Stellar neutron capture cross sections of the Ba isotopes

Journal Article · Tue Nov 01 00:00:00 EST 1994 · Physical Review, C (Nuclear Physics); (United States)

DOI:https://doi.org/10.1103/PhysRevC.50.2582· OSTI ID:6837141

Voss, F; Wisshak, K; Guber, K; Kaeppeler, F ^[1]; Reffo, G ^[2]

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1. Kernforschungszentrum Karlsruhe, Institut fuer Kernphysik, Postfach 3640, D-76021 Karlsruhe (Germany)
2. ENEA, Laboratorio Dati Nucleari, Viale Ercolani 8, I-40138 Bologna (Italy)

The neutron capture cross sections of [sup 134]Ba, [sup 135]Ba, [sup 136]Ba, and [sup 137]Ba were measured in the energy range from 5 to 225 keV. Neutrons were produced via the [sup 7]Li ([ital p],[ital n])[sup 7] Be reaction by bombarding metallic Li targets with a pulsed proton beam. Capture events were registered with the Karlsruhe 4[pi] barium fluoride detector. The cross section ratios were determined with an overall uncertainty of [similar to]3%, an improvement by factors of 5 to 8 compared to existing data. Severe discrepancies were found with respect to previous results. As a new possibility in time of flight experiments, isomeric cross section ratios could be determined for [sup 135]Ba, [sup 136]Ba, and [sup 137]Ba. Maxwellian averaged neutron capture cross sections were calculated for thermal energies between [ital kT]=10 keV and 100 keV. These stellar cross sections were used in an [ital s]-process analysis. For the [ital s]-only isotopes [sup 134]Ba and [sup 136]Ba the [ital N][sub [ital s]][l angle][sigma][r angle] ratio was determined to 0.875[plus minus]0.025. Hence, a significant branching of the [ital s]-process path at [sup 134]Cs can be claimed for the first time, in contrast to predictions from the classical approach. This branching yields information on the [ital s]-process temperature, indicating values around [ital T][sub 8]=2. The new cross sections are also important for the interpretation of barium isotopic anomalies, which were recently discovered in SiC grains of carbonaceous chondrite meteorites. Together with the results from previous experiments on tellurium and samarium, a general improvement of the [ital N][sub [ital s]][l angle][sigma][r angle] systematics in the mass range [ital A]=120--150 is achieved. This yields a more reliable separation of [ital s]- and [ital r]-process contributions for comparison with stellar observations, but reveals a 20% discrepancy with respect to the solar barium abundance.

• OSTI ID: 6837141
• Journal Information: Physical Review, C (Nuclear Physics); (United States), Vol. 50:5; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BARIUM 134 TARGET
NEUTRON REACTIONS
BARIUM 135 TARGET
BARIUM 136 TARGET
BARIUM 137 TARGET
CAPTURE
ABSORPTION
CROSS SECTIONS
EXPERIMENTAL DATA
MEV RANGE
R PROCESS
S PROCESS
TEMPERATURE DEPENDENCE
BARYON REACTIONS
DATA
ENERGY RANGE
HADRON REACTIONS
INFORMATION
NUCLEAR REACTIONS
NUCLEON REACTIONS
NUMERICAL DATA
SORPTION
STAR EVOLUTION
TARGETS
663430* - Nucleon-Induced Reactions & Scattering- (1992-)
663560 - Nuclear Mass Ranges- A=90-149- (1992-)