Investigation of the reaction {sup 208}Pb({sup 18}O, f): Fragment spins and phenomenological analysis of the angular anisotropy of fission fragments

Journal Article · Mon Oct 15 00:00:00 EDT 2007 · Physics of Atomic Nuclei

DOI:https://doi.org/10.1134/S106377880710002X· OSTI ID:21077601

Adeev, G D ^[1]; Itkis, M G; Karpov, A V ^[2]; Nadtochy, P N ^[1]; Pashkevich, V V; Pokrovsky, I V; Salamatin, V S ^[2]; Chubarian, G G ^[3]

---

1. Omsk State University (Russian Federation)
2. Joint Institute for Nuclear Research (Russian Federation)
3. Texas A and M University, Cyclotron Institute (United States)

The average multiplicity of gamma rays emitted by fragments originating from the fission of {sup 226}Th nuclei formed via a complete fusion of {sup 18}O and {sup 208}Pb nuclei at laboratory energies of {sup 18}O projectile ions in the range E{sub lab} = 78-198.5 MeV is measured and analyzed. The total spins of fission fragments are found and used in an empirical analysis of the energy dependence of the anisotropy of these fragments under the assumption that their angular distributions are formed in the vicinity of the scission point. The average temperature of compound nuclei at the scission point and their average angular momenta in the entrance channel are found for this analysis. Also, the moments of inertia are calculated for this purpose for the chain of fissile thorium nuclei at the scission point. All of these parameters are determined at the scission point by means of three-dimensional dynamical calculations based on Langevin equations. A strong alignment of fragment spins is assumed in analyzing the anisotropy in question. In that case, the energy dependence of the anisotropy of fission fragments is faithfully reproduced at energies in excess of the Coulomb barrier (E{sub c.m.} - E{sub B} {>=} 30 MeV). It is assumed that, as the excitation energy and the angular momentum of a fissile nucleus are increased, the region where the angular distributions of fragments are formed is gradually shifted from the region of nuclear deformations in the vicinity of the saddle point to the region of nuclear deformations in the vicinity of the scission point, the total angular momentum of the nucleus undergoing fission being split into the orbital component, which is responsible for the anisotropy of fragments, and the spin component. This conclusion can be qualitatively explained on the basis of linear-response theory.

• OSTI ID: 21077601
• Journal Information: Physics of Atomic Nuclei, Vol. 70, Issue 10; Other Information: DOI: 10.1134/S106377880710002X; Copyright (c) 2007 Nauka/Interperiodica; Article Copyright (c) 2007 Pleiades Publishing, Ltd; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-7788
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ANGULAR DISTRIBUTION
ANISOTROPY
COMPOUND NUCLEI
COULOMB FIELD
EMISSION
ENERGY DEPENDENCE
EXCITATION
FISSION
FISSION FRAGMENTS
GAMMA RADIATION
LANGEVIN EQUATION
LEAD 208 TARGET
MEV RANGE
MOMENT OF INERTIA
NUCLEAR DEFORMATION
OXYGEN 18
OXYGEN IONS
SPIN
THORIUM 226
THREE-DIMENSIONAL CALCULATIONS