학술논문
Isospin symmetry in $B(E2)$ values: Coulomb excitation study of ${}^{21}$Mg
Document Type
Working Paper
Author
Ruotsalainen, P.; Henderson, J.; Hackman, G.; Sargsyan, G. H.; Launey, K. D.; Saxena, A.; Srivastava, P. C.; Stroberg, S. R.; Grahn, T.; Pakarinen, J.; Ball, G. C.; Julin, R.; Greenlees, P. T.; Smallcombe, J.; Andreoiu, C.; Bernier, N.; Bowry, M.; Buckner, M.; Caballero-Folch, R.; Chester, A.; Cruz, S.; Evitts, L. J.; Frederick, R.; Garnsworthy, A. B.; Holl, M.; Kurkjian, A.; Kisliuk, D.; Leach, K. G.; McGee, E.; Measures, J.; Mücher, D.; Park, J.; Sarazin, F.; Smith, J. K.; Southall, D.; Starosta, K.; Svensson, C. E.; Whitmore, K.; Williams, M.; Wu, C. Y.
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Abstract
The $T_z$~=~$-\frac{3}{2}$ nucleus ${}^{21}$Mg has been studied by Coulomb excitation on ${}^{196}$Pt and ${}^{110}$Pd targets. A 205.6(1)-keV $\gamma$-ray transition resulting from the Coulomb excitation of the $\frac{5}{2}^+$ ground state to the first excited $\frac{1}{2}^+$ state in ${}^{21}$Mg was observed for the first time. Coulomb excitation cross-section measurements with both targets and a measurement of the half-life of the $\frac{1}{2}^+$ state yield an adopted value of $B(E2;\frac{5}{2}^+\rightarrow\frac{1}{2}^+)$~=~13.3(4)~W.u. A new excited state at 1672(1)~keV with tentative $\frac{9}{2}^+$ assignment was also identified in ${}^{21}$Mg. This work demonstrates large difference of the $B(E2;\frac{5}{2}^+\rightarrow\frac{1}{2}^+)$ values between $T$~=~$\frac{3}{2}$, $A$~=~21 mirror nuclei. The difference is investigated in the shell-model framework employing both isospin conserving and breaking USD interactions and using modern \textsl{ab initio} nuclear structure calculations, which have recently become applicable in the $sd$ shell.
Comment: 8 pages, 6 figures, submitted to Phys. Rev. C, Rapid Communication
Comment: 8 pages, 6 figures, submitted to Phys. Rev. C, Rapid Communication