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The formation of continuum neutron distribution in $^{7}\mathrm{Li}(p,n)$ has been identified as due to the coupling of the $^{7}\mathrm{Be}$ breakup levels to the final state of the reaction. The continuum neutron spectra produced by the $^{7}\mathrm{Li}(p,n)$ reaction has been estimated by measuring the double differential cross sections for continuum and resonant breakup of $^{7}\mathrm{Be}$, through the $^{7}\mathrm{Li}(p,n)^{7}\mathrm{Be}^{*}$ reaction at 21 MeV of proton energy. The breakup contributions from continuum and $5/{2}^{\ensuremath{-}}$, $7/{2}^{\ensuremath{-}}$ states of $^{7}\mathrm{Be}$ have been identified. The measured double differential cross sections have been reproduced through continuum-discretized coupled channel-coupled reaction channel calculations. The cross sections were projected to neutron spectrum using the Monte Carlo approach and validated using experimentally measured $^{3}\mathrm{He}$ gated neutron spectra. $^{7}\mathrm{Li}(p,n)$ neutron spectrum at 20 MeV incident proton energy measured by McNaughton et al. [Nucl. Instrum. Methods 130, 555 (1975)] has been reproduced by adapting estimated model parameters for the reaction.

An array of eight CsI(Tl) detectors has been set up to measure the light charged particles in nuclear reactions using heavy ions from the Pelletron Linac Facility, Mumbai. The energy response of CsI(Tl) detector to α -particles from 5 to 40 MeV is measured using radioactive sources and the 12C(12C, α ) reaction populating discrete states in 20Ne. The energy non-linearity and the count rate effect on the pulse shape discrimination property have also been measured and observed the deterioration of pulse shape discrimination with higher count rate.

To disentangle the role of shell effects and dynamics, fission fragment mass distributions of 191Au, a nucleus in the newly identified island of mass asymmetric fission in the sub-lead region, have been measured down to excitation energy of ≈20 MeV above the fission barrier via two different entrance channels, viz. 16O+175Lu and 37Cl+154Sm reactions. Apart from having signature of the shell effects in both the cases, clear experimental evidence of quasifission has been observed in the mass distributions of the Cl induced reaction, that has also been substantiated by the theoretical calculations. This crucial evidence along with a systematic analysis of the available experimental data has revealed that the dynamics in the entrance channel has significant influence on most of the reactions used earlier to explore the persistence of recently discovered mass asymmetry in β-delayed fission at low energy in this mass region, ignoring which might lead to ambiguity in interpreting the heavy-ion data. Keywords: Fusion-fission, Mass asymmetric fission, Shell effects, Quasifission

We measured neutron emission spectra for $^{19}\mathrm{F}$-induced reactions on $^{181}\mathrm{Ta}$, $^{89}\mathrm{Y}$, and $^{51}\mathrm{V}$ at beam energies of 130, 140, 145, and 150 MeV. Measurements were made using liquid scintillator detectors at eight angles in the range of ${25}^{\ensuremath{\circ}}\ensuremath{-}{143}^{\ensuremath{\circ}}$ using time-of-flight and pulse-shape discrimination. A comparison has been made with alice2014 and pace4 calculations to understand the role of incomplete fusion and pre-equilibrium effects. Global predictions with alice2014 without parameter adjustment gives a fair agreement with the measured data.

This paper reports the first observation of the Jacobi shape transition in $^{31}\mathrm{P}$ using high energy $\ensuremath{\gamma}$ rays from the decay of giant dipole resonance (GDR) as a probe. The measured GDR spectrum in the decay of $^{31}\mathrm{P}$ shows a distinct low energy component around 10 MeV, which is a clear signature of Coriolis splitting in a highly deformed rotating nucleus. Interestingly, a self-conjugate $\ensuremath{\alpha}$-cluster nucleus $^{28}\mathrm{Si}$, populated at similar initial excitation energy and angular momentum, exhibits a vastly different GDR lineshape. Even though the angular momentum of the compound nucleus $^{28}\mathrm{Si}$ is higher than the critical angular momentum required for the Jacobi shape transition, the GDR lineshape is akin to a prolate deformed nucleus. Considering the present results for $^{28}\mathrm{Si}$ and similar observation recently reported in $^{32}\mathrm{S}$, it is proposed that the nuclear orbiting phenomenon exhibited by $\ensuremath{\alpha}$-cluster nuclei hinders the Jacobi shape transition. The present experimental results suggest a possibility to investigate the nuclear orbiting phenomenon using high energy $\ensuremath{\gamma}$ rays as a probe.

Exclusive measurements of high-energy $\ensuremath{\gamma}$ rays have been performed in $^{124}\mathrm{Ba}$ and $^{136}\mathrm{Ba}$ at the same excitation energy $(\ensuremath{\sim}49\phantom{\rule{4pt}{0ex}}\mathrm{MeV})$ to study the properties of the giant dipole resonance (GDR) over a wide $N/Z$ range. The high-energy $\ensuremath{\gamma}$ rays are measured in coincidence with the multiplicity of low-energy $\ensuremath{\gamma}$ rays to disentangle the effect of temperature $(T)$ and angular momentum $(J)$. The GDR parameters are extracted employing a simulated Monte Carlo statistical model analysis. The observed $\ensuremath{\gamma}$-ray spectra of $^{124}\mathrm{Ba}$ can be explained with prolate deformation, whereas a single-component Lorentzian function which corresponds to a spherical shape could explain the $\ensuremath{\gamma}$-ray spectra of $^{136}\mathrm{Ba}$. The observed GDR width in $^{136}\mathrm{Ba}$ is narrower compared to that of $^{124}\mathrm{Ba}$. The statistical model best-fit GDR cross sections are found to be in reasonable agreement with the thermal shape fluctuation model (TSFM) calculations. Further, it is shown that the variation of GDR width with $T$ is well reproduced by the TSFM calculations over the temperature range of 1.1--1.7 MeV.

Proton and alpha particle spectra have been measured in the 12C+93Nb and 12C+58Ni reactions at E(12C)=40 and 50 MeV and in the 16O + 93Nb reaction at E(16O) =75 MeV. The spectra are compared with the statistical model calculations. The shapes of the calculated spectra are in agreement with experimental data except for the alpha spectrum in the 12C + 93Nb reaction at 40 MeV. The observed evaporation bump is at ∼2 MeV lower energy compared to the calculated one. This discrepancy could imply alpha particle emission from a deformed configuration before compound nucleus formation at this near Coulomb barrier beam energy.

Pulse shape discrimination (PSD) with totally depleted transmission type Si surface barrier detector in reverse mount has been investigated to identify fission fragments in the presence of elastic background in heavy ion-induced fission reactions by both numerical simulation and experimental studies. The PSD method is compared with the other conventional methods adopted to identify fission fragments with solid-state detectors such as ΔE–E telescope and single thin ΔE detector and the data for the10B +232Th fission reaction are presented. Results demonstrate the usefulness of a single transmission-type surface barrier detector for the identification of fission fragments and projectiles like heavy ions

An earlier measurement on the ${4}^{+}$ to ${2}^{+}$ radiative transition in $^{8}\mathrm{Be}$ provided the first electromagnetic signature of its dumbbell-like shape. However, the large uncertainty in the measured cross section does not allow a stringent test of nuclear structure models. This Letter reports a more elaborate and precise measurement for this transition, via the radiative capture in the $^{4}\mathrm{He}+^{4}\mathrm{He}$ reaction, improving the accuracy by about a factor of 3. Ab initio calculations of the radiative transition strength with improved three-nucleon forces are also presented. The experimental results are compared with the predictions of the alpha cluster model and ab initio calculations.

The damping of the nuclear shell effect with excitation energy has been measured through an analysis of the neutron spectra following the triton transfer in the (7)Li induced reaction on (205)Tl. The measured neutron spectra demonstrate the expected large shell correction energy for the nuclei in the vicinity of doubly magic (208)Pb and a small value around (184)W. A quantitative extraction of the allowed values of the damping parameter γ, along with those for the asymptotic nuclear level density parameter a, has been made for the first time.

Gamma ray multiplicity gated proton spectra have been measured in the reactions 12C+93Nb at E(12C)= 40 and 45.5 MeV and 16O+89Y at E(16O)= 51 and 54 MeV populating the CN 105 Ag at EX between 35 and 40 MeV. Broad structures are seen in all spectra at high gamma ray multiplicities. The present data, along with those from our earlier work on the former reaction at E(12C)= 42.5 MeV, establish the compound nuclear origin of the structures. The data can be explained by incorporating a localised enhancement of nuclear level density in the excitation energy and angular momentum space. Multiplicity gated Îś spectra have also been measured in the same reaction at E(12C)= 37.5 – 45 MeV. Broad structures seen in these spectra seem to have contribution from other reaction mechanisms also.

A large area plastic scintillator detector array(~ 1 m x1m) has been set up for fast neutron spectroscopy at the BARC-TIFR Pelletron laboratory, Mumbai. The energy, time and position response has been measured for electrons using radioactive sources and for mono-energetic neutrons using the 7Li(p,n1)7Be*(0.429 MeV) reaction at proton energies between 6.3 and 19 MeV. A Monte Carlo simulation of the energy dependent efficiency of the array for neutron detection is in agreement with the 7Li(p,n1) measurements. The array has been used to measure the neutron spectrum, in the energy range of 4-12 MeV, in the reaction 12C+ 93Nb at E(12C)= 40 MeV. This is in reasonable agreement with a statistical model calculation., Comment: 31 pages, 17 figures, submitted to NIM A

Electromagnetic transition rates provide an important test for nuclear structure models. The nucleus 8Be exhibits a pronounced alpha-cluster structure and is a building block for more complex cluster nuclei. Here we report on the first observation of the gamma transition between the 4(+) and 2(+) states of 8Be in the 4He+4He reaction. The measured on-resonance cross section of 165+/-54 nb leads to a B(E2) of25+/-8e(2) fm(4), in good agreement with alpha-cluster models and sophisticated ab initio structure calculations.

Influence of 1n-transfer coupling on quasi-elastic scattering excitation function has been investigated for 6 Li + 209 Bi system. Coupled Reaction Channels Calculations have been carried out for the energies around the Coulomb barrier. Corresponding barrier distributions obtained with and without including 1n-transfer cou- pling, have been compared with experimental data. 1n-transfer effect on quasi-elastic excitation function has been observed to be insignificant for the present system. In the reaction of 6 Li with 208 Pb and 209 Bi, an ex- perimental relative contributions for breakup and 1n-transfer channels have been reproduced by simultaneous calculation using CDCC and CRC formalism.

Gamma-ray multiplicity gated proton spectra have been measured in the 12C + 93Nb and 16O + 89Y reactions producing the same compound nucleus 105Ag at an excitation energy of ~39.8 MeV, and in the 12C + 89Y reaction at E(12C) = 40 MeV. Multiplicity gated alpha particle spectra have been measured in the 12C + 93Nb reaction at E(12C) = 37.5–45 MeV. All these measurements were aimed at gaining more insight into the origin of the unexpected broad structures seen earlier in the high energy part of the proton spectra at high gamma-ray multiplicities. Two possible explanations, one of the enhanced nuclear level density within the statistical model and the other of a massive cluster transfer process, were suggested by us to understand the earlier data. The former prescription appears to be favoured by the present proton data.