Complete Fusion Excitation Functions Research Articles

Systematic study of suppression of complete fusion in reactions involving weakly bound nuclei at energies above the Coulomb barrier

Complete fusion excitation functions of reactions involving breakup are studied by using the empirical coupled-channel (ECC) model with breakup effects considered. An exponential function with two parameters is adopted to describe the prompt-breakup probability in the ECC model. These two parameters are fixed by fitting the measured prompt-breakup probability or the complete fusion cross sections. The suppression of complete fusion at energies above the Coulomb barrier is studied by comparing the data with the predictions from the ECC model without the breakup channel considered. The results show that the suppression of complete fusion is roughly independent of the target for the reactions involving the same projectile.

Systematic study of breakup effects on complete fusion at energies above the Coulomb barrier

A large number of complete fusion excitation functions of reactions including the breakup channel were measured in recent decades, especially in the last few years. It allows us to investigate the systematic behavior of the breakup effects on the complete fusion cross sections. To this end, we perform a systematic study of the breakup effects on the complete fusion cross sections at energies above the Coulomb barrier. The reduced fusion functions $F(x)$ are compared with the universal fusion function which is used as a uniform standard reference. The complete fusion cross sections at energies above the Coulomb barrier are suppressed by the breakup of projectiles. This suppression effect for reactions induced by the same projectile is independent of the target and mainly determined by the lowest energy breakup channel of the projectile. A good exponential relation between the suppression factor and the energy corresponding to the lowest breakup threshold is held.

Measurement of Li+Sn fusion excitation functions around the Coulomb barrier using an improved activation technique

Fusion excitation functions have been measured for the 6 Li+120 Sn and 7 Li+119 Sn systems at energies around the Coulomb barrier, to investigate the effects of neutron transfer and breakup on the fusion process. At energies above the barrier, a suppression of the complete fusion excitation function with respect to the prediction of the 1D - Barrier Penetration Model has been observed, in both cases. At energies below the Coulomb barrier, no significant difference between the two excitation function, imputable to the different neutron transfer Q-values of the two systems has been observed.

Dynamical decay process of 219, 220Ra* formed in 10, 11B + 209Bi reactions

The excitation functions for both the evaporation residue and fission have been calculated for 10B + 209Bi and 11B + 209Bi reactions forming compound systems 219, 220Ra* , using the dynamical cluster-decay model (DCM) with effects of deformations and orientations of the nuclei included in it. In addition to this, the excitation functions for complete fusion (CF) are obtained by summing the fission cross-sections, neutron evaporation and charged particle evaporation residue cross-sections produced through the $\ensuremath \alpha xn$ and $\ensuremath pxn$ (x = 2, 3, 4) emission channels for the 219Ra system at various incident centre-of-mass energies. Experimentally the CF cross-sections are suppressed and the observed suppression is attributed to the low binding energy of 10, 11B which breaks up into charged fragments. The reported complete fusion (CF) and incomplete fusion (ICF) excitation functions for the 219Ra system are found to be nicely fitted by the calculations performed in the framework of DCM, without invoking a significant contribution from quasi-fission. Although DCM has been applied for a number of compound nucleus decay studies in the recent past, the same is being used here in reference to ICF and subsequent decay processes along with the CF process. Interestingly the main contribution to complete fusion cross-section comes from the fission cross-section at higher incident energies, which in DCM is found to consist of an asymmetric fission window, shown to arise due to the deformation and orientation effects of formation and decay fragments.

Reactions involving loosely bound cluster nuclei: Heavy ions and new technologies

Experimental results on excitation functions for complete-fusion and transfer reactions in the interaction of 6He and 6,8,9Li nuclei with various target nuclei are presented. Data on fusion-reaction cross sections in the case of 6He differ strongly from the predictions of the statistical model. A strong enhancement of the cross section at barrier energies is observed for this reaction channel. Also, an increase in the cross sections for neutron-transfer reactions (in the case of 6He and 8,9Li beams) and deuteron-transfer reactions (in the case of 6Li) is observed in the deep-subbarrier energy region. The results are discussed from the point of view of the effect of the cluster structure of nuclei on the probability of interaction at barrier energies. The results of employing heavy-ion beams in new technologies are presented.

Influence of projectile breakup on complete fusion

Complete fusion excitation functions for 11,10B+159Tb and 6,7Li+159Tb have been reported at energies around the respective Coulomb barriers. The measurements show significant suppression of complete fusion cross-sections at energies above the barrier for 10B+159Tb and 6,7Li+159Tb reactions, when compared to those for 11B+159Tb. The comparison shows that the extent of suppression of complete fusion cross-sections is correlated with the α-separation energies of the projectiles. Also, the measured incomplete fusion cross-sections show that the α-particle emanating channel is the favoured incomplete fusion process. Inclusive measurement of the α-particles produced in 6Li+159Tb reaction has been carried out. Preliminary CDCC calculations carried out to estimate the α-yield following 6Li breaking up into α+d fail to explain the measured α-yield. Transfer processes seem to be important contributors.

Suppression of complete fusion in theLi6+Sm144reaction

Complete fusion excitation function for the $^{6}\mathrm{Li}+^{144}\mathrm{Sm}$ reaction has been measured at near barrier energies by the activation technique. Coupled-channel calculations show an enhancement in fusion cross section at energies below the barrier compared to the one-dimensional barrier penetration model calculation, but they overpredict it in the entire energy range compared to the experimental data. Reduced fusion cross sections for the present system at energies normalized to the Coulomb barrier were also found to be systematically lower than those with strongly bound projectiles forming a similar compound nucleus. These two observations conclusively show that the complete fusion cross section, at above barrier energies, is suppressed by $~32%$ in the $^{6}\mathrm{Li}+^{144}\mathrm{Sm}$ reaction. Reanalyses of existing fusion data for $^{7}\mathrm{Li}+^{165}\mathrm{Ho}$ and $^{7}\mathrm{Li}+^{159}\mathrm{Tb}$ also show a suppression compared to those with strongly bound projectiles, which contradicts earlier conclusions. The fusion suppression factor seems to exhibit a systematic behavior with respect to the breakup threshold of the projectile and the atomic number of the target nucleus.

Excitation functions for complete fusion and transfer reactions in the interaction of 6He with 197Au nuclei

The excitation functions for the fusion reactions with subsequent neutron evaporation, 197Au(6He, xn)203 − xnTl (x = 2−7), and the neutron transfer reactions with production of the 196Au and 198Au isotopes have been measured. Unusually high cross section of the 198Au isotope production at energies below the Coulomb barrier has been observed. Possible mechanisms of production and decay of the transfer reaction products are considered.

Excitation functions for complete-fusion and transfer reactions in 4He interaction with 197Au nuclei

Excitation functions are measured for the fusion reactions {sup 197}Au({sup 4}He, xn){sup 201-xn}Tl that are induced by alpha-particle interaction with gold nuclei in the energy range 14-36 MeV and in which x neutrons (0 {<=} x {<=} 3) are evaporated. The stack-activation technique was used to record and separate reaction products. Experimental data on the fusion reactions followed by evaporation of one to three neutrons agree with results of previous studies. For the radiative-capture reaction {sup 197}Au({sup 4}He,{gamma}){sup 201}Tl, the upper limit on the cross section proved to be much lower. The excitation functions for the reactions subjected to measurements are compared with the results of calculations based on the statistical model and with the results of an experiment performed previously in a {sup 6}He beam.

Influence of projectile α-breakup threshold on complete fusion

Complete fusion excitation functions for B11,10+Tb159 have been measured at energies around the respective Coulomb barriers, and the existing complete fusion measurements for Li7+Tb159 have been extended to higher energies. The measurements show significant reduction of complete fusion cross sections at above-barrier energies for both the reactions, B10+Tb159 and Li7+Tb159, when compared to those for B11+Tb159. The comparison shows that the extent of suppression of complete fusion cross sections is correlated with the α-separation energies of the projectiles. Also, the two reactions, B10+Tb159 and Li7+Tb159 were found to produce incomplete fusion products at energies near the respective Coulomb barriers, with the α-particle emitting channel being the favoured incomplete fusion process in both the cases.

Fusion versus Breakup: Observation of Large Fusion Suppression for9Be+208Pb

Complete fusion excitation functions for $^{9}$Be + $^{208}$Pb have been measured to high precision at near barrier energies. The experimental fusion barrier distribution extracted from these data allows reliable prediction of the expected complete fusion cross-sections. However, the measured cross-sections are only 68% of those predicted. The large cross-sections observed for incomplete fusion products support the interpretation that this suppression of fusion is caused by $^{9}$Be breaking up into charged fragments before reaching the fusion barrier. Implications for the fusion of radioactive nuclei are discussed.

The code FRANPIE: A semiclassical friction free model for calculating excitation functions for complete fusion of heavy ions

The code FRANPIE: A semiclassical friction free model for calculating excitation functions for complete fusion of heavy ions

Influence of Dynamic Processes upon Complete Fusion of Heavy Nuclei at Subbarrier Energies

Excitation functions for complete fusion of $^{90}\mathrm{Zr}$+$^{90}\mathrm{Zr}$ and $^{90}\mathrm{Zr}$+$^{94}\mathrm{Zr}$ have been found to decrease gradually over a broad energy range below the nominal barrier. The effective barrier for $^{90}\mathrm{Zr}$+$^{94}\mathrm{Zr}$ was 10.5 \ifmmode\pm\else\textpm\fi{} 3.0 MeV higher than the nominal barrier implying a critical effective fissility of 31.5 \ifmmode\pm\else\textpm\fi{} 0.5. Although deep-interpenetration processes appear to limit fusion at near-barrier energies, weak-contact dynamics enable these cold, heavy nuclei to fuse with comparative ease at lower energies.

Sub-barrier fusion ofNi58,64withNi64andGe74

Differential cross sections for evaporation residue formation following complete fusion of /sup 64/Ni and /sup 74/Ge with 171 to 215 MeV /sup 58/Ni and /sup 64/Ni ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation functions for complete fusion ranged in magnitude from 10 ..mu..b to 300 mb. The excitation functions exhibited a strong response, at subbarrier energies, to changes in the underlying nuclear structure. We interpreted these variations as evidence that the fusion proceeds through dynamic single-particle/softness-related processes. A phenomenological analysis was performed. In the analysis, we employed the WKB method, constructed a simple interaction potential and introduced a radially-dependent effective mass. The use of the variable effective mass led to a meaningful description of our above-barrier data and to improvements towards describing our subbarrier data.

Dynamic Influence of Valence Neutrons upon the Complete Fusion of Massive Nuclei

Excitation functions for complete fusion of $^{58}\mathrm{Ni}$ + $^{58}\mathrm{Ni}$, $^{58}\mathrm{Ni}$ + $^{64}\mathrm{Ni}$, and $^{64}\mathrm{Ni}$ + $^{64}\mathrm{Ni}$ have been determined over a range of energies from just above to well below the fusion barrier. The response of these excitation functions to the addition of valence neutrons is found to be surprisingly complex. We suggest that at least part of the observed variations may be due to dynamic, single-particle effects.

Systematics of fusion barriers obtained with a modified proximity potential

A systematic semiempirical analysis is presented for excitation functions for complete fusion of complex nuclei. Barrier penetration is included as is the $l$ dependence of the fusion radius. The general form of the proximity potential is assumed and small but important parameter adjustments are made to achieve a fit to experimental data. A correction is presented of $s$-wave barrier heights and radii for complete fusion. For ${Z}_{t}{Z}_{p}&lt;500$ these fusion radii are greater than the empirical reaction radii obtained at energies well above the barrier. This result implies weak surface absorption for ${Z}_{t}{Z}_{p}&lt;500$ and the contrary for higher ${Z}_{t}{Z}_{p}$.NUCLEAR REACTIONS Semiempirical analysis of complete fusion excitation functions with a modified proximity potential; correlation between $s$-wave barrier heights and fusion radii; fusion radii exceed empirical interaction radii for ${Z}_{t}{Z}_{p}&lt;500$ and the contrary.

Further evidence for resonance anomalies in the12C+16O system

Excitation functions for six nuclides resulting from the 16O+12C reaction, as well as for inelastic scattering to the 3- state of 16O, have been measured by gamma -ray techniques in the centre-of-mass energy range ECM=12.8-18.2 MeV and a complete fusion excitation function deduced. Resonance anomalies, which may be due to the excitation of quasimolecular states, are observed at 14.7, 16.7 17.6 and 18.6 MeV. These and other results are considered in terms of theoretical models for quasimolecular states.

Fusion and interaction barrier parameters and critical angular momenta fromCl35-induced reactions

Cross sections for evaporation residue formation and fission following complete fusion of /sup 35/Cl with /sup 27/Al, /sup 48/Ti, /sup 54/,/sup 56/Fe, /sup 58/,/sup 60/,/sup 62/,/sup 64/Ni, /sup 90/Zr, and /sup 116/,/sup 124/Sn have been measured with counter telescopes for laboratory projectile energies between 70 and 170 MeV. Elastic scattering of /sup 35/Cl + /sup 58/,/sup 62/Ni has been measured near the interaction barrier. The excitation functions for complete fusion are analyzed with a semiclassical model, and fusion barrier heights and radii are extracted. These data are discussed in terms of the nuclear density overlap and the nuclear potential contributions to the fusion barrier. The results are compared with the predictions of several heavy ion potential models and with parameters for the interaction deduced from elastic scattering data. For the systems with masses A < 100 about 70% of the total reaction cross section appears as complete fusion. This fraction decreases with increasing mass of the compound system. Evaporation residue and fission excitation functions have been analyzed by the Bohr-Wheeler model using the rotating liquid drop model of Cohen, Plasil, and Swiatecki. To first order these calculations give a satisfactory description of both sets of results. (AIP)

Barrier penetrability and/or deformation effects inCl35induced fusion onNi58,60,62,64

Excitation functions for complete fusion have been measured for $^{35}\mathrm{Cl}$ projectiles on $^{58,60,62,64}\mathrm{Ni}$. Deviations from the predictions of the sharp cutoff model are observed and compared with calculations based on the formalism of Wong. In this picture tunneling and static deformation of target and projectile can explain the experimental data in the barrier region.NUCLEAR REACTIONS complete fusion, $^{58,60,62,64}\mathrm{Ni}$ + $^{35}\mathrm{Cl}$, ${E}_{\mathrm{lab}}=91\ensuremath{-}170$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta}, E)$ for evaporation residues.