Helium-filled proportional counter for low-temperture opration(1.5-4.2k) and its application to cryogenic resonance electron Mossbauer spectroscopy.

在我们以前的工作中，我们研究了充氦正比计数管（HFPC）在低至5 K的低温下的工作。首次发现HFPC在非常低的温度（接近液氦温度，即，4.2 K）在比例区域工作良好，但气体增益低于200。本工作的主要目的是将HFPC技术推广到4.2K以下，并将其应用于低温共振电子穆斯堡尔谱（REMS），我们采用一种新的由金属恒干器和专门设计的HFPC组成的计数器系统，成功地探测了低温（1.75- 4.2K）样品的电子发射。用氦抽气法测得的最低温度为1.75K。对HFPC在低温下的运行机理也得到了新的认识：（1）气体增益与气体温度无关。(2)随着气体孔径的减小，引起连续放电的阳极电压变得更低。利用本工作开发的技术，现在可以在4.2K以下的区域进行REMS测量。许多使用低温REMS的研究，例如，京都大学放射性同位素研究中心正在研究铁箔和超薄氧化铁层的腐蚀。

In our previous works, the opration of the helium-filled proportional counter (HFPC) was investigated at low tempertures down to 5 K. It was found for the first time that the HFPC cooled at very low temperatures (near liquid-helium temperature, i.e., 4.2 K) works well in the proportional region, but with low gas gains below 200. A main purpose of the present work is to extend the HFPC technique to temperatures below 4.2 K and to apply it to the cryogenic resonance electron Mossbauer spectroscopy (REMS).Using a new whole counter system with a metal dryostat and a HFPC specially designed for this work, we hver succeeded to detect electrons emitted from samples cooled at low temperatures (1.75-4.2 K). The lowest temperature we obtained by helium pumping is 1.75 K. New informations on the mechanism of the HFPC operation at such low temperatures have also been obtained: (1) The gas gain does not depent on the gas temperature. (2) The anode voltage to induce the continuous discharge becomes lower as the gas emperture is decreased.The REMS measurements in the region below 4.2 K is now possible with the technique develiped by the present work. Many studies with the cryogenic REMS, e.g., corrosions on iron foil and ultra thin iron oxide layers, are now in progress in Radioisotope Research Center of Kyoto University.