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Title: Evidence for Coulomb effects on the fusion barrier distribution for deformed projectile nuclei

Abstract

Coulomb effects during the interaction of light deformed projectile nuclei with a heavy collision partner have been predicted to modify the fusion barrier distribution leading to a hindrance in the sub-barrier fusion cross section. In order to verify this experimentally, we have determined the fusion barrier distributions from the measurement of quasielastic excitation functions for {sup 16}O(spherical)+{sup 115}In, {sup 28}Si(oblate)+ {sup 115}In, and {sup 30}Si(prolate)+ {sup 115}In systems. For {sup 16}O+{sup 115}In system, the fusion barrier distribution is single peaked, whereas for {sup 28}Si+{sup 115}In and {sup 30}Si+{sup 115}In systems, one observes broadening and well defined structures in fusion barrier distribution, which could be explained by coupled-channel calculations performed using the CCFULL code after including deformation and Coulomb effects on the projectile in the field of target nucleus.

Authors:
; ; ; ; ; ; ; ; ;  [1];  [2]
  1. Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India)
  2. Microtron Center, Department of Physics, Mangalore University, Mangalore-574 199 (India)
Publication Date:
OSTI Identifier:
20995301
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevC.75.054615; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; COUPLED CHANNEL THEORY; DEFORMED NUCLEI; DISTRIBUTION; EXCITATION FUNCTIONS; HEAVY ION REACTIONS; INDIUM 115; OXYGEN 16; SILICON 28; SILICON 30; VISIBLE RADIATION

Citation Formats

Nayak, B. K., Choudhury, R. K., Saxena, A., Sahu, P. K., Thomas, R. G., Biswas, D. C., John, B. V., Mirgule, E. T., Gupta, Y. K., Bhike, M., and Rajprakash, H. G.. Evidence for Coulomb effects on the fusion barrier distribution for deformed projectile nuclei. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.054615.
Nayak, B. K., Choudhury, R. K., Saxena, A., Sahu, P. K., Thomas, R. G., Biswas, D. C., John, B. V., Mirgule, E. T., Gupta, Y. K., Bhike, M., & Rajprakash, H. G.. Evidence for Coulomb effects on the fusion barrier distribution for deformed projectile nuclei. United States. doi:10.1103/PHYSREVC.75.054615.
Nayak, B. K., Choudhury, R. K., Saxena, A., Sahu, P. K., Thomas, R. G., Biswas, D. C., John, B. V., Mirgule, E. T., Gupta, Y. K., Bhike, M., and Rajprakash, H. G.. Tue . "Evidence for Coulomb effects on the fusion barrier distribution for deformed projectile nuclei". United States. doi:10.1103/PHYSREVC.75.054615.
@article{osti_20995301,
title = {Evidence for Coulomb effects on the fusion barrier distribution for deformed projectile nuclei},
author = {Nayak, B. K. and Choudhury, R. K. and Saxena, A. and Sahu, P. K. and Thomas, R. G. and Biswas, D. C. and John, B. V. and Mirgule, E. T. and Gupta, Y. K. and Bhike, M. and Rajprakash, H. G.},
abstractNote = {Coulomb effects during the interaction of light deformed projectile nuclei with a heavy collision partner have been predicted to modify the fusion barrier distribution leading to a hindrance in the sub-barrier fusion cross section. In order to verify this experimentally, we have determined the fusion barrier distributions from the measurement of quasielastic excitation functions for {sup 16}O(spherical)+{sup 115}In, {sup 28}Si(oblate)+ {sup 115}In, and {sup 30}Si(prolate)+ {sup 115}In systems. For {sup 16}O+{sup 115}In system, the fusion barrier distribution is single peaked, whereas for {sup 28}Si+{sup 115}In and {sup 30}Si+{sup 115}In systems, one observes broadening and well defined structures in fusion barrier distribution, which could be explained by coupled-channel calculations performed using the CCFULL code after including deformation and Coulomb effects on the projectile in the field of target nucleus.},
doi = {10.1103/PHYSREVC.75.054615},
journal = {Physical Review. C, Nuclear Physics},
number = 5,
volume = 75,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • By the end of the last century, the precision of heavy-ion-fusion cross-section measurement had been increased up to 1%. This allowed the measured cross sections to be converted into experimental fusion-barrier distributions. In the experimental analysis, the barrier distributions were analyzed using a Woods-Saxon shape for the nuclear part of the bare nucleus-nucleus potential. This potential was defined along the line joining the centers of the two nuclei ('centerline potential'), which, for deformed nuclei, contradicts the short-range character of the nucleon-nucleon (N N) nuclear interaction. We present the results of our theoretical study of the significant deviations of the simplifiedmore » potential from a 'realistic' nuclear potential. The finite-size effects on the potential for deformed nuclei were first investigated in an approximate geometrical way. Then a more rigorous approach, namely, a semimicroscopic double-folding model, was applied to calculate the nucleus-nucleus potential. The angle-dependent fusion barriers calculated with a simple delta-function-like exchange term of the N N M3Y interaction was found to be very similar to those calculated with a finite-range expression. This circumstance enables us to perform rather quick calculations of the fusion cross sections and the corresponding barrier distributions. Comparison of the results with the experimental data showed that the finite-size effects are substantial and cannot be ignored in a quantitative analysis of experimental fusion cross sections and barrier distributions.« less
  • Fission-fragment mass distribution has been studied for the {sup 16}O+{sup 232}Th,{sup 209}Bi systems over an energy range of 102.8-78.6 MeV and 81.6-72.6 MeV, respectively, in a laboratory frame. The variance of the mass distribution ({sigma}{sub m}{sup 2}) for the {sup 16}O+{sup 209}Bi system varies linearly with center of mass energy, while a significant anomalous behavior is found for the system {sup 16}O+{sup 232}Th. Coupled with our earlier observation for the system {sup 19}F+{sup 232}Th [T. K. Ghosh et al., Phys. Rev. C 69, 031603(R) (2004)], we propose that the accurate measurement of mass distribution is a powerful tool to lookmore » for the onset of a nonstatistical reaction mechanism in heavy-ion-induced fission of deformed heavy nuclei.« less
  • Fusion excitation functions have been measured spanning the entire barrier region in 1 MeV energy steps for the two systems {sup 40}Ca+{sup 192}Os,{sup 194}Pt. Precautions were taken to ensure sufficiently small errors to allow for extraction of the distribution of fusion barriers from the second differential of the product of {ital E} and {sigma}. These results are compared with coupled channels calculations which take into account the most important degrees of freedom of both projectile and target. The influence of the prolate deformation of {sup 192}Os and the oblate deformation of {sup 192}Pt as well as the octupole vibration ofmore » {sup 40}Ca is apparent. {copyright} {ital 1996 The American Physical Society.}« less
  • The authors comment on the Letter by J.D. Bierman et al., Phys. Rev. Lett. 76, 1587(1996), and show the method by which they have been constructed is not the most appropriate. A Comment on the Letter by J.D. Bierman, {ital et al. }, Phys.Rev.Lett.{bold 76}, 1587 (1996). The authors of the Letter offer a Reply. {copyright} {ital 1997} {ital The American Physical Society}
  • Quasielastic excitation function measurement has been carried out for the {sup 4}He + {sup 232}Th system at {theta}{sub lab}=160 deg. with respect to the beam direction, to obtain a representation of the fusion-barrier distribution. Using the present data along with previously measured barrier distribution results on {sup 12}C, {sup 16}O, and {sup 19}F + {sup 232}Th systems, a systematic analysis has been carried out to investigate the role of target and/or projectile structures on fusion-barrier distribution. It is observed that for {sup 4}He, {sup 12}C, and {sup 16}O + {sup 232}Th reactions, the couplings due to target states only aremore » required in coupled-channel fusion calculations to explain the experimental data, whereas for the {sup 19}F + {sup 232}Th system along with the coupling of target states, inelastic states of {sup 19}F are also required to explain the experimental results on fusion-barrier distribution. The width of the barrier distribution shows interesting transition behavior when plotted with respect to the target-projectile charge product for the above systems.« less