Nuclear Structure of Manganese-56

The ${\mathrm{Mn}}^{55}(d,p){\mathrm{Mn}}^{56}$ reaction was investigated with 10-keV resolution at a deuteron bombarding energy of 7.5 MeV. Angular distributions were obtained for most states up to 5.5 MeV and for strong states up to about 6.5 MeV of excitation energy. A distorted-wave (DW) analysis yielded the orbital angular momentum transfer $l_n$ and the transition strength $(2\mathrm{}{J}_f+1)S_{\mathrm{lj}}$ for most states. A comparison with the ($d,p$) sum rules gives evidence that the DW calculations may be accurate to about 20%. Considerable configuration mixing between the $2p_{\frac{3}{2}}$, $2p_{\frac{1}{2}}$, and $1f_{\frac{5}{2}}$ neutron orbitals was found. A discussion of possible spin assignments is given, particularly for states below 1 MeV. The statistical model is found to be reasonably consistent with the present data, but the distribution of nearest-neighbor spacings has some features of a Wigner, and not an exponential, distribution. Shell-model calculations are discussed, and the possibility that ${\mathrm{Mn}}^{56}$ may have a large static deformation is considered.