Spectroscopy of the Proton Rich Nuclei by the use of Secondary Beams and Direct Observation of Giant M1 Resonance

我们之前已经在大阪大学核物理研究中心成功地调试了反冲分离器CARAP。该装置使我们能够对核反应产物进行质量分离，并以二次束的形式将它们运送到探测位置。考虑到使用分离器的优点，本研究的目的是精确测量SD壳层中丰质子T_z=-3/2和-2的Gamow-Teller(GT)β跃迁率。这是为了加深对巨型M1共振猝灭机制的理解，通过详细比较远离β稳定线的大范围核的GT强度，促进对巨型M1共振猝灭机制的深入理解。在研究的早期阶段，重点是实现反应产物的反冲分离器的大立体角，并建立对β射线及其伴随的辐射和产物的衰变高度敏感但对外部背景辐射不敏感的探测器系统。考虑到T_z=-3/2核的产生截面较大，第一个实验确定在^&lt；13&gt；O，^&lt；25&gt；Si，^&lt；21&gt；S，^&lt；37&gt；Ca和^&lt；41&gt；Ti上进行。到编写本报告时，我们已经成功地完成了对所有这些T_z=-3/2核的测量。对^&lt；25&gt；Si进行了数据分析，确定了GT强度的淬火因子。在^&lt；25&gt；Al中的^&lt；25&gt；Si等压模拟态中发现了出乎意料的大的GT强度。对于其他原子核，数据分析正在进行中。T_z=-2原子核的实验即将开始。

We have previously succeeded in commissioning the recoil separator CARP at the Research Center for Nuclear Physics, Osaka University. This device allows us to mass-separate nuclear reaction products and transport them into the detecting position in the form of a secondary beam. Considering the advantage of the use of the separator, the objective of the present investigation was set at the accurate measurement of the Gamow-Teller (GT) beta-transition rates of the proton rich T_z = -3/2 and -2 nuclei in the sd-shell. This was to promote deeper understanding of the quenching mechanism of the giant M1 resonance, by facilitating the detailed comparison of the GT-strength between the theory and experiment for a wide range of nuclei far off the beta-stability line.In the early stage of the investigation, an emphasis was placed on the achievement of a large solid angle of the recoil separator for the reaction products and on the construction of a detector system which is highly sensitive to the beta-rays and associated radiations with the decay of the products but insensitive to the external background radiations. Following these developments of the apparatus, a gain of a factor of no smaller than 20 over the previous experimental set-up was found achieved in the overall collection efficiency of the data.Taking account of the relatively large production cross sections of the T_z = -3/2 nuclei, the first experiment was determined to be carried out on ^<13>O, ^<21>Mg, ^<25>Si, ^<21>S, ^<37>Ca and ^<41>Ti. We have successfully completed the measurements for all these T_z = -3/2 nuclei by the time of preparing this report. The analysis of the data has been completed for ^<25>Si and the quenching factor of the GT-strength was determined. An unexpectedly large concentration of the GT-strength was found in the isobaric analog state of ^<25>Si in ^<25>Al. For the other nuclei, the data analysis is under way. The experiments for the T_z = -2 nuclei are about to start.