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

东北大学原子核科学研究室用连续电子束对双核子发射机制进行了研究。在光子能量高于巨偶极共振而低于π介子阈值的范围内，由于原子核集体运动和同量异位素的影响而被强烈抑制，直接核子发射和两核子光吸收过程主导反应过程。从末态出发研究两核子的角关联和能量关联，可以提供关联核子和介子交换效应的信息。为了获得高效率的符合测量，本项目建立了一个大立体角质子探测器系统。该系统由30对总立体角为1.02sr、能量分辨率为质子能量的5-10%的E-E型塑料计数器望远镜组成，在24 - 102 MeV准单能光子能量范围的标记光子装置上进行测量。测量了（γ，n，），（γ，p），（γ，np）和（γ，pp）在^4He，^&lt;6，7&gt;Li和^ B靶上的微分截面<10>，在低漏能区研究了s壳层和p壳层轨道的单核子发射.用准自由敲出分析方法推导了这些核子的动量分布。动量区域为200-450 MeV/c，对应于比目前通过（e，e ′ N）实验获得的动量范围高得多的区域。在高能区，反应过程以双核子发射为主。发射的中子和质子之间的角关联显示出与氘核光致衰变运动学相似的形状。这一事实表明了核内关联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.