Reaction mechanism of Coulomb dissociation induced by high-speed heavy ions

通过精确测量碎片的角分布和角关联，研究了中能库仑解离反应机理。一个大的真空室被构造成一个塑料闪烁体的壳体。该腔室安装在RIKEN加速器研究设施的实验室中，用于放射性核束的实验。相对能量低于0.5 MeV时，无背景测量成为可能。研究了^<208>Pb(^8B, ^7Be p)^<208>Pb和^<208>Pb(^9C, ^ 8bp)^<208>Pb反应。测量的主要目的是确定^7Be (p, γ)^8B和^8B(p, γ)^9C反应。前一种反应产生高能太阳中微子，后一种反应是恒星内高温pp模式核燃烧的关键反应。在库仑解离法中，在提取（p, γ）截面的过程中，假设了一步跃迁机制。然而，有人指出可能存在少量的E2混合跃迁。我们注意到，在El和E2跃迁中，碎片的角分布是不同的。在测量中，新装置覆盖了100角以内的散射角，得到了完整的分布。结果表明E2成分非常小，不影响提取的（p, γ）截面。

Reaction mechanism of intermediate-energy Coulomb dissociation has been studied by precise measurements of angular distribution and angular correlation of the fragments. A large vacuum chamber has been constructed as a housing of a plastic scintillator hodoscopes. The chamber was installed in a experimental hail of RIKEN Accelerator Research Facility, and was used for experiments with radioactive nuclear beams. Background-free measurements become possible for the relative energy lower than 0.5 MeV.The ^<208>Pb(^8B, ^7Be p)^<208>Pb and ^<208>Pb(^9C, ^8B p) ^<208>Pb reactions were studied. The primary aim of the measurements are to determine the ^7Be (p, gamma)^8B and ^8B(p, gamma)^9C reactions. The former reaction produce high-energy solar-neutrinos, and the latter is a key reaction in the hot pp mode nuclear burning in stars. In the Coulomb dissociation method, a one-step El transition mechanism is assumed in the process of extracting the (p, gamma) cross section. However, possible small mixture of E2 transition had been pointed out. We notice that the fragments' angular distributions are different for El and E2 transitions. In the measurements, the scattering angle up to 100 was covered by the new setup to obtain complete distributions. The results suggested very small E2 components which do not affect the extracted (p, gamma) cross sections.