Quasi-elastic and massive transfer reactions in the16O+89Yreaction at beam energies around ≈4–5 MeV/nucleon

Abstract

Kinetic energy spectra, angular distributions, and cross sections of projectilelike fragments (PLFs) with Z PLF = 3−7 have been measured in 16 O + 89 Y reaction at E lab = 62. 2, 73.4, 78.5, and 83.5 MeV respectively. Comparison of angular distributions of PLFs, particularly of nitrogen (N), at different beam energies showed increasing contribution from overlapping collision trajectories at higher beam energies. Angular distributions of PLFs became more forward peaked with the amount of mass transfer indicating an increasing overlap of the projectile and the target nuclei with increasing mass transfer. PLF cross sections could be reasonably explained by the modified sum-rule model except for carbon (C) indicating the role of alpha cluster structure of 16 O nucleus in the transfer process. Large cross section for PLF emitted in the α transfer channel in 16 O + 89 Y reaction compared to that in 19 F + 89 Y reaction further supported this observation. PACS number(s): 25.70.HiReactions involving incomplete mass transfer such as quasielastic transfer (QET) and massive transfer or incomplete fusion (ICF) have been an active area of investigation for a long time. Several models such as sum-rule model [1,2], overlap model [3-6], break-up fusion model [7-9] and multi-step direct reaction theory [10] were proposed to explain these reactions. In the studies by Morgenstern et al. [11,12], the probability of incomplete fusion reaction was related to the entrance channel mass asymmetry. However, these models hold good at beam energies of about ∼10 MeV/nucleon and above. At even higher beam energies ( 15 MeV/nucleon), it has been shown that incomplete mass transfer reactions have contribution from projectile break-up and coalescence of nucleons during nucleon-nucleon interaction [13][14][15][16][17][18]. At lower beam energies (∼5 MeV/nucleon), the mechanism of incomplete mass transfer is not well understood, particularly the contribution from collision trajectories with different impact parameters as a function of beam energy. Several studies have been carried out in the recent past to investigate the reactions involving incomplete mass transfer at lower beam energies [19][20][21][22][23][24][25]. At energies very close to the entrance channel Coulomb barrier, such reactions are dominated by quasi-elastic transfer (QET) of a few nucleons [26,27]. Kinetic energy spectra of projectilelike fragments (PLFs) formed in QET peak at an optimum Q value i.e., Q opt decided by the kinematics of the reaction [28]. In QET dissipative effects are negligible. On the other hand in deep inelastic collisions (DIC), projectile and targetlike products appear at energies corresponding to the exit channel Coulomb barrier. The transition from QET to DIC represents a shift in the reaction mechanism and massive transfer or incomplete fusion reactions lie in-between these two extremes in terms of impact parameter and kinetic energy dissipation. In the studies by Mermaz et al. in 19 F + 89 Y reaction at E lab = 140 MeV [29], it was shown that the full ...