Production of a strong slow-positron beam and its application to material sciences

近年来，慢单色正电子束的产生技术取得了显著的进展，在表面物理和气体分子的^+散射中得到了许多成功的应用。在这种新的形势下，我们的研究小组于三年前在ETL(筑波电工实验室)利用电子直线加速器建造了一条用于慢正电子的强束线，意在将其广泛应用于材料科学。在第一财年结束之前(从1985年4月开始)，我们小组的成员谷川和Sueoka在ETL完成了一条中等束流线，在下一财年，我们最初计划在ETL建造一条正电子束线，在得到科技厅的大笔资金后，我们的计划得到了极大的改进，我们小组的一些成员(Akahane、Shiotani和Chiba)与ETL工作人员合作建造了一条新的束线。一些初步试验的结果证明，当直线加速器满功率运转时，将获得10^8量级或更高的强慢正电子束流。他们还成功地将正电子束展宽为10毫秒的脉冲，这是世界上第一次应用线性存储系统来慢化正电子。除了ETL计划，还有其他几个项目来建造慢正电子束线路；最近，我们课题组的Ito、Sueoka、Hasegawa和Hyodo在日本原子能研究所的电子直线加速器上成功地建造了一条束线，目前正在努力改善束流的光度等特性。可以说，本课题组的组织确实有助于激活日本的慢正电子研究，从而成功地实现了我们的初步目的。

In recent years, a remarkable progress has been achieved in the techniques for producing slow monochromatic positron beam, with many successful applications to surface physics and ^+-scattering by gas molecules.Under such a new situation, our research group was organized three years ago to construct a strong-beam line for slow positrons using an electron-linac at ETL (Electrotechnical Laboratory, Tsukuba) with an intension to use it widely in material sciences.Before the end of the first fiscal year (starting from April, 1985), Tanigawa and Sueoka, the members of our group, completed a modest beam line at ETL, but it was used only for some preliminary tests for handling slow-positron beams.In the next fiscal year, our initial plan for constructing a positron-beam line at ETL was drastically improved upon receiving a big fund from the Science and Technology Agency, and a new beam line has been constructed by some members of our group(Akahane, Shiotani, and Chiba) in cooperation with the ETL staff. The results of some preliminary tests have ensured them that a strong slow-positron beam of order 10^8/sec or a little higher will be obtained when the linac is operated in the full power. They have succeeded also in stretching the positron beam into a 10msec-pulse by applying, for the first time in the world, a linear-storage system to slow positrons.Besides the ETL-Project, there are a few other projects for constructing slow-positron-beam lines; recently, Ito, Sueoka, Hasegawa and Hyodo of our group succeeded in constructing a beam line at an electron linac in The Japan Atomic Energy Research Institute, and are now trying to improve the luminosity and other characteristics of the beam.It can be concluded that the organization of our research group has really been helpful in activating the Japanese researches with slow positrons, and hence our initial purpose has been successfully accomplished.