Physik Department E12, Technische Universität München, D-85748 Garching, Germany.
Nature. 2012 Jun 20;486(7403):341-5. doi: 10.1038/nature11116.
The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During β(+)-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of (100)Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the β-decay of (100)Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear β-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, (100)In, are well reproduced by modern, large-scale shell model calculations.
原子核的壳层结构与“幻数”有关，它起源于中子和质子在所有核子产生的平均势中的近乎独立运动。在 β(+)-衰变中，一个质子在先前未完全占据的轨道中转变为一个中子，分别发射一对正电子-中微子，其自旋平行或反平行，分别为戈麦脱-泰勒或费米跃迁。戈麦脱-泰勒跃迁的跃迁概率或强度对底层壳层结构非常敏感，通常分布在相邻核中的许多状态中。在这里，我们报告了（100）Sn 衰变的半衰期和衰变能的测量结果，（100）Sn 是具有相同质子数和中子数的最重的双幻核。在（100）Sn 的 β 衰变中，由于衰变能很大，很大一部分强度是可以观察到的。我们确定了迄今为止在允许的核 β 衰变中测量到的最大戈麦脱-泰勒强度，确立了这个戈麦脱-泰勒跃迁的“超允许”性质。在母核（100）In 中，较大的强度和低能态都可以通过现代的大规模壳模型计算得到很好的再现。
