Fabrication of a new position sensitive neutron counter and its application to the analysis of nuclear reactor dynamic characteristics

本研究的目的是研制一种几何细长的位置灵敏中子计数器，该计数器能够插入狭窄的空间甚至水中。为实现上述目的，将位置灵敏计数器所需的两个前置放大器通过高压电容将阳极线一端交流接地，置于计数器的一端，并制作了一个计数器样机，研究了电容与位置线性度或位置分辨率的关系。位置非线性仅为0.2%，相对位置分辨率为0.24%，He-3位置灵敏中子计数器外径25 mm，长1.3m，电容2200 pF。位置分辨率为7 mm，位置非线性为0.5%。该计数器用于京都大学研究堆临界组件中子注量率分布的测量。测量时间仅为4-5分钟，与传统的金丝活化法的几个小时相比非常短。虽然这两种方法的结果彼此一致，但在位置灵敏计数器方法中，存在通过计数器的中子流的轻微影响。相反，人们发现，中子流本身的测量是可能的。

The purpose of this research is the development of a position sensitive neutron counter which is geometrically thin and long and is able to insert into a narrow space or even into water. To realize the above purpose, two preamplifiers which are needed for position sensitive counter were put at only one end of the counter by alternative-electric-currently grounding the one end of the anode wire through a high voltage capacitor.A prototype counter was fabricated to examine the relation between the capacitance and position linearity or position resolution. Position non-linearity was only 0.2% and relative position resolution was 0.24%.He-3 position sensitive neutron counter was fabricated with dimension of 25mm outer diameter and 1.3m length and with capacitance of 2200pF. Position resolution was 7mm and position non-linearity was 0.5%. The counter was used for the measurement of neutron flux distribution in the critical assembly of The Institute of Kyoto University Research Reactor. The measurement time was only 4-5 minutes which was very short compared with several hours for the conventional gold wire activation method. Although the results of the both methods agreed each other, in the position sensitive counter method there was a slight effect of neutron streaming through the counter. On the contrary, it was found that the measurement of neutron streaming itself could be effectively possible.