Spin distribution of the compound nucleus formed byO16+154

Abstract

Gamma-ray multiplicities for the 0+ Sm system have been determined using two different coincidence techniques. Fusion events are tagged either by observation of low-lying gamma transitions in the evaporation residues or by direct detection of the residues exploiting an electrostatic deflector and time-of-flight identification. The gamma-ray tagging measurements have been made with higher sensitivity than previously, allowing us to include the contribution of the 3n channel. The contribution of this channel modifies the conclusions made before in regard to the spin distribution of the compound nucleus produced at near-barrier energies. The procedure for conversion of gamma-ray multiplicities to mean spin values has been calibrated by measuring gamma-ray multiplicities and fusion cross sections for the He+' Er and He+' Er reactions that lead to the same compound nucleus as 0+ Sm, at bombarding energies that span the same region of excitation energies and spin. The use of an electrostatic deflector enables an inclusive tag on all evaporation residues, and has sufEcient sensitivity to enable measurements at a lower energy than is possible with gamma-ray tagging techniques. The energy dependence of the mean spin deduced from gamma-ray multiplicity measurements is in qualitative agreement with model calculations which include the effects of the static and dynamical deformations of the target nucleus. There is, however, a tendency for the calculations to underestimate somewhat the mean spin near and below the barrier.

Coupled-channels analyses of scattering and fusion cross sections ofO16+

“…14, we present calculated average values of spin distribution (L) for the 0 + is ' Sm systems in comparison with the experimental data [17,18]. The calculated (L) are again in good agreement with the measured values.…”

“…[8,9], together with elastic and inelastic scattering data [14 -16] for the xsO + xsz~»4Sm axid isO + xssW systems. Data of partial fusion cross sectioxis [17] and average spin of the fused systems [17,18] will also be considered in the analysis. In the extended CC approach [6,13], the fusion and other direct reactions (mainly particletransfer reactions that are not taken into account explicitly in the calculations) are described in terms of the imaginary part of the optical potential; the imaginary part thus consists of two parts, i.e.…”

“…Calculated average spin values (L) for (a) the 0 + Sm system and (b) the 0 + Sm system in comparison with the experimental data of Refs [17,18],. respectively.…”

Subbarrier fusion in the interacting boson model

“…For comparison we show with the dashed curve the average angular momentum calculated using the coupledchannels code CCDEF [33], including quadrupole, octupole and hexadecapole couplings [31]. The better agreement of the coupled-channels calculation than the IBM calculation with the data may be due to our neglect of the octupole vibration state and of g bosons.…”

Description of nuclear structure effects in sub-barrier fusion by the interacting boson model

“…Vandenbosch and his collaborators at the University of Washington, Seattle devoted considerable time to the measurement of angular momentum distributions [6,19]. In Fig.…”