Transition Probabilities within the (f72)3 Configuration of Ar41

Abstract

The lifetimes of the 165- and 518-keV levels of ${\mathrm{Ar}}^{41}$ have been measured by fast timing techniques. Halflives of 410±30 and 340±20 psec, respectively, were obtained from logarithmic slopes of the time-delay distributions. The time delays were marked by protons from the ${\mathrm{Ar}}^{40}(d, p\gamma ){\mathrm{Ar}}^{41}$ reaction detected in a solid-state counter and gamma rays detected with a plastic scintillator. The lower error limit for the half-life of the 165-keV level is somewhat uncertain because of difficulties in obtaining a true prompt resolution function for this measurement. $M1\mathrm{}$ hindrances relative to Moszkowski estimates for the 165- and 353-keV gamma rays are approximately 100 and 3000, respectively. These hindrances are consistent with dominant ${\left(f_{\frac{7}{2}}\right)}^3$ configurations predicted for the first three levels of ${\mathrm{Ar}}^{41}$ by Shadmi and Talmi plus a 2% ${\left(f_{\frac{7}{2}}\right)}^2\left(f_{\frac{5}{2}}\right)$ admixture into the 165-keV state. The 518-keV $E2\mathrm{}$ transition to the ground state, which is enhanced by a factor of approximately 5 relative to single-particle estimates, requires an effective neutron charge of $2.3e$ for ${\left(f_{\frac{7}{2}}\right)}^3$ configurations.