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Title: Channel coupling effects on the fusion excitation functions for {sup 28}Si+{sup 90,94}Zr in sub- and near-barrier regions

Abstract

Fusion excitation functions and angular distributions of evaporation residues (ERs) have been measured for {sup 28}Si+{sup 90,94}Zr systems around the Coulomb barrier using the recoil mass spectrometer, Heavy Ion Reaction Analyzer (HIRA). For both systems, the experimental fusion cross sections are strongly enhanced compared to the predictions of the one-dimensional barrier penetration model (1-d BPM) below the barrier. Coupled channels formalism has been employed to theoretically explain the observed sub-barrier fusion cross section enhancement. The enhancement could be explained by considering the coupling of the low-lying inelastic states of the projectile and target in the {sup 28}Si+{sup 90}Zr system. In the sub-barrier region, the measured fusion cross sections for {sup 28}Si+{sup 94}Zr turned out to be about an order of magnitude higher than the ones for the {sup 28}Si+{sup 90}Zr system, which could not be explained by coupling to inelastic states alone. This observation indicates the importance of multinucleon transfer reaction channels with positive Q values in the sub-barrier fusion cross section enhancement, because {sup 90,94}Zr are believed to have similar collective strengths. This implies that no strong isotopic dependence of fusion cross sections is expected as far as the couplings to collective inelastic states are concerned. In addition, themore » role of projectile and multiphonon couplings in the enhancement has been explored.« less

Authors:
; ; ; ; ; ; ; ;  [1]; ; ; ; ; ; ;  [2];  [3]; ;  [4];  [5]
  1. Department of Physics and Astrophysics, University of Delhi, Delhi-110007 (India)
  2. Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi-110067 (India)
  3. Department of Physics, Calicut University, Calicut-673635 (India)
  4. Department of Physics, Panjab University, Chandigarh-160014 (India)
  5. Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar, Kolkata-700064 (India)
Publication Date:
OSTI Identifier:
21388941
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 81; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevC.81.044610; (c) 2010 The American Physical Society
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ANGULAR DISTRIBUTION; COULOMB FIELD; COUPLED CHANNEL THEORY; COUPLING; EVAPORATION; EXCITATION FUNCTIONS; FORECASTING; HEAVY ION REACTIONS; MASS SPECTROMETERS; MULTI-NUCLEON TRANSFER REACTIONS; ONE-DIMENSIONAL CALCULATIONS; PROJECTILES; RECOILS; RESIDUES; SILICON 28; THERMONUCLEAR REACTIONS; ZIRCONIUM 90; ZIRCONIUM 94; CROSS SECTIONS; DIFFERENTIAL CROSS SECTIONS; DIRECT REACTIONS; DISTRIBUTION; ELECTRIC FIELDS; EVEN-EVEN NUCLEI; FUNCTIONS; INTERMEDIATE MASS NUCLEI; ISOMERIC TRANSITION ISOTOPES; ISOTOPES; LIGHT NUCLEI; MEASURING INSTRUMENTS; MILLISECONDS LIVING RADIOISOTOPES; NUCLEAR REACTIONS; NUCLEI; NUCLEOSYNTHESIS; PHASE TRANSFORMATIONS; RADIOISOTOPES; SILICON ISOTOPES; SPECTROMETERS; STABLE ISOTOPES; SYNTHESIS; TRANSFER REACTIONS; ZIRCONIUM ISOTOPES

Citation Formats

Kalkal, Sunil, Mandal, S., Verma, Shashi, Saxena, Mansi, Goyal, Savi, Siwal, Davinder, Garg, Ritika, Kumar, Suresh, Singh, R., Madhavan, N., Jhingan, A., Nath, S., Gehlot, J., Varughese, T., Golda, K. S., Muralithar, S., Prasad, E., Sandal, Rohit, Behera, B. R., and Pramanik, U. D.. Channel coupling effects on the fusion excitation functions for {sup 28}Si+{sup 90,94}Zr in sub- and near-barrier regions. United States: N. p., 2010. Web. doi:10.1103/PHYSREVC.81.044610.
Kalkal, Sunil, Mandal, S., Verma, Shashi, Saxena, Mansi, Goyal, Savi, Siwal, Davinder, Garg, Ritika, Kumar, Suresh, Singh, R., Madhavan, N., Jhingan, A., Nath, S., Gehlot, J., Varughese, T., Golda, K. S., Muralithar, S., Prasad, E., Sandal, Rohit, Behera, B. R., & Pramanik, U. D.. Channel coupling effects on the fusion excitation functions for {sup 28}Si+{sup 90,94}Zr in sub- and near-barrier regions. United States. doi:10.1103/PHYSREVC.81.044610.
Kalkal, Sunil, Mandal, S., Verma, Shashi, Saxena, Mansi, Goyal, Savi, Siwal, Davinder, Garg, Ritika, Kumar, Suresh, Singh, R., Madhavan, N., Jhingan, A., Nath, S., Gehlot, J., Varughese, T., Golda, K. S., Muralithar, S., Prasad, E., Sandal, Rohit, Behera, B. R., and Pramanik, U. D.. 2010. "Channel coupling effects on the fusion excitation functions for {sup 28}Si+{sup 90,94}Zr in sub- and near-barrier regions". United States. doi:10.1103/PHYSREVC.81.044610.
@article{osti_21388941,
title = {Channel coupling effects on the fusion excitation functions for {sup 28}Si+{sup 90,94}Zr in sub- and near-barrier regions},
author = {Kalkal, Sunil and Mandal, S. and Verma, Shashi and Saxena, Mansi and Goyal, Savi and Siwal, Davinder and Garg, Ritika and Kumar, Suresh and Singh, R. and Madhavan, N. and Jhingan, A. and Nath, S. and Gehlot, J. and Varughese, T. and Golda, K. S. and Muralithar, S. and Prasad, E. and Sandal, Rohit and Behera, B. R. and Pramanik, U. D.},
abstractNote = {Fusion excitation functions and angular distributions of evaporation residues (ERs) have been measured for {sup 28}Si+{sup 90,94}Zr systems around the Coulomb barrier using the recoil mass spectrometer, Heavy Ion Reaction Analyzer (HIRA). For both systems, the experimental fusion cross sections are strongly enhanced compared to the predictions of the one-dimensional barrier penetration model (1-d BPM) below the barrier. Coupled channels formalism has been employed to theoretically explain the observed sub-barrier fusion cross section enhancement. The enhancement could be explained by considering the coupling of the low-lying inelastic states of the projectile and target in the {sup 28}Si+{sup 90}Zr system. In the sub-barrier region, the measured fusion cross sections for {sup 28}Si+{sup 94}Zr turned out to be about an order of magnitude higher than the ones for the {sup 28}Si+{sup 90}Zr system, which could not be explained by coupling to inelastic states alone. This observation indicates the importance of multinucleon transfer reaction channels with positive Q values in the sub-barrier fusion cross section enhancement, because {sup 90,94}Zr are believed to have similar collective strengths. This implies that no strong isotopic dependence of fusion cross sections is expected as far as the couplings to collective inelastic states are concerned. In addition, the role of projectile and multiphonon couplings in the enhancement has been explored.},
doi = {10.1103/PHYSREVC.81.044610},
journal = {Physical Review. C, Nuclear Physics},
number = 4,
volume = 81,
place = {United States},
year = 2010,
month = 4
}
  • The fragment angular distributions and excitation functions of the fission following complete fusion (FFCF) have been measured after separating them from targetlike-fragment fission (TLFF) for the {sup 19}F+{sup 232}Th system in the bombarding energy range of 84.5 to 106.5 MeV. The fraction of the targetlike-fragment fission was observed to increase with decreasing bombarding energy below the Coulomb barrier. The excitation function for fission following complete fusion reaction agrees well with coupled channel calculations. However, the {l_angle}{ital l}{sup 2}{r_angle} values derived from the fragment anisotropy data of the FFCF events are found to be much larger than those calculated using themore » coupled channel transmission coefficient values. The discrepancy between the experimental and calculated {l_angle}{ital l}{sup 2}{r_angle} values increases as the bombarding energy is decreased below the barrier.« less
  • To date, the possible effects of coupling to nucleon transfer reactions on the elastic scattering and fusion of weakly bound exotic nuclei have been largely neglected. The {sup 15}C nucleus presents a virtually unique opportunity to test these effects for an almost pure s{sub 1/2} single neutron halo nucleus. We present a series of coupled reaction channel calculations of the sub-barrier elastic scattering and single neutron transfer reactions, plus near-barrier excitation functions of the total fusion cross section for the {sup 12}C, {sup 13}C, and {sup 15}C+{sup 208}Pb systems. The method is validated against data for {sup 12}C and {supmore » 13}C+{sup 208}Pb. A large effect on the sub-barrier elastic scattering due to coupling to the ({sup 15}C,{sup 14}C) single neutron stripping reaction is found, ascribed to the 2s{sub 1/2} halo nature of the {sup 15}C ground state, in contrast to the two stable carbon isotopes. We also find a significant diminution of the above barrier total fusion cross section for {sup 15}C due to this coupling, again in contrast to the stable isotopes.« less
  • We study the formal structure of the influence of channel coupling on near- and sub-barrier fusion. The reduction to a one-channel description is studied, with emphasis on the channel-coupling effects being manifest primarily as an energy dependence (the ''threshold anomaly'') of the real nuclear potential. The relation to the barrier penetration model is examined critically. The results of large-scale coupled-channel calculations are used as ''data'' to illustrate the discussion. Particular emphasis is placed on the importance of reproducing correctly the partial-wave (or ''spin'') distributions. The simple barrier penetration model is found to be adequate to exhibit the strong enhancements duemore » to channel couplings when the threshold anomaly is taken into account, although there may be important corrections due to the long-ranged peripheral absorption, especially from Coulomb excitation. copyright 1987 Academic Press, Inc.« less
  • The influence on fusion of coupling to the breakup process is investigated for reactions where at least one of the colliding nuclei has a sufficiently low binding energy for breakup to become an important process. Elastic scattering, excitation functions for sub- and near-barrier fusion cross sections, and breakup yields are analyzed for {sup 6,7}Li+{sup 59}Co. Continuum-discretized coupled-channels (CDCC) calculations describe well the data at and above the barrier. Elastic scattering with {sup 6}Li (as compared to {sup 7}Li) indicates the significant role of breakup for weakly bound projectiles. A study of {sup 4,6}He induced fusion reactions with a three-body CDCCmore » method for the {sup 6}He halo nucleus is presented. The relative importance of breakup and bound-state structure effects on total fusion is discussed.« less
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