Time scales for fusion-fission and quasifission from giant dipole resonance decay

Journal Article · Tue Oct 01 04:00:00 EDT 1991 · Physical Review, C (Nuclear Physics); (United States)

DOI:https://doi.org/10.1103/PhysRevC.44.1515· OSTI ID:5129053

Butsch, R; Hofman, D J; Montoya, C P; Paul, P ^[1]; Thoennessen, M ^[2]

---

1. Department of Physics, State University of New York at Stony Brook, Stony Brook, New York (USA)
2. Department of Physics, State University of New York at Stony Brook, Stony Brook, New York (USA) Oak Ridge National Laboratory, Oak Ridge, Tennessee (USA)

Giant dipole resonance (GDR) {gamma} rays in coincidence with fission fragments were measured in the reactions {sup 16}O+{sup 208}Pb at 120 and 140 MeV, {sup 24}Mg+{sup 196}Pt at 150 MeV, and {sup 32}S+{sup nat}W at 185 MeV. {gamma}-ray--fission angular correlation measurements for {sup 16}O+{sup 208}Pb (120 and 140 MeV) and {sup 32}S+{sup nat}W confirm the strong contribution of prescission {gamma} rays to the total {gamma}-ray spectrum. The data were analyzed with a modified statistical model code which includes the effects of nuclear dissipation in the fission process, {gamma} decay at equilibrium and between saddle and scission, and the decay of the mononucleus formed in quasifission reactions. The extracted value for the nuclear friction coefficient of {gamma}=10{plus minus}3 at temperatures between 1 and 2 MeV is much larger than the upper limit for the ground state and indicates strongly overdamped large-scale mass motion. The extracted total fission time scale {tau}{sub fiss}({gamma}=10){congruent}2.9{times}10{sup {minus}19} s at 64 MeV excitation energy agrees with that extracted from recent neutron multiplicity experiments. A strong dependence of the GDR {gamma}-ray yield on the target-projectile mass asymmetry is interpreted in terms of the quasifission process. {gamma}-ray spectra and correlations could be fitted with the assumption of a GDR contribution from the mononucleus but required an arbitrary reduction of the total fission fragment excitation energy by 30 MeV. The quasifission lifetime was estimated to {tau}{sub qf}=(2--9){times}10{sup {minus}20} s.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5129053
• Journal Information: Physical Review, C (Nuclear Physics); (United States), Journal Name: Physical Review, C (Nuclear Physics); (United States) Vol. 44:4; ISSN 0556-2813; ISSN PRVCA
• Country of Publication: United States
• Language: English

Related Subjects

651820 -- Nuclear Properties & Reactions
A=150-189
Experimental
651920* -- Nuclear Properties & Reactions
A=190-219
Experimental
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ANGULAR CORRELATION
CHARGED-PARTICLE REACTIONS
COINCIDENCE METHODS
COINCIDENCE SPECTROMETRY
COMPOUND NUCLEI
CORRELATIONS
COUNTING TECHNIQUES
DATA
ELEMENTS
EXPERIMENTAL DATA
GAMMA SPECTRA
GIANT RESONANCE
HEAVY ION REACTIONS
INFORMATION
LEAD 208 TARGET
MAGNESIUM 24 REACTIONS
MATHEMATICAL MODELS
METALS
NUCLEAR REACTIONS
NUCLEAR TEMPERATURE
NUMERICAL DATA
OXYGEN 16 REACTIONS
PLATINUM 196 TARGET
QUASI-FISSION
RESONANCE
SPECTRA
STATISTICAL MODELS
SULFUR 32 REACTIONS
TARGETS
TRANSITION ELEMENTS
TUNGSTEN