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Measuring the Th-229 isomer energy with a microcalorimeter

用微量热计测量 Th-229 异构体能量

基本信息

批准号：
252104822
负责人：
Dr. Andreas Fleischmann
金额：
--
依托单位：
Atominstitut
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/252104822?language=en
关键词：
Measuring Th 229 isomer energy

项目摘要

The nuclear level scheme of the Thorium-229 isotope is expected to feature a long-lived isomer state, extremely close to the nuclear ground state. The corrently most accepted Isomer energy value is 7.8 eV, corresponding to a wavelength of 160 nm. Probably the lowest excited nuclear state of all isotopes, this Th-229 isomer could be accessible to laser manipulation, creating an exciting link between atomic and nuclear physics. However, there is yet no unambiguous proof of the existence of this state, and the exact isomer energy remains elusive.Progress in determining the isomer energy is triggered by advances in gamma detector technology. All available experimental data relies on measuring higher levels of the Th-229 nuclear structure in the 10-1000 keV regime, excited in the alpha decay of Uranium-233. The isomer energy on the eV level is then determined indirectly by substracting gamma energies corresponding to decay paths into the ground and isomer state respectively. Measuring high energies to derive a small difference obviously leads to large errors. Furthermore, some of the details of the decay paths (interband transitions) could not yet be resolved, so theoretical asumptions for specific branching ratios enter the energy determination, which is hence heavily disputed.Here we propose to use a state-of-the-art magnetic microcalorimeter to resolve the 29.19 keV doublet of Th229, that only has a direct decay path into either the ground, or the isomer state. Resolving this doublet will provide ultimate proof for the existence and measure the isomer energy without involving further assumptions and with an accuracy, that will enable direct laser spectroscopy investigations.The project will be carried out as an international collaboration between the Vienna University of Technology (project leader) and the University of Heidelberg. The Vienna team will produce and characterize the U-233 samples at the Institute for Atomic and Subatomic Physics, assist in the measuremens in Heidelberg, and perform the data analysis. The Heidelberg team will provide the cryogenic microcalorimeter, optimize it for the project described here, and perform the measurement. As the project partners have demonstrated in a joint feasability study arXiv:1306.3069, the measurment can be successful with the already available detector technology, however an even more dedicated detector is currently under development. Combining the expertise and equipment available in Vienna and Heidelberg, the measurement can be performed in only 18 months and very little additional resources.

钍-229同位素的核能级图预计具有长寿命的异构体状态，非常接近核基态。目前最被接受的异构体能量值是7.8 eV，对应于160 nm的波长。可能是所有同位素中最低的激发态，这种Th-229异构体可以进行激光操作，在原子物理和核物理之间建立了令人兴奋的联系。然而，目前还没有明确的证据证明这种状态的存在，而且确切的异构体能量仍然难以捉摸。确定异构体能量的进展是由伽马探测器技术的进步引发的。所有可用的实验数据都依赖于在10 - 1000 keV范围内测量更高水平的Th-229核结构，在铀-233的α衰变中激发。eV能级上的异构体能量则通过减去对应于分别进入基态和异构体态的衰变路径的伽马能量来间接确定。测量高能量以获得小的差异显然会导致大的误差。此外，衰变路径（带间跃迁）的一些细节尚未得到解决，因此对特定分支比的理论假设进入了能量确定，因此存在很大争议。在这里，我们建议使用最先进的磁性微量热计来解析Th 229的29.19 keV双重态，它只有一条直接衰变路径进入基态或异构体状态。解决这一双重态将提供存在的最终证据，并在不涉及进一步假设的情况下精确测量异构体能量，这将使直接的激光光谱研究成为可能。该项目将作为维也纳理工大学（项目领导者）和海德堡大学之间的国际合作进行。维也纳小组将在原子和亚原子物理研究所制作铀233样品并确定其特性，协助海德堡的测量工作，并进行数据分析。海德堡团队将提供低温微量热计，为这里描述的项目进行优化，并进行测量。正如项目合作伙伴在一项联合可行性研究arXiv：1306.3069中所证明的那样，使用现有的探测器技术可以成功进行测量，但目前正在开发一种更专用的探测器。结合维也纳和海德堡的专业知识和设备，只需18个月就可以完成测量，而且额外资源很少。