Neutron capture in [sup 148,150]Sm: A sensitive probe of the [ital s]-process neutron density

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Physical Review, C (Nuclear Physics); (United States)

DOI:https://doi.org/10.1103/PhysRevC.48.1401· OSTI ID:6275955

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

---

1. Kernforschungszentrum Karlsruhe, Institut fuer Kernphysik, D-76021 Karlsruhe (Germany)
2. Comitato Nazionale dell'Energia Nucleare e dell'Energie Alternative, I-40138, Bologna (Italy)

The neutron capture cross sections of [sup 147,148,149,150,152]Sm were measured in the energy range from 3 to 225 keV at the Karlsruhe Van de Graaff accelerator using gold as a standard. 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. Several runs were performed under different experimental conditions to study the systematic uncertainties in detail. For the first time, data were recorded with an ADC system that allows one to register gamma-ray energy and time of flight of the individual detector modules. The cross-section ratios were determined with an overall uncertainty of [similar to]1%. This is an improvement by about a factor of 5 compared to the existing data. Severe discrepancies were found with the results of previous measurements. Maxwellian-averaged neutron capture cross sections were calculated for thermal energies between [ital kT]=10 and 100 keV by normalizing the cross-section shape up to 700 keV neutron energy reported in literature to the present data. These stellar cross sections were used in an [ital s]-process analysis. The ratio of the values of the [ital s]-process current [l angle][sigma][r angle][ital N][sub [ital s]] (Maxwellian-averaged neutron capture cross section times [ital s]-process abundance) for the [ital s]-only isotopes [sup 148,150]Sm is 0.870[plus minus]0.009 rather than unity as expected by the local approximation. The corresponding branching in the [ital s]-process path is analyzed in the framework of the classical approach. The resulting mean neutron density, [ital n][sub [ital n]]=(3.8[plus minus]0.6)[times]10[sup 8] cm[sup [minus]3], is the most stringent value obtained so far.

• OSTI ID: 6275955
• Journal Information: Physical Review, C (Nuclear Physics); (United States), Journal Name: Physical Review, C (Nuclear Physics); (United States) Vol. 48:3; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: English

Related Subjects

663430* -- Nucleon-Induced Reactions & Scattering-- (1992-)
663560 -- Nuclear Mass Ranges-- A=90-149-- (1992-)
663570 -- Nuclear Mass Ranges-- A=150-189-- (1992-)
663610 -- Neutron Physics-- (1992-)
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BARYON REACTIONS
CAPTURE
CROSS SECTIONS
ENERGY RANGE
GAMMA SPECTROSCOPY
HADRON REACTIONS
INTEGRAL CROSS SECTIONS
ISOTOPES
KEV RANGE
NEUTRON DENSITY
NEUTRON REACTIONS
NUCLEAR REACTIONS
NUCLEON REACTIONS
RARE EARTH ISOTOPES
S PROCESS
SAMARIUM ISOTOPES
SPECTROSCOPY
STAR EVOLUTION