Incomplete Fusion Products Research Articles

Further investigation on the fusion of 6Li with 209Bi target at near-barrier energies

Abstract The complete and incomplete fusion cross sections for 6Li+209Bi were measured via the in-beam γ-ray method around the Coulomb barrier. The cross sections of (deuteron captured) incomplete fusion (ICF) products were re-quantified experimentally for this reaction system. The results reveal that the ICF cross section is equivalent to that of complete fusion (CF) above the Coulomb barrier and dominant near or below the barrier. A theoretical calculation based on the Continuum Discretized Coupled Channel (CDCC) method is performed for the aforementioned CF and ICF cross sections, and the result is consistent with the experimental ones. The universal fusion function (UFF) is also compared with the measured CF cross section with different barrier parameters, demonstrating that the CF suppression factor is quite sensitive to the choice of potential, which can reflect both dynamic and static effects of breakup on the fusion process.

Effects of entrance channels on breakup fusion induced by F19 projectiles

The study of breakup fusion of $^{19}\mathrm{F}$ with $^{154}\mathrm{Sm}$ target was studied through offline $\ensuremath{\gamma}$ ray spectrometry. Partial cross sections of evaporation residues produced in this reaction were measured in center-of-mass energies ranging $\ensuremath{\approx}3--30$ MeV above the fusion barrier. The excitation functions of the evaporation residues populated through $xn/pxn$ channels were found to be satisfactorily reproduced by statistical model calculations, whereas for the $\ensuremath{\alpha}$ emitting channels the cross sections show an enhancement over the theoretical predictions. The critical angular momentum deduced from the measured cross sections was found to be in good agreement with statistical model calculations. The degree of fusion incompleteness in the $^{19}\mathrm{F}+^{154}\mathrm{Sm}$ reaction is estimated by comparing the fusion excitation functions with coupled channels calculations and the extracted fusion function with the universal fusion function. The large cross sections observed for incomplete fusion products support the interpretation that this suppression of fusion is caused by $^{19}\mathrm{F}$ breaking up into charged fragments before reaching the fusion barrier. The incomplete fusion probability was also found to increase with the reduced mass and charge of the entrance channel, indicating the influence of entrance channel mass asymmetry and Coulomb repulsion on incomplete fusion. The present analysis shows the presence of strong clustering in the $^{19}\mathrm{F}$ projectile as $\ensuremath{\alpha}$ and $^{15}\mathrm{N}$.

Production of transuranium isotopes in Ne20 -induced incomplete fusion reactions

Using a semiclassical dynamical model that combines a classical trajectory model with stochastic breakup with a dynamical fragmentation theory treatment of two-body clusterization and decay of a projectile, results are presented for $^{20}\mathrm{Ne}$-induced incomplete fusion reactions for the production of superheavy elements. Targets include $^{247,248,250}\mathrm{Cm}$ and $^{251,252,254}\mathrm{Cf}$, and results include angular, excitation energy, and angular momentum distributions in addition to total integrated cross sections for heavy incomplete fusion products. The results show that at Coulomb energies, the studied Cf isotopes are generally the more favorable choice of target over the studied Cm isotopes for the production of `colder' and more stable $^{263}\mathrm{Lr}$, $^{263,264,266}\mathrm{Rf}$, and $^{265}\mathrm{Db}$ isotopes through the incomplete fusion mechanism. Also presented are evaporation residue cross sections for the dominant primary incomplete fusion products of each of the six reactions: $^{263,264,266}\mathrm{Rf}$ and $^{267,268,270}\mathrm{Sg}$, as well as for the primary incomplete fusion products $^{269,270,272}\mathrm{Bh}$.

Investigation of contribution of complete and incomplete fusion in the total fusion process of 6Li+90,96Zr reactions in vicinity of the Coulomb barrier

The impacts of breakup channel on fusion of L6i with Z90,96r-nuclei are investigated within the context of the coupled channel model and the energy dependent Woods-Saxon potential (EDWSP) model. For studied reactions, the complete fusion (CF) cross-sections data at above barrier energies are found to be suppressed with respect to the calculated results. In case of L6i+90Zr (L6i+96Zr) reaction, the CF data at above barrier energies is found to be less by 34% (25%) with reference to the estimations of the coupled channel approach. However, EDWSP model calculations predict fusion suppression up to 20% (10%) for L6i+90Zr (L6i+96Zr) reaction. The extracted suppression factor for L6i+90Zr(L6i+96Zr) reaction is smaller by 14% (15%) than the reported value. Such effects can be accredited to the low threshold of α-breakup channel associated with the weakly bound system and hence may be responsible for incomplete fusion (ICF) products. Therefore, the total fusion (TF) cross-sections that are the sum of complete fusion (CF) and incomplete fusion (ICF) yields, are not expected to reduce in the above barrier regions when compared with no-breakup case. In this regard, the TF cross-sections data are analyzed within the view of the EDWSP model and so obtained calculations have close agreement with the TF cross-sections data. The EDWSP based results appreciably explained CF, ICF and TF cross-sections data over a wide range of energies around the Coulomb barrier. Although, the cluster-transfer or stripping process from the ground state of weakly bound nucleus L6i may significantly contribute to ICF yields, therefore, the presence of ICF product is an indication of the partial absorption of projectile by target, henceforth, reduces the CF cross-section data in above barrier regimes.

Origins of Incomplete Fusion Products and the Suppression of Complete Fusion in Reactions of ^{7}Li.

Above-barrier complete fusion involving nuclides with low binding energy is typically suppressed by 30%. The mechanism that causes this suppression, and produces the associated incomplete fusion products, is controversial. We have developed a new experimental approach to investigate the mechanisms that produce incomplete fusion products, combining singles and coincidence measurements of light fragments and heavy residues in ^{7}Li+^{209}Bi reactions. For polonium isotopes, the dominant incomplete fusion product, only a small fraction can be explained by projectile breakup followed by capture: the dominant mechanism is triton cluster transfer. Suppression of complete fusion is therefore primarily a consequence of clustering in weakly bound nuclei rather than their breakup prior to reaching the fusion barrier. This implies that suppression of complete fusion will occur in reactions of nuclides where strong clustering is present.

Effects of unconventional breakup modes on incomplete fusion of weakly bound nuclei

The incomplete fusion dynamics of $^6$Li + $^{209}$Bi collisions at energies above the Coulomb barrier is investigated. The classical dynamical model implemented in the {\sc platypus} code is used to understand and quantify the impact of both $^6$Li resonance states and transfer-triggered breakup modes (involving short-lived projectile-like nuclei such as $^8$Be and $^5$Li) on the formation of incomplete fusion products. Model calculations explain the experimental incomplete-fusion excitation function fairly well, indicating that (i) delayed direct breakup of $^6$Li reduces the incomplete fusion cross-sections, and (ii) the neutron-stripping channel practically determines those cross-sections.

Effect of the Target Deformation on Incomplete Fusion Dynamics

To investigate the role of target deformation on incomplete fusion dynamics, a particle-gamma coincidence experiment has been performed at Inter University Accelerator Centre, New Delhi. Spin distributions for various evaporation residues populated via complete and incomplete fusion of 16 O with 124 Sn at 6.3MeV/nucleon have been measured. Experimentally measured spin distributions of the residues produced as incomplete fusion products associated with fast α and 2α-emission channels observed in forward cone are found to be distinctly different from those of the residues produced as complete fusion products. The mean value of input angular momentum J0 for evaporation residues produced through xn channels (complete fusion products) is found to be J0 ≈ 7ħ, while the mean value of input angular momentum J0 for the residues produced through direct αxn and 2αxn channels (incomplete fusion products) in forward cone, are found to be J0 ≈ 9ħ and ≈ 12ħ respectively for 16 O + 124 Sn (spherical) system [7]. The mean value of input angular momentum J0 for the system 16 O + 169 Tm (deformed) reported in ref. [8], are found to be ≈10ħ for xn-channels (complete fusion products) and for direct αxn and 2αxn channels (incomplete fusion products) the value of J0 approaches to ≈ 13ħ and ≈16ħ, respectively. The mean values of the input angular momentum observed for xn (complete fusion products), αxn and 2αxn (incomplete fusion products) in 16 O + 124 Sn (spherical) system are smaller than that of the mean values of the input angular momentum observed for xn (complete fusion products), αxn and 2αxn (incomplete fusion products) in 16 O + 169 Tm (deformed) system. The comparison of data inferred that the mean values of the input angular momentum are smaller in case of spherical target than that of deformed target at same projectile energy of 16 O-ion beam. It means that the target deformation affect the incomplete fusion dynamics.

Probing of complete and incomplete fusion dynamics in heavy-ion collision

Three different types of experiments have been performed to explore the complete and incomplete fusion dynamics in heavy-ion collisions. In this respect, first experiment for the measurement of excitation functions of the evaporation residues produced in the 20Ne + 165Ho system at projectile energy ranges ≈2–8 MeV /nucleon has been done. Measured cumulative and direct cross-sections have been compared with the theoretical model code PACE-2, which takes into account only the complete fusion process. It has been observed that, incomplete fusion fraction is sensitively dependent on projectile energy and mass asymmetry between the projectile and the target systems. Second experiment for measuring the forward recoil range distributions of the evaporation residues produced in the 20Ne + 165Ho system at projectile energy ≈8 MeV /nucleon has been done. It has been observed that, some evaporation residues have shown additional peaks in the measured forwardrecoil range distributions at cumulative thicknesses relatively smaller than the expected range of the residues produced via complete fusion. The results indicate the occurrence of incomplete fusion involving the breakup of 20Ne into 4He + 16O and /or 8Be + 12C followed by one of the fragments with target nucleus 165Ho. Third experiment for the measurement of spin distribution of the evaporation residues produced in the 16O + 124Sn system at projectile energy ≈6 MeV /nucleon, showed that the residues produced as incomplete fusion products associated with fast α and 2 α-emission channels observed in the forward cone, are found to be distinctly different from those of the residues produced as complete fusion products. The spin distribution of the evaporation residues also inferred that in incomplete fusion reaction channels input angular momentum (J0) increases with fusion incompleteness when compared to complete fusion reaction channels. Present observation clearly shows that the production of fast forward α-particles arises from relatively larger angular momentum in the entrance channel leading to peripheral collision.

Incomplete fusion dynamics by spin distribution measurements

Spin distributions for various evaporation residues populated via complete and incomplete fusion of $^{16}\mathrm{O}$ with $^{124}\mathrm{Sn}$ at $6.3$ MeV/nucleon have been measured, using charged particles ($Z=1,2$)-$\ensuremath{\gamma}$ coincidence technique. Experimentally measured spin distributions of the residues produced as incomplete fusion products associated with ``fast'' $\ensuremath{\alpha}$- and $2\ensuremath{\alpha}$-emission channels observed in the ``forward cone'' are found to be distinctly different from those of the residues produced as complete fusion products. Moreover, ``fast'' $\ensuremath{\alpha}$-particles that arise from larger angular momentum in the entrance channel are populated at relatively higher driving input angular momentum than those produced through complete fusion. The incomplete fusion residues are populated in a limited, higher-angular-momentum range, in contrast to the complete fusion products, which are populated over a broad spin range.

Disentangling full and partial linear momentum transfer events in theO16+Tm169system atEproj⩽5.4MeV/nucleon

Forward recoil ranges of heavy reaction products have been measured to disentangle full and/or partial linear momentum transfer events in the {sup 16}O+{sup 169}Tm system at E{sub proj}{approx_equal}76 and 81 MeV. The experimentally measured forward recoil ranges of complete and/or incomplete fusion products are found to be in satisfactory agreement with that estimated using range-energy formulations. The angular distributions of several heavy reaction products have also been measured at E{sub proj}{approx_equal}81 MeV to get complementary information about incomplete fusion. To figure out the influence of incomplete fusion on complete fusion at such low projectile energies, the relative strengths of their contributions in {alpha}-emitting channel(s) have been deduced from the measurement of recoil range distributions.

Probing of incomplete fusion dynamics by spin-distribution measurement

Aiming to probe incomplete fusion dynamics in 16O + 169Tm system, spin-distributions of various reaction products populated via xn-, α/2αxn-channels have been measured at E≈5.6MeV/nucleon. Prompt γ-rays in coincidence with fast charged particles (Z=1,2) have been recorded to achieve the information about involved reaction processes on the basis of their experimentally observed spin-populations during de-excitation. The experimentally observed spin-distributions for direct-α-emitting channels (associated with incomplete fusion) have been found to be distinctly different than that observed for fusion–evaporation (complete fusion) channels. The mean value of driving input angular momenta associated with various direct-α/2αxn-channels have been found to be higher than that observed for fusion–evaporation xn/αxn-channels, and increases with direct-α-multiplicity in forward cone. Experimentally measured, normalized production yields of fusion–evaporation xn/αxn-channels have been found to be in good agreement with the predictions of theoretical model code PACE4. Further, in order to understand the feeding probability in both complete and incomplete fusion reaction products, an attempt has been made to generate feeding intensity profiles from spin-distribution data. It has been observed that the complete fusion products are strongly fed over a broad spin range, while incomplete fusion products are found to be less fed and/or the population of lower spin states are strongly hindered.

Spin-distribution measurement: A sensitive probe for incomplete fusion dynamics

Spin distributions of various reaction products populated via complete and/or incomplete fusion of {sup 16}O with {sup 169}Tm have been measured at projectile energy {approx_equal}5.6 MeV/nucleon. Particle (Z=1,2) {gamma}-coincidences have been employed to achieve the information about involved reaction modes on the basis of their entry state spin populations. The experimentally measured spin distributions for incomplete fusion products have been found to be distinctly different than those observed for complete fusion products. The driving input angular momenta associated with incomplete fusion products have been found to be relatively higher than complete fusion products, and increases with direct {alpha}-multiplicity. It has also been observed that incomplete fusion products are less fed and/or the population of lower spin states are strongly hindered, while complete fusion products indicating strong feeding over a broad spin range.

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.

INCOMPLETE FUSION IN THE EXCITATION FUNCTIONS OF 12C + 115In REACTIONS AT 4–7 MeV/NUCLEON

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.

Linear momentum transfer in incomplete fusion reactions of 12C and 13C with 181Ta

Recoil range distribution of evaporation residues formed in complete and incomplete fusion of 82.5 MeV 12C and 13C with 181Ta have been measured by recoil catcher technique followed by off-line gamma-ray spectrometry. The recoil range distributions of incomplete fusion products were found to be in good agreement with that simulated on the basis of direct surface transfer reaction model. The cross-sections for complete and incomplete fusion were delineated from the measured excitation function data at the same beam energy. The fraction of incomplete fusion in the total cross-section was found to be more in the case of 12C than that in the case of 13C indicating the dependence of incomplete fusion probability on the cluster structure of the projectile.

Effect of projectile structure on evaporation residue yields in incomplete fusion reactions

The excitation functions of heavy residues, representing complete and incomplete fusion products, produced in the reaction of 12C and 13C on 181Ta have been measured over the projectile energy range of 5 to 6.5 MeV/nucleon by the recoil catcher method and off-line γ-ray spectrometry. Comparison of the measured excitation functions with those calculated using the PACE2 code based on the statistical model revealed the occurrence of incomplete fusion reactions in the formation of α emission products. The fraction of incomplete fusion cross sections in the 12C + 181Ta reaction was found to be higher, by a factor of ∼2, than that in the 13C + 181Ta reaction. The results have been discussed in terms of the effect of alpha cluster structure of the projectile on incomplete fusion reactions.

Complete and incomplete fusion reactions in the [formula omitted] C [formula omitted] Tm

Excitation functions of evaporation residues produced in 12 C + 169 Tm reaction have been measured at several beam energies in the range of 60–84 MeV using recoil catcher technique followed by off-line gamma-ray spectrometry. Comparison of the experimental excitation functions with those calculated using the statistical model code PACE2 revealed dominance of incomplete fusion in the cross section of alpha-emission products. Measurement of recoil-range distributions of evaporation residues at 84 MeV beam energy corroborated these observations. Analysis of the cross sections of incomplete fusion products showed that these reactions are associated with peripheral collisions. Comparison of the present data with similar data on 16 O + 165 Ho system revealed that incomplete fusion probability is more in a mass asymmetric system than in a mass symmetric system.

Complete and incomplete fusion in the reaction of 16O with 93Nb at 6 MeV/nucleon

Excitation functions for 17 evaporation residues were measured for the 16O+ 93Nb system in the energy range 4-6 MeV/nucleon. The experimental results were compared with the theoretical values calculated using the Monte Carlo simulation code PACE2. Several complete and incomplete fusion products were observed in the present study. It was observed that a definite amount of incomplete fusion contribution is present even at the lowest energy. The results indicate the occurrence of incomplete fusion involving breakup of 16O into 8Be+ 8Be followed by fusion of one of the fragments with the target nucleus.

Exploiting barrier distributions to investigate breakup effects in the fusion of 9Be+208Pb

The availability of precisely measured fusion excitation functions have allowed the determination of experimental fusion barrier distributions. This concept is utilised in 9Be+208Pb reaction, to reliably predict the expected complete fusion cross-sections. However, the measured cross-sections are found to be 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 9Be breaking up into charged fragments before reaching the fusion barrier.

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.