Abstract
Mean lifetimes of bound states in were inferred from the Doppler-shift-attenuation (DSA) of γ rays produced in the inverse reaction N,pγ) and from the primary gamma-ray-induced Doppler broadening (GRID) of secondary γ rays in the thermal-neutron capture reaction (n,γ). Targets for the DSA measurements were prepared by implanting first neon into a gold backing and then deuterium into the same region such that deuterium was trapped at the neon precipitates. To find out experimentally the initial velocity distributions of the recoiling nuclei, another target was prepared by implanting deuterium into silicon, which is a slow stopping-power medium. Computer simulations with the Monte Carlo method and experimental stopping powers were used in the DSA analysis of the γ-ray line shapes. This analysis yielded the following lifetimes for eight bound levels in : 43±4 fs (5.30 MeV), <12 fs (6.32 MeV), 11±2 fs (7.16 MeV), <3 fs (7.30 MeV), 129±6 fs (7.57 MeV), <3 fs (8.31 MeV), <10 fs (8.57 MeV), and <4 fs (9.05 MeV). GRID measurements were made with melamine () and with silicon nitride () as both targets and slowing-down media. Measurements were also made with air (80% nitrogen). The Doppler-broadened γ-ray line shapes were analyzed by molecular-dynamics simulations of the slowing-down process to obtain the lifetime values of 40±3 fs (5.30 MeV), <2 fs (6.32 MeV), <3 fs (7.30 MeV), and <3 fs (8.31 MeV) for levels in . The extent to which the mirror symmetry of levels in and is valid is examined in some detail.
- Received 24 February 1994
DOI:https://doi.org/10.1103/PhysRevC.50.682
©1994 American Physical Society