Photoneutron cross sections for the silicon isotopes

Journal Article · Tue Mar 01 04:00:00 EST 1983 · Phys. Rev. C; (United States)

DOI:https://doi.org/10.1103/PhysRevC.27.960· OSTI ID:6031847

Pywell, R E; Berman, B L; Jury, J W; Woodworth, J G; McNeill, K G; Thompson, M N

The photoneutron cross sections for /sup 28/Si, /sup 29/Si, and /sup 30/Si have been measured up to 33 MeV with monoenergetic photons from the annihilation in flight of fast positrons, using neutron multiplicity counting. Average neutron energies were obtained simultaneously with the cross-section data by the ring-ratio technique. The giant dipole resonances for /sup 28/Si and /sup 30/Si exhibit appreciable fragmentation; that for /sup 29/Si does not. The (..gamma..,2n) cross section for /sup 30/Si is large; that for /sup 29/Si is consistent with zero. The (..gamma..,1n) cross section for /sup 30/Si decreases sharply with energy to values near zero as the (..gamma..,2n) cross section grows, then increases to appreciable values as the (..gamma..,2n) cross section diminishes; this extreme behavior, although never seen before, is attributable to the competition between the (..gamma..,n), (..gamma..,2n), and (..gamma..,pn) decay channels. Some properties of the isospin components of the giant resonance are inferred. Other features of the data, including the integrated cross sections, are found to be similar in many respects to corresponding results for the oxygen and magnesium isotopes. The /sup 28/Si nucleus is found to be a better ''core'' for /sup 29/Si and /sup 30/Si than might have been expected from previous descriptions of its open-shell character.

• Research Organization: Accelerator Laboratory, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0
• OSTI ID: 6031847
• Journal Information: Phys. Rev. C; (United States), Journal Name: Phys. Rev. C; (United States) Vol. 27:3; ISSN PRVCA
• Country of Publication: United States
• Language: English

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73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BARYONS
CROSS SECTIONS
DIPOLE MOMENTS
DIRECT REACTIONS
ELEMENTARY PARTICLES
FERMIONS
GIANT RESONANCE
HADRONS
ISOSPIN
KNOCK-OUT REACTIONS
MULTIPLICITY
NEUTRONS
NUCLEAR REACTIONS
NUCLEONS
PARTICLE PROPERTIES
PHOTONEUTRONS
PHOTONUCLEAR REACTIONS
PHOTONUCLEONS
RESONANCE
SILICON 28 TARGET
SILICON 29 TARGET
SILICON 30 TARGET
TARGETS