Mean lifetimes of levels in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ have been measured using the Doppler-shift-attenuation (DSA) method in conjunction with the reactions ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$${(}^{16}$O,pn${)}^{28}$Si and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$(p,γ${)}^{28}$Si. The lifetime values were determined for 16 bound levels below the excitation energy of 10 MeV and for the 10.42-, 10.67-, 11.10-, and 11.51-MeV alpha unstable states, and the 12.99-MeV proton or alpha unbound state. The lifetimes of the three last levels are reported for the first time. The targets were prepared by implanting ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ into Ta, and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ into Ta and Si substrates. The experimental stopping power of Ta for Si ions was determined by application of the inverted analysis of DSA data from the reaction ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${(}^{28}$Si,pγ${)}^{29}$Si. Computer simulations with the Monte Carlo method and experimental stopping power were used in the DSA analysis. Experimental transition matrix elements, based on the measured mean lifetime values, are compared with predictions of the universal sd-shell model.

• Received 18 August 1992

DOI:https://doi.org/10.1103/PhysRevC.47.145