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

在东北大学(Kakuriken)核科学实验室用TOE连续电子束研究了两个核子的发射机制。在高于巨偶极子共振、低于π阈值的光子能量范围内，直接核子发射和双核子光吸收过程控制着反应过程，因为核集体运动和等压线的影响受到强烈的抑制。从最终的核态研究两个核子的角和能量关联可以提供关联核子和介子交换效应的信息。在本项目中，为了获得有效的符合测量，建立了一个大立体角质子探测器系统。该系统由30对E-E型塑料计数望远镜组成，总立体角为1.02sr，能量分辨率为质子能量的5%-10%。测量是在标记光子装置上进行的，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，^&lt；6，7&gt；Li和^&lt；10&gt；B靶上的微分截面。在低遗失能区，研究了S壳层和p壳层轨道的单核子发射。通过准自由击穿分析，得到了这些核子的动量分布。动量范围为200-450 MeV/c，比(e，e‘n)实验测得的动量范围高得多。在高能区，两个核子发射主导着反应过程。出射的中子和质子之间的角关联已显示出与氚光解运动学相似的形状。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.