Identification of isotopes of 1 Ge V/n heavy ions using liquid argon calorimeters

为了研究高能重离子的能量分辨和同位素识别，本研究项目旨在研究光电离液体Ar量热计的性能。我们测量了日本NIRS HIMAC公司的一台掺联烯液体Ar量热计对重离子的响应。量热计的电极由机械上精确的G10薄板制成，形成多个平行板电离室。为了测量入射离子的位置和研究多次散射的影响，在电极系统中插入了两组条形电极。加速器束流为500~650 MeV/n Ne、Ar和Fe离子，束流强度为100~200次/次。在电离室中，感应电荷信号受到正离子空间电荷的影响。总的来说，HIMAC的束流溢出时间结构是不均匀的。我们使用了结构更均匀的束流，最大限度地减少了空间电荷的影响。通过加入烯，电子-离子对的复合减少，信号尺寸增加。这导致了能量分辨率的提高，但分辨率仍然比计算预期的要差。如果选择了特定的散射角，这是相同的。这意味着散射不是分辨率降低的主要原因。这一事实表明，人们必须考虑另一种影响，如液体的密度波动。停止细胞和前一个细胞的信号散点图显示元素有明显的分离，但同位素分离是关键。将进行进一步的分析。

This research project aims to study the performance of liquid argon calorimeter with photoionization process in order to investigate the energy resolution and isotopes identification for high energy heavy ions.We have measured responses of an allene-doped liquid argon calorimeter to heavy ions from HIMAC of NIRS, Japan. Electrodes of the calorimeter are made of thin G10 plates which are mechanically precise and form multi-parallel-plate ionization chambers. For measurement of position of incident ions and study of the effect of multiple scattering, two sets of strip electrodes are inserted to the electrode system. These give information of track of the particles.Accelerator beams were 500〜650 MeV/n Ne, Ar and Fe ions and the beam intensity was 100〜200 counts per spill. In ionization chambers, induced charge signals are affected by space charge of positive ions. In general, the time structure of beam spills at HIMAC is not uniform. We used beams of more uniform structure and minimized the effect of space charge.By adding allene, recombination of electron-ion pairs decreased and signal size increased. This led the improvement of energy resolution, but the resolution was still worse than that expected from calculation. This is the same if a specific scattering angle is selected.This means that the scattering is not a main cause of degradation of resolution. This fact suggests that one must consider another effect such as density fluctuation of liquid. A scatter plot of signals of stopping cell and those of the preceding cell shows a clear separation of element but the isotope separation is critical. Further analysis will be done.