Framework Of Dynamical Cluster-decay Model Research Articles

Implication of compact configuration of hexadecapole deformed actinides in the synthesis of superheavy nuclei

The quadrupole (β2) deformed targets in the actinide region are found to be of great relevance in the production of superheavy nuclei (SHN), in the compact fusion mechanism. Recently, the application of “elongated” and “compact” configurations of pear-shape octupole (up to β3) deformed nuclei was found to play a significant role in the fusion-fission dynamics of heavy-ion induced reactions. In the present work, we intend to explore the relevance of higher-order deformed (up to β4) actinides and their compact configuration in the production cross-section as well as de-excitation of SHN (dynamics of 48Ca + 238U →286Cn∗ → A1 + A2 reaction). For the above analysis, we have calculated σER within the framework of dynamical cluster-decay model developed on the basis of quantum mechanical fragmentation theory, which has been extended with the inclusion of deformations up to β4 and corresponding compact optimum orientation. Besides, on the basis of this theory, the fragmentation structure of 286Cn∗ superheavy nucleus is examined in terms of fragmentation potential (Vη) and preformation probability (P0) as a function of fragment mass number.

Across barrier fission analysis of At⁎ isotopes formed in 3,4,6,8He+209Bi reactions

The fission decay mechanism of various 212,213,215,217At⁎ isotopes formed in tightly (3,4He) and loosely bound (6,8He) projectile induced reactions on 209Bi target, is studied within the framework of dynamical cluster-decay model (DCM), over a wide range of excitation energies spread across the Coulomb barrier. By optimizing appropriate neck-length parameter ΔR, the fission cross-sections are calculated for 212,213,215At⁎ compound nuclei (CN) at above barrier energies, where some experimental data is available. The DCM calculations are extended at below barrier region for these nuclei, and for one more reaction 8He+209Bi→217At⁎, using the systematics of 212,213,215At⁎ isotopes. The magnitude of fission cross-sections increase with the addition of neutrons in the He-projectile (or say in the At compound nucleus since the target nucleus of each reaction is same). To obtain better description of fission dynamics involved for neutron-deficient and neutron-rich He-induced reactions, the fragmentation potential and prefromation probability P0 of decaying fragments are analyzed along with corresponding barrier tunneling probability P. The fission fragment mass distributions are explored for all ‘At’ isotopes, and most probable fission fragments are identified. It has been observed that asymmetric fission forms the predominant decay mode for all isotopes, although a minor hump with very small preformation factor appears around symmetric fragments for lighter 212,213At⁎ nuclei. Finally, the N/Z dependence of fission cross-sections and most probable decaying fragments is explored in view of fragmentation structure and related cross-sectional yields.

Fine structure effect among heavy-ion induced fission fragments at near and above barrier energies

The fission decay analysis of 201Bi*, 206Po*, 212Rn*, 216Ra*, 227Pa* and 228U* nuclei produced in 19F-induced reactions at near and above barrier energies is carried out within the framework of dynamical cluster-decay model (DCM) based on quantum mechanical fragmentation theory (QMFT). The interplay between two modes of fission, i.e. symmetric (SF) and asymmetric (aSF), in the fission fragment mass distributions is investigated. For the present set of calculations the SF to aSF peak ratio is less than unity ($ \frac{P_{SF}}{P_{aSF}} < 1$), which in turn suggests the dominance of asymmetric fission for above mentioned compound nuclei. The role of shell corrections and deformations of fragments in the fission dynamics is duly addressed. The calculated fission cross-sections show nice agreement with the experimental data, except for few energies above the Coulomb barrier. This disagreement is associated with the possible presence of non-compound nucleus (nCN) fission as higher energies are more prone to the nCN process. The study of fission fragment mass distributions is further extended to the isotopic analysis of above mentioned pre-actinide and actinide nuclei at common centre-of-mass energy $ E_{c.m.} \approx 80$ MeV near the Coulomb barrier. It is observed that the lighter isotopes exhibit symmetric fission distribution, whereas heavier ones prefer to decay via asymmetric path. A transition between SF and aSF occurs around fissioning nuclei with $ N/Z \approx 1.4$, showing the triple humped mass distribution suggesting comparable contribution of symmetric and asymmetric fission. Finally, the most energetic asymmetric light ($ A_L$) and heavy ($ A_H$) fission fragments are identified for a long isotopic chain of pre-actinide and actinide nuclei. Interestingly, the heavier asymmetric fission fragments are located near a proton number around $ Z=50$ for the pre-actinide region and $ Z=54$ for actinide nuclei.

Fission Cross Sections and Fragment Mass Distribution of Actinide Nuclei Formed in n-Induced Reactions

The fission dynamics of odd mass actinide nuclei, 233Th∗ and 239U∗ formed in n-induced reactions, is studied in the framework of dynamical cluster-decay model (DCM). The analysis is carried out over a range of incident energies varying from En = 32.8 to 59.9 MeV. A description of deformation effects is provided by considering spherical as well as deformed choice of fragmentation and the fragment mass distribution is examined accordingly. The study is extended to two more actinide nuclei (233Pa∗ and 239Np∗) and the barrier characteristics are compared for chosen reactions and corresponding preformation factor is worked out to estimate the relative influence on fragment mass distribution. In addition to this, the relative role of sticking (IS) and non-sticking (INS) moment of inertia on the decay of 233Th∗ is explored. Finally, the comparative analysis of n-induced reaction with p-induced reactions is carried out for Th and U nuclei.

Competing analysis of α and 2p2n-emission from compound nuclei formed in neutron induced reactions

The decay mechanism of compound system 61Ni⁎ formed in fast neutron induced reactions is explored within the collective clusterization approach of the Dynamical Cluster-decay Model (DCM) in reference to a recent experiment over an energy spread of En=1–100 MeV. The excitation functions for the decay of the compound nucleus 61Ni⁎ formed in the n+Ni60 reaction show a double humped variation with incident beam energy where the peak at lower energy corresponds to α-emission while the one at higher energy originates from 2p2n-emission. The experimentally observed transmutation of α-emission at lower energy into 2p2n-emission at higher incident energies is explained on the basis of temperature dependence of the binding energies used within the framework of DCM. The cross-sections for the formation of the daughter nucleus 57Fe after emission of α-cluster from the 61Ni⁎ nucleus are addressed by employing the neck length parameter (ΔR), finding decent agreement with the available experimental data. The calculations are done for non-sticking choice of moment of inertia (INS) in the centrifugal potential term, which forms the essential ingredient in DCM based calculations. In addition to this, the effect of mass (and charge) of the compound nucleus is exercised in view of α and 2p2n emission and comparative study of the decay profiles of compound systems with mass A = 17–93 is employed to get better description of decay patterns.

Fission dynamics of240Cf*formed in34,36S induced reactions

We have studied the entrance channel effects in the decay of Compound nucleus 240 Cf * formed in 34 S+ 206 Pb and 36 S+ 204 Pb reactions by using energy density dependent nuclear proximity potential in the framework of dynamical cluster-decay model (DCM). At different excitation energies, the fragmentation potential and preformation probability of decaying fragments are almost identical for both the entrance channels, which seem to suggest that decay is independent of its formation and entrance channel excitation energy. It is also observed that, with inclusion of deformation effects upto quadrupole within the optimum orientation approach, the fragmentation path governing potential energy surfaces gets modified significantly. Beside this, the fission mass distribution of Cf* isotopes is also investigated. The calculated fission cross-sections using SIII force for both the channels find nice agreement with the available experimental data for deformed choice of fragments, except at higher energies. In addition to this, the comparative analysis with Blocki based nuclear attraction is also worked out. It is observed that Blocki proximity potential accounts well for the CN decay at all energies whereas the use of EDF based nuclear potential suggests the presence of some non-compound nucleus process (such as quasi-fission (qf)) at higher energies.

Fragment mass identification and related aspects in the decay of 40Ca* and 39K* nuclei

The dynamics involved in the decay of light mass nuclei formed in asymmetric channels 12 C + 28 Si , 11 B + 28 Si and 12 C + 27 Al have been investigated using the dynamical cluster-decay model (DCM). In reference to the experimentally measured charge particle cross-sections, the fragment masses contributing towards the decay of 40 Ca * and 39 K * nuclei have been identified using spherical choice of fragmentation. Also, the role of entrance channel has been investigated by studying the decay of 39 K * nuclear system formed in two different reactions at same excitation energy. The behavior of fragmentation potential, preformation probability, penetrability and emission time, is analyzed to figure out the favorable mass fragments, their relative emergence and the entrance channel effects observed in the decay of light mass nuclei. In addition to this, the cross-sections for the light particles (LPs) and heavier charge fragments have been estimated for the compound nucleus (CN) decay. Besides this, one of the noncompound nucleus (nCN) process, deep inelastic collision (DIC) has been addressed in context of DCM approach for the first time. The cross-sections obtained in framework of DCM for both CN and nCN processes are found to have nice agreement with the available experimental data.

Role of rotational energy and deformations in the dynamics of Li6+Zr90 reaction

Abstract In reference to recent experimental data, the dynamical cluster-decay model (DCM) has been applied to study the neutron evaporation residue (ER) cross sections of intermediate mass nucleus 96Tc⁎ spread over a wide range of incident energy across the Coulomb barrier. In order to analyze the effect of rotational energy in the dynamics of Li 6 + Zr 90 reaction, the cross sections have been calculated using the sticking ( I S ) and the non-sticking ( I NS ) limits of moment of inertia with inclusion of quadrupole ( β 2 ) deformation within optimum orientation approach. The effect of either of the two approaches on the angular momentum, and hence the rotational energy associated with it, is assessed through the fragment mass distribution, preformation factor and the barrier penetrability. Also, the role of deformations is studied through a comparative analysis of decay path for spherical and β 2 deformed fragmentation. The calculated evaporation residue cross sections show excellent agreement with the reported data at all incident energies for both spherical and β 2 -deformed approach. Finally, the incomplete fusion (ICF) process observed due to loosely bound projectile 6Li is addressed within the framework of DCM.

Analysis of fragment distribution and associated effects in 12,13C induced reactions

The decay of 220 Ra * nucleus formed in two different entrance channels 12 C +208 Pb and 13 C +207 Pb 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 [Formula: see text] 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 13 C weakly bound stable projectile with a variety of target nuclei resulting in 13 C +159 Tb , 13 C +181 Ta and 13 C +207 Pb 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 12 C and 13 C channels by applying necessary energy corrections in the framework of DCM.

Compound and non-compound nucleus contributions in the evaporation residue cross-sections of 20Ne + 181Ta → 201Bi⁎ reaction at and 162 MeV

Abstract The simultaneous existence of Compound Nucleus (CN) and Non-Compound Nucleus (NCN) processes in the decay of a nuclear system, provide a comprehensive picture of nuclear reaction dynamics and related phenomenon in low energy region. The CN and NCN based Evaporation Residue (ER) cross-section data is available for 20 Ne + 181 Ta → 201 Bi ⁎ reaction at two energies i.e. E lab = 150 MeV and E lab = 180 MeV , and the same is tested in the framework of Dynamical Cluster Decay Model (DCM). Experimentally, the NCN component is reported to have major contribution from Incomplete Fusion (ICF) channel and the Deep Inelastic Collision (DIC) component is shown to be negligibly small. The ER formed in CN and NCN (ICF in present case) are nicely reproduced in the framework of DCM. The available CN based ER cross-sections are fitted for spherical, β 2 deformed and β 2 – β 4 deformed fragmentation paths, which in turn provide a nice description of deformation effects in the decay of 201 Bi ⁎ formed in 20 Ne induced reaction. The role of barrier modification and angular momentum dependence is also addressed in addition to deformation and orientation effects.

Decay mechanism of the204Po*nucleus formed in16O and28Si induced reactions

The basic aim of the present study is to investigate the role of deformations, orientations, angular momentum dependence along with possible presence of noncompound nucleus (nCN) component in the decay of preactinide nucleus ${}^{204}$Po${}^{*}$ formed in ${}^{16}$O and ${}^{28}$Si induced reactions over a wide range of projectile energies having comparable ${E}_{\mathrm{c}.\mathrm{m}.}/{V}_{c}$ values for two channels. Recently, an experiment was performed to extract fusion-fission and evaporation residue cross sections for ${}^{16}$O + ${}^{188}$O $\ensuremath{\rightarrow}$ ${}^{204}$Po${}^{*}$ and ${}^{28}$Si + ${}^{176}$Yb $\ensuremath{\rightarrow}$ ${}^{204}$Po${}^{*}$ reactions over a wide range of energies (${E}_{\mathrm{lab}}=84$--155 MeV). Within the dynamical cluster decay model (DCM), we have calculated the evaporation residue and the fission cross sections in reference to the available data at various incident energies by simultaneously fitting the only parameter, neck-length ($\ensuremath{\Delta}R$) for evaporation residue and fission. The choice of different neck-length parameter ($\ensuremath{\Delta}R$) values for ER and fission indicate that the two decay processes do not occur simultaneously, i.e., they occur in different time scales and evolve subject to the nature of dynamics of compound nucleus formed. The effects of nuclear deformations and orientations are duely incorporated in the framework of DCM and role of ${\ensuremath{\beta}}_{2}$ deformations is investigated in reference to decay path of ${}^{204}$Po${}^{*}$ nucleus. The calculated evaporation residue cross sections and fission cross sections show excellent agreement with the reported data at all incident center of mass energies, except at one highest energy for the channel ${}^{28}$Si + ${}^{176}$Yb $\ensuremath{\rightarrow}$ ${}^{204}$Po${}^{*}$ for fission. The disagreement between DCM calculations and reported data at highest incident center of mass energy for the ${}^{28}$Si + ${}^{176}$Yb entrance channel may be associated with the presence of small amount of nCN effects which is in line with the predictions of the preequilibrium model. Also the in-built property of barrier lowering effect of DCM seems to be operating in context of these reactions. The fission fragment anisotropies are also calculated using DCM-based parameters for the nonsticking moment of inertia, and they find reasonable comparison with experimental data. Finally, the isotopic effect is worked out by studying the decay of ${}^{202}$Po${}^{*}$ and ${}^{204}$Po${}^{*}$ nuclei formed in ${}^{16}$O induced reactions at comparable ${E}_{\mathrm{c}.\mathrm{m}.}/{V}_{c}$ value.

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.