Narrow Results

In this paper, we investigated excitation functions of (n, 2n) reactions on the target nuclei in the mass region (144≤A≤160) for some samarium, europium and gadolinium isotopes. Studies were performed for incident neutron energies between 1 MeV and 20 MeV. We used the ALICE/ASH and TALYS 1.4 codes to investigate the pre-equilibrium effects and the ALICE/ASH were used for the equilibrium effects. The effects of collision probabilities on pre-equilibrium excitation functions were also investigated.

This work deals with the decay analysis of three compound nuclei ${}^{77}{\mathrm{\text{As}}}^{\ast }$, ${}^{83}{\mathrm{\text{Br}}}^{\ast }$ and ${}^{86}{\mathrm{\text{Sr}}}^{\ast }$ formed in proton-induced reactions $\mathrm{\text{p}}+{}^{76}\mathrm{\text{Ge}}$, $\mathrm{\text{p}}+{}^{82}\mathrm{\text{Se}}$ and $\mathrm{\text{p}}+{}^{85}\mathrm{\text{Rb}}$ at incident beam energies of 1–5 MeV using the Dynamical Cluster-decay Model (DCM). The motive is to explore the decay of compound systems formed via light charged particles as projectiles. The experimentally available data of n-evaporation for the aforementioned systems are addressed by optimizing the neck-length parameter $\mathrm{\Delta }R$, using spherical fragmentation approach. The comparative analysis of the decay structure of the chosen systems is carried out at a common incident beam energy $E_{\mathrm{\text{beam}}}\sim 3.6$ MeV. The effect of angular momentum $(\ell )$ and quadrupole $({\beta }_2)$-deformations is explored in reference to the decay structure/fragmentation of compound systems. In addition to this, the sensitivity of DCM-based cross-sections toward level density parameter (LDP) $a$ is also analyzed. The relative role of mass-dependent level density parameter $a(A)$ is also investigated for compound systems belonging to light and heavy mass region. Lastly, a theoretical systematics is explored where the proton beam in the reaction $\mathrm{\text{p}}+{}^{76}\mathrm{\text{Ge}}$ is replaced by a neutron beam forming the compound system ${}^{77}{\mathrm{\text{Ge}}}^{\ast }$, having the same $A$, but $Z$ one less than that of the compound system formed in the reaction using proton beam, and its effect on the decay characteristics such as preformation probability, penetration probability and barrier height is analyzed.

A systematic study of dynamical aspects associated with heavy-ion-induced ${}^{16}\mathrm{\text{O}}+{}^{89}\mathrm{\text{Y}}$ reaction is carried out at center-of-mass energy $E_{\mathrm{\text{c.m.}}}=89$ MeV. The complete fusion (CF) and incomplete fusion (ICF) contributions are estimated by using the dynamical cluster-decay model (DCM). The incomplete fusion component is examined by normalizing the incident beam energy for each of the breakup fragment. The fusion evaporation cross-sections that emerged from CF and ICF channels are duly addressed using the optimized value of neck-length parameter $\mathrm{\Delta }R$. Further, the mass yield of compound nuclei (CN) formed in the CF and ICF processes is analyzed with respect to angular momentum $\ell$ values. The DCM-based calculations indicate the possible contribution of deep inelastic collision (DIC) in the decay of ${}^{105}{\mathrm{\text{Ag}}}^{\ast }$ at higher $\ell$ values, and DIC cross-sections are predicted which call for future validation.

In this paper, a formalism consisting of multi-dimensional Langevin equation (LE) and Scission point Transition State Model (SCTSM) have been applied to study the angle dependence of fragment's average spin for ¹⁶O + ²⁰⁹Bi and ¹⁶O + ²³²Th systems. The influence of asymmetry and deformation parameters, neck thickness of compound nucleus and pre-scission neutron multiplicity on the fragment's average spin is discussed. Results obtained using this approach are in better agreement with the experimental data as compared with the SCTSM.

The decay of ²²⁰Ra* nucleus formed in two different entrance channels ¹²C+²⁰⁸Pb and ¹³C+²⁰⁷Pb is investigated over a wide range of incident energies using the dynamical cluster decay model (DCM). The DCM is a non-statistical model used to account for the decay of hot and rotating nuclei formed in low energy heavy ion reactions. The excitation functions are calculated by considering quadrupole (β₂) deformations with optimum orientations of decaying fragments. The DCM-based cross-sections for evaporation residue (ER), fusion–fission, αxn and neutron decay processes find nice agreement with the reported experimental data over wide range of incident energies. The cross-sections corresponding to different decay mechanism are worked out within DCM by fitting neck length parameter (ΔR). The entrance channel and angular momentum effects are investigated in reference to the above-mentioned reaction channels. In addition to this, the fragment mass distribution is worked out by colliding ¹³C weakly bound stable projectile with a variety of target nuclei resulting in ¹³C+¹⁵⁹Tb, ¹³C+¹⁸¹Ta and ¹³C+²⁰⁷Pb reactions. At comparable projectile energies, the increase in target mass is shown to favor asymmetric fragmentation in the fissioning region. Besides this, the incomplete fusion (ICF) contribution is worked out for ¹²C and ¹³C channels by applying necessary energy corrections in the framework of DCM.

The fusion dynamics of ${}^{30}\mathrm{\text{Si}}+{}^{238}\mathrm{\text{U}}$ reaction has been studied using different theoretical approaches like energy-dependent Woods–Saxon potential (EDWSP) model, coupled channel formulation and Wong approach. At sub-barrier energies, the anomalously large enhancement of the fusion cross-section signifies the importance of barrier modification effects for the adequate addressal of experimental data. The EDWSP model, wherein barrier modification effects are introduced via the energy-dependent diffuseness parameter, is used to examine the sub-barrier fusion anomalies. In the framework of coupled channel model, the impacts of collective excitations and/or static deformations of colliding partners are incorporated in the fusion dynamics. In Wong formula, the role of different Skyrme forces such as SIII, KDE0v1, SkT1, SSk, GSkI is analyzed to address the observed fusion enhancement around the Coulomb barrier. Among these, GSkI and SSk forces seem more appropriate for the addressal of fusion dynamics at sub-barrier energies while SIII, SkT1 and KDE0v1 forces give relatively better results at the above barrier region. The SSk (GSkI) force at higher energies overestimate the experimental data and hence treated with the $\ell$-summed Wong approach. The effect of deformations and optimum orientations is duly incorporated in the calculation and hence gives better description to the observed data. In addition, the fusion cross-sections are predicted over extreme energies using EDWSP and $\ell$-summed Wong approach. It is worth mentioning here that the different theoretical approaches (EDWSP, coupled channel and Wong) induce similar kinds of barrier lowering effects, henceforth, they reasonably describe the sub-barrier fusion data of ${}^{30}\mathrm{\text{Si}}+{}^{238}\mathrm{\text{U}}$ reaction.

In this paper, we applied the method developed by Santhosh and Safoora in [Phys. Rev. C  94 (2016) 024623; 95 (2017) 064611] to theoretically investigate the fusion, evaporation-residue (ER) and fission cross-sections of the synthesis of the unknown superheavy ${}^{309,312}$126 nuclei produced by using the ${}^{58}$Ni + ${}^{251}$Cf and ${}^{64}$Zn + ${}^{248}$Cm combinations. The charge asymmetry, mass asymmetry and fissility of the DiNuclear System (DNS) in the synthesis of the mentioned combinations are also estimated. The calculated results show that the ER cross-sections for the synthesis of the ${}^{309-317}$126 nuclei are predicted to be much less than 1.0fb. In particular, it has been found that there may exist a valley of the ER cross-sections in the synthesis of a superheavy $Z=126$ element, which produces the ${}^{313}$126 isotope. Subsequently, a model for the mass dependence of the ER cross-section in the synthesis of the ${}^{307-320}$126 isotopes has been proposed for the first time. On the other hand, the quasi-fission process strongly dominates over the fusion in the two concerned interacting systems. The present results, together with those reported in the previous studies, indicate that the investigated projectile–target combinations are not capable for the synthesis of the ${}^{309,312}$126 isotopes due to tiny fusion cross-sections (about 2–3zb), which go beyond the limitations of available facilities. Further studies are thus recommended to search for alternative interacting systems. In conclusion, this work provides useful information for the synthesis of the gap isotopes ${}^{308-317}$126, which have not been well studied up to date.

The fusion evaporation residue (ER) cross-sections ${\sigma }_{xn}$ for the decay of compound nucleus (CN) ${}^{252,254,255,256}$No${}^{\ast }$ via 1$n$–4$n$ decay channels, synthesized in ${}^{204,206,207,208}$Pb$+$${}^{48}$Ca reaction, are studied, including deformations ${\beta }_{2i}$ for cold-optimum orientations ${𝜃}_i$ at various ${}^{48}$Ca excitation energies of $E^{\ast }=20$ to 45MeV. For the nuclear interaction potentials, we use the Skyrme energy density functional (SEDF)-based on semi-classical extended Thomas Fermi (ETF) approach under frozen density approximation on our earlier study of fusion ER cross-section for the decay of ${}^{252,254-256}$No${}^{\ast }$, via 1$n$–4$n$ decay channels synthesized in ${}^{204,206-208}$Pb$+$${}^{48}$Ca reaction based on the Dynamical cluster-decay model (DCM) using the pocket formula for nuclear proximity potential in which the above reaction was investigated by using hot-optimum orientations. In this work the above reaction has been investigated in two parts, in the first part, $E^{\ast }<25$MeV is used for cold elongated configurations and in the second part, $E^{\ast }>25$MeV is used for hot compact configurations. The Skyrme forces used here are the old SIII, and new GSkI and KDE0(v1) given for both normal and isospin-rich nuclei, with densities added in frozen density approximation. Interestingly, independent of the Skyrme force used, the DCM gives an excellent fit within one-parameter fitting of $\mathrm{\Delta }R$ to the measured data on fusion ER for cold fusion. Of all the three Pb-isotopes and three $E^{\ast }$ considered, at each $E^{\ast }$, the $\mathrm{\Delta }R$ is largest for compound system with mass numbers 256 and 254, and smallest for 252, which means that the neutrons emission occur earliest for 256, then 255 followed by 254 and finally for 252, in complete agreement with experimental data. The possible fusion–fission (ff) and quasi-fission (qf) mass-regions of fragments on DCM are also predicted. The DCM with Skyrme forces is further used to look for all the possible target-projectile ($t$-$p$) combinations forming the “cold” CN ${}^{254}$No${}^{\ast }$ at the CN excitation energy of $E^{\ast }$ for “optimum cold” configurations. The fusion ER cross-sections, for the proposed new reactions in synthesizing the CN ${}^{254}$No${}^{\ast }$, are also estimated for the future experiments.

In this paper, we have studied all possible ${}^{48}\mathrm{\text{Ca}}$ and ${}^{58}\mathrm{\text{Fe}}$-induced fusion reactions for the synthesis of superheavy nuclei $104\le Z\le 125$. The semi-empirical formula for fusion barriers of ${}^{48}\mathrm{\text{Ca}}$ and ${}^{58}\mathrm{\text{Fe}}$ is constructed. Fusion and evaporation residue cross-sections are studied using advance statistical model (ASM). The fusion and evaporation residue cross-sections of this work are compared with that of experiments. We have also predicted suitable targets and production cross-sections for the synthesis of superheavy elements using the ${}^{48}\mathrm{\text{Ca}}$ and ${}^{58}\mathrm{\text{Fe}}$-induced fusion reactions. The ${}^{58}\mathrm{\text{Fe}}$-induced fusion reactions can be used to synthesize superheavy elements $Z=120,122$ and 124 using the targets ${}^{245}$Cm, ${}^{249}$Bk and ${}^{249}$Cf have half-lives greater than one year and produce the cross-sections in terms of pb.

The dependence of decay modes of hot compound nuclei formed in ${}^{86}$Kr$+{}^{134,138}$Ba reactions on the angular momentum has been analyzed using the dynamical cluster-decay model. This has been done by analyzing the change of fragmentation potential, preformation probability, penetrability and cross-section as a function of the fragment mass number at various values of the angular momentum. The evaporation residue cross-section calculated using dynamical cluster-decay model has been compared with the measured one for the channels: $n+\alpha n$, $2n+\alpha 2n$, $np+\alpha np$ for the decay of ${}^{220}$U${}^{\ast }$ and $n+\alpha n+2\alpha n$ for ${}^{224}$U${}^{\ast }$. The summed up fragment cross-sections for the light particles, intermediate mass fragments and fission fragments as a function of angular momentum have been studied which gives an idea for the change of reaction mechanism with angular momentum. The charge distribution of the fission fragment cross-section shows an odd–even staggering, i.e., the probability of even-Z fission fragments is relatively higher than others. The mass distributions obtained within the dynamical cluster-decay model for the decay of ${}^{220,224}$U${}^{\ast }$ are in conformity with mass distributions determined by means of the double kinetic-energy technique in literature. The position of the most probable channel has been found to be fixed to a constant atomic number instead of mass number.

Recently several complete-fusion reactions have been studied at the DGFRS setup (FLNR, JINR) with an aim of exploring the boundaries of the “Island of Stability” of the superheavy elements (nuclei around Z=114-126 and N=184). During the ^249-251Cf+⁴⁸Ca run with mixed Cf target (50.7% of ²⁴⁹Cf, 12.9% of ²⁵⁰Cf, and 36.4% of ²⁵¹Cf ) just one decay chain was detected at the 252-MeV beam energy which was attributed to the previously observed ²⁹⁴Og isotope, the product of the ²⁴⁹Cf(⁴⁸Ca,3n)²⁹⁴Og reaction; the corresponding reaction cross section was measured. For the ²⁵¹Cf(⁴⁸Ca, 3-4n)^295,296Og reactions no Og decays were detected during this run. Future possibilities for synthesis of new nuclides in the region of SHEs, namely more neutron-rich Lv, Ts and Og isotopes and new nuclides with higher Z (119 and 120), are discussed.

Kinetics energies, angular distributions and cross sections of fragments with atomic number 6≤Z≤28 were measured in ^78,82Kr + ⁴⁰Ca reactions at 5.5 AMeV incident energy by means of the 4π-INDRA array at GANIL. Global features are compatible with a binary fission from compound nucleus. The cross-sections indicate the coexistence of macroscopic behaviour and structure effects that depend on the chemical composition of the emitting nucleus. Fragment-particle coincidences show that fragment with 12≤Z are excited below the separation energies of light particles.