Large-angle correlations between /sup 4/He and /sup 1,2,3/H or /sup 4/He in the reactions 247 and 337 MeV /sup 40/Ar+/sup nat/Ag: Unexpected properties of the nuclear stratosphere

Journal Article · Wed Jun 01 00:00:00 EDT 1988 · Phys. Rev. C; (United States)

DOI:https://doi.org/10.1103/PhysRevC.37.2561· OSTI ID:5226633

Lacey, R; Ajitanand, N N; Alexander, J M; de Castro Rizzo, D M; Peaslee, G F; Vaz, L C; Kaplan, M; Kildir, M; La Rana, G; Moses, D J; others, and

We have measured coincidences between /sup 4/He and /sup 1,2,3/H or a second /sup 4/He (large-angle correlations) in the reactions 247 and 337 MeV /sup 40/Ar+/sup nat/Ag. These coincidences are dominated by reactions leading to evaporation residues with spins of about 0--70(h2..pi..). Large values of the angle-integrated double and triple coincidence cross sections indicate that many particle evaporation chains involve 2 or 3 protons andor 2 or 3 alphas. The angular and energy distributions are well described by an evaporation model with Hauser-Feshbach coupling. However, one must employ effective evaporation barriers for /sup 1/H and /sup 4/He that are strongly reduced compared to empirical fusion barriers. The barrier reduction required for /sup 2/H is rather small, and for /sup 3/H no barrier reduction is needed. Evaporation calculations that include emitter deformation do not give a satisfactory explanation for these results. We suggest a new aspect of composite nucleus excitation and evaporation-like decay. A hot, very diffuse nuclear surface may be formed that promotes evaporative decay prior to its relaxation. The low barriers for /sup 1/H and /sup 4/He reflect the radial extent of this transitory, diffuse surface.

• Research Organization: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794
• OSTI ID: 5226633
• Journal Information: Phys. Rev. C; (United States), Vol. 37:6
• Country of Publication: United States
• Language: English

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73 NUCLEAR PHYSICS AND RADIATION PHYSICS
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CROSS SECTIONS
DEUTERONS
ENERGY SPECTRA
EVAPORATION MODEL
HAUSER-FESHBACH THEORY
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HADRONS
HEAVY ION REACTIONS
HELIUM ISOTOPES
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LIGHT NUCLEI
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NUCLEAR MODELS
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651820* - Nuclear Properties & Reactions
A=150-189
Experimental