Narrow Results

We have analyzed the incomplete fusion (ICF), complete fusion (CF) and total fusion (TF) excitation functions for reactions induced by ${}^9\mathrm{\text{Be}}$ on ${}^{169}\mathrm{\text{Tm}}$, ${}^{187}\mathrm{\text{Re}}$ and ${}^{209}\mathrm{\text{Bi}}$ targets at near barrier energies using Wong’s formula in conjunction with the energy dependent Woods–Saxon potential. A phenomenological selection function is proposed to separate out the contribution of ICF and CF cross-sections in TF cross-section. The variation of relative contribution of ICF and CF in TF with respect to incident beam energy is very well reproduced through this approach.

We measured the excitation functions for nine evaporation residues for the ¹²C + ¹¹⁵In system in the energy range well beyond the Coulomb barrier. The experimental results are compared with the theoretical values calculated using the Monte Carlo simulation code PACE2. Several complete and incomplete fusion products are observed in the present study. It is observed that a definite amount of incomplete fusion contribution is present, even at the lowest energy. The results clearly show the incomplete fusion contributions in the iodine and antimony products.

The experiments were performed to study excitation functions (EFs) of evaporation residues (ERs), i.e. ^103,102,101Ag, ^101,100,99Pd, ^101,100Rh, ⁹⁷Ru, ⁹⁶Tc, ⁹⁵Tc, ⁹⁴Tc, ⁹³Mo^m, ⁹²Nb^m populated in the reactions induced by ¹²C on ⁹³Nb for exploring the reaction dynamics involved at energies ≈ 47–75 MeV. The activation technique followed by offline γ-ray spectrometry has been employed to measure EFs. These measurements were simulated with other reported values available in literature as well as with theoretical predictions based on computer code PACE-2. The effect of variation of level density parameter involved in this code has also been studied. An excellent agreement was found between theoretical and experimental values in some of the fusion evaporation channels. However, significant enhancement of cross-section as observed in α-emission channels may be due to incomplete fusion (ICF) process and/or direct reaction process. To confirm the aforesaid reaction mechanism, Recoil Range Distributions (RRDs) of various ERs have been measured at ≈ 80 MeV. Moreover, an attempt is made to separate the percentage relative contributions of complete and incomplete fusion components from the analysis of the measured RRDs data. Further, the relative percentage ICF fraction, also estimated from EFs data, was found to be sensitive with the projectile energy.

Formation cross-sections of evaporation residues have been measured in ¹⁹F+¹⁵⁹Tb reaction at E_lab=83, 88, 93, 98 and 103 MeV using recoil catcher technique followed by off-line gamma-ray spectrometry. Significant contribution from incomplete fusion has been observed at these low beam energies indicating the contribution to incomplete fusion from collision trajectories with angular momentum (l) less than the critical angular momentum for complete fusion (l_cr(CF)). Incomplete fusion cross-sections could be explained using a modified sum-rule model which allows effective competition from incomplete fusion for collision trajectories with l<l_cr(CF).

Cross sections of reaction products were measured in ${}^{28}$Si${+}^{93}$Nb reaction using recoil catcher technique involving by off-line gamma-ray spectrometry at beam energies of 105 and 155MeV. At $E_{\mathrm{\text{lab}}}=155$MeV, the contribution from different incomplete mass transfer processes is investigated. Results of the present studies show the contribution from deep inelastic collision (DIC), massive transfer or incomplete fusion (ICF) and quasi-elastic transfer (QET). The contribution from massive transfer reactions was confirmed from the fractional yield of the reaction products in the forward catcher foil. The present results are different from those from the reactions with comparatively higher entrance channel mass asymmetry with lighter projectiles, for which dominant transfer processes are ICF and QET which involve mass transfer predominantly from projectile to target. The $N/Z$ values of the products close to the target mass were observed to be in a wide range, starting from $N/Z$ of the target (${}^{93}$Nb) and extending slightly below the $N/Z$ of the composite system, consistent with the contribution from DIC and QET reactions. At $E_{\mathrm{\text{lab}}}=105$MeV, a small contribution from QET was observed in addition to complete fusion.

This work emphasized the role of the projectile breakup channel by studying the complete fusion (CF) and incomplete fusion (ICF) dynamics of ${}^{6,7}\mathrm{\text{Li}}+{}^{144,152}\mathrm{\text{Sm}}$ reactions. The theoretical calculations for the chosen reactions have been done by opting for the coupled channel approach and the energy dependent Woods–Saxon potential (EDWSP) model. The below barrier fusion enhancements of the studied reactions are reasonably addressed by the outcomes of the adopted models, which in turn can be attributed to the couplings of nuclear structure degrees of freedom of the collision partners to their relative motion. In contrast, at above barrier energies, the CF cross-section data of the chosen reactions are found to be suppressed significantly when compared with the predictions made by using the present models. Interestingly, the fusion suppression factors of the given reactions can be minimized considerably with respect to the reported value when it is analyzed within the framework of the EDWSP model. For instance, in case of ${}^6\mathrm{\text{Li}}+{}^{144}\mathrm{\text{Sm}}$ (${}^6\mathrm{\text{Li}}+{}^{152}\mathrm{\text{Sm}})$ reaction, the magnitude of fusion suppression factor is minimized up to 7% (13%) relative to the reported value whereas for ${}^7\mathrm{\text{Li}}+{}^{144}\mathrm{\text{Sm}}$ (${}^7\mathrm{\text{Li}}{+}^{152}\mathrm{\text{Sm}})$ reaction, the fusion suppression factor is found to be less by 7% (8%) with reference to the reported value. Such suppression effects can be correlated with the low breakup threshold of alpha breakup channel associated with the loosely bound projectile. The projectiles being weakly bound systems split into two charged fragments and either of the breakup components is absorbed by the target resulting in the reduction of incoming flux going into fusion channel. The flux lost from the CF channel appears in the form of ICF yields. For ${}^6\mathrm{\text{Li}}{+}^{152}\mathrm{\text{Sm}}$, total fusion (TF) cross-sections that are sum of CF and ICF cross-sections are also analyzed in conjunction with the EDWSP model and thus reasonably explained by the model calculations. In order to identify the ICF contribution, the ratio of ICF/TF cross-section data of ${}^6\mathrm{\text{Li}}{+}^{152}\mathrm{\text{Sm}}$ reaction has been examined and thus properly addressed by using the EDWSP model. The presence of ICF component in TF cross-section clearly pointed out the breakup of projectile due to its loosely bound nature prior to the Coulomb barrier. Although ICF data of other systems are not available in the literature, a similar behavior is expected for ICF and TF data for ${}^6\mathrm{\text{Li}}{+}^{144}\mathrm{\text{Sm}}$ and ${}^7\mathrm{\text{Li}}+{}^{144,152}\mathrm{\text{Sm}}$ reactions.

Breakup and incomplete fusion are strongly related. Experimental evidence is first presented, then a new 3-D classical model with stochastic breakup introduced, which is able to consistently explain experimental observables such as complete and incomplete fusion cross-sections and sub-barrier breakup cross-sections.

High-spin states of ^{194, 195}Au, ¹⁹⁵Pt and ¹⁹³Ir have been studied using an in-beam γ-ray spectroscopic technique following the reaction of ⁷Li on an ¹⁹²Os target at 44 MeV. The emitted γ rays were observed using an array of 14 Compton-suppressed HPGe detectors. Several bands in these nuclei have been identified and extended up to high-spin states. The α and t emission channels leading to ¹⁹³Ir and ¹⁹⁵Pt, respectively, are strongly enhanced which may be explained by incomplete fusion reaction; the t and α fragments from the break-up of weakly bound ⁷Li nucleus fusion with ¹⁹²Os target.