Study of two nucleon emission mechanism by using tagged photons and continuous electron beams in the intermediate energy region.

在日本东北大学（Kakuriken）核科学实验室用连续电子束对两种核子发射机制进行了研究。在巨偶极子共振以上和介子阈值以下的光子能量范围内，直接核子发射和双核子光吸收过程在反应过程中占主导地位，由于核集体运动和等压线的影响而受到强烈抑制。有人提出，从最终核态研究两核子的角和能量相关可以提供相关核子和介子交换效应的信息。在本项目中，为了获得高效的符合测量，建立了一个大立体角质子探测器系统。该系统由30对E-E型塑料反望远镜组成，总立体角为1.02 sr，能量分辨率为质子能量的5-10%。在标记光子装置上进行了测量，其准单能光子的能量范围为24 ~ 102 MeV。测量了（gamma,n,）、（gamma,p）、（gamma,np）和（gamma,pp）在^4He、^<6,7>Li和^<10 >b靶上的微分截面。在低缺失能区，研究了s壳层轨道和p壳层轨道的单核子发射。通过准自由敲除分析，推导了这些核子的动量分布。在200-450 MeV/c的动量范围内，比目前（e,e - n）实验得到的动量范围高得多。在高能区，双核子发射主导了反应过程。发射的中子和质子之间的角相关性与氘核光分解运动学具有相似的形状。这一事实表明了原子核内相关核子对光吸收的重要性。

Study of the two nucleon emission mechanism have been performed by using toe continuous electron beam at Laboratory for Nuclear Science, Tohoku University (Kakuriken). In the photon energy range above the giant dipole resonance and below the pion threshold, the direct nucleon emission and two nucleon photoabsorption process dominate the reaction process, because the effects of the nuclear collective motion and the isobar and strongly suppressed. It has been suggested that investigations of two nucleon angular and energy correlation from the final nuclear states may provide informations of correlated nucleons and meson exchange effect. In this project, in order to obtain a efficient coincidence measurements, a large solid angle proton detector system has been build. This system is consisted of 30 pair of E-E type plastic counter telescopes whose total solid angle is 1.02 sr and energy resolution is 5-10% of the proton energy.The measurements were carried out at the Tagged Photon Facility whose energy range of the quasi-monoenergetic photon was 24 to 102 MeV. The differential cross sections of (gamma,n,), (gamma,p), (gamma,np) and (gamma,pp) on ^4He, ^<6,7>Li and ^<10>B targets were measured.In the low missing energy region, single nucleon emissions from the s- and p-shell orbit were investigated. The momentum distributions of these nucleons were deduced by means of quasi-free-knockout analysis. The momentum region was 200-450 MeV/c corresponding to much higher region than the presently obtainable momentum range by (e,e'N) experiments. in the high missiong energy region, two nucleon emission dominates the reaction process. The angular correlation between emitted neutrons and protons has shown a similar shape with the deuteron photo-disintegration kinematics. This fact indicates the importance of the photoabsorption by a correlated nucleon pair inside the nucleus.