Nuclear structure of calcium isotopes from inelasticαscattering

Abstract

Angular distributions were measured for elastic and inelastic $\ensuremath{\alpha}$ scattering from $^{40}\mathrm{Ca}$ at 24.0, 28.5, and 31.0 MeV, from $^{41}\mathrm{Ca}$ at 24.0 MeV and from $^{43,44}\mathrm{Ca}$ at 25.5 MeV. Analyses in terms of distorted-wave Born-approximation and coupled-channel theory, employing a vibrational collective model form factor, yield inelastic transition strengths, and many new spin and parity assignments or restrictions for levels in $^{40,41,43,44}\mathrm{Ca}$. The inelastic multipole transition strengths are in excellent agreement with known electromagnetic strengths. Quadrupole strengths are interpreted in terms of the coexistence model. The data imply that the ground-state excited-core admixtures to ${(fp)}^{n}$ spherical configurations are 4% in $^{48}\mathrm{Ca}$, 10% in $^{40,41}\mathrm{Ca}$, 14% in $^{43}\mathrm{Ca}$, and 30% in $^{42,44}\mathrm{Ca}$. The octupole inelastic strength is strong and mainly localized in the lowest ${3}^{\ensuremath{-}}$ state in $^{40}\mathrm{Ca}$, but becomes more fractionated and weaker with addition of neutrons and exhibits in $^{41}\mathrm{Ca}$ characteristic weak-coupling fragmentation of the lowest ${3}^{\ensuremath{-}}$ state in $^{40}\mathrm{Ca}$. These results are consistent with previous observations that the structure of the $^{41}\mathrm{Ca}$ ground state is with high purity a $1{f}_{\frac{7}{2}}$ neutron coupled to the $^{40}\mathrm{Ca}$ ground state.NUCLEAR REACTIONS $^{40}\mathrm{Ca}(\ensuremath{\alpha},\ensuremath{\alpha})$, $E=24.0, 28.5, 31.0$ MeV, $^{41}\mathrm{Ca}(\ensuremath{\alpha},\ensuremath{\alpha})$, $E=24.0$ MeV, $^{43,44}\mathrm{Ca}(\ensuremath{\alpha},\ensuremath{\alpha})$, $E=25.5$ MeV, measured $\ensuremath{\sigma}(\ensuremath{\theta})$, ${E}_{\ensuremath{\alpha}}$; DWBA, coupled-channel analyses, $^{40,41,43,44}\mathrm{Ca}$ deduced levels, $J$, $\ensuremath{\pi}$, $B(IS,l)\ensuremath{\uparrow}$ for $l=2,3,4,5$. Enriched targets. Coexistence model, deduced excited-core admixtures in $^{40,41,42,43,44,48}\mathrm{Ca}$.