Properties of the Two States inCa40near 9.87 MeV

Abstract

The close-lying pair of resonances in the ${\mathrm{K}}^{39}(p, \gamma ){\mathrm{Ca}}^{40}$ reaction, which correspond to excitation in ${\mathrm{Ca}}^{40}$ of about 9.87 MeV, have been measured to be at $E_p=1575.5\mathrm{}\pm 0.8 \mathrm{and} 1580.0\pm 0.8$ keV by comparison with the ${\mathrm{Al}}^{27}(p, \gamma ){\mathrm{Si}}^{28}$ resonance at 992 keV. Gamma-ray spectra obtained for both resonances show both have strong transitions to the ground state and to the first excited state. Weaker cascades through higher levels are also shown. The angular distribution of the ground-state radiation from the $E_p=1580\mathrm{}$ keV level leads to an assignment of $2^{+}$ for the level. The radiation from this level to the 3.35 MeV ($0^{+}$) first excited state appears enhanced, thus lending support to the suggestion by Pope et al. that the 3.35-MeV level may have a stable deformation and that upon this level is built a band of vibrational states at higher excitation. Resonant absorption measurements on the ground-state radiation from the $E_p=1575.5\mathrm{}$-keV level gave ${\Gamma }_t=110\mathrm{}\pm 30$ eV and ${\Gamma }_{\gamma 0}=1.36\mathrm{}\pm 0.25$ eV. For the $E_p=1580\mathrm{}$ keV level, the yield curve gave ${\Gamma }_t=1060\mathrm{}\pm 200$ eV and a yield measurement gave ${\Gamma }_{\gamma 0}=0.80\mathrm{}\pm 0.26$ eV. At both levels, the ($p, \alpha$) cross section was measured to be ≤68 μb and thus ${\Gamma }_{\alpha }<~0.012 \mathrm{and} 0.068$ eV for the lower and upper levels, respectively. The proton widths are thus 110±30 and 1060±200 eV. Arguments are given for $J=1\mathrm{}$ assignment for the lower level. An even parity assignment is favored slightly by the experimental data. The possibility of "cross excitation" between the levels in the resonant absorption measurements is considered.