A study of compressibility in nuclei far from the stability line

我们用逆运动学方法研究了富质子或丰中子不稳定核的(α，α‘)反应，为研究E0巨共振和核可压缩性提供了一个里程碑。建立了一个液态氦靶系统，在该系统中，从激发态发出的伽马射线路径中的材料被最小化，并且通过两周的实验保持了温度的稳定性。靶的厚度在10 0-2 5 0 mg/cm^2的范围内是可选择的。使用来自理研加速器碎片分离器RIPS的60 MeV次级束流，测量了(A)^lt；14；O+α和(B)^lt；12；Be+α的散射。探测器系统由一个用于带电粒子探测的塑料闪烁体和68个用于伽马射线的NaI(TI)闪烁体阵列组成。(A)在^&lt；14&gt；O中发现了向0^+、1^-、2^+和3^-激发态的跃迁，并用转移角动量表征了微分截面的角分布。我们还测量了各种碎片的产生截面，发现碳同位素的产生比半经验规则的预测要大得多。(B)我们在2.24 MeV处发现了一个同质异能的0^+态，正好位于^&lt；12&>Be的第一激发态上方，它的自旋由伽马-伽马角关联图样决定。还测量了2+态和1-态的α非弹性散射，其中角分布用转移角动量来表征。我们新发现(α，t)和(α，^3He)核子转移反应具有显著的截面，这为研究不稳定核中的单粒子态提供了一个新的光谱工具。

We have studied (α, α') reactions for proton- or neutron-rich unstable nuclei by using inverse kinematics in order to get a milestone for investigating E0 giant resonances and nuclear compressibility. A Liquid He target system was constructed where materials in a path of gamma rays from excited states were minimized and stability of the temperature were maintained through a 2-weeks experiment. The thickness of the target are selectable in a range of 100-250 mg/cm^2. By using 60-MeV secondary beams from the fragment separator RIPS in RIKEN accelerator facility, (a) ^<14>O+α and (b) ^<12>Be+α scatterings were measured. The detector system consisted of a hodoscope of plastic scintillators for charged particle detection and an array of 68 NaI(TI) scintillators for gamma rays. (a) The transition to 0^+, 1^-, 2^+ and 3^- excited states in ^<14>O were identified and the angular distributions of the differential cross sections were characterized by the transferred angular momenta. We also measured production cross sections of various fragments and found that production of carbon isotopes are much larger than a prediction of a semi-empirical rule. (b) We found an isomeric 0^+ state at 2.24 MeV just above the first excited state of the ^<12>Be, where its spin was determined by a gamma-gamma angular correlation pattern. Alpha inelastic scattering to the 2+ and 1- states were also measured, where the angular distributions are characterized by the transferred angular momenta. We newly found that the (α, t) and (α, ^3He) nucleon transfer reactions have significant cross sections, which gives a new spectroscopic tool for single particle states in unstable nuclei.