Development of Positron Mass-Production Method

利用强流直线加速器大量生产正电子的研究和发展已经进行了三年。在低能正电子的产生效率方面取得了以下改进.研制了一种高效的转换器，称为“模块化光子-正电子转换器”（MPPC），它将高能光子转换为慢正电子。这种转换器可以扩大钨箔的正电子发射面，使其在高能光子轰击下发射慢正电子，并通过施加有效电场将其提取出来。实验结果表明，MPPC算法能够有效地实现该原理，其产率与基于EGS 4程序的蒙特-卡罗模拟结果基本一致.研制了高效的光子-非热正电子转换器（PNPC）。低能区正电子的提取可以显著提高正电子的净产生效率。实验证明，单位表面积钨箔的生产率是（1）情况的15-20倍。在<13>使用30 MeV的低能量电子直线加速器的情况下，获得了2 × 10^ [e ^+/s]的脉冲产生率，100 pps的时均产生率达到了8 × 10 ^8 [e^+/s].在用磁导管输送正电子和对正电子进行再减速方面也取得了其他进展。得到的低于6电子伏的正电子的时均产生率为3.3 × 10^7[e^+/s]。

The research and development on positron mass-production by using a high current LINAC have been performed for three years. The following improvements in Production Efficiency of Low Energy Positrons have been obtained.1. Efficient converter, named "Modular Photon-Positron Converter"(MPPC), form energetic photons to slow positrons were developed. This converter can enlarge the positron emitting surface of tungsten foils which emit slow positrons at bombardment of energetic photons, and also extract them by applying effective electric field. Experiments on the proof of the principle showed that MPPC works well and the production rate is in agreement of the estimation based on Monte-Carlo simulations using EGS4 code.2. Efficient converter, named "Photon-Nonthermal Positron Converter"(PNPC), was developed. Extraction of positrons of low energy region can increase the net positron production efficiency dramatically. It was experimentally proved that the production rate per unit surface area of tungsten foil became 15-20 times that in the case of (1). The attained production rate during the LINAC beam pulse was 2 X 10^<13>[e^+/s] and the time averaged one for 100 pps reached 8 X 10^8[e^+/s], in spite of the used low LINAC beam energy as 30 MeV.This converter is very simple in structure and it can be fablicated easily.3. Other developments in transportation of positrons with a magnetic duct and also in remoderation of them were made. The attained time averaged production rate of positrons below 6 eV was 3.3 X 10^7[e^+/s].