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The small cross-section of the synthesis of the superheavy elements (SHEs) is caused by the hindrance to complete fusion and small survival probability of the compound nucleus against fission. The hindrance to complete fusion is related with such peculiarities of the entrance channel as the mutual orientation angles of the axial symmetry of the colliding deformed nuclei, their mass (charge) asymmetry, the shell effects in their microscopic structure and orbital angular momentum. The appearance of the hindrance to complete fusion has been analyzed in the framework of the dinuclear system (DNS) model by the description of the experimental data obtained in the reactions of the SHE synthesis. [ABSTRACT FROM AUTHOR]

Production of 155Tb radioisotope for medical purposes is still a challenge. In this regard the present study has been done using 16O beam and 146Nd target within the 3–7 MeV/nucleon energy range. The γ-ray spectrometry has been used to identify the residues produced in the reaction. The EF measurements have been done and cross-sections of 155Tb have been reported and compared with the theoretical model code PACE 4. A strong indication of the occurrence of incomplete fusion has been realized within the energy range considered. The highest cross-section of 124 ± 12 mb has been obtained at Elab 101.7 ± 0.5 MeV. [ABSTRACT FROM AUTHOR]

Measurements of the excitation function (EF) of the observed evaporation residues (ERs) populated in the 20Ne + 93Nb reaction at E lab ≈ 91−145 MeV are carried out to explore the systematic of fusion suppression and its dependency on projectile breakup threshold energy, by employing the offline γ -ray detection method. The EF of the observed ERs populated through complete and/or incomplete fusion processes are analysed in the framework of statistical mode code PACE4. The fusion function, derived from the experimentally measured fusion cross section data, is compared with the universal fusion function (UFF) to estimate the degree of fusion incompleteness. Based on the observed results, an empirical formula is proposed to interrelate the degree of fusion suppression and breakup threshold energy of the incident projectile. [ABSTRACT FROM AUTHOR]

This work emphasized the role of the projectile breakup channel by studying the complete fusion (CF) and incomplete fusion (ICF) dynamics of 6 , 7 Li + 1 4 4 , 1 5 2 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 Li + 1 4 4 Sm ( 6 Li + 1 5 2 Sm) reaction, the magnitude of fusion suppression factor is minimized up to 7% (13%) relative to the reported value whereas for 7 Li + 1 4 4 Sm ( 7 Li + 1 5 2 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 Li + 1 5 2 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 Li + 1 5 2 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 Li + 1 4 4 Sm and 7 Li + 1 4 4 , 1 5 2 Sm reactions. [ABSTRACT FROM AUTHOR]

Spin distributions for several evaporation residues populated in the 16O+154Sm system have been measured at projectile energy ≈ 6.2 MeV/A by using the charged particle–γ-coincidence technique. The measured spin distributions of the evaporation residues populated through incomplete fusion associated with ‘fast’ α and 2α-emission channels are found to be entirely different from fusion–evaporation channels. It is observed that the mean input angular momentum for the evaporation residues formed in incomplete fusion channel is relatively higher than that observed for evaporation residues in complete fusion channels. The feeding intensity profile of evaporation residues populated through complete fusion and incomplete fusion have also been studied. The incomplete fusion channels are found to have narrow range feeding only for high spin states, while complete fusion channels are strongly fed over a broad spin range and widely populated. Comparison of present results with earlier data suggests that the mean input angular momentum values are relatively smaller for spherical target than that of deformed target using the same projectile and incident energy highlighting the role of target deformation in incomplete fusion dynamics.

Abstract In the present work, channel-by-channel excitation functions of different evaporation residues populated via complete and/or incomplete fusion in C 12 + 169 Tm system have been measured for an energy range E lab ≈ 53 – 90 MeV , using recoil-catcher activation technique followed by off-line γ -spectroscopy. Experimentally measured excitation functions have been analysed in the framework of statistical model code pace. To probe the effect of entrance-channel parameters on the onset and strength of incomplete fusion, relative contributions of complete and incomplete fusion have been deduced from the analysis of experimentally measured excitation functions. The percentage fraction of incomplete fusion deduced from the analysis of excitation functions has been studied in terms of incident energy, entrance-channel mass-asymmetry, ground state alpha-Q-value, neutron skin thickness of target nuclei, and nuclear potential parameters. It has been found that incomplete fusion start competing with complete fusion even at slightly above barrier energies where complete fusion is assumed to the sole contributor. The probability of incomplete fusion increases with incident energy, entrance channel mass-asymmetry, large negative ground state alpha-Q-value, neutron skin thickness, and nuclear potential parameters for individual projectiles. [ABSTRACT FROM AUTHOR]

The experimental verification of compound nucleus theory has successfully been performed for light ion induced reactions using proton and α -particle beams on different targets. However, such studies using the heavy ion beams are scarce due to the complex nature of heavy ion interaction process. The present work is an attempt to validate the Bohr's independent hypothesis using heavy ion beam of 18O beam on 159Tb targets and 12C on 165Ho targets, forming the same compound nucleus 177Ta. A channel wise analysis of cross section data for evaporation residues produced in 18O+159Tb and 12C+165Ho systems has been performed within the framework of statistical model code PACE4 and found to reasonably agree with the experimental data. Further, a comparison of reaction cross section data for the same evaporation residues produced in the two different systems has been found to follow Bohr's compound nucleus hypothesis at relatively higher excitation energies. However, at relatively lower excitation energies, a significant deviation in the measured cross section data of the same residues in the above mentioned systems have been observed and is attributed to the discrepancies in angular momentum values. Such discrepancies are well explained on the basis of input angular momentum involved in the reactions. [ABSTRACT FROM AUTHOR]

Abstract We present detailed results of a theoretical investigation on the production of evaporation residue nuclei obtained in a heavy ion reaction when charged particles (proton and α -particle) are also emitted with the neutron evaporation along the deexcitation cascade of the formed compound nucleus. The almost mass symmetric 82Se+138Ba reaction has been studied since there are many experimental results on individual evaporation residue (ER) cross sections after few light particle emissions along the cascade of the 220Th compound nucleus (CN) covering the wide 12–70 MeV excitation energy range. Our specific theoretical results on the ER cross sections for the 82Se+138Ba are in good agreement with the available experimental measurements, but our overall theoretical results concerning all possible relevant contributions of evaporation residues are several times greater than the ERs measured in experiment. The discrepancy could be due to the experimental difficulties in the identification of ER nuclei after the emission of multiple neutral and charged particles, nevertheless the analysis of ER data is very important to test the reliability of the model and to stress the importance on the investigation of ER nuclei also obtained after charged particle emissions. [ABSTRACT FROM AUTHOR]

The dynamics of 17 F + 58 Ni reaction induced via a loosely bound projectile ( 17 F) is examined using the collective clusterization approach of the dynamical cluster decay model (DCM) with respect to the recent experimental data available at beam energies E b e a m = 54.1 and 58.5 MeV. The calculations are done for quadrupole deformations of fragments using the optimum orientation approach. In view of the loosely bound nature of 17 F, the main focus of the present work is on the comparison of complete and incomplete fusion. It is studied using various components such as fragmentation potential, mass distribution, and barrier modification. Different decay modes (ER, IMF, HMF, and fission) are also compared to determine the complete fusion and incomplete fusion paths. Additionally, the decay paths of the nucleus formed from loosely bound ( 17 F) and tightly bound ( 16 O) projectiles are compared. Furthermore, the role of temperature-dependent pairing strength is analyzed in terms of the binary fragmentation of the compound system formed. [ABSTRACT FROM AUTHOR]

We have analyzed the incomplete fusion (ICF), complete fusion (CF) and total fusion (TF) excitation functions for reactions induced by on , and 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. [ABSTRACT FROM AUTHOR]

A new process of arc welding in shielding gases with alternate pulsed supply of dissimilar gases – helium and argon, and also the welding technology based on the process are described. It is shown that as a result of combining the advantages of argon-arc and helium-arc welding in the new process it is possible to increase the strength properties, precision and leak tightness of the welded joints, to ensure absence of defects and to reduce the volume of welding operations. Various physical effects, accompanying the process, are discussed. These processes accompany the process and produce the weld metal with the equiaxed fine-grained structure. [ABSTRACT FROM PUBLISHER]

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, 93Mom, 92Nbm 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. [ABSTRACT FROM AUTHOR]

Abstract: The role of the entrance channel has been studied to ascertain a cause of the observed difference between the evaporation residue cross sections normalized to the fusion cross sections in the 19F+ 181Ta and 16O+ 184W reactions at high excitation energies. The theoretical analysis performed in the framework of the dinuclear system and advanced statistical models showed that the more intense yield of evaporation residues in the 16O+ 184W reaction in comparison with that in the 19F+ 181Ta reaction was explained by the large capture and fusion cross sections in the former reaction, which is in agreement with the experimental data. The observed decrease in the evaporation residue cross section normalized to the fusion cross section in the 19F+ 181Ta reaction, in comparison with one in the 16O+ 184W reaction at large excitation energies, is caused by the unintentional inclusion of the quasifission and fast fission contributions in the fissionlike fragment yields that were used in reconstructing the experimental fusion cross section in the normalizing procedure. The range of the angular momentum distribution for both systems was similar, but the partial cross sections are different, showing the presence of a difference in the hindrance to complete fusion in both reactions. [Copyright &y& Elsevier]

The effect of entrance channel on decrease of the complete fusion cross sections and on the yield of reaction products are associated with the quasifission which depends on the mass asymmetry and shell structure of colliding nuclei. In reactions of massive projectile and target nuclei, the competition between complete fusion and quasifission appears at the stage of compound nucleus formation, in addition to the increase of the fission probability. It is shown that the yield of quasifission products may be symmetric or asymmetric in dependence on peculiarities of shell structure of reaction fragments. Marima of mass or charge distributions are connected with the peculiarities of shell structure of reaction fragments. [ABSTRACT FROM AUTHOR]

An attempt has been made to reveal the most realistic picture of the mechanism of the compound nucleus formation in complete fusion of two massive nuclei. [ABSTRACT FROM AUTHOR]

The breakup of the 9Be projectile on the 209Bi target at bombarding energies above and near the Coulomb barrier is studied in the adiabatic two-center shell model approach. The effect of 9Be→n+2α breakup channel on complete fusion, elastic and inelastic cross sections is investigated. Results show that the breakup of the projectile 9Be could be due to a molecular single-particle effect shortly before the colliding nuclei reach the Coulomb barrier. [Copyright &y& Elsevier]

The α-particle production in the dissociation of 9Be on 209Bi and 64Zn at energies just above the Coulomb barrier is studied within the two-center shell model approach. The dissociation of 9Be on 209Bi is caused by a molecular single-particle effect (Landau–Zener mechanism) before the nuclei reach the Coulomb barrier. Molecular single-particle effects do not occur at that stage of the collision for 9Be+64Zn, and this explains the absence of fusion suppression observed for this system. The polarisation of the energy level of the last neutron of 9Be and, therefore the existence of avoided crossings with that level, depends on the structure of the target. [Copyright &y& Elsevier]

The reaction dynamics of 12C + 52 Cr reaction induced via a cluster-structured projectile (12C) is examined theoretically using the dynamical cluster decay model (DCM) with respect to the recent experimental data available at wide span of center-of-mass energies (E c. m. = 41.84-71.20 MeV). In view of the cluster-structured projectile, a systematic analysis is carried out for both complete fusion (CF) and incomplete fusion (ICF) channel. The calculations are done by including the quadrupole (β 2) deformations and optimum (θ i o p t.) orientation criteria of the decaying fragments. With an aim to have comprehensive analysis of the decay of compound nuclei formed via CF and ICF processes, the role of center-of-mass energy (E c. m.) and angular momentum (ℓ) is explored in terms of various parameters of DCM such as fragmentation potential, preformation probability, penetrability and barrier modification. Further, the role of diffuseness parameter is also studied for 12C + 52 Cr reaction. For the given reaction, the contribution of light particles (LPs), and energetically favored intermediate mass fragments (IMFs) constitutes the decay cross sections. Therefore, the contribution of emitted LPs and IMFs is estimated for the decay of both compound nuclei formed via CF and ICF channels. Furthermore, the comparative analysis of different proximity potentials is also worked out for ICF. Finally, the effect of E c. m. on the contribution of ICF cross sections is studied and compared with the experimental data. [ABSTRACT FROM AUTHOR]

This work is aimed to explore the reaction mechanism induced via loosely bound projectile (9Be). Various peculiar properties of such projectiles for example low binding energy per nucleon leading to low breakup threshold, larger rms radii, higher transfer probability, captivate the attention of scientists working in related field. Thus, an effort is made to analyze the complete fusion (CF) and incomplete fusion (ICF) contributions in 9Be + 89Y reaction over energy range (E c. m. = 17.7-29.8 MeV). The projectile used in the present reaction 9Be may dissociate via 5He, 4He and 1n, which subsequently lead to ICF contribution via three different channels. Thus, the cross-sections corresponding to these ICF channels (5He + 89Y→94Nb⁎, 4He + 89Y→93Nb⁎ and 1n+89Y→90Y⁎) are duly examined. The calculations are done for quadrupole (β 2 -deformed) choice of fragments using optimum orientations approach of dynamical cluster decay model (DCM). The calculated cross-sections for both CF and ICF channels find nice agreement with the available experimental data. Besides this, the CF contributions are estimated for different isotopes of Tc (with A C N = 96-104) and some predictions are made for future validation. [ABSTRACT FROM AUTHOR]

By using the statistical model and the characteristics for fission and neutron evaporation predicted in different theoretical models, the survival probabilities of superheavy nuclei are analyzed. [ABSTRACT FROM AUTHOR]