Fluctuation effects in radiative capture to unstable final states: A test via the {sup 89}Y({ital {rvec p}},{gamma}) reaction at {ital E}{sub {ital p}}=19.6 MeV

Journal Article · Sat Jul 01 04:00:00 EDT 1995 · Physical Review, C

DOI:https://doi.org/10.1103/PhysRevC.52.252· OSTI ID:69527

Parker, W E; Chadwick, M B; Dietrich, F S; Kammeraad, J E; Luke, S J; Sale, K E ^[1]; Chasteler, R M; Godwin, M A; Kramer, L H; Schmid, G J; Weller, H R ^[2]; Kerman, A K ^[3]

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1. Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States)
2. Duke University, Durham, North Carolina 27708 (United States)
3. Center for Theoretical Physics and Physics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

We have developed an extended direct-semidirect (DSD) model for fast-nucleon capture to virtual single-particle configurations that subsequently damp into the compound nucleus or (at sufficiently high excitation energies) escape into the continuum. The inclusion of final-state fluctuation effects is an important feature of this model. To test the model we have measured the spectra of gamma rays from approximately 10 MeV to the endpoint in the {sup 89}Y({ital {rvec p}},{gamma}) reaction with 19.6 MeV polarized protons from the TUNL tandem accelerator. Gamma spectra were measured with a pair of 25.4 cm{times}25.4 cm anticoincidence-shielded NaI detectors at angles of 30{degree}, 55{degree}, 90{degree}, 125{degree}, and 150{degree} with respect to the incident beam. The spectra show significant analyzing powers and forward peaking of the angular distributions. These features allow for the discrimination between compounds processes and direct processes. Analyzing powers and fore-aft asymmetries were observed for gamma energies below those associated with direct-semidirect transitions to known bound final states. We have also performed Hauser-Feshbach calculations of the statistical component of the gamma emission, which dominates below approximately 15--16 MeV. The extended DSD model reproduces the spectral shapes and analyzing powers above this energy quite well. There is no evidence in the present reaction that additional mechanisms, such as multistep compound or multistep direct emission, are required.

• Research Organization: Duke University
• DOE Contract Number: FG05-91ER40619
• OSTI ID: 69527
• Journal Information: Physical Review, C, Journal Name: Physical Review, C Journal Issue: 1 Vol. 52; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CAPTURE
FLUCTUATIONS
GAMMA SPECTRA
MEV RANGE 10-100
PHOTONS
POLARIZATION-ASYMMETRY RATIO
PROTON REACTIONS
SINGLE-PARTICLE MODEL
YTTRIUM 89 TARGET