Seiferle Benedict, von der Wense Lars, Thirolf Peter G
Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching bei München, Germany.
Phys Rev Lett. 2017 Jan 27;118(4):042501. doi: 10.1103/PhysRevLett.118.042501. Epub 2017 Jan 26.
The first excited isomeric state of ^{229}Th possesses the lowest energy among all known excited nuclear states. The expected energy is accessible with today's laser technology and in principle allows for a direct optical laser excitation of the nucleus. The isomer decays via three channels to its ground state (internal conversion, γ decay, and bound internal conversion), whose strengths depend on the charge state of ^{229m}Th. We report on the measurement of the internal-conversion decay half-life of neutral ^{229m}Th. A half-life of 7±1 μs has been measured, which is in the range of theoretical predictions and, based on the theoretically expected lifetime of ≈10^{4} s of the photonic decay channel, gives further support for an internal conversion coefficient of ≈10^{9}, thus constraining the strength of a radiative branch in the presence of internal conversion.
钍-229的第一激发异构态在所有已知的激发核态中能量最低。利用当今的激光技术可以获得预期的能量，并且原则上允许对原子核进行直接光学激光激发。该异构体通过三种通道衰变为基态（内转换、γ衰变和束缚内转换），其强度取决于钍-229m的电荷态。我们报告了中性钍-229m内转换衰变半衰期的测量结果。测量得到的半衰期为7±1微秒，这在理论预测范围内，并且基于光子衰变通道理论预期寿命约为10⁴秒，进一步支持了约10⁹的内转换系数，从而限制了存在内转换时辐射分支的强度。
