Tests for equilibration of {sup 149}Tb{sup *} composite nuclei produced in the reactions 337 MeV {sup 40}Ar+{sup nat}Ag and 640 MeV {sup 86}Kr+{sup 63}Cu

Journal Article · Tue Mar 01 04:00:00 EST 1994 · Physical Review, C

DOI:https://doi.org/10.1103/PhysRevC.49.1587· OSTI ID:142680

Boger, J; Alexander, J M; Lacey, R A; Narayanan, A ^[1]

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1. Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794 (United States)

Experimental results are compared for the two matched heavy ion reactions 337 MeV {sup 40}Ar+{sup nat}Ag and 640 MeV {sup 86}Kr+{sup 63}Cu as a test of the extent of equilibration of the intermediate composite nucleus {sup 149}Tb{sup *}({ital E}{sup *}=194 MeV). Spin zones associated with the evaporation residues (ER) are found to agree well for these entrance channels. Agreement is not as close for the fission class due to the inclusion of deeply inelastic reactions (DIR) along with fusion-fission (FF) for the {sup 86}Kr reaction. Inclusive and coincidence measurements of energy spectra and angular distributions for the light charged particles indicate that these reactions produce composite nuclei with similar temperatures, spins, and moments of inertia. The energy spectra for both reactions are identically shifted relative to statistical model calculations. This suggests that the composite nuclei are highly distended prior to their cooling by particle evaporation. Multiplicities also agree for {sup 1}H and {sup 4}He production in association with the ER and FF reaction classes. It is noteworthy that prescission {sup 1}H and {sup 4}He multiplicities are in such good agreement, because the magnitude of these multiplicities seems to be dictated by the dynamical time scale of the fission process. That these prescission multiplicities are large suggests that the fission time scale is slow relative to particle evaporation; that they match for these reactions indicates that this is an equilibrium property of the intermediate composite nuclei. We conclude that extensive and rapid thermalization and shape equilibration have occurred despite estimates that the nuclear relaxation time and decay lifetime are nearly the same.

• OSTI ID: 142680
• Journal Information: Physical Review, C, Journal Name: Physical Review, C Journal Issue: 3 Vol. 49; ISSN PRVCAN; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ALPHA PARTICLES
ANGULAR DISTRIBUTION
ARGON 40 REACTIONS
CHARGED PARTICLES
COMPOUND NUCLEI
COPPER 63 TARGET
ENERGY SPECTRA
EXCITED STATES
EXPERIMENTAL DATA
FISSION
KRYPTON 86 REACTIONS
MEV RANGE 100-1000
PROTONS
SILVER 107 TARGET
STATISTICAL MODELS
TERBIUM 149