Prescission and postscission neutrons from the reactions p + sup 235,236,238 U with E sub p le 25. 6 MeV

Journal Article · Tue May 01 00:00:00 EDT 1990 · Physical Review, C (Nuclear Physics); (USA)

DOI:https://doi.org/10.1103/PhysRevC.41.2172· OSTI ID:6847767

Strecker, M; Wien, R; Plischke, P; Scobel, W ^[1]

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1. I. Institut fuer Experimentalphysik, Universitaet Hamburg, D-2000 Hamburg 50, Federal Republic of Germany (DE)

Prescission ({nu}{sub iso}) and postscission ({nu}{sub post}) neutron multiplicities have been measured for the reactions {ital p}+{sup 235,236,238}U at several projectile energies between 12.7 and 25.6 MeV in coincidence with binary fragments. Separation of {nu}{sub iso} from {nu}{sub post} was achieved under the assumption of isotropic emission in the respective source frames. Both multiplicities increase with initial excitation energy {ital E}{sub CN}{sup *} with comparable rates {Delta}{ital E}{sub CN}{sup *}/{Delta}{nu}{approx}17{plus minus}3 MeV. {nu}{sub iso}({ital E}{sub CN}{sup *}) extends existing data of heavy-ion induced fusion-fission with {ital E}{sub CN}{sup *}{ge}50 MeV; for {ital E}{sub CN}{sup *}{ge}20 MeV it is incompatible with the transition-state model and cannot be reproduced without a delay time for the fission competition in the order of 3{times}10{sup {minus}20}--10{sup {minus}19} s. The fragment mass dependence {nu}{sub post}({ital m}) shows a clear sawtooth structure for all three targets at {ital E}{sub {ital p}}=12.6 MeV that is gradually washed out with increasing {ital E}{sub {ital p}} or decreasing total kinetic energy TKE, because the heavier fragment receives most of the additional excitation energy. The nuclear temperatures of the heavy fragments exceed those of the light ones, but seem to approach each other with increasing fragment excitation.

• OSTI ID: 6847767
• Journal Information: Physical Review, C (Nuclear Physics); (USA), Vol. 41:5; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
PROTON REACTIONS
FISSION
PRECOMPOUND-NUCLEUS EMISSION
URANIUM 235 TARGET
URANIUM 236 TARGET
URANIUM 238 TARGET
ANGULAR MOMENTUM
COINCIDENCE SPECTROMETRY
FISSION FRAGMENT DETECTION
KINETIC ENERGY
MASS SPECTRA
MEV RANGE 10-100
MULTIPLICITY
NEUTRON EMISSION
STATISTICAL MODELS
TIME-OF-FLIGHT SPECTROMETERS
BARYON REACTIONS
CHARGED-PARTICLE REACTIONS
DETECTION
EMISSION
ENERGY
ENERGY RANGE
HADRON REACTIONS
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
MEV RANGE
NUCLEAR REACTIONS
NUCLEON REACTIONS
RADIATION DETECTION
SPECTRA
SPECTROMETERS
TARGETS
652020* - Nuclear Properties & Reactions
A=220 & above
Experimental