Fine Structure of Isobaric Analog State Studied by (p, np) Reaction

对电荷交换反应后巨共振衰变性质的研究仅限于少数情况，特别是对于（p，n）反应，由于在测量中子和衰变质子时遇到足够的效率和合理的分辨率的实验困难，没有可靠的数据报道。为了进一步研究同量异位素模拟态等高激发态的微观衰变特性，本研究采用了日本东北大学CYRIC的AVF回旋加速器的35 MeV动量分析质子束，利用（p，np）反应进行了符合测量。衰变质子与中子的一致使用SSD望远镜的Si表面势垒型安装在8厘米的长度从目标，并在rhetap=135度相对于束方向。SSD-望远镜由DELTAE（250 μ m厚）、E（1000 μ m厚）和具有100 mm_2有效表面积的否决计数器组成。否决探测器被用来拒绝高能质子散射在向后的角度。质子探测的立体角为15.6msr。利用中子-质子符合实验，通过35 MeV的（p，n）反应，对<@D1208@> D1 Bi中IAS的质子衰变进行了直接测量。[)21)%，在统计误差范围内与之前的结果一致。进一步测量了<@D1140@>D1Ce和<@D1174@> D1 Yb的（p，np）反应。IAS的质子衰变的分支比已被确定为（230）SY ± 1.25。[)3)前者为（35（]SY. ±. [)8)%为后者。这些数据可望为研究核中的同位旋混合提供重要的信息。

Studies of the decay property for giant resonances following charge-exchange reactions limited to a few cases, especially for the (p, n) reaction, no reliable data has been reported due to experimental difficulties encountered with measuring neutrons and decay protons with a sufficient efficiency, and with reasonable resolution. In this report, we describe the newly equipped coincidence measurement system with the (p, np) reaction for further investigation of microscopic decay properties of highly excited states such as isobaric analog state.The experiment was performed using a 35 MeV momentum-analyzed proton beams obtained from the AVF cyclotron at CYRIC,Tohoku University. Decay protons were detected in coincidence with neutrons using a SSD-telescope of Si surface-barrier type mounted at the length of 8 cm from the target, and at rhetap=135 degree relative to the beam direction. The SSD-telescope consisted of DELTAE (250mum thick), E (1000mum thick) and veto counters with a 100 mm_2 active surface area. The veto detector was used to reject energetic protons scattered at backward angles. The solid angle for the proton detection was 15.6 msr.Direct measurement of the proton decay from the IAS in <@D1208@>D1Bi was performed by means of the neutron-proton coincidence experiment through the (p, n) reaction at 35 MeV.The branching ratio for the proton decay of the IAS has been determined to be (57(]SY.+-。[)21)%, which is in consistent with the previous results within the statistical error. Further measurements have been carried out for the (p, np) reactions on <@D1140@>D1Ce and <@D1174@>D1Yb. The branching ratio for the proton decay of the IAS has been determined to be (23(]SY.+-。[)3)% for the former case, while it is (35(]SY.+-。[)8)% for the latter. These data are expected to provide significant information for the isospin mixing in nuclei.