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器(HFPC)在5K以下的低温工作。首次发现在很低的温度(接近液氦温度，即4.2K)下冷却的HFPC工作在正比区，但在200℃以下气体增益很低。本工作的一个主要目的是将HFPC技术推广到4.2K以下的温度，并将其应用于低温共振电子穆斯堡尔谱(REMS)。利用一种新的带有金属干燥器和专门为这项工作设计的HFPC的完整计数器系统，我们成功地探测到了低温(1.75-4.2K)冷却样品中发射的电子。氦泵浦获得的最低温度为1.75K，还获得了关于HFPC在这种低温下工作的机理的新信息：(1)气体增益不依赖于气体温度。(2)随着气体温度的降低，诱导连续放电的阳极电压变低，现在可以在4.2K以下的区域进行REMS测量。京都大学放射性同位素研究中心目前正在进行许多低温REMS的研究，例如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.