Entrance Channel Effects Research Articles

First investigation on the isomeric ratio in multinucleon transfer reactions: Entrance channel effects on the spin distribution

The multinucleon transfer (MNT) reaction approach was successfully employed for the first time to measure the isomeric ratios (IRs) of 211Po isomer (25/2+) and its ground state (9/2+) at the IGISOL facility using a 945 MeV 136Xe beam impinged on 209Bi and natPb targets. The dominant production of isomers compared to the corresponding ground states was consistently revealed in the α-decay spectra. Deduced IR of 211Po populated through the 136Xe+natPb reaction was found to have an enhancement of ≈1.8-times than that observed for the 136Xe+209Bi. State-of-the-art Langevin-type model calculations have been utilized to estimate the spin distribution of an MNT residue. The computations qualitatively corroborate with the considerable increase in the IRs of 211Po produced from 136Xe+natPb compared to 136Xe+209Bi. Theoretical investigations indicate a weak dependence of target spin on the IRs. The enhancement of the 211Po isomer in the 136Xe+natPb over 136Xe+209Bi can be attributed to the different proton (p)-transfer production routes. Estimations demonstrate an increment in the angular momentum transfer, favorable for isomer production, with increasing projectile energy. Comparative analysis reveals the two entrance channel parameters, projectile mass and p-transfer channels, strongly influencing the population of the high-spin isomer of 211Po (25/2+). This letter reports the first experimental and theoretical study on the IRs of nuclei formed from two different p-transfer channels via two independent MNT reactions.

Study of Entrance Channel Effects on Fusion–Fission and Quasi-fission Processes

Study of Entrance Channel Effects on Fusion–Fission and Quasi-fission Processes

Systematic study of prescission neutron multiplicity: Revealing the role of entrance channel magicity

The prescission neutron multiplicities (νpre) are studied for a systematic understanding of the influence of entrance-channel shell closure in fusion-fission dynamics. The existing νpre data are analyzed for reactions with a wide variety of target and projectile combinations. For completeness, the measured νpre data for the fusion-fission reactions with the doubly closed shell 16O projectile on the targets having either proton (204,206Pb) or both proton and neutron (208Pb) shell closure is reanalyzed. Although the measured νpre for 224Th disagree with the available data reported by Rossner et al. (1992) [1], our results are found to be more consistent and follow a systematic trend as described in this letter. Theoretical analysis is performed within the standard statistical model framework, where dissipation strength is used as a tunable parameter. It is observed that irrespective of the compound nuclear excitation energy, the entrance channel magicity imparts an intriguing impact on the dissipation strength. A similar entrance channel effect in the evaporation residue cross-section is also demonstrated. In conclusion, the present analysis establishes an entanglement of the exit channel observables with the entrance channel shell closure. It contradicts the hypothesis of complete equilibrium in compound nuclear reactions.

Fragmentation analysis of various compound nuclei formed in the mass region 200 and the associated entrance channel effects

Fragmentation analysis of various compound nuclei formed in the mass region 200 and the associated entrance channel effects

Low Energy Incomplete Fusion Reactions: Probing of Entrance Channel Effect

Low Energy Incomplete Fusion Reactions: Probing of Entrance Channel Effect

Exploring Entrance Channel Effects in the Interaction of \(^{16}\)O with \(^{93}\)Nb

Exploring Entrance Channel Effects in the Interaction of \(^{16}\)O with \(^{93}\)Nb

Quasifission barrier of heavy ion fusion reactions leading to the formation of the superheavy nucleus 120302

We study the quasifission barriers of different fusion reactions leading to synthesis of the superheavy element $Z=120$ using the dinuclear system approach. In particular, the influence of the projectile-target orientation and angular momentum on quasifission barriers has been investigated. The quasifission barrier height is observed to be maximum when the angle of orientation of projectile-target is about ${90}^{\ensuremath{\circ}}$ (tip-tip orientation). The role of entrance channel effects on quasifission barriers is investigated, and also suggested are suitable empirical formulas for the same. The striking results leading to larger quasifission barriers, whose cross sections are $>10$ fb, are also mentioned. As a result, the current research might be valuable in developing corrective techniques for future experimental attempts to synthesize superheavy nuclei with $Z=120$.

Investigating the fission dynamics of the following neutron shell closed nuclei within a stochastic dynamical approach: 210Po, 212Rn, and 213Fr* *D.A. acknowledges the financial support from the University Grants Commission (UGC), Government of India, received in the form of a research fellowship (Ref. No. 19/06/2016/(i) EU-V, Sr. No. 2061651303)

The dissipative dynamics of nuclear fission is a well confirmed phenomenon that can be either described by a Kramers-modified statistical model or by a dynamical model employing the Langevin equation. Although dynamical models as well as statistical models incorporating fission delays have been found to explain the measured fission observables in several studies, they present conflicting results for shell closed nuclei in the mass region of 200. Notably, an analysis of the recent data on neutron shell closed nuclei in the excitation energy range of 4080 MeV failed to provide a satisfactory description of the data, which was attributed to a mismatch with shell effects and/or entrance channel effects, without reaching a definite conclusion. In the present study, we demonstrate that a well established stochastic dynamical code can simultaneously reproduce the available data for pre-scission neutron multiplicities and fission and evaporation residue excitation functions for the following neutron shell closed nuclei Po and Rn and their isotopes Po and Rn without the need for including any extra shell or entrance channel effects. The relevant calculations are performed by using a phenomenological universal friction form factor with no ad-hoc adjustment of the model parameters. However, we note a significant deviation, beyond experimental errors, for some Fr isotopes.

The entrance channel effect on the synthesis of a superheavy element 296119

In this study, we investigated the entrance channel effect on the evaporation residue cross section of a superheavy element 296119. Using 29 projectile-target combinations, we investigated the role of the entrance channel on the 3n and 4n evaporation channels in hot combinations. This effect can be evaluated based on the entrance channel asymmetry and Q value of complete fusion. We calculated the variation of the maximum evaporation residue cross sections ( and ) with for the reactions , , , and . With an increase in , and increase. In addition, we studied the role of asymmetry and mean fissility parameters in the synthesis of the superheavy element. The obtained results in this study can be utilized in future studies.

Probing entrance channel effects in fusion-fission dynamics through neutron multiplicity measurement of 208Rn

The pre- and post-scission neutron multiplicities are measured for the fission of 208Rn, populated with the reactions 30Si+178Hf and 48Ti+160Gd in the excitation energy range of 54.5 - 80.8 MeV. We found significant differences in the pre-scission neutron multiplicities of these two systems. Also, both the reactions exhibit an enhancement in the pre-scission multiplicity with respect to the existing data for the 16O+194Pt reaction populating 210Rn. The measured multiplicities are compared with the theoretical predictions obtained from the Langevin dynamical model for fission. Dynamical simulations are also performed to estimate the capture cross-sections. Contribution of the neutrons, emitted during the fusion process, is shown to be crucial in determining the neutron multiplicities for the present systems. Moreover, in case of the 48Ti+160Gd reaction, rapid quasi-fission dynamics prevents neutron emission from the thermalized target-projectile composite. The present measurement helps us to understand the relative importance of fusion and quasi-fission processes and their timescales depending on the entrance channel mass asymmetry.

Entrance channel dependent hot fusion reactions for superheavy element synthesis

We have studied the compound nucleus probability, the survival probability, and the evaporation residue cross sections for 6645 projectile-target combinations to synthesize the superheavy nuclei with atomic numbers $Z=110$--126 in the light of the entrance channel effects such as mass asymmetry, charge asymmetry, isospin asymmetry, non-compound nuclear fission probability, and Businaro-Gallone mass asymmetry. The role of quasifission in every reaction has also been considered. Decay chains of various superheavy nuclei produced from the reactions are portrayed as well. The most striking results are that the measured evaporation residue cross sections are of the order of picobarns, whereas the proposed reactions can yield up to microbarn cross sections for the superheavy nuclei with $110\ensuremath{\le}Z\ensuremath{\le}126$. We suggest future experiments may utilize these hot fusion reactions to synthesize new elements ($Zg118$) or to study the properties of the known superheavy nuclei in greater detail. In particular, a proposed reaction containing both projectiles and targets that are naturally abundant, for example, $_{36}^{82}\mathrm{Kr}+_{90}^{232}\mathrm{Th}\ensuremath{\rightarrow}^{314}126+0n$, yields evaporation residue cross sections as high as 31 nb. The presently available experimental setup can test the prediction with ease to make a dream come true by putting a footstep into the eighth row of the periodic table.

Investigations on the study of entrance channel effects in synthesis of superheavy elements using Cr-induced fusion reactions

We have investigated the synthesis of superheavy elements using Cr-induced fusion reactions. We have studied all possible Cr-induced fusion reactions for the synthesis of super heavy nuclei [Formula: see text]. We have achieved the semi-empirical formula for fusion barrier heights ([Formula: see text]), positions ([Formula: see text]), curvature of the inverted parabola ([Formula: see text]) of Cr-induced fusion reactions for the synthesis of superheavy nuclei with atomic number range [Formula: see text]. The proposed formula produces fusion barriers of Cr-induced fusion reactions for the synthesis of super heavy nuclei with the simple inputs of mass number ([Formula: see text]) and atomic number ([Formula: see text]) of projectile-targets. We have also identified the targets for Cr-induced fusion reactions to synthesis superheavy elements of [Formula: see text]. We have also studied the entrance channel parameters such as mass asymmetry ([Formula: see text]), charge asymmetry ([Formula: see text]), coulomb interaction parameter ([Formula: see text]’), Businaro–Gallone mass asymmetry parameter ([Formula: see text]) and Isospin asymmetry parameter [[Formula: see text]]. We hope that our predictions may be the guide for the future experiments in the synthesis of more superheavy elements using [Formula: see text]Cr-induced fusion reactions.

Probing of incomplete fusion dynamics in $${}^{{14}}\text {N} + {}^{{124}}\text {Sn}$$ system and its correlation with various entrance channel effects

Measurements of excitation functions were done for the evaporation residues populated in $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ system at low energy. The present analysis shows the appearance of incomplete fusion by the breakup of non- $$\upalpha $$ cluster structured projectile $$^{{14}}\text {N}$$ into $$\upalpha + {}^{{10}}\text {B}$$ . A correlation between the combined effects of total asymmetry and $$\text {Z}_{\mathrm {P}}\text {Z}_{\mathrm {T}}$$ has been studied through three new parameters total asymmetry ( $$S_{{ TAS}}$$ ), Coulomb asymmetry parameters; $$Z_{P} Z_{T} /S_{{ TAS}} $$ and $$Z_{P} Z_{T} .S_{{ TAS}} $$ . These new parameters were found more sensitive and effective to encounter the combined effects of coulomb interactions and entire asymmetry effect of the system on incomplete fusion dynamics. The complete fusion and total fusion cross-sections of two systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{124}\text {Sn}$$ have been reduced using two different standard reduction procedures, which shows that the incomplete fusion probability for reactions induced by projectile $${}^{{16}}\text {O}$$ is generally larger than $${}^{{14}}\text {N}$$ induced reactions. The experimental fusion functions are found to be suppressed as compared to universal fusion function for systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{{124}}\text {Sn}$$ . The different values of suppression factor for projectiles $${}^{{14}}\text {N}$$ and $${}^{{16}}\text {O}$$ indicate that the probability of $$\upalpha $$ -breakup is different for these projectiles. Further, the total fusion functions for systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{{124}}\text {Sn}$$ agree well with the universal fusion function. However, the present results clearly show that the shell closure of nuclei also affect the low energy incomplete fusion dynamics along with the structure of projectile.

Entrance channel effects on the alpha decay probabilities of neutron and proton induced reactions for target mass A=55

In the present work, we investigate the entrance channel effects on the alpha decay probabilities for the neutron and proton induced reactions for target mass A=55 from few MeV up to 20 MeV. In particular, we studied two combinations, 55Fe(n,α)52Cr and 55Mn(p,α)52Cr; 55Mn(n,α)52V and 55Cr(p,α)52V reactions. Each combination is producing the same compound nucleus at the same excitation energy, but with different Jπ distributions. We investigate how the difference in the Jπ distributions of the compound nuclei at the same excitation energy formed by the neutron and proton induced reactions influence the alpha decay channel. The theoretical simulation is done using the nuclear reaction code TALYS-1.9. The results are compared with experimental results whenever available, and are discussed in detail.

Study of entrance channel effects on pre-equilibrium emissions in proton and alpha induced reactions on 64Ni: Basic pre-equilibrium parameters

The effect of entrance channel on the relative strength of pre-equilibrium emission, basic pre-equilibrium parameters, excitation functions for proton and alpha induced reactions on 64 Ni have been analyzed over the energy range from threshold up to 40 MeV. The results have been compared with the theoretical cross-sections calculated by means of the code EMPIRE3.2.3-MALTA and TALYS 1.6

Entrance channel effects on the quasifission reaction channel in Cr + W systems

Background: Formation of a fully equilibrated compound nucleus is a critical step in the heavy-ion fusion reaction mechanism but can be hindered by orders of magnitude by quasifission, a process in which the dinuclear system breaks apart prior to full equilibration. To provide a complete description of heavy-ion fusion it is important to characterize the quasifission process. In particular, the impact of changing the neutron-richness of the quasifission process is not well known. A previous study of Cr + W reactions at a constant 13 % above the Coulomb barrier concluded that an increase in neutron-richness leads to a decrease in the prominence of the quasifission reaction channel. Purpose: The interplay between the fusion-fission and quasifission reaction channels, with varying neutron-richness, was explored at a constant excitation energy, closer to the interaction barrier than the previous work, to see if the correlation between neutron-richness and quasifission is valid at lower energies. Methods: Mass distributions were determined for eight different combinations of Cr + W reactions at the Australian National University at 52.0 MeV of excitation energy in the compound nucleus. Results: A curvature parameter was determined for the fission-like fragment mass distributions and compared to various reaction parameters known to influence quasifission. Conclusions: The present work demonstrates that at energies near the interaction barrier the deformation effects dominate over the neutron-richness effects in the competition between quasifission and compound nucleus formation in these Cr + W systems and is an important consideration for future with heavy and superheavy element production reactions.

Mass and isotopic yield distributions of fission-like events in the F19+Tm169 system at low energies

In the present work, 22 fission-like residues with mass number $67\ensuremath{\le}A\ensuremath{\le}156$ produced via complete fusion-fission and/or incomplete fusion-fission have been identified and their production cross sections measured at three projectile energies, viz., $92.0\ifmmode\pm\else\textpm\fi{}1.8$, $102.5\ifmmode\pm\else\textpm\fi{}1.5$, and $105.4\ifmmode\pm\else\textpm\fi{}1.6$ MeV in the $^{19}\mathrm{F}+^{169}\mathrm{Tm}$ system. The absolute cross section of each fission-like residue is measured by recoil-catcher activation technique using off-line $\ensuremath{\gamma}$-ray spectroscopy. The data have been analyzed to deduce the parameters for isotopic yield and isobaric charge distributions. The deduced isotopic yields for indium ($^{107,108,109,110m}\mathrm{In}$) and neodymium ($^{134,135,137,139}\mathrm{Nd}$) isotopes are reproduced by Gaussian distribution and their variance is in good agreement with that reported in literature. The mass distributions of fission-like residues at three energies are also found to be Gaussian peaked, which confirms their production via deexcitation of a compound nucleus through complete fusion-fission and/or incomplete fusion-fission processes. It has been observed that, the mass variance (${\ensuremath{\sigma}}_{M}^{2}$) values of fission fragments for two different systems, $^{12}\mathrm{C}+^{169}\mathrm{Tm}$ and $^{19}\mathrm{F}+^{169}\mathrm{Tm}$, at nearly the same excitation energy and angular momentum are distinctly different, indicating the importance of the entrance channel effect in fission reaction dynamics. The theoretically calculated isobaric charge dispersion parameters for these residues are found to be in good agreement with those obtained from the experimental data.

Predictions for the synthesis of superheavy elements Z=119 and 120

Within the framework of dinuclear system model, the synthesis of the superheavy elements (SHEs) $Z=119$ and $Z=120$ is investigated. The entrance channel effects on capture cross section, fusion probability, survival probability, and evaporation residue cross section are investigated. We calculate the production cross sections in 276 possible reactions (with stable projectiles of $Z=20$--30 and targets with the half-lives longer than 20 days) and show the promising ones for the synthesizing SHEs $Z=119$ and $Z=120$. It is found that the systems $^{44}\mathrm{Ca}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{252}\mathrm{Es}$ and $^{40}\mathrm{Ca}\phantom{\rule{0.16em}{0ex}}+\phantom{\rule{0.16em}{0ex}}^{257}\mathrm{Fm}$ are the most favorable to produce the SHEs $Z=119$ and $Z=120$ with maximal production cross sections (optimal incident energies) of 4.32 pb (204.27 MeV) and 1.24 pb (205.66 MeV), respectively.

The entrance channel effects on the deexcitation ways of the same compound nucleus at a fixed excitation energy

The investigation of various properties of deexcitation of the same 220Th compound nucleus (CN), formed by the different mass (charge) asymmetric 16O+204Pb, 40Ar+180Hf, 82Se+138Ba and 96Zr+124Sn reactions is presented. The effective fission barrier < Bfis > value, as a function of the excitation energy , determined for each intermediate excited nucleus reached along the deexcitation cascade of the CN obtained by the four considered reactions is strongly sensitive to the various orbital angular momentum L=ℓℏ distributions of CN formed with the same excitation energy by the various entrance channels. Therefore, the competition between the fission and evaporation of light particles (neutron, proton, and α-particle) processes along the deexcitation cascade of CN is dependent on the orbital angular momentum distribution of CN. In fact, the ratio between the evaporation residue cross sections obtained when also the charged particles are emitted and the ones obtained after neutron emission only for the same CN with a fixed excitation energy is sensitive to the mass (charge) asymmetry of the entrance channel.

Dynamical and statistical bimodality in nuclear fragmentation

The origin of bimodal behavior in the residue distribution experimentally measured in heavy ion reactions is reexamined using Boltzmann-Uehling-Uhlenbeck simulations. We suggest that, depending on the incident energy and impact parameter of the reaction, both entrance channel and exit channel effects can be at the origin of the observed behavior. Specifically, fluctuations in the reaction mechanism induced by fluctuations in the collision rate, as well as thermal bimodality directly linked to the nuclear liquid-gas phase transition are observed in our simulations. Both phenomenologies were previously proposed in the literature, but presented as incompatible and contradictory interpretations of the experimental measurements. These results indicate that heavy ion collisions at intermediate energies can be viewed as a powerful tool to study both bifurcations induced by out-of-equilibrium critical phenomena, as well as finite size precursors of thermal phase transitions.