Identification of atomic numbers and mass numbers of high-energy heavy ions using a counter telescope

使用计数器望远镜识别高能重离子的原子序数和质量数

• 批准号: 17540274
• 负责人: KIMURA Kikuo
• 金额: $ 2.18万
• 依托单位: Nagasaki Institute of Applied Science
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2005
• 资助国家: 日本
• 起止时间: 2005 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-17540274/
• 关键词: counter telescope; high-energy heavy ion; particle identification; ΔE counter; time of flight measurement; gas ionization chamber; plastic scintillator; プラスチックシンチレータ; NaI検出器; 飛行時間側定

A counter telescope composed of three different types of detectors was developed using a tilted electrode gas ionization chamber as a ΔE-counter, an NaI(Tl) detector as an energy counter and a plastic scintillator as a TOF counter. Among them a combination of the A E-counter and the NaI(Tl) detector was first tested for identifying atomic numbers of high-energy heavy ions at the HIMAC accelerator of the National Institute of Radiological Sciences. Heavy ion beams of Kr(Z=36) and Xe(Z=54) with energies up to 400MeV/N, which is close to the energy region of the RI beam factory, were used. It was found that the identification of atomic numbers was quite good for heavy ions up to Z=54. But the quality of the NaI(Tl) detector was limited to the region of low beam intensity around 100 particles/spill. At the higher beam intensities, output pulse heights of the NaI(Tl) detector decreased with increasing beam intensities and the linear relation between beam energy and pulse height was distorted. Such distortion renders deterioration of mass resolution when the NaI(Tl) detector together with a TOF counter was used to identify mass numbers. Thus it remains necessary to develop a high-rate energy counter.As for a plastic scintillator used as a TOF counter, time resolution was tested by reading light outputs from four sides of the square scintillator using fast photomultiplier tubes. Arrival times of light to the four phototubes were determined not using electronic circuits, like constant fraction discriminators, but by analyzing waveforms of the phototube signals measured by a 4-channel digital storage scope. By this analysis, we could reduce the effect of noise on the waveform data. In a test experiment using cosmic rays, we obtained the time resolution of 90 ps. For heavy ions which yield much larger light outputs than cosmic rays, a timing resolution of much better than 90 ps is expected.

利用倾斜电极气体电离室作为ΔE-counter， NaI（Tl）探测器作为能量计数器，塑料闪烁体作为TOF计数器，研制了一种由三种不同类型探测器组成的反望远镜。其中，a -e计数器与NaI（Tl）探测器的组合首次在国家放射科学研究所的HIMAC加速器上进行了高能重离子原子序数识别试验。使用了能量高达400MeV/N的重离子束Kr（Z=36）和Xe(Z=54)，接近RI束流工厂的能量区。对于Z=54以下的重离子，原子序数的识别效果很好。但NaI（Tl）探测器的质量仅限于100个粒子/溢出左右的低光束强度区域。在较高的光束强度下，NaI（Tl）探测器的输出脉冲高度随光束强度的增加而降低，并且光束能量与脉冲高度之间的线性关系被扭曲。当NaI（Tl）探测器与TOF计数器一起用于识别质量数时，这种畸变会导致质量分辨率的恶化。因此，开发一种高速率的能量计数器仍然是必要的。至于用作TOF计数器的塑料闪烁体，则通过使用快速光电倍增管读取方形闪烁体四面的光输出来测试时间分辨率。光到达四个光电管的时间不是通过电子电路来确定的，比如常数分数鉴别器，而是通过分析光电管信号的波形，由一个4通道数字存储示波器测量。通过这种分析，可以减少噪声对波形数据的影响。在使用宇宙射线的测试实验中，我们获得了90 ps的时间分辨率。对于比宇宙射线产生更大光输出的重离子，预计时间分辨率将远远优于90 ps。