Study of photo-neutron reaction below the pion threshold

本文的主要目的是阐明介子交换电流在光核反应中的作用。自1982年以来，东北和墨尔本的研究人员一直在利用东北大学的标记光子失败进行光子核实验。该合作发现了双核子吸收过程在超过巨共振但低于光子介子阈值的光核反应中的重要性。在目前的短期项目中，对双核子吸收机理进行了进一步的详细研究。在项目的第一阶段，我们准备了实验环境，如建设新的束流线，大体积中子探测器和新的数据采集系统。所有这些都已成功完成，并已发表演出。本项目期间开展的协同实验为^<16>O（gamma, n）、^<12>C（gamma, n）和^<31>P（gamma， P）。^<12>C(γ, p)，这是在项目之前制作的，已被重新分析并发表在《物理学》上。rev . c .墨尔本的合作者之一G.J.O'keefe已经完成了他的博士论文，结果是^<16>O（gamma, n）。完成了^<31>P（gamma， P）实验的分析。我们发现残余的^<30>Si核的巨大共振区有大量的人口，这是光子与介子交换电流相互作用的明确证据。1995年在的里雅斯特/阿法尔举行的ICTP会议上提出了部分结果。1994-1995年，共有6名东北大学的研究人员访问了墨尔本大学。1994年至1995年，墨尔本大学共有9名研究人员访问了东北大学。1996年1月，墨尔本大学的3名研究人员应邀到东北大学讨论合作事宜。1996年3月，将邀请墨尔本大学的2名研究人员参加下一个合作实验的讲习班。

Main purpose of the profect was to elucidate the role of meson exchange current in photonuclear reactions. Tohoku and Melbourne resarchers have collaborated in photonuclear experiments using tagged photon faility of Tohoku University since 1982. The collaboration has found the importance of two nucleon absorption process in photonuclear reactions above the giant resonances but below the photo-pion threshold. Further detailed studies of the two-nucleon absorption mechanism have been pursued in the present short term project.In the first stage of the project, we have prepared experimental environment such as constructions of a new beam line, large volume neutron detectors and a new data acquisition system. All of these have been completed with success, and the performanses have been published.Collaborative experiments caried out in this term of the project are ^<16>O(gamma, n), ^<12>C(gamma, n) and ^<31>P(gamma, p). Also^<12>C(gamma, p) which was made before the project has been reanalyzed and published in Phys. Rev.C.One of the Melbourn collaborator, G.J.O'keefe, has completed his PhD thesis by the ^<16>O(gamma, n) result. The analysis of the ^<31>P(gamma, p) experiment has been finished. We have found a large population to the giant resonance region of the residual ^<30>Si nucleus, which shows a clear evidence of the interaction of photons with the meson exchange current. A part of the results has been presented at 1995 ICTP conference in Trieste/Itary.Altogether 6 researchers from Tohoku university have visited Melbourne university in 1994-1995. Altogether 9 researchers from Melbourne university have visited Tohoku university in 19941995.In January, 1996,3 researchers from Melbourne university have been invited to Tohoku university for discussions on the collaboration.In March, 1996,2 researchers from Melbourne university will be invited for the workshop on next collaborative experiments.