Study on electro-magnetic calorimeter with lead fluorite crystal

本研究的目的是建立一种制备氟化铅晶体的方法，并探索其在高能粒子量热检测器中的应用。由于氟化铅晶体没有闪烁，它将被用作切伦科夫散热器。氟化铅的性能与广泛使用的铅玻璃有很大的不同。它具有更大的密度，更大的折射率和在短波长的光中更好的透明度，并且有望改善使用切伦科夫光的高能量热检测。我们首先研究了氟化铅晶体的制备方法，最终得到了9个2 × 2 × 10 cm^3的样品。它们非常透明，并显示出与世界上最好的晶体相媲美的良好性能。我们还发现大晶体的制作也不容易。大多数样品在抛光过程中损坏。这是由于在高温冷却生长晶体的过程中仍然存在内应力。由于氟化铅在高温和室温下具有两种不同的晶体结构，因此在冷却晶体中，两种结构可以共存于一个晶体中。我们试图通过改变冷却速度来寻找一种避免共存的方法，但最好的方法尚未确定。2001年11月，我们用高能电子束、介子和介子对这9个样品进行了测试。数据正在分析中。此外，我们还研究了利用闪烁体和切伦科夫辐射体的叠加作为分离GeV中子和γ能量的工具的可能性。铅萤石是切伦科夫散热器的可能候选材料。模型试验结果已发表。

The purpose of the present study is to establish the method to make lead fluoride crystal and to find application to calorimetric detector of the high energy particle. Since lead-fluoride crystal has no scintillation, it will be used as a Cherenkov radiator. The properties of lead fluoride are quite different from those of lead-glass which is widely used. It has heavier density, larger refractive index and better transparency in short wave length of light and has been expected to improve high-energy calorimetric detection using Cherenkov light. Ai first we studied the fabrication method of lead fluoride crystal and finally obtained nine samples of 2 X 2 X 10 cm^3. They are very transparent and show a good property comparable to the world best crystals. We found also non-easiness for fabrication of large crystal. Most of samples are broken during polish. This is due to the fact that an internal stress remains after the process of cool-down from high temperature to grow crystal. Since lead fluoride has two different crystal structures in high and room temperature, two structure can co-exist in one crystal for the cool-down crystals. We tried to find a method to avoid the co-existence by changing the cool-down speed, but the best way has not yet been established. For the nine samples, we performed a test using a high energy beam of electrons, pions and muons in November 2001. The data are being analyzed now. Moreover, we studied a possibility to use as a tool to separate neutron and gamma of GeV energy by stacking scintillator and cherenkov radiators. Lead fluorite is a possible candidate of the cherenkov radiator. The results of its model test was published.