Lifetimes of Al-26 and Cl-34 in an astrophysical plasma - art. no. 015801

Citation
A. Coc et al., Lifetimes of Al-26 and Cl-34 in an astrophysical plasma - art. no. 015801, PHYS REV C, 6101(1), 2000, pp. 5801
Citations number
20
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physics
Journal title
PHYSICAL REVIEW C-NUCLEAR PHYSICS
ISSN journal
0556-2813 → ACNP
Volume
6101
Issue
1
Year of publication
2000
Database
ISI
SICI code
0556-2813(200001)6101:1<5801:LOAACI>2.0.ZU;2-F
Abstract
We study here the onset of thermal equilibrium affecting the lifetimes of A l-26 and Cl-34 nuclei within a hot astrophysical photon gas. The Al-26 isot ope is of prime interest for gamma-ray astronomy with the observation of it s delayed (t(1/2) = 0.74 My) 1.809 MeV gamma-ray line. Its nucleosynthesis is complicated by the presence of a short lived (t(1/2) = 6.34 a) spin isom er. A similar configuration is found in Cl-34 where the decay of its isomer (Cl-34m, t(12) = 32 m) is followed by delayed gamma-ray emission with char acteristic energies. The lifetimes of such nuclei are reduced at high tempe rature by the thermal population of shorter lived levels. However, thermal equilibrium within Al-26 and Cl-34 levels is delayed by the presence of the isomer. We study here the transition to thermal equilibrium where branchin g ratios for radiative transitions are needed in order to calculate lifetim es. Since some of these very small branching ratios are not known experimen tally, we use results of shell model calculations.