Sikorsky Tomas, Geist Jeschua, Hengstler Daniel, Kempf Sebastian, Gastaldo Loredana, Enss Christian, Mokry Christoph, Runke Jörg, Düllmann Christoph E, Wobrauschek Peter, Beeks Kjeld, Rosecker Veronika, Sterba Johannes H, Kazakov Georgy, Schumm Thorsten, Fleischmann Andreas
Kirchhoff-Institute for Physics, Heidelberg University, INF 227, 69120 Heidelberg, Germany.
Institute for Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
Phys Rev Lett. 2020 Oct 2;125(14):142503. doi: 10.1103/PhysRevLett.125.142503.
We present a measurement of the low-energy (0-60 keV) γ-ray spectrum produced in the α decay of ^{233}U using a dedicated cryogenic magnetic microcalorimeter. The energy resolution of ∼10 eV, together with exceptional gain linearity, allows us to determine the energy of the low-lying isomeric state in ^{229}Th using four complementary evaluation schemes. The most precise scheme determines the ^{229}Th isomer energy to be 8.10(17) eV, corresponding to 153.1(32) nm, superseding in precision previous values based on γ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be b_{29}=9.3(6)% and b_{42}<0.7%.
我们展示了使用专用低温磁微热量计对(^{233}U)的α衰变中产生的低能（0 - 60 keV）γ射线谱进行的测量。约10 eV的能量分辨率以及出色的增益线性度，使我们能够使用四种互补的评估方案来确定(^{229}Th)中低激发同质异能态的能量。最精确的方案确定(^{229}Th)同质异能态能量为8.10(17) eV，对应于153.1(32) nm，在精度上超过了先前基于γ光谱学的值，并且与最近基于内转换电子的测量结果一致。我们还测量了相关激发态的分支比，(b_{29}=9.3(6)%)且(b_{42}<0.7%)。
