对竞争性双核衰变的观察
C Walz1, H Scheit1, N Pietralla1
1Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.
Nature
|October 16, 2015
概括
研究人员在激发的核状态中观察到双马 (γγ) 衰变,这是一个罕见的量子过程. 这一发现扩大了我们对核结构和量子电动学的理解,超出了先前研究的0(+) 到0(+) 过渡.
科学领域:
- 核物理
- 量子电动力学
背景情况:
- 双马 (γγ) 衰变是一种基本的二次量子电动力学过程,涉及两个马量子的同时发射.
- 以前,只有在特定的核过渡 (J(π) = 0(+) → 0(+)) 时才观察到γ-衰变,而单一的玛衰变则是禁止的.
- 单玛 (γ) 衰变是观察γγ衰变的主要实验挑战.
研究的目的:
- 从激发的核状态报告γγ-衰变的观察结果,其中J(π) = 11/2(-).
- 调查与允许的单一γ-衰变直接竞争的γ-衰变.
- 确定γγ衰变过程的分支比和多极性.
主要方法:
- 对-137 ((137) Ba) 的 11/2 ((-) 异构体的γ-衰变进行实验观察.
- 测量发射的马射线的角相关性和能量谱.
- 使用准粒子-声子模型计算过渡矩阵元素.
主要成果:
- 观察到137Ba的11/2(-) 异构体的γγ-衰变与允许的γ-衰变竞争到3/2(+) 的基本状态.
- 这种竞争性γγ衰变的分支比被确定为 (2.05 ± 0.37) × 10(-6).
- 对角度相关性和能量光谱的分析允许确定有助于多极性.
结论:
- 观察到的γγ衰变为探测核结构提供了新的途径.
- 这种衰变模式提供了以前未经探索的核特性,包括核电极化和磁性易感性.
- 准粒子-声子模型成功地重现了实验测量结果.
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