Production of low energy spin-polarized radioactive nuclear beam using superfluid helium

本研究的目的是研制放射性核束和介子束的超流氦靶。我们已经意识到，大约30%的注入粒子以离子状态留在氦中。我们计划从氦靶中提取这些离子，并通过引入带有极化电子转移反应的自旋极化器产生低能极化核束。为了高效地将不稳定原子核输运到偏振器中，有必要对其位置进行监测。我们通过重建射线轨迹测量了衰变位置。此外，我们安装了一个具有6个塑料层的距离堆栈型探测器来测量β衰变的端点能量。每层产生的闪烁光子通过嵌入计数器的光纤传输，使我们不会干扰其他探测器元件。通过使终点探测器和伽马探测器重合，可以为核光谱学提取更详细的信息。此外，我们计划使用超流氦作为K束的停止目标。这就是为什么与标准固体靶相比，靶材料的二次粒子能量损失大大减少的原因。通过K束线的调谐和二次粒子动量谱的测量进行了可行性研究。因此，在K束在目标位置的低动量色散条件下，超流氦适用于J-PARC的停止目标。

This study is aiming at developing a superfluid helium target for radioactive nuclear beam and meson beam. We have realized that approximately 30% of implanted particles remain as an ion state in the helium. We have planed to extract these ions from the helium target and generate low-energy polarized nuclear beam by introducing a spin polarizer with a polarized electron transfer reaction. In order to transport unstable nuclei into the polarizer with high efficiency it is necessary to monitor their positions. We have measured the decay position by reconstructing the beta-ray trajectory. Moreover, we installed a range-stack type detector with 6 plastic layers to measure end-point energy of beta decays. Scintillation photons produced in each layer were transferred through optical fiber embedded in the counter, which enable us not to interfere with other detector elements. By making coincidence this end-point detector and gamma detector, it can be extracted much more detailed information for the nuclear spectroscopy. Also, we are planing to use superfluid helium as a stopping target for K beam. This is why energy loss of secondary particles by the target material is drastically reduced comparing with standard solid target. The feasibility study was performed by tuning of the K beam line and by measuring momentum spectra of the secondary particles. As a consequence, superfluid helium is applicable fox the stopping target at J-PARC under the condition of low momentum dispersion of K beam at the target position.