The ($p,p^{\prime }\gamma$) reaction has been used to study ${\mathrm{Ca}}^{42}$. Back-scattered protons were detected in an annular solid-state detector of 0.8-sr solid angle. The $\gamma$ rays were detected in a 32-cc Ge(Li) detector placed at 55° and 125° with respect to the beam. By the Doppler-shift attenuation method (DSAM) the lifetimes of states in ${\mathrm{Ca}}^{42}$ with the following energies have been measured: 2.422 MeV [0.30(+0.04, -0.03) psec]; 2.750 MeV [3.4(+11, -0.17) psec]; 3.250 MeV [0.3(+0.15, -0.10) psec]; 3.297 MeV [$3.4(+\infty ,-2.1)$ psec]; 3.389 MeV (0.325±0.075 psec); 3.442 MeV [1.35(+1.3, -1) psec]; and 3.651 MeV [0.06(±0.08, -0.06) psec]. The 1.523-MeV $2^{+}$ state was measured to have a lifetime in close agreement with the known lifetimes. The Doppler shift on the 4.43-MeV state in ${\mathrm{C}}^{12}$ was also measured. Branching ratios are reported for 14 states. The reduced matrix elements $B\left(\sigma \lambda \right)$ are given for 26 transitions. On the basis of branching-ratio information, $B\left(\sigma \lambda \right)$, and previously existing information, spin and parity inferences have been made for the following states: 3.250 MeV ($4^{+}$);3.297 MeV ($2^{+}$, $1^{-}$); 3.883 MeV ($1^{-}$, $2^{+}$); and 4.043 MeV ($2^{+}$, $3^{-}$, $4^{+}$). For other states, we support recent assignments from ($t,p$) data. Our transition rates for the 2.422-MeV ($2^{+}$), 2.750-MeV ($4^{+}$), and 3.250-MeV ($4^{+}$) states show strong enhancement over single-particle rates. These results, together with the known enhanced rates for the 1.523-MeV ($2^{+}$) and 1.836-MeV ($0^{+}$) states, strongly support the interpretation of the low-lying levels in ${\mathrm{Ca}}^{42}$ as mixtures of a rotational band and simple shell-model configurations. The level at 3.250 MeV, ($4^{+}$) fits naturally into this scheme.

• Received 19 August 1968

DOI:https://doi.org/10.1103/PhysRev.177.1725