Nuclear Laser Spectroscopy of Be Isotopes with Ion-trap

本研究项目旨在发展一种实验方法，对不稳定Be同位素进行核激光光谱分析。原子超精细相互作用中的超精细耦合常数A表现出一种微弱但有限的同位素依赖性，称为超精细异常，其主要原因是核内磁化分布的有限大小（Bohr-Weisskopf效应）。这种效应为价中子在原子核中的分布提供了一种独特而有趣的探测，特别是在所谓的中子晕核中，如be - 1。利用被困在弱磁场下的线性稀土捕集器中的Be-9的稳定同位素，对实验技术进行了各种发展。采用激光和微波连续照射的方法，实现了微波共振的高灵敏度检测。在几秒钟的测量中，观察到高信噪比共振信号。采用脉冲法进行了高精度测量。通过重复激光和微波交替辐照的短周期（几英寸），获得了2* 10 -7的相当高的精度。研究Be-7第一个不稳定同位素的试验实验已经进行了，但是到目前为止还没有观察到荧光信号。这种困难被认为是由于在共振波长方面的知识的运气，以及陷阱中be -7离子的数量是关键的事实。在比同位素位移的理论计算和提高Be-7离子在阱中的密度的实验技术方面，各种改进正在进行中。对于寿命较短的同位素，如Be-ll，利用新提出的re -离子引导技术，一种从碎片同位素分离器中捕获高能光束的在线捕获方法也在开发中。

This research project aimed at developing an experimental method to perform nuclear laser spectroscopy of unstable Be isotopes. The hyperfine coupling constant A in the atomic hyperfine interaction shows a weak but finite isotope dependence called hyperfine anomaly, the main part of which stems from the finite size of the magnetization distribution in the nucleus (Bohr-Weisskopf effect). This effect affords a unique and interesting probe for valence neutron distribution in a nucleus, particularly in a so-called neutron halo nucleus such as Be-ll.Various developments for the experimental technique have been carried out using the stable isotope of Be-9 trapped in a linear RE trap placed at a weak magnetic field. High sensitive detection of microwave-resonance was demonstrated using continuous irradiation method where laser and microwave radiations were continuously applied. A high S/N resonance signal was observed with in a few seconds of measurement. A high precision measurement was also tested using a pulsed method. By repeating the short cycle (a few ins) of alternative irradiation of laser and microwave radiation, reasonably high accuracy of 2*1O-7 was obtained.Trial experiments for investigating the first unstable isotope of Be-7 have been carried out, however, no fluorescence signal was observed so far. The difficulty is considered to be due to the luck of knowledge in the resonant wave-length and to the fact that the number of Be-7 ions in the trap are critical. Various kind of improvements in the theoretical calculation of the specific isotope shift as well as in the experimental technique to increase the density of Be-7 ions in the trap are under progress.For shorter lifetime isotopes, such as Be-ll, an on-line trapping method for energetic beams from a fragment isotope separator is also under development using a newly proposed RE-ionguide technique.