Fission fragment mass ratio distributions have been measured for the reactions 19F+178Hf and 16O + 181Ta, both leading to the same compound nucleus, 197Tl, at near-Coulomb barrier energies. The measured fission fragment mass width for both these systems does not show any substantial deviation from the statistical model predictions, which indicates the absence of non-compound nuclear reactions like quasi-fission. The measured mass widths of both the reactions at the same excitation energy are comparable within the experimental uncertainty and show a gradual increase with excitation energy. No noticeable influence of effect of entrance channel mass asymmetry on fragment mass distribution in these reactions, which differs from the previously reported entrance channel-dependent variation in average pre-scission neutron multiplicity.

The fission timescale of the compound nucleus (CN) 206Rn, formed through the reaction 28Si+178Hf, has been investigated using pre-scission neutron multiplicities as a diagnostic probe within the excitation energy range of 61–90 MeV. The obtained results for the 206Rn system have been compared with available experimental data for other radon isotopes (208,210,212,214,216Rn) to examine the influence of shell closures on the total neutron multiplicity. A distinct trend has been identified in the neutron-to-proton (N/Z) ratio dependence, wherein the total neutron multiplicity decreases as the compound nucleus approaches shell closure and subsequently increases as it moves away from it. Furthermore, clear signatures of shell effects have been observed at excitation energies exceeding 50 MeV; an energy regime where such effects were not reported in earlier investigations.

Two back-to-back experiments, 28Si + 178Hf and 28Si + 186W, were intentionally conducted to validate the role of shell closure in pre-actinides by studying neutron multiplicity in compound nucleus (CN) 206Rn and 214Ra. In the first experiment [Dubey et al., Phys. Rev. C 112, L011602 (2025)], we established the influence of the neutron-shell closure. In the present work, the CN 214Ra was deliberately selected to investigate the dependence of the total neutron multiplicity (Mtotal) on the proton number (Z), while keeping the neutron number constant at N = 126 in the pre-actinide region. The objective of the study is twofold: (i) to examine the effect of proton-shell closure when moving away from Z = 82, and (ii) to correlate the present results on proton-shell closure with our previous finding on neutron-shell closure. We have also used the previous reported data for N = 126 isotones 210Po, 212Rn, and 213Fr to establish the validation of shell closure. A systematic increase in Mtotal with increasing Z was observed from Z = 82 to Z = 88. Furthermore, comparison of the present results on proton-shell closure with our earlier neutron-shell closure observation, reveals that the cross correlation between neutron- and proton-shell closure shows a systematic increase in Mtotal as one moves away from 208Pb, whether along isotonic or isotopic chains.

The fission fragment mass distribution and neutron multiplicity from the fission of 227Pa, produced through the complete fusion reaction 19F + 208Pb, were measured to study the influence of neutron emission on fission dynamics. The measurements were carried out in the excitation energy range of approximate to 30-60 MeV. The experimental data were analyzed within the framework of the semi-empirical GEF model to understand the evolution of mass distributions at different excitation energies and their dependence on particle emission. The calculations, which incorporate multi-chance fission, suggest that the observed enhancement in mass width at lower excitation energies (E* approximate to 32 MeV) arises from fragments shell effects, restored due to the sequential nature of fission. In contrast, no significant influence of microscopic effects is observed at higher excitation energies (E* approximate to 60 MeV). To further elucidate and compare the role of shell effects, GEF model calculations were also performed for a heavier actinide 250Cf in a similar energy range. These results indicate that the interplay between symmetric and asymmetric fission modes leads to the characteristic flat-top mass distribution seen in heavier actinides, unlike the shoulder-like structures observed in lighter actinides.

Background: Quasifission substantially hinders the formation of the compound nucleus in heavy ion fusion reactions. It poses a major obstacle to superheavy element formation. This process has a strong entrance channel dependence. Purpose: To study the interplay between fission and quasifission in 30Si + 197Au reaction at energies around the Coulomb barrier. Methods: Binary fragments from 30Si + 197Au reaction were measured in coincidence using a pair of large area multiwire proportional counters. The mass-ratio and mass angle distributions of the fragments were obtained using the kinematic re-construction method. Experimental results are interpreted using different theoretical methods. Further, the results of present reaction have been compared with that of 28Si + 197Au reaction available in literature. Results: Broadened mass ratio distributions have been observed in the range of energy studied compared to the theoretical calculations assuming compound nucleus formation. No mass angle correlation is observed. Fission fragment mass distribution of the present reaction is compared with that of other neptunium isotopes at low excitation energies. A fast transition from asymmetric fission to symmetric fission is observed with decrease of N/Z along the isotopic chain of neptunium. The difference between the asymmetric and symmetric fission barrier is higher for the 238Np at all temperatures, compared to 225,227Np resulting in asymmetric mass division in the fission of 238Np and symmetric split at low excitation energies in 225,227Np. Calculated quasifission yields in the mass range 80 A 150 show significant dependence on collision energy for both 28,30Si+ 197Au reactions. Conclusions: Measured fragment mass distribution has significant contribution from slow quasifission in 30Si + 197Au reaction. 40-60 % fusion probability is obtained for the 28,30Si+ 197Au reactions. Quasifission yields show strong dependence on energy and angular momentum.

In this study, we measured both the pre-scission and post-scission neutron multiplicities for the 31P + 170Er reaction at excitation energies in the range of 62-84 MeV, using the National Array of Neutron Detectors (NAND) at Inter University Accelerator Centre (IUAC), New Delhi. Theoretical calculations to reproduce the measured neutron multiplicities have been performed using the dynamical model code VECLAN. These calculations show that the dissipation strength parameter (beta) increases with excitation energy. Dynamical model calculations also have been performed using HICOL code to understand the fusion dynamics and formation time. It has been observed that transitioning from an asymmetric to a symmetric entrance channel leads to a gradual increase in the compound nucleus formation time, accompanied by more emission of neutrons during its formation.

Two back-to-back experiments, 28Si + 178Hf and 28Si + 186W, were intentionally conducted to validate the role of shell closure in pre-actinides by studying neutron multiplicity in compound nucleus (CN) 206Rn and 214Ra. In the first experiment, Dubey et al. [Phys. Rev. C 112, L011602 (2025)], we established the influence of the neutron shell closure. In the present work, the CN 214Ra was deliberately selected to investigate the dependence of the total neutron multiplicity (Mtotal) on the proton number (Z), while keeping the neutron number constant at N = 126 in the pre-actinide region. The objective of the study is two-fold : (i) to examine the effect of proton shell closure when moving away from Z = 82, and (ii) to correlate the present results on proton shell closure with our previous finding on neutron shell closure. We have also used the previous reported data for N = 126 isotones 210Po, 212Rn, and 213Fr to establish the validation of shell closure. A systematic increase in Mtotal with increasing Z was observed from Z = 82 to Z = 88. Furthermore, comparison of the present results on proton shell closure with our earlier neutron shell closure observation, reveals that the cross-correlation between neutron and proton shell closure shows a systematic increase in Mtotal as one moves away from 208Pb, whether along isotonic or isotopic chains.

The pre-and postscission neutron multiplicities have been determined for the fission of the compound nucleus (CN) 206Rn, induced by the reaction 28Si + 178Hf within the excitation energy interval of 61.0-90.0 MeV. We intentionally formed the CN 206Rn, which is below the shell closure CN, to examine the variation in N/Z with total neutron multiplicity, as data for other compound nuclei of 208,210,212,214,216Rn have already been published in the literature. The present experimental investigations between N/Z and total multiplicities validate the theoretical claims made by various calculations. Specifically, it was observed that the total neutron multiplicity decreases as the compound nucleus approaches the shell closure and subsequently increases as it moves away from the shell closure. Furthermore, we have observed that, below the neutron shell closure, the dissipation in compound nuclei escalates with rising excitation energy, remains stable at the shell closure CN, and thereafter diminishes with increasing excitation energy above the shell closure CN.

The pre and post-scission neutron multiplicities have been determined for the fission of the compound nucleus (CN) 206Rn, induced by the reaction 28Si+178Hf within the excitation energy interval of 61.0-90.0 MeV. We intentionally formed CN 206 Rn, which is below the shell closure CN, to examine the variation in N/Z with total neutron multiplicity, as data for other CNs of 208,210,212,214,216Rn have already been published in the literature. We identified a new trend in the N/Z ratio, where the total neutron multiplicity initially decreases as we approach the shell closure of the compound nucleus and then starts to increase as we move away from the shell closure. Furthermore, we have observed that below the neutron shell closure, the dissipation in compound nuclei (CN) escalates with rising excitation energy, remains stable at the shell closure CN, and thereafter diminishes with increasing excitation energy above the shell closure CN.

The present study primarily reports on the complete characterization of 2 '' x 2 '' LaBr3(Ce) scintillators coupled to fast Hamamatsu R2083 photomultiplier tubes (PMTs). The energy characteristics of the detector, such as linearity response, energy resolution, and intrinsic efficiency, are thoroughly investigated using standard radioactive sources (137Cs, 60Co, and 152Eu). The experimentally measured energy spectra and the intrinsic efficiency are compared with the GEANT4 simulations, indicating an overall good agreement between the measured and simulated results. In addition, the timing characteristics of the detectors are studied with a 60Co source. The time resolution is optimized by varying the PMT bias voltages and Constant Fraction Discriminator (CFD) delays. The best time resolution for an individual LaBr3(Ce) scintillator coupled to R2083 PMT is measured to be 243(2) ps for 1173-1332 keV gamma-ray energies. The measured time resolution is compared with the best values reported for different sizes of LaBr3(Ce) scintillators coupled to various PMTs.

An attempt has been made very recently to perform a scattering experiment on 10,11B+40Ca systems at the energy of 50 MeV at General Purpose Scattering Chamber (GPSC) of Inter-University Accelerator Centre (IUAC), New Delhi, India. A comprehensive analysis of the elastic scattering data is carried out using different versions of optical potentials, such as the Woods-Saxon (WS) potential, the M3Y-Paris double-folding (DF) potential and the semi-microscopic Sao Paulo potential (SPP2). We have arrived at a new set of optical model (OM) parameters which are compared with the data obtained by Glover et al. (1980) at 46.6 MeV and 51.5 MeV. There is substantial change in the real and imaginary potential strengths when analyzed using WS potential. Both the systems exhibited absorption and showed structural differences between 10B and 11B, with the former having a deeper real potential and a more confined interaction region. With a combination M3Y-Paris (real) and WS Volume (imaginary) potential, experimental cross-sections are reproduced which also reveals the extended structure of 11B. SPP2 potential provides significant information on reaction dynamics providing larger proton and neutron radii of 11B as compared to 10B. Finally, We extracted a new set of consistent OM parameters that is applicable in understanding the reaction dynamics of light-heavy ion interactions.

The fission dynamics has been studied for a near super heavy compound nucleus 260Rf populated through 28Si + 232Th reaction at an excitation energy of 85.7 MeV. Full momentum transfer binary events were separated from the transfer induced fission events. The contribution from transfer induced fission has been found to be 7±2%. Mas ratio distribution, mass-total kinetic energy (TKE), and mass angle correlation have been extracted for the full momentum transfer events using two body kinematics. The experimentally extracted width of mass distribution is higher than the mass width calculated theoretically using the saddle-point model, which indicates the presence of non-compound nuclear fission in the reaction under study. The mass-TKE distribution obtained for 260Rf nucleus matches with the theoretical predictions from the Viola systematics and GEneral description of Fission observables (GEF) model. The mass-angle distribution for the reaction under study indicates no significant correlation between the mass and emission angles of the fission fragments.

The present work concerns the study of fission dynamics of ^48 Ti+ ^232 Th reaction resulting in the superheavy composite system ^280 Cn _112 at an incident energy of 280 MeV. Mass distribution studies play an important role in understanding the fusion-fission mechanism involved in the heavy-ion induced nuclear reaction. The studies related to the superheavy nucleus ^280 Cn are limited till date and in order to achieve a better insight of the reaction dynamics, mass and total kinetic energy (TKE) distribution of the binary fragments populated in the reaction ^48 Ti+ ^232 Th has been measured at an excitation energy 63.5 MeV. Correlation between the mass and TKE and mass-angle distribution of the binary fragments have been investigated. The mass-energy distribution of the reaction fragments obtained from the analysis confirms the dominance of quasi-fission over fusion-fission. A sudden rise in the width of σ ^2_TKE (M) has been observed in the mass symmetric region. This has been interpreted in terms of the mixing of fusion-fission and quasi-fission events. A deviation from the Viola systematic is observed in the measured TKE of the fragments due to the presence of quasi-fission (QF) process. Theoretical results performed to understand the experimental results in the framework of the DNS model show that the peaks in the mass distribution of the binary products around the mass numbers A = 40–60 and A = 220–240 is related with the contribution of the DIC and quasi-fission products. The contribution of the quasi-fission products to the yield of the binary fragments with the mass numbers around A = 80–110 and A = 170–200 is dominant. The contribution of the symmetric quasi-fission products to the yield of the mass symmetric region is comparable with the yield of the fusion-fission products.

Background: Enhanced prescission neutron multiplicity (${\ensuremath{\nu}}_{\mathrm{pre}}$) over statistical model calculations assuming Bohr-Wheeler fission width is explained using Kramers' fission width incorporating dissipative effects. The dissipation strength obtained from such studies reported significant effect of the neutron shell closure of $N=126$ of the fissioning system as well as nuclear temperature. The dependence of dissipation strength on shell effect and temperature is also attributed to the choice of input parameters in the statistical model calculations.Purpose: We investigate the role of $N/Z$, shell effect, collective enhancement of level density (CELD), and excitation energy on ${\ensuremath{\nu}}_{\mathrm{pre}}$ in reactions forming isotopes of the Ra nucleus.Methods: The neutron multiplicity excitation function is measured for the $^{30}\mathrm{Si}+^{182,184,186}\mathrm{W}$ reactions populating $^{212,214,216}\mathrm{Ra}$ nuclei using the National Array of Neutron Detectors (NAND) at the Inter-University Accelerator Centre, New Delhi. Among these compound nuclei, $^{214}\mathrm{Ra}$ has a major neutron shell closure of $N=126$. Measured ${\ensuremath{\nu}}_{\mathrm{pre}}$ are analyzed within the framework of a statistical model incorporating dynamical hindrance in nuclear fission due to dissipation, shell corrections in the fission barrier and level density, and CELD.Results: Experimental ${\ensuremath{\nu}}_{\mathrm{pre}}$ show a marginal isotopic dependence at all excitation energies. ${\ensuremath{\nu}}_{\mathrm{pre}}$ values do not show any noticeable effect of neutron magic number $N=126$. Dissipation strength of $\ensuremath{\beta}=8\phantom{\rule{4pt}{0ex}}{\mathrm{zs}}^{\ensuremath{-}1}$ ($5.27\phantom{\rule{4pt}{0ex}}\mathrm{MeV}/\ensuremath{\hbar}$) reasonably reproduces the experimental ${\ensuremath{\nu}}_{\mathrm{pre}}$ excitation functions for all three nuclei in the measured energy range. Appreciable variations in presaddle neutron emissions are observed when shell effect or CELD is excluded in the calculations. Even though both the shell and CELD are found to impact primarily in the presaddle sector, they alter the excitation energy and multiplicity in the saddle-to-scission sector as well in a complementary manner.Conclusions: A temperature independent dissipation coefficient is observed to reproduce the experimental results in this study throughout the excitation energy range measured. Shell corrections in fission barrier and level density parameters and CELD in fission and particle evaporation widths also influence the neutron multiplicities. The observed effect of CELD in the presaddle phase is attributed to the large enhancement of level density at the saddle due to its large deformation and consequent enhancement of fission width.

Neutron multiplicities, folding angle distribution, mass distribution, and mass-energy distribution are measured for the compound nucleus Po-210 populated through the C-12+ Pt-198 reaction at an excitation energy of 61.6 MeV. The measured neutron multiplicities are compared with the statistical model code JOANNE2 to extract total fission time for the Po-210 compound nucleus. The total fission time (tau(tot)) obtained for this system is (10 +/- 5) x 10(-21) s at 49 MeV and increases to (23 +/- 5) x 10(-21) at 61.8 MeV excitation energy indicating that dissipation increases with excitation energy. A comparison with tau(tot) of the O-18+ Os-192 reaction populating the same compound nucleus indicates the influence of entrance channel mass asymmetry on the fission time. Dynamical model calculations have been performed to understand the fusion dynamics for these reactions and it is observed that the formation time of the compound nucleus increases as we go from the asymmetric to the symmetric entrance channels. Also, these calculations predict that 93% of the total angular momentum lead to the formation of a fully equilibrated compound nucleus for the C-12+ (19)8Pt reaction whereas this percentage decreases to 84%, for the O-18+ Os-192 reaction indicating a higher percentage of noncompound nuclear processes in the latter case.

We investigate the influence of neutron emission in the fission of Pa-227 populated by complete fusion of F-19 with Pb-208 at various excitation energies (E*). Mass gated pre-scission neutron multiplicities (.pre) were determined by fragment-neutron angular correlation and time of flight of fission fragments and neutrons using the National Array of Neutron Detectors facility. Obtained Mass - nu(pre) correlation showed that, at lower E* = 24.2 and 32.4 MeV, larger nu(pre) is correlated with asymmetric mass division. On the other hand, at higher E* = 46.1 and 59.6 MeV, larger nu(pr)e is correlated with symmetric mass division. The results were analyzed within the framework of the general description of fission observables GEneral description of Fission observables (GEF) model with multichance fission included. The analysis of fragment mass-total kinetic energy correlation for different chance fission clearly indicates a revival of shell effects at E* = 24.2 and 32.4 MeV as a consequence of sequential fission decay. At these energies, higher chance fission decreases the saddle point excitation energy considerably where shell effects are prominent. The interplay of shell mediated mass asymmetric fission and symmetric fission gives rise to an energy dependent Mass - nu(pre) correlation. We have compared the experimental results with Mass -nu(pre) correlation predicted by the GEF model. It is concluded that the correlation of larger nu(pre) with asymmetric mass at lower excitation energies is a signature of shell effects reinstated by sequential fission decay. At the two higher excitation energies, despite the multichance fission and consequent decrease in saddle point energy, the available excitation energy appears sufficient for the attenuation of shell effects.

Background: Enhanced prescission neutron multiplicity (vpre) over statistical model calculations assuming Bohr-Wheeler fission width is explained using Kramers' fission width incorporating dissipative effects. The dissipation strength obtained from such studies reported significant effect of the neutron shell closure of N = 126 of the fissioning system as well as nuclear temperature. The dependence of dissipation strength on shell effect and temperature is also attributed to the choice of input parameters in the statistical model calculations.Purpose: We investigate the role of N/Z, shell effect, collective enhancement of level density (CELD), and excitation energy on vpre in reactions forming isotopes of the Ra nucleus.Methods: The neutron multiplicity excitation function is measured for the 30Si + 182,184,186W reactions populat-ing 212,214,216Ra nuclei using the National Array of Neutron Detectors (NAND) at the Inter-University Accelerator Centre, New Delhi. Among these compound nuclei, 214Ra has a major neutron shell closure of N = 126. Measured vpre are analyzed within the framework of a statistical model incorporating dynamical hindrance in nuclear fission due to dissipation, shell corrections in the fission barrier and level density, and CELD.Results: Experimental vpre show a marginal isotopic dependence at all excitation energies. vpre values do not show any noticeable effect of neutron magic number N = 126. Dissipation strength of & beta; = 8 zs-1 (5.27 MeV/h over bar ) reasonably reproduces the experimental vpre excitation functions for all three nuclei in the measured energy range. Appreciable variations in presaddle neutron emissions are observed when shell effect or CELD is excluded in the calculations. Even though both the shell and CELD are found to impact primarily in the presaddle sector, they alter the excitation energy and multiplicity in the saddle-to-scission sector as well in a complementary manner.Conclusions: A temperature independent dissipation coefficient is observed to reproduce the experimental results in this study throughout the excitation energy range measured. Shell corrections in fission barrier and level density parameters and CELD in fission and particle evaporation widths also influence the neutron multiplicities. The observed effect of CELD in the presaddle phase is attributed to the large enhancement of level density at the saddle due to its large deformation and consequent enhancement of fission width.

The light output response and efficiency of 5 '' x 5 '' BC501A liquid scintillator neutron detectors composing the NAND detector array have been measured by time of flight technique using(252)Cf source. Energy dependent de-tection efficiency was calculated using FLUKA Monte Carlo code and validated by experimental measurement. FLUKA simulation incorporated fission neutron correlation and kinematics of neutron emission from fission source determining the energy distribution of neutrons in the laboratory frame. The intrinsic features of the scintillator were studied by including particle dependent quenching and light output resolution. Comparison of FLUKA simulation of scintillation light produced by neutrons and gamma rays with measurements provided realistic results. The calculated neutron detection efficiency at similar to 0.5 MeV threshold reproduces the experimental data reasonably well in the studied energy range, 0.5 < E-n < 12 MeV. Neutron scattering from target chamber material in NAND was investigated using FLUKA concluding that the loss in neutron flux due to scattering from the chamber wall is similar to 12%. The scattering amounts to background neutron counts in neighbouring detectors comparable to cross-talk events. The absolute efficiency of the NAND array was estimated to be similar to 1.40% after taking into consideration the intrinsic efficiency of liquid cells, geometrical efficiency and flux loss due to scattering.