Entrance Channel Parameters Research Articles

Unexpected show up of incomplete fusion at low projectile energies

In this paper, some of the important findings of recent measurements performed to study incomplete fusion at low bombarding energies (i.e., Elab ≈ 4-7 MeV/nucleon) in 12 C, 16 O+169 Tm systems are briefly summarized. The spin-distributions of xn, pxn, α xn/2α xn- channels have been measured to probe entirely different γ -emission patterns (and feeding intensity profiles) during the de-excitation of complete and incomplete fusion objects. Incomplete fusion strength function has been deduced (from the analysis of experimental excitation functions in context of equilibrated compound nucleus decay) to achieve information of onset and strength of incomplete fusion in terms of various entrance channel parameters. Presence of incomplete fusion at slightly above barrier energies has been confirmed by the measurement of linear momentum distribution of heavy recoils. Present results conclusively demonstrate, the existence of incomplete fusion at low bombarding energies, its strong dependence on entrance channel parameters, and the possibility to populate high spin states.

Entrance channel effect in the incomplete fusion reactions

In the present work the effect of various entrance channel parameters on incomplete fusion strength and the reaction dynamics in 12 C+159 Tb system at energies ≈ 4-7MeV/A have been investigated by measuring the excitation functions of individual reaction channels. Experimental excitation functions have been analyzed in the framework of compound nucleus decay using statistical model code PACE4. Analysis of data suggests the production of x n/px n-channels via complete fusion of 12 C with 159 Tb, as these are found to be well reproduced by PACE4 predictions, while, a significant enhancement in the excitation functions of α-emitting channels has been observed over the theoretical ones. This enhancement has been attributed due to incomplete fusion. For better insight into the underlying dynamics, fraction of incomplete fusion to the total fusion has been deduced and compared with 16 O+159 Tb and other nearby systems as a function of various entrance channel parameters. The fraction of incomplete fusion has been found to be sensitive to the projectile type, energy and entrance-channel mass-asymmetry.

Effect of entrance channel parameters on the fusion of two heavy ions: Excitation functions of reaction products in16O +66Zn and37Cl +45Sc reactions

Excitation functions of reaction products formed in16O +66Zn and37Cl +45Sc systems, leading to the same compound nucleus,82Sr, were measured using recoil-catcher technique and off-line γ-ray spectrometry. The contribution of non-compound processes like transfer and incomplete fusion (ICF) reactions to the cross-sections of different evaporation residues were delineated by comparing the experimental data with the predictions of Monte Carlo simulation code PACE2. The results show that non-compound processes become a significant fraction of the total reaction cross-section in16O +66 systems in the beam energy range studied, while37Cl +45Sc gives mainly compound nucleus products. The mass asymmetry dependence of the fusion and non-compound cross-sections have been analysed in terms of the static fusion model and sum rule model

Emission-angle dependence of fission fragment spin.

The average spin of fission fragment at specific mass asymmetry has been obtained as a function of emission angles in the $^{238}\mathrm{U}$ (${\mathrm{\ensuremath{\alpha}}}_{39.1\mathrm{M}\mathrm{e}\mathrm{V}}$,f) system from radiochemically determined independent isomeric yield ratios of $^{132}\mathrm{I}$. The fragment average spin is seen to decrease from 11.2\ensuremath{\Elzxh} to 6.5\ensuremath{\Elzxh} with change in emission angle from 90\ifmmode^\circ\else\textdegree\fi{} to 20\ifmmode^\circ\else\textdegree\fi{}, due to the angle-dependent tilting component over and above the statistical wriggling, bending, and twisting components as per the collective mode model. Effects of entrance channel parameters and multichance fission are also discussed.

Photochemistry in Excited States of Van der Waals Complexes

For studying the chemical reaction occurring when one of the collision partner is electronically excited, one can use the unique property of the intermolecular interaction: at long distance the potential is attractive and often present a small minimum, the van der Waals minimum. It is then possible by cooling the gas mixture of the reactives in a supersonic expansion to freeze the collisional complex into this van der Waals potential depth. The reactive process is triggered by an optical excitation, which promotes the system onto the reactive surface and the products obtained are analysed by laser induced fluorescence.In this technique all the entrance channel parameters are known: the kinetic energy is zero, and the partner are initially oriented. Moreover the spectroscopic studies of the complex give direct grasp of the potential energy surface, and on the alignment of the electronic orbitals upon the intermolecular axis.

The heavy-ion fusion in terms of the Rutherford trajectories

In the present work we suggest for the closest-distance approach, defined in the «elastic» model for heavy-ion fusion, a new expression depending on theQ-value of the compound nucleus. This dependence points out the existence of a saturation law which is a common property of all the systems. The saturation law can be connected with the properties of the nucleus-nucleus potential. Moreover, we give a condition by which the nucleus-nucleus potential can be expressed as a function of the entrance channel parameters.

Determination of the nucleus-nucleus potential from the generalized critical-distance model

In the present work we get an analytical expression of the nuclear part VN of the nucleus-nucleus potential in terms of the critical-distance and entrancechannel parameters. The critical distance is obtained in the framework of the generalized critical-distance model. By using VN, we derive for several reactions the universal function U(s), which displays the known scaling behaviour.

A study of some 3He induced reactions on 13C and the structure of 16O

A study of angular distributions and excitation functions of several reactions produced by bombarding 13C with 3He ions with energies from 2.0 to 8.0 MeV indicates the importance of the structure of 16O in this process. An optical-model analysis of the elastic scattering from 13C provided the entrance channel parameters for a DWBA calculation of the ( 3He, α) reaction. The results of this calculation indicate the inadequacy of this approach. An optical- model-plus-resonance analysis was also attempted for the elastic scattering of 3He from both 12C and 13C to account for some observed anomalies. A statistical analysis of the 13 C( 3 He, α) 12 C data indicates that the assumption Λ ≫ D is a credible one, although at 6.0 MeV 3He energy, a resonance in 16O becomes apparent. A spin and parity assignment J π = 3 − is suggested for this new state in 16O. The eigenchannel calculations of Wahsweiler, Danos and Greiner predict a 3 −( T = 0) state in 16O near this excitation energy.