AI 中文总结
本研究提出在真空紫外透明晶体中掺杂$^{228}$Ra，通过中子俘获及衰变原位生产$^{229m,g}$Th，明确了相关条件、最优测量参数及空间分布，为核钟技术相关研究提供了新途径。
AI 中文摘要
由于独特的核能级结构，$^{229m}$Th的低能同质异能态被广泛视为研发核钟的最具潜力候选者之一。然而，具备足够活度的合适$^{229}$Th源供应有限，仍是$^{229m}$Th同质异能态实验研究面临的主要挑战。我们提出一种基于中子俘获的原位生产$^{229m,g}$Th的方法，即将$^{228}$Ra掺杂到晶体基质中，$^{229m,g}$Th通过中子俘获反应及后续一系列放射性衰变过程生成。我们系统研究了三种掺杂晶体基质（CaF$_2$、SrF$_2$和LiF）相关的本底贡献，并评估其对$^{229m}$Th探测与鉴别的影响。在中子注量率为$10^{15}\mathrm{n/cm^{2}/s}$、$^{228}$Ra掺杂浓度为$10^{19}\mathrm{cm^{-3}}$的条件下，所提方法仅在1秒辐照时间内即可产生约$10^{12}$个$^{229}$Th和$^{229m}$Th原子核，信噪比高达$10^5$。此外，我们还系统分析了探测器波长分辨率及辐照后测量时间对$^{229m}$Th信号可探测性的影响，并确定了相应的最优测量条件。进一步研究了晶体中中子产生的$^{229}$Th的空间分布，为未来连续波真空紫外吸收光谱实验中优化晶体几何结构与辐照配置提供了实用指导。这些结果表明，所提方案为$^{229m,g}$Th的生产与探测提供了一条有前景的替代途径，有望推动基于核钟技术的未来研究。
英文摘要
The low-lying isomeric state of $^{229m}$Th, owing to its unique nuclear energy structure, has been widely regarded as one of the most promising candidates for the development of a nuclear clock. However, the limited availability of suitable $^{229}$Th sources with sufficiently high activity remains a major challenge for experimental investigations of the $^{229m}$Th isomer. We propose a neutron-capture-based approach for the in-situ production of $^{229m,g}$Th by doping $^{228}$Ra into crystal hosts, where $^{229m,g}$Th is generated through neutron-capture reactions followed by a sequence of radioactive decay processes. We systematically investigate the background contributions associated with the three doped crystal hosts, namely CaF$_2$, SrF$_2$, and LiF, and evaluate their impact on the detection and identification of $^{229m}$Th. Under a neutron flux of $10^{15}\ \mathrm{n/cm^{2}/s}$ and a $^{228}$Ra doping concentration of $10^{19}\ \mathrm{cm^{-3}}$, the proposed method is capable of producing on the order of $10^{12}$ $^{229}$Th and $^{229m}$Th nuclei within only 1 s of irradiation, with a signal-to-noise ratios as high as $10^5$. In addition, the influences of detector wavelength resolution and post-irradiation measurement time on the detectability of the $^{229m}$Th signal are systematically analyzed, and the corresponding optimal measurement conditions are identified. Furthermore, the spatial distribution of neutron-produced $^{229}$Th within the crystal is investigated, providing practical guidance for optimizing crystal geometry and illumination configuration in future continuous-wave VUV absorption spectroscopy experiments. These results suggest that the proposed scheme provides a promising alternative pathway for the production and detection of $^{229\mathrm{m,g}}$Th, which may facilitate future studies toward the realization of nuclear-clock-based technologies.
