Magnetic Moments of Proton Drip-Line Nuclei and Abnormal Breaking of Isospin Symmetry

我们测定了^9 C、^<113>Q、^<19>Q和21 F的核磁矩，结果发现，在^9 C-^0对中观察到的异常磁矩行为<13>，即异常的自旋期望值或异常的g因子关联，在^0-^ B的镜像对中没有观察到<13><13>。对于^<19>O和^<21>F的情况，由于缺少^ Q的配对，<19>而<21>^ F的配对原子^ Mg<21>的磁矩还不知道，所以不能用镜像对分析进行讨论。然而，与每个原子核的理论计算进行比较是可能的。用壳模型程序OXBASH（int. psdMK，PW）计算的^ Q、^ Q和^ F的结果与实验值在百分之几以内吻合得很好<13><19><21>，这一事实使得^9C-^9Li对的不规则性非常突出。因此，这意味着^9C-^9Li对的反常并不是T = 3/2的同位旋镜像对的共同特征，而是由于^9C-^9Li对的特殊情况造成的。至今还没有一个成功的理论能很好地再现^9C-^9Li对的反常现象。对于^9C-^9Li对，仍然存在如下三种可能性。i）同位旋对称性破缺，ii）偶核子群配对大幅度破缺，iii）核子有效g因子大幅度重整化。如果我们使用在双闭壳层实验确定的有效g因子，我们发现^9C-^9Li的自旋期望值接近理论计算值。这一事实使上述iii）引起注意。近年来，随着AMD和集团模型对A=9系统核结构的理论研究的不断深入，这一问题的解决可能会在不久的将来得到解决。

We have determined the nuclear magnetic moments of ^9C, ^<113>Q, ^<19>Q, and 21F.As a result, the abnormal behavier of magnetic moments seen in ^9C-^<13>0 pair, i.e. the abnormal spin expectation value or the unusual g-factor correlation, was not seen in the mirror pair of ^<13>0-^<13>B, For the cases of ^<19>O and ^<21>F, discussions using mirror-pair analyses can not be made because the partner of ^<19>Q is absent and the magnetic moment of ^<21>Mg, the partner of ^<21>F, has not been known yet. However, comparisons with theoretical calculations for each nucleus are possible. The results of calculations with the shellmodel code OXBASH (int. psdMK, PW) are all in good agreement with the experimental values within a few % for ^<13>Q, ^<19>Q, and ^<21>F.This fact has made the irregularity of ^9C-^9Li pair stand out. Therefore that is an implication that the abnormality of ^9C-^9Li pair is not a common feature of isospin T = 3/2 mirror pairs and it is due to the special situation for ^9C-^9Li pair. There has not been a successful theory yet that well reproduces the abnormality of ^9C-^9Li pair. There are still three possiblities for ^9C-^9Li pair as follows. i) Isospin symmetry breaks, ii) pairing of the even-number nucleon group breaks largely, iii) effective g-factors of nucleons are largely renormalized. If we use the effective g-factors determined experimentally at the double closed shell, the spin expectation value for ^9C-^9Li is found to get a value near the theoretical calculation. This fact makes the above iii) attract an attention. Recent theoretical works with AMD or cluster models on the nuclear structure of the A=9 system developping intensively might give a key to this problem in the near future.