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.

The dynamics of sub-barrier fusion reactions are well explained by incorporating channel coupling effects to various degrees of freedom, such as deformations and vibrations, within the coupled channel formalism. In many systems, sub-barrier fusion cross-sections are enhanced by couplings to inelastic excited states and nucleon transfer channels with positive Q-values. However, several systems show no such effect from positive Q-value transfer channels. Conventional coupled channel approaches effectively handle even-even systems, but for odd-even systems, odd-A nuclei are often approximated as pure rotors or vibrators, assuming ground state spin-parity and neglecting spin reorientation effects. Furthermore, single nucleon transfer is not included in codes like CCFULL, which only account for ground-state pair transfers without considering transfers involving excited states. To address these limitations, the quantum mechanical coupled reaction channel (CRC) code FRESCO is employed. For the 19F + 68Zn system, experimental data are explained by including couplings to inelastic states of both projectile and target. However, for 19F + 54,56Fe, 64Zn and 142,150Nd systems, inelastic couplings alone fail to reproduce fusion excitation functions (EFs). Couplings to one-proton (pickup) or triton (stripping) transfer channels with positive Q-values show no significant effect on sub-barrier fusion cross-sections. Overall, CRC calculations indicate that coupling to inelastic states of both projectile and target enhance sub-barrier fusion cross-sections. The treatment of the projectile/target nuclei based on certain assumptions has resulted in different sub-barrier fusion cross-sections in earlier studies. The current study suggests that channel coupling effects on fusion excitation function is a complex process in interaction with odd-A projectile and one needs to include exact spin-parity of odd-A nuclei in theoretical calculations.

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 National Array of Neutron Detectors (NAND) at IUAC is one of the big detector arrays used in experiments to study nuclear fission through the measurement of the neutrons emitted during the process. The array is installed at IUAC heavy ion accelerator facility. NAND consists of 100 liquid scintillators mounted on a semi-spherical geometry covering a total of 3.3 % of 4 π solid angle. The 175-cm-long flight path provides good energy resolution of the emitted neutrons, enabling precise measurement of neutron multiplicity for very heavy nuclei. The fission fragment time-of-flight spectrometer coupled with large array of neutron detectors makes it a versatile tool for exploring the properties of nuclear fission using heavy ions from IUAC accelerators. Over the past two decades, several experiments were performed using NAND facility providing valuable information on traditional fission research extending to new mass region. This article reviews overall details of NAND facility and highlights some important research activities carried out at IUAC. The future research possibilities are also discussed.

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 efficacy of pulse shape discrimination (PSD) methods for distinguishing between neutrons and 7-rays using liquid scintillators is significantly impacted by the sampling characteristics of fast waveform digitizers. This study specifically delves into investigating the digitization prerequisites of the discrete wavelet transforms (DWT) method, utilizing digitized pulses obtained from an experimental mixed radiation field comprising neutron and 7-ray events from AmBe source with an energy threshold of 250 keVee, collected by BC501A liquid scintillator. The DWT method has been optimized to determine processing gate duration and the form of discrimination parameter for various sampling rates ranging from 250 MS/s to 2.5 GS/s. The performance of the DWT method is compared with the Charge Comparison (CC) method in terms of the figure of merit (FoM). Notably, the DWT method outperforms the CC method at 250 MS/s with a 12-bit Analog-to-Digital Converter (ADC), when the digitized pulses are processed for a short processing gate of 46 ns. This attribute of the DWT method proves advantageous in high-count rate environments where pulse-tail contamination by pile-up events occurs more frequently. Furthermore, to achieve a FoM greater than unity for the radiation field with energy threshold of 250 keVee, a maximum sampling rate of 500 MS/s suffices for the DWT method.

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 channel coupling effects of internal degrees of freedom like deformations of the interacting nuclei and vibrations have been accounted very well in fusion reactions. The neutron transfer channels with positive Q-values have resulted in the enhancement in the sub-barrier fusion cross-sections in various systems. However, there are few cases in which such effects are not observed, thus, remaining an open question for discussion and further studies. In this respect, the fusion cross-sections of the various combination of projectile - targets have been calculated and compared with experimental data using the coupled channel approach by employing CCFULL and ECC codes. Fusion excitation functions were calculated for ^30 Si + ^58,62,64 Ni and ^32,34,36 S + ^58,64 Ni systems using two different approaches to unravel the effect of different collective excitations and neutron transfer channels on the sub-barrier fusion cross-sections. Inclusion of coupling to the inelastic excitations in the calculations for ^30 Si + ^62,64 Ni, ^32 S + ^58 Ni and ^36 S + ^64 Ni systems explained the experimental data. The coupling to the transfer channels with positive Q-values along with the inelastic channels was incorporated in calculations and showed a significant influence on fusion cross-sections in ^32,34 S + ^64 Ni and ^34,36 S + ^58 Ni systems. Upon investigating the role of the two-neutron transfer channels (pick-up and stripping), it was concluded that in the case of ^30 Si, ^34 S, ^36 S + ^58 Ni systems, the coupling to the two-neutron stripping channel with positive Q-value showed a weak channel coupling effect in the sub-barrier region. For ^32,34 S + ^64 Ni systems, a two-neutron pick-up channel with positive Q-value showed a strong influence on the fusion cross-sections.

We review the developmental activities in the field of radiation detectors and coupled instrumentation/electronics at IUAC (formerly NSC). The facility focuses on nuclear reaction and structure studies around the Coulomb barrier using ion beams from the accelerator. To execute these experiments, IUAC has a detector development program for preparing detector systems based on position sensitive fast timing proportional/avalanche counters, particle identification detectors such as segmented ionization chambers, hybrid gas-silicon telescopes, segmented and resistive position sensitive silicon detectors, and scintillators for light-charged particle, neutron and γ-ray detection, and germanium detectors for high resolution γ-ray spectroscopy. This is further exalted by a strong front-end electronics development program for detector signal processing. Different types of stand-alone and multi-channel low noise preamplifiers (charge sensitive and fast timing), spectroscopy amplifiers, discriminators, logic units, etc. have been developed. Customized high resolution analog to digital converters, trigger generator cum event identifier module for handling trigger signals for multi-detector arrays, crate controllers, synchronizing and time stamping units have been developed in CAMAC as well as VME standards for the data acquisition system. This nuclear instrumentation has been routinely used to perform experiments of fusion and fusion-fission dynamics, and nuclear spectroscopy using the facilities of recoil mass spectrometers, scattering chamber, neutron and gamma detector arrays etc. New detector systems are being planned and developed for these facilities as well as for the future international facilities such as NUSTAR. This article describes an overview of detector instrumentation activities.

Kavita [] analyze the width of the mass distributions of fission fragments from Si28+Gd160 and C12+Hf178 collisions. The authors report that the distributions “are reproducible with a single Gaussian at all studied energies”. However, the fits presented in the figures show functions that do not correspond to single-Gaussian distributions. A critical analysis, presented here, sheds doubts on the characterization of the mass distributions. Published by the American Physical Society 2024

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.

Measurements of mass and angular distributions of fission fragments from actinide nuclei 249Bk and 257Md, produced in fusion reactions 11B and 19F + 238U, are presented. Experimentally observed mass ratio distributions indicate “multi-chance fission” through the interplay of fission modes in the fission process, and they agree well with predictions from calculations using the GEF (“GEneral description of Fission observables”) model code. Furthermore, to test the signatures of events from non-compound nuclear processes in the fission of 249Bk and 257Md nuclei, Monte Carlo statistical decay model calculations using GEMINI++ were performed for the measured mass distribution at all energies. For comparison purposes, the fission fragment mass distributions of neighboring heavy actinide nuclei, previously measured in the fission of 250Cf and 254Fm nuclei produced by 12C and 16O projectiles on a 238U target, are also presented. The measured angular anisotropy data for the 19F + 238U reaction differ from the results of the Transition State Model (TSM) at energies below the fusion barrier. As a result of the present study, we suggest considering the interplay between K relaxation time, dynamic dissipation, and their influence on shell correction to understand the evolution of fission dynamics in heavy-ion-induced actinide nuclei.

An attempt has been made to understand the effect of transfer channels on reaction dynamics for the O-16+Ho-165 system through the measurement of a quasi-elastic excitation function at backward angles, which was translated to the corresponding barrier distribution. The results were explained in light of coupled channel calculations performed with the inclusion of different possible coupling schemes describing the structure of the projectile and target nuclei. Analysis reveals that the rotational coupling of the target nuclei along with the coupling due to the 2n-transfer (pick-up) channel satisfactorily reproduces the experimental data.

Fission dynamics of ^188 Pt, a neutron deficient nucleus in newly discovered mass asymmetric sub-Pb region, have been explored via fission fragments mass-angle and mass-total kinetic energy distributions, at energies around and above the barrier. The observed correlations of fragment mass and emission angle indicate the presence of fission events originating from a non-equilibrated source. Mass-total kinetic energy spectra are relatively broader and the dependence of measured mean total-kinetic-energy on fragment mass is also broader than the expected parabolic dependence for liquid drop fission behaviour, at all studied energies. The measured mean total kinetic energy values are higher than the prediction of Viola systematics. The widths of measured total kinetic energy distributions are also inconsistent with the observed systematic behaviour of compound nucleus (CN) in this mass region. These observation of mass-angle and mass-total kinetic energy distributions revealed the clear signatures of the presence of slow quasifission in the fission of ^188 Pt compound nucleus. These findings indicate the role of entrance channel parameters such as mass asymmetry and charge product Z_P Z_T in Fusion-Fission and quasi-fission dynamics. Dynamical model calculations do not predict the presence of quasi-fission for the present reaction system.

Background: Asymmetric mass splits observed in the extremely neutron-deficient (1.15 <= N/Z <= 1.55) lead-island isotopes brought much interest for the scientific community to explore this region. Although several experiments have been performed adopting beta-delayed fission and heavy-ion induced reactions, the role of shell effects associated with asymmetric fission is still not fully understood. Purpose: This article demonstrates the fission fragment mass distributions and associated fission fragment properties of Pt-186, populated via fusion of Si-28 with Gd-158, at three excitation energies (E*s). Further, a comparison of experimental mass distributions with the theoretical results has been carried out to test their prediction efficiency. Method: Thin layer of Gd-158 ((Gd2O3)-Gd-158) backed by the carbon was bombarded by Si-28 ions within 120-140 MeV laboratory energy. Time-of-flight information, provided by the two symmetrically placed multiwire proportional counters having an area of 200 cm(2), was utilized to get the velocities, which were further used to estimate the fission fragment mass and kinetic energy distributions. Results: A single Gaussian could not satisfactorily fit the flat-topped mass distribution at each excitation energy. Later, the two- and three-Gaussian fits efficiently reproduced the distributions, signifying the crucial role of the quadrupole deformed (Z approximate to 34, 36, 42, 44, and 46) shell gaps in deciding the fate of compound nucleus's disintegration. No signature of the quasifission process has been observed in this study. Moreover, an increment in the symmetric contribution with increasing E* is spotted experimentally as well as theoretically for the present system. Further, a comparison with the nearby Pt isotopes revealed the symmetric contributions decrease with decreasing neutron number. To some extent, GEneral Fission (GEF) model is found to predict the fragment properties of the present system. Conclusions: The structure observed in the middle section of the mass distribution confirms the presence of an asymmetric mode along with the symmetric mode. The extracted Zpeak values are influenced by the deformed shell gaps. GEF-predicted Z(peak) values, N-peak values, and symmetric contributions are observed to agree with the experimental results.

We have studied the mass distribution of (256,260)Rf compound nuclei produced in the Ti-48+Pb-208 and Si-28+Th-232 reactions at an excitation energy of 57 MeV. The results confirmed the presence of quasi-fission processes in the Ti-48+Pb-208 system and a non-negligible contribution in the Si-28+Th-232 system. The observed mass distributions of the fission fragments are also compared with the predictions from dinuclear system calculations.

We have measured the fission fragment mass-angle and mass-total kinetic energy (TKE) distributions for the neutron-deficient Pt-190 compound nucleus (CN) populated via C-12 + Hf-178 reaction, at around and above barrier energies. No mass-angle correlation was observed in the fission of Pt-190 signifying the absence of quasi-fission events in the studied reaction. The observed mass-TKE distributions have expected triangular shape and TKE distributions are well described with the single Gaussian fits, and mean TKE shows parabolic dependence on fragment mass as predicted based on liquid drop fission behaviour. The widths of measured TKE distributions agree well with the observed systematics for CN fission in this mass region. Though the CN is relatively neutron deficient, these observations suggest a clear picture of true CN fission behaviour for the chosen reaction in the studied energy domain.

Background: Light particle (alpha particle, proton, and neutron) spectra were used to probe the dynamics of the compound nucleus formation and decay of systems with A < 100. At high excitation energies, the same compound nucleus was populated, revealing that fusion is hindered in mass-symmetric entrance channels. Over the years, authors have explored diverse explanations for the experimental light particle spectra from fusion-evaporation reactions, contributing to a rich understanding of the field. Notably, prior research has primarily emphasized high-energy excitation of the compound nucleus, highlighting an exciting opportunity to explore the critical dynamics of near-barrier studies. Purpose: We investigated the evaporation spectra of proton, neutron, and alpha particles from near-barrier energies to around 25% above-barrier energies. The focus is on understanding the role of entrance channel mass asymmetry, excitation energy, and angular dependence in shaping the reaction dynamics and particle emission processes. Method: The compound nucleus 80Sr was populated via two different entrance channels: 16O + 64Zn (mass asymmetric system) and 32S + 48Ti (mass symmetric system). Angular coverage ranged from 47 degrees-113 degrees for proton and alpha particles, and from 30 degrees-120 degrees for neutrons. The exclusive spectra were obtained by gating these with evaporation residues obtained in a multiwire proportional counter. The experimental results were compared with CASCADE and GEMINI++ statistical model calculations. Results: Proton spectra exhibited good agreement with statistical model predictions for both mass asymmetric and mass symmetric entrance channels. However, an anomaly was observed in the alpha-particle spectra at nearbarrier energy for the mass asymmetric system, necessitating a reduction in the level density parameter to a = A/10 MeV-1 in CASCADE calculations to match the experimental data. This suggests enhanced alpha emission, potentially due to alpha-cluster emission at these energies. Neutron spectra, which are unaffected by emission and transmission barriers, showed deviations from statistical model predictions at higher energies. These deviations necessitated a reduced level density parameter, indicating neutron emission from a compound nucleus at higher temperatures. Conclusion: Our findings highlight the significant role of pre-equilibrium emission and dynamical effects in nuclear reactions at higher excitation energies for both the systems. The formation, thermal equilibration, and shape equilibration times were calculated using HICOL, and decay times using PACE, revealing the importance of these processes. Further measurements with alpha-cluster-rich beams and time-dependent Hartree-Fock (TDHF) calculations are suggested to provide deeper insights into these phenomena.

The electromagnetic structure of Sc-45 at low excitation energy was investigated via low-energy Coulomb excitation at the Heavy Ion Laboratory (HIL) of the University of Warsaw and at the Inter-University Accelerator Centre (IUAC) in New Delhi. A set of reduced E2, E3, and M1 matrix elements was extracted from the collected data using the GOSIA code. The reduced transition probability B(E2; 11/2(-) -> 7/2(-)) has been determined, allowing us to deduce the lifetime of the 11/2(-) state at 1237 keV. In addition, the upper limit on the reduced transition probability B(E3; 7/2(-) -> 5/2(+)) has been determined for the first time. New large-scale shell-model and beyond-mean-field calculations were performed to interpret the structure of this nucleus.