，但它的不确定性仍然太大，不能用于激光光谱学。减少这种不确定性是该领域最紧迫的挑战之一。在这里，我们提出了一种方法来推断能量的异构体从光谱的电子发射时，异构体通过内部转换（IC）去激发。该实验建立在U-233上，其衰变为Th-229，并以2%的分支比填充异构态。在探测器和电子探测器之间放置一层厚度为几nm的U-233膜，使粒子和IC电子能同时被探测到。减速场电极允许能量测量。在本设计中，Th-229 m IC电子的信号被从金属停止层的表面发射的低能电子掩蔽。我们用U-232和U-234进行参考测量，以研究系统效应，并研究各种方法来减少低能电子的背景。我们的研究提供了指导方针的实验设计，是能够检测IC电子和测量异构体的能量。
The first excited isomeric state of Th-229 has an exceptionally low energy of only a few eV and could form the gateway to high-precision laser spectroscopy of nuclei. The excitation energy of the isomeric state has been inferred from precisionspectroscopy, but its uncertainty is still too large to commence laser spectroscopy. Reducing this uncertainty is one of the most pressing challenges in the field. Here we present an approach to infer the energy of the isomer from spectroscopy of the electron which is emitted when the isomer de-excites through internal conversion (IC). The experiment builds on U-233, which-decays to Th-229 and populates the isomeric state with a 2% branching ratio. A film of U-233 is covered by a stopping layer of few-nm thickness and placed between andetector and an electron detector, such that theparticle and the IC electron can be detected in coincidence. Retarding field electrodes allow for an energy measurement. In the present design, the signal of the Th-229m IC electrons is masked by low-energy electrons emitted from the surface of the metallic stopping layer. We perform reference measurements with U-232 and U-234 to study systematic effects, and we study various means to reduce the background of low-energy electrons. Our study gives guidelines to the design of an experiment that is capable of detecting the IC electrons and measuring the isomer energy.