The isoscaling behaviour of intermediate-mass fragments emitted in the reactions involving 14N, 20Ne + 112,116,124Sn at 18-30MeV/nucleon is clearly observed, and the isoscaling parameters α has been extracted. The nuclear temperature, T , was determined using double isotope ratio method. The coefficient of the symmetry energy term in the nuclear equation of state, Csym, was extracted from the values of α and T . The result shows that Csym decreases from approximately 24 to 17 MeV, with the increase of excitation energy from 2.1 to 2.8 MeV/nucleon. Based on this trend, Csym would be expected to exceed 24 MeV at energies below 2.1 MeV/nucleon. Instead, it drops to around 20 MeV at 1.8 MeV/nucleon. Theoretical calculations have been performed using an isospin-dependent hybrid model for nuclear multifragmentation. The results show good agreement with experimental data, except at lowest excitation (E*/A = 1.8 MeV), suggesting that multifragmentation is not the dominant mechanism at this lower energy.

The low-temperature evolution of the isovector giant dipole resonance (IVGDR) width has been systematically investigated for the 116Te, 120Te, and 128Te nuclei to explore the roles of shell closure, neutron-to-proton ratio, and thermal shape fluctuations in the damping of collective motion. High-energy γ-rays, produced in alpha-induced fusion reactions, were measured using the LAMBDA spectrometer, with angular-momentum selection provided by γ-multiplicity detectors. The experimental γ-ray spectra were analyzed using a statistical-model framework and Bayesian inference method was applied to extract the IVGDR parameters over the temperature range T ≈  0.8-1.5 MeV. Subsequently, a self-consistent nuclear energy-density-functional framework was employed to calculate the IVGDR widths at finite temperature and to interpret the observed temperature dependence. For the near-spherical 128Te nucleus, which lies close to the neutron magic number N=82, a stronger shell-induced inhibition of the evolution of IVGDR width is observed at low temperature compared to 116Te and 120Te. It has been observed that the low-temperature damping mechanism depends strongly on the proximity to shell closure, which can be quantified using a single dimensionless parameter δm (see main text for its definition). A systematic comparison across isotopic chains in different mass regions further confirms that larger values of δm correspond to relatively broader IVGDR widths, whereas variations in isospin asymmetry do not significantly influence the width.

The neutron energy spectrum measured at the Earth’s surface shows three distinct peaks: a thermal energy peak, an evaporation peak between 2-3 MeV, and a cascade peak near 100 MeV. However, the spectrum measured at a depth of 1604 metres water equivalent reveals the absence of cascade peak. This indicates an effective shielding of cosmogenic component of neutron background by the rock overburden. A comprehensive analysis of measured neutron fluence data from various facilities, combined with simulation data, indicates that the radiogenic component is the primary source of neutron background at the underground laboratories even at a depth of 1000 metres water equivalent. The concentrations of uranium and thorium in the surrounding rock are identified as the major factors influencing this background.

The excited states of odd-A nucleus 55Mn have been investigated using alpha-induced fusion evaporation reaction to explore the shape driving effect of proton f7/2 orbital below Z = 28 shell gap. A deformed band structure, based on pi f7/2 configuration has been identified at lower excitation with firm spin-parity assignments of the levels. Band crossing has been identified for the first time in this nucleus through the observation of back bending in one of the signature partners. The properties of this band has been compared with the similar bands in the neighboring isotopes, 57,59Mn. The Total Routhian Surface calculations predict prolate shape for all the three Mn isotopes below the band crossing. However, a change in shape is predicted by these calculations at higher frequencies beyond the particle alignment. An unnatural parity state has also been identified in 55Mn which has been found to decay by E3 and E1 transitions. This observation indicates, for the first time, the presence of octupole correlation in this nucleus. It has been discussed in the light of the octupole correlation observed in its isobar 55V and other nearby odd-odd nuclei.

The Facility for Research in Experimental Nuclear Astrophysics (FRENA) has recently been setup at Saha Institute of Nuclear Physics, Kolkata to study charged-particle induced nuclear reactions of astrophysical interest. The heart of this facility is a high-current, low-energy tandem (3 MV TandetronT ) accelerator which can deliver a variety of energetic ions. Providing ion beams with highly stable energy over prolonged durations is a major requirement for nuclear astrophysics experiments. In order to ascertain the precise energy of ion beams, proper calibration of beam energy in terms of the terminal voltage of the accelerator is required. In this study, the well-established neutron threshold energies of7Li(p,n)7Be,11B(p,n)11C,19F(p,n)19Ne and resonance energies in19F(p, alpha gamma)16O,24Mg(p, gamma)25Al were utilized for the calibration. Additionally, this work presents an analysis of the energy stability of the proton beam across a wide range of the terminal voltage.

Characterization of first beam from K500 cyclotron at VECC, Kolkata, was performed using the elastic scattering experiment with a 197Au target. Two independent approaches have been used to calibrate the detector system to estimate beam energy and its energy spread. Apart from the beam characterization, the fragment emission mechanism, particularly the isospin equilibrium and isoscaling behaviour, has been studied using 14N, 16O and 20Ne beams from the cyclotron. This article provides details of the beam characterization of the cyclotron and also an overview of the experiments conducted.

The isoscaling behavior of intermediate-mass fragments has been investigated in reactions involving N-14,Ne-20 + Sn-112,Sn-116,Sn-124 at 18-30 MeV/nucleon at K500 superconducting cyclotron facility, VECC. In all cases, the isoscaling property is clearly observed, and the isoscaling parameters alpha and 3 have been extracted. The systematic evolution of the isoscaling parameters with respect to difference in isospin composition and excitation energy has been studied. The nuclear temperature was extracted using the double isotope ratio method. The coefficient of the symmetry energy term in the nuclear equation of state, C-sym, was derived from the extracted values of isoscaling parameter and nuclear temperature. The values obtained are approximately 24-17 MeV, for E & lowast;/A = 2.1-2.8 MeV. The inconsistency of Csym at E & lowast;/A = 1.8 MeV, compared to the decreasing trend of C(sym )for E & lowast;/A > 2 MeV, could be due to the reduction or vanishing of multifragmentation at this energy.

A comparative study was performed among various pulse height unfolding codes used in fast neutron spectroscopy. Pulse height distribution measured in a liquid scintillator BC501A based detector was unfolded using FERDOR, MAXED, GRAVEL and RooUnfold. Spectra were measured for both poly-energetic neutron sources 252 Cf, 241 Am- 9 Be and quasi mono-energetic neutrons from 7 Li(p,n) 7 Be. The unfolded spectra obtained from different unfolding codes were compared to the reference spectrum measured using the time-of-flight method. Relative mean square deviation of the unfolded spectrum with respect to the time-of-flight/reference spectrum is found to be the lowest for GRAVEL in the neutron energy region 1–15 MeV. Energy resolution of the unfolded spectrum from GRAVEL is the lowest among all the methods.

The present study unfolds the relative importance of N/Z, shell effects, and thermal fluctuations in shaping the temperature dependence of the isovector giant dipole resonance (IVGDR) width. To this end, we measured the γ-ray spectra from excited Zn62,68 populated through 4He+58,64Ni reactions at beam energies of 28 MeV and 40 MeV, and compared the corresponding IVGDR widths with those for nuclei close to the doubly magic 56Ni and moderately away from it. The large-area modular BaF2 detector array was used to detect high-energy γ rays (Eγ>4 MeV). The Bayesian inference approach was combined with the statistical model analysis to extract the IVGDR parameters from the measured spectra. Calculation of IVGDR widths was performed using various theoretical approaches, specifically the thermal shape fluctuation model (TSFM) with microscopic energy density functional inputs. TSFM calculation was also performed using the free energy surfaces from the deformed liquid drop model. For 68Zn, the width is observed to increase closely following the TSFM prediction. In contrast, suppression of the width is noticed for 62Zn at low temperatures, similar to other nearby nuclei with N and/or Z closer to 28. Moreover, 68Zn indicates an early onset of the saturation in the IVGDR width, mimicking structural changes appropriately comprehended by the microscopic calculations. These findings suggest that the relative influence of microscopic effects and thermal broadening in the IVGDR width is strongly governed by the proximity of the decaying nucleus to magicity.

Proton and alpha-particle emission spectra have been measured in 4He + 58Ni and 4He + 64Ni reactions at energies >= 10 MeV/nucleon to understand the complex interplay between the equilibrium and pre-equilibrium (PE) emission processes and effect of N/Z asymmetry on them. Theoretical analyses of the experimental spectra were performed using the TALYS code, including contributions from both equilibrium or compound nuclear (CN), and PE components. While the alpha-particle spectra aligned well with default TALYS predictions, the proton spectra showed significant deviations due to an over-prediction of the PE component. The relative contributions of CN and PE components were extracted from the energy spectra and compared for the two systems at different angles. The analyses showed a significantly higher PE fraction in the 4He +64Ni reaction compared to 4He +58Ni, suggesting a link between the N/Z asymmetry and PE emission. The present study provides crucial information in refining available theoretical models and offers key insights into the underlying reaction mechanisms.

The medium-high spin states in 207Po were investigated by the 208Pb( α , 5n)207Po fusion-evaporation reaction at a beam energy of 60 MeV. The γ rays were detected using the VENUS (VECC NUclear Spectroscopy) array, consisting of 6 Compton-Suppressed clover HPGe detectors. In this work, a new and improved level scheme of 207Po has been proposed that extends up to an excitation energy of ∼ 6.9 MeV and a spin of (49/2) ħ . The DCO (Directional Correlation of Oriented state) and IPDCO (Integrated Polarization Directional Correlation of Oriented state) ratios were measured to assign the spins and parities of the levels. A magnetic rotational band has been identified for the first time in this nucleus with 5-qp configuration at an excitation energy of 4.8 MeV. This band has been interpreted using a semi-classical shears-band model. A possible crossing with a 7-qp MR band is also suggested.

A Magnetic Rotational (MR) band in 57Fe nucleus has been newly identified and established from the decreasing behaviour of the experimental electric dipole transition probabilities, B(M1), determined from the measured lifetimes of the states. This becomes the first nucleus in the lighter mass (A<60) region in which, the B(M1) values of an MR band are measured. A single-particle configuration of πf7/2−2⊗ν(p3/2f5/2p1/2)3 has been assigned to this MR band. This configuration, which involves only the negative parity proton and neutron orbitals below and above the Z,N = 28 shell closures, respectively, is a unique one which was not identified before for an MR band. The range of observed angular momenta for this band is congruent with this configuration and the experimental data are found to be in agreement with the SPAC (Shears mechanism with Principal Axis Cranking) and semi-classical calculations. Shell model calculations with GXPF1A interaction reproduce the observed levels in 57Fe including the band head of the MR band. This validates the assigned configurations of this band.

Nuclear level density (NLD) parameters for the constant temperature and back-shifted Fermi gas models were determined for 129 nuclei, spanning from 43Sc to 243Pu. These parameters were extracted using a Bayesian optimization technique by fitting the experimentally measured NLD data obtained from the Oslo method and particle evaporation experiments. For each model, the extracted NLD parameters were further fitted using various functional forms, leading to the identification of optimal expressions based on fractional root-mean-square deviations. The resulting expressions reveal that the NLD parameters primarily depend on three key quantities: the mass number, shell correction energy, and deuteron pairing energy. The accuracy and reliability of these optimized formulations were assessed by comparing the predicted values with measured neutron resonance spacing data. This validation confirms their effectiveness in describing NLDs across the nuclear chart, capturing the signatures of nuclear magicity and deformation.

The Hoyle state, the second excited state of 12C at an excitation energy of 7.65 MeV, plays a vital role in nucleosynthesis. Its radiative decay width serves as a crucial channel for the formation of 12C and all heavier elements in the Universe. To investigate this, exclusive experiments were conducted to measure the radiative decay width of the Hoyle state via the 12C(p, p ')12C reaction. The radiative decay branching ratio Gamma rad/Gamma was determined to be 4.03(21) x 10-4. Based on the currently accepted values of Gamma pi(E0)/Gamma and Gamma pi(E0), the radiative width of the Hoyle state was calculated as 3.75(40) x 10-3 eV.

Neutron energies and angular distributions were measured in 9 Be(a,n) 12 C reaction for a energies of 5.5 and 6.5 MeV. Three major neutron groups were observed in the spectrum, which correspond to the ground and first two excited states of 12 C. Measured data could only be explained by the TALYS calculation if reaction at more than one location within the target is considered for a given beam energy. The preferred locations are driven by the resonance energy levels existing in 13 C. Neutron yield due to the 9 Be breakup process was determined which is found to be 12.6 +/- 0.2% and 18.4 +/- 0.5% of the total reaction cross-section for 5.5 and 6.5 MeV respectively.

Background: The excitation energy dependence of the fission fragment mass distributions for heavy ion-induced reactions on preactinides targets well above the Coulomb barrier energies has received limited attention due to the lack of data. An extensive study is required to understand the reaction mechanism at high excitation energy as it bridges our understanding of the mechanism of fission and noncompound nuclear reactions. Purpose: The purpose was to understand the fusion-fission dynamics well above the Coulomb barrier energies, particularly to address if the theoretical models that are valid near the Coulomb barrier can explain the fission data at high excitation energies. Methods: In the experiment, a pulsed heavy-ion beam from the cyclotron was utilized, and the resulting binary fragments were detected using two position-sensitive multiwire proportional counters. By analyzing the time-offlight differences and position information (theta, phi) of the binary fragments, mass distributions were obtained for the reactions 16O + 181Ta, 197Au, 205Tl, and 208Pb. Results: The variance of the fission fragment mass distributions exhibits a smooth increase with excitation energy, although values are smaller compared to the predicted values of the semiempirical calculation GEF. The measured variation of the variance of the mass distribution with the fissility showed an exponential increase. The contribution of fast fission have been identified at high energies with mass asymmetry value approximate to 0.22. Conclusion: Our systematic measurements over a wide range of excitation energy and target mass indicate that the fission fragment mass distributions are consistent with statistical models up to approximate to 2 times the Coulomb barrier energies for the pre-actinides target nuclei when bombarded with 16O. The result provides benchmark data to test the new reaction models at high excitation energies.

Neutron energies and angular distributions were measured in 9Be(α,n)12C reaction for α energies of 5.5 and 6.5 MeV. Three major neutron groups were observed in the spectrum, which correspond to the ground and first two excited states of 12C. Measured data could only be explained by the TALYS calculation if reaction at more than one location within the target are considered for a given beam energy. The preferred locations are driven by the resonance energy levels existing in 13C. Neutron yield due to the 9Be breakup process was determined which is found to 12.6 ± 0.2% and 18.4 ± 0.5% of the total reaction cross-section for 5.5 and 6.5 MeV respectively.

Temperature-dependent photon strength function (PSF) models, along with the widely accepted temperatureindependent Brink-Axel Lorentzian model, are investigated in their application to determine the properties of the giant dipole resonance (GDR) built on the excited states of nuclei up to a temperature approximate to 1.5 MeV. Three temperature-dependent models, namely, the simple modified Lorentzian model, the hybrid model by Goriely, and the generalized Lorentzian model of Kopecky and Uhl, are studied. The statistical model calculations with all PSF models reproduce the high-energy (E gamma approximate to 5-25 MeV) gamma -ray spectra originating from the decay of 62Zn and 201Tl compound nuclei reasonably well, and put forward approximately the same peak energy and strength of the GDR. Nevertheless, at a given temperature, significant variation is observed in the predicted GDR width, which may influence the theoretical models used to calculate the GDR width.

The radiative decay of the Hoyle state serves as the gateway to the production of heavier elements in a stellar environment. Here, we present an exclusive measurement of electric quadruple (E2) transitions of the Hoyle state to the ground state of 12C through the 12C(p, p′γγ)12C reaction. A triple coincidence measurement yields the radiative branching ratio Γrad/Γ = 4.01 (30) × 10−4. This result was corroborated by an independent experiment based on the complete kinematical measurement via 12C(p, p′)12C reaction, yielding a consistent result of Γrad/Γ = 4.04 (30) × 10−4. Combining our results with the currently adopted values of Γπ(E0)/Γ and Γπ(E0), the radiative width of the Hoyle state is determined to be 3.75 (40) × 10−3 eV. It is important to note that our finding do not align with a recently reported 34% increase in the radiative decay width of the Hoyle state but is consistent with the currently accepted value.