S. Raman et al., LIFETIMES IN N-15 FROM GAMMA-RAY LINE-SHAPES PRODUCED IN THE H-2(N-14,P-GAMMA) AND N-14(THERMAL N,GAMMA) REACTIONS, Physical review. C. Nuclear physics, 50(2), 1994, pp. 682-697
Mean lifetimes of bound states in N-15 were inferred from the Doppler-
shift-attenuation (DSA) of gamma rays produced in the inverse reaction
H-2(N-14, pgamma) and from the primary gamma-ray-induced Doppler broa
dening (GRID) of secondary gamma rays iu the thermal-neutron capture r
eaction N-14(n, gamma). 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 precipitat
es. To find out experimentally the initial velocity distributions of t
he recoiling N-15 nuclei, another target was prepared by implanting de
uterium into silicon, which is a slow stopping-power medium. Computer
simulations with the Monte Carlo method and experimental stopping powe
rs were used in the DSA analysis of the gamma-ray line shapes. This an
alysis yielded the following lifetimes for eight bound levels in N-15:
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 me
lamine (C3H6N6) and with silicon nitride (Si3N4) as both targets and s
lowing-down media. Measurements were also made with air (80% nitrogen)
. The Doppler-broadened gamma-ray line shapes were analyzed by molecul
ar-dynamics simulations of the slowing-down process to obtain the life
time 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 N-15. The extent to which t
he mirror symmetry of levels in N-15 and O-15 is valid is examined in
some detail.