Coupling effects on the fusion ofLi6+Sm154at energies slightly above the Coulomb barrier

Abstract

Measurements of complete and incomplete fusion cross sections for 6 Li+ 154 Sm have been performed at energies above the Coulomb barrier by the online γ -ray method, to investigate the effect of breakup and inelastic couplings on the complete fusion (CF) of this weakly bound system. We show that inelastic excitation couplings have non-negligible effects, when compared with the breakup effect, for deformed nuclei at energies very close to the Coulomb barrier. The average CF suppression corresponding to dynamic breakup effects was found to be around 35%. The total fusion cross section is not affected by the breakup coupling. A comparison between the 6 Li-induced CF suppression for three different samarium isotopes shows that the breakup effect is larger for the more spherical isotope.

Asymptotic and near-target direct breakup ofLi6andLi7

“…Such a suppression is not observed [24,26] in reactions with well-bound nuclei (where breakup should be negligible) forming the same compound system. A smaller suppression of complete fusion has been reported in measurements for reactions of 6 Li with 64 Ni [27], 96 Zr [9], and 9 Be with 89 Y [28]. * sunil.kalkal@anu.edu.au Complete fusion measurements are, however, sparse for light and medium-mass nuclei, since separation of complete and incomplete fusion products is difficult.…”

“…Breakup prior to reaching the fusion barrier is thought to be one reason for the observed ∼30% suppression of above-barrier complete fusion cross sections for reactions of 6,7 Li and 9 Be with heavy target nuclei [4][5][6][7][24][25][26]. Such a suppression is not observed [24,26] in reactions with well-bound nuclei (where breakup should be negligible) forming the same compound system.…”

“…Collisions involving weakly bound stable and unstable nuclei are interesting from the perspective of understanding both nuclear structure and nuclear reactions. Information has been obtained on clusters in nuclei [1][2][3], the effect of breakup on other reaction observables [4][5][6][7][8][9][10][11][12][13][14][15][16][17], and nuclear structure near drip lines [18,19]. In astrophysics, direct Coulomb breakup has been used to probe radiative capture reactions at low energies [20][21][22][23].…”

“…A modified version of the Monte Carlo classical trajectory model code PLATYPUS, which explicitly takes into account lifetimes associated with unbound states, is used to simulate sub-barrier breakup reactions. Conclusions: Near-target breakup in interactions with 6,7 Li is an important mechanism only for the heavy targets 208 Pb and 209 Bi. There is insignificant near-target direct breakup of 6 Li and no direct breakup of 7 Li in reactions with 58 Ni and 64 Zn.…”

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Background: 6,7 Li and 9 Be are weakly bound against breakup into their cluster constituents. Breakup location is important for determining the role of breakup in above-barrier complete fusion suppression.

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