Coulomb Excitation with Fluorine-1 8 Isomeric Secondary Beam

为了在很低的能量下精确测定天体物理核反应速率，这对恒星演化的研究具有重要意义，九州大学串列加速器实验室(KUTL)建造了一台高分辨率反冲质量分离器(RMS)。利用能量和动量的差异，均方根能够以较高的S/N比将反应产物与初级束分离。利用KUTL均方根系统可以产生不稳定核的二次束。在本研究中，我们以实现二次束诱导反应光谱为目标，发展了产生二次束的方法。该方法采用逆运动学的聚变蒸发反应，其中来自加速器的重弹和轻靶核结合在一起。利用逆运动学原理，反应产物被反冲到一个有限的正向立体角区域，具有足够的运动能用于二次反应。由于加速器和均方根的限制，很难产生氟-18次级束流，因此我们重点研究了由氟-19束流和氦-4靶产生的钠-22次级束流的研制。证实了利用本系统可以产生强度大于10000 cps的钠-22次级束流，而不会产生任何来自初级束流的明显污染。我们还研制了用于次级束流实验的带电粒子探测/监测系统。探测器由塑料闪烁体和位置敏感光电倍增管连接而成。该系统具有较高的抗辐照能力和较快的定时特性，适用于顶层测量。利用二次光束进行库仑激发实验，将进一步实现光谱测量。

In order to precisely determine the astro-physical nuclear reaction rate at very low energy, which is important for the study of stellar evolutions, a high-resolution recoil mass separator (RMS) has been constructed at the Kyushu university tandem accelerator laboratory (KUTL). By using the differences in the energy and momentum, the RMS is capable of separating with high S/N ratio the reaction products from the primary beams. It is possible to produce the secondary beams of unstable nuclei by using this KUTL RMS system.In the present study, aiming the realization of the spectroscopy with secondary beam induced reactions, we developed the method for production of the secondary beams. The method employs the fusion evaporation reactions of inverse kinematics where heavy projectile from the accelerator and the light target nucleus are combined. By using the inverse kinematics, the reaction products are recoiled into a limited region of forward solid angle with a kinematic energies enough for the secondary reactions.Since the fluorine-18 secondary beam was turned out to be very difficult to produce, due to the limitations in the accelerators and the RMS, we then focused on the development of the sodium-22 secondary beam which is produced by fluorine-19 beam and helium-4 target. It was confirmed that with the present system it is possible to produce the sodium-22 secondary beam at an intensity of more than 10000 cps without any significant contamination originating from the primary beam.We also developed the charged particle detection/monitor system for the secondary beam experiments. The detectors are made of plastic scintillators coupled to position sensitive photo multiplier tubes. The system has the high endurance against irradiation and the fast timing characteristics suitable for the TOP measurements. Further development will be made to realize the spectroscopy by Coulomb excitation experiments with secondary beams.