Development of Positron Mass-Production Method

用大电流直线加速器进行正电子大批量生产的研究和开发已经进行了三年。在低能正电子的生产效率方面取得了以下改进1。研制了一种高效的从高能光子到慢正电子的转换装置，称为“模块化光子-正电子转换器”(MPPC)。这种转换器可以扩大在高能光子轰击下发射慢正电子的钨箔的正电子发射表面，并通过施加有效电场来提取它们。实验结果表明，基于EGS4的蒙特卡罗模拟结果表明，MPPC算法具有较好的预测效果，生产效率与预测值基本一致。研制了一种高效的光子-非热正电子转换器(PNPC)。提取低能区的正电子可以显著提高净正电子的生产效率。实验证明，钨箔的单位表面积产率是文献(1)的15-20倍。在加速器束流能量为30 MeV的情况下，获得了2×10~(-3)~13×10~(-3)[e~+/S]的脉冲产生率，100pps的平均时间达到8×10~(-8)[e~+/S]。在用磁管运输正电子以及对正电子进行改装方面也取得了其他进展。6 eV以下正电子的时间平均产生率为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].