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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.

In order to investigate the interplay between nuclear structure (shell closure) and dynamics, fission fragment mass distributions have been measured for reactions $^{35,37}\mathrm{Cl}+^{206,208}\mathrm{Pb}$. These reactions have similar entrance channel parameters except for the number of closed shell configuration in the entrance channel. Fission fragment mass distributions have been measured for these reactions in the energy region close to the Coulomb barrier. No mass-angle correlation was observed in any of the four reactions, indicating the absence of fast quasifission (QF), but mass distributions were wider than that of compound nucleus (CN) fission, which indicates the presence of slow QF. With comparable fissility and deformation values, extra stability against QF was observed for reactions which have more closed shell configurations in the entrance channel. Mass-angle distributions of these reactions do not follow the systematics with respect to mean fissility. A new systematics has been obtained by considering quadrupole deformation of the heavy reaction partner along with the fissility, which explains the absence of mass-angle correlation in the presently measured reactions.

The neutron energy spectra in coincidence with both the correlated fission fragments in $^{32}\mathrm{S}+^{184}\mathrm{W}$ reaction forming the compound nucleus $^{216}\mathrm{Th}$ at an excitation energy of 71.31 MeV have been measured at various angles with respect to one of the fission fragments. Pre- and post-scission neutron multiplicities of $2.68\ifmmode\pm\else\textpm\fi{}0.48$ and $3.3\ifmmode\pm\else\textpm\fi{}0.20,$ respectively, have been extracted by analyzing angular correlation of the neutron energy spectra using moving source fitting procedure. The excess pre-scission neutron multiplicity in comparison to statistical model joanne2 code predictions have been converted into total fission delay. A comparative study of fission delay has been carried out for the $^{16}\mathrm{O}+^{208}\mathrm{Pb}$ reaction forming the compound nucleus $^{224}\mathrm{Th}$ at similar excitation energy as in $^{32}\mathrm{S}+^{184}\mathrm{W}$ reaction. Both the reactions have been analyzed within the frame work of joanne2 code including fission delay, deformation dependent level densities, particle binding energies, and transmission coefficients. The observed fission delay for both the reactions can be quantitatively understood if different formation time predicted by dynamical model hicol code are considered.

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

The $^{54}\mathrm{Mn}^{*}$ (surrogate of $n+^{53}\mathrm{Mn}$) and $^{61}\mathrm{Ni}^{*}$ (surrogate of $n+^{60}\mathrm{Ni}$) compound systems have been populated at overlapping excitation energies by transfer reactions $^{52}\mathrm{Cr}(^{6}\mathrm{Li},\ensuremath{\alpha})^{54}\mathrm{Mn}^{*}$ at ${E}_{\mathrm{lab}}=33.0\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $^{59}\mathrm{Co}(^{6}\mathrm{Li},\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{61}\mathrm{Ni}^{*}$ at ${E}_{\mathrm{lab}}=40.5\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, respectively. The proton decay probabilities of the compound systems have been determined by measuring evaporated protons at backward angles in coincidence with projectilelike fragments detected around the grazing angle. The $^{53}\mathrm{Mn}(n,xp)$ cross sections in the equivalent neutron energy range of 8.2--16.4 MeV have been determined within the framework of the surrogate reaction ratio method using $^{60}\mathrm{Ni}(n,xp)$ cross-section values from the literature as a reference. The measured $^{53}\mathrm{Mn}(n,xp)$ cross-section values are found to be consistent with the predictions of the talys-1.8 statistical model code using microscopic level densities and results of various evaluated nuclear data libraries: eaf-2010, rosfond-2010, and jeff-3.3 within the experimental uncertainties.

Several experimental investigations have reported evidence of collective enhancement of the nuclear level density and its fadeout. However, a suitable method is needed for experimental determination of the enhancement factor as a function of excitation energy. In this study, neutron spectra were measured in coincidence with evaporated $\ensuremath{\alpha}$ particles produced in the reactions $^{11}\mathrm{B}+^{181}\mathrm{Ta},^{197}\mathrm{Au}$. The nuclear level density parameter has been extracted for the $\mathrm{Os}\phantom{\rule{0.16em}{0ex}}(A\ensuremath{\approx}188)$ and $\mathrm{Pb}\phantom{\rule{0.16em}{0ex}}(A\ensuremath{\approx}204)$ isotopes by comparing neutron spectra with statistical model prediction. Evidence for collective enhancement has been found for Os nuclei whereas no such enhancement has been seen for Pb nuclei. The energy-dependent enhancement factor has been extracted by simultaneous fitting of the neutron spectra at various excitation energies. Near a temperature of 0.8 MeV, the enhancement starts to fadeout which is lower than the theoretically predicted temperature of 1.4 MeV for $^{187}\mathrm{Os}$. Also, free energy surface calculation shows that the $^{187}\mathrm{Os}$ nucleus undergoes a transition from collective prolate to noncollective oblate shape close to the temperature of 0.8 MeV, corroborating the early fadeout. No such shape transition is seen for $^{203}\mathrm{Pb}$.

The $^{59}\mathrm{Ni}(n,xp)$ reaction cross sections have been measured following the surrogate reaction ratio method in the equivalent neutron energy range of 11.9--15.8 MeV by populating the compound nucleus $^{60}\mathrm{Ni}^{*}$ through transfer reaction $^{56}\mathrm{Fe}(^{6}\mathrm{Li},d)$ at ${E}_{\text{lab}}=35.9$ MeV. The $^{59}\mathrm{Co}(^{6}\mathrm{Li},\ensuremath{\alpha})^{61}\mathrm{Ni}^{*}$ transfer reaction at ${E}_{\text{lab}}=40.5$ MeV has been used as the reference reaction which is the surrogate of $^{60}\mathrm{Ni}(n,xp)$ reaction populating the compound nucleus $^{61}\mathrm{Ni}^{*}$. The proton decay probabilities have been determined by measuring evaporated protons at backward angles in coincidence with projectile like fragments (PLFs, either $d$ or $\ensuremath{\alpha}$) detected around grazing angles. The cross sections for the reference reaction $^{60}\mathrm{Ni}(n,xp)$ are taken from jendl-4.0 library, which closely reproduce the available experimental data. The cross sections for the desired $^{59}\mathrm{Ni}(n,xp)$ reaction so obtained compare well with the nuclear-reactions-model code talys-1.8 using microscopic level densities. The present experimental data are consistent with the evaluated data library of rosfond-2015 but not with tendl-2015 and endf/b-viii, indicating the need of new evaluations for this reaction of importance to fusion technology.

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.

Transfer-induced fission fragment angular distribution measurements have been carried out in $^{6}\mathrm{Li}+^{238}\mathrm{U}$ reaction at beam energies of 36 and 40 MeV in coincidence with projectile-like fragments. The fission fragment anisotropies for $\ensuremath{\alpha}$- and deuteron-transfer-induced fission reactions are obtained with respect to the recoil direction. The anisotropy values for transfer-induced fissions are observed to be either similar or lower than the inclusive measurement. In order to quantitatively understand the present experimental data on transfer-induced fission, anisotropy values have been compared with the preequilibrium fission model considering ground-state spin of the projectile and/or target. It is found that the model predicts the inclusive and exclusive anisotropy data reasonably well.

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.

Elastic-scattering angular distributions were measured for the $^{7}\mathrm{Li}+^{159}\mathrm{Tb}$ system at various energies; namely, 24, 26, 28, 30, 35, 40, and 44 MeV. The optical-model analysis was performed to investigate the energy dependence of real and imaginary potentials, employing a Woods--Saxon form of potential. The dispersion-relation analysis were also carried out to check the consistency of real and imaginary parts of the potentials. The energy dependence of real and imaginary potentials does not follow the trend of conventional threshold anomaly but rather represents unusual behavior of the increase of imaginary part of the potential and corresponding decrease in real part of the potential near the Coulomb barrier energy. The effect of breakup coupling on elastic-scattering angular distributions was studied by a continuum-discretized coupled-channels (CDCC) calculation. The behavior of dynamic polarization potentials obtained due to the breakup coupling is discussed. The total reaction cross sections for the present and various other systems are also compared involving $^{7}\mathrm{Li}$ projectile on different target nuclei in the mass range $A=16$ to 232.

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.

Gamma ray spectra in the energy range of ∼4–25 MeV were measured in the reaction 28 Si + 124 Sn at E ( 28 Si) ∼ 150 MeV in coincidence with low energy γ -multiplicities. The spectra were analysed using a simulated Monte Carlo CASCADE code. The centroid energy and width of the giant dipole resonance were extracted for various multiplicity windows. The average angular momentum and temperature of the final states populated after the giant dipole photon emission range from ∼25 ℏ and 1.5 MeV to ∼56 ℏ and 1.3 MeV, respectively. The extracted widths are almost constant for the lower multiplicity windows and show an increase of ∼1.4 MeV at the highest window. The nuclei are expected to be near the liquid drop regime and the experimental results are not inconsistent with the liquid drop behaviour.

Gamma multiplicity gated proton spectra have been measured in the 12C + 93Nb reaction at E ( C 12 ) = 40 MeV at backward angles. The shape of the spectrum shows a drastic change with the increase in multiplicity acquiring a broad structure at proton energies beyond ∼ 15 MeV corroborating our earlier measurements at E ( C 12 ) = 42.5 MeV . Measurements made in coincidence with residue γ rays, detected in an array of eight HPGe clover detectors, confirm these observations. An excitation energy and angular momentum-dependent enhancement of the nuclear level density or a massive cluster transfer of 11B to the 93Nb can explain the data.

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

Proton and alpha spectra in the energy range E p c.m. ∼6 –24 MeV and E α c.m. ∼12 –40 MeV, respectively, have been measured in the reaction 28 Si + 58 Ni at E lab ( 28 Si )=100 and 125 MeV. The spectra at various laboratory angles from 100° to 160° were corrected for angular distribution effects to obtain the angle-integrated spectra. An asymptotic (liquid drop) level density parameter of a =A/7.5 describes the proton and alpha spectra at both the beam energies. No lowering of emission barrier is needed to explain the alpha spectra although the spin dependence of level density has to be tuned. The derived value of a is somewhat larger than that for other near-stable nuclei and possibly arises due to the excitation energy dependent collective enhancement of the nuclear level density.

High-energy proton spectra in the energy range E p c.m. ∼8.5–25 MeV are measured in the reaction 12 C+ 93 Nb at E lab ( 12 C)=42.5 MeV and at laboratory angles of 130°, 145° and 160°. The spectra, recorded in coincidence with a gamma ray multiplicity detector array, show a broad structure which becomes more prominent at higher multiplicity. The centroid of the structure shifts with multiplicity. These features could arise from an unusual spin and excitation energy dependence of the nuclear level density in Pd and Ag nuclei with mass around A =104. However, a non-statistical process, viz. , the massive cluster transfer, cannot be ruled out.

A compact array of seven hexagonal BaF2 detectors, with cosmic ray background suppression, has been set up for the measurement of high energy photons up to ∼30 MeV. The array has been used in the measurement of giant dipole photons in low energy heavy-ion reactions.

The effects of breakup reactions on elastic and α-production channels for the 6Li+116Sn system have been investigated at energies below and near the Coulomb barrier. The angular distributions of α-particle production differential cross sections have been obtained at several projectile energies between 22 and 40 MeV. The measured breakup α-particle differential cross sections and elastic scattering angular distributions have been compared with the predictions of continuum-discretized coupled channels (CDCC) calculations. The influence of breakup coupling has also been investigated by extracting dynamic polarization potentials (DPP) from the CDCC calculations. From the predictions of CDCC calculations the relative importance of the nuclear, Coulomb, and total breakup contributions have also been investigated. The nuclear breakup couplings are observed to play an important role in comparison to the Coulomb breakup for the direct breakup mechanisms associated in the reaction of 6Li projectile with 116Sn target nuclei. The influence of strong nuclear breakup coupling exhibits suppression in the Coulomb-nuclear interference peak. The direct breakup cross sections from the CDCC calculations under-predict the measured α-particle differential cross sections at all energies. This suggests that the measured α particles may also have contributions from other possible breakup reaction channels.

The fusion barrier distributions for $^{28,30}\mathrm{Si}$ + $^{124}\mathrm{Sn}$ systems were extracted from quasielastic excitation function measurements at backward angles. The experimental barrier distributions were then compared with coupled-channel (CC) calculations. The fusion barrier distribution for the $^{30}\mathrm{Si}$ + $^{124}\mathrm{Sn}$ reaction was well reproduced by the CC calculations with the inclusion of projectile and target inelastic couplings and only one possible positive $Q$-value 2$n$-transfer channel coupling using the ccfull code. However, CC calculations with similar coupling schemes for inelastic excitation of target and projectile with the 4$n$-transfer channel corresponding to the highest positive $Q$ value failed to reproduce the barrier distribution for the $^{28}\mathrm{Si}$ + $^{124}\mathrm{Sn}$ reaction, because it has many positive $Q$-value multi-neutron transfer channels. A better agreement between the experimental fusion barrier distribution for the $^{28}\mathrm{Si}$ + $^{124}\mathrm{Sn}$ system and the prediction of semiempirical CC calculations based on the Zagrebaev framework [V. I. Zagrebaev, Phys. Rev. C 67, 061601(R) (2003)] was obtained only after considering positive $Q$-value multi-neutron transfer couplings. The sensitivity of the fusion barrier distribution to the hexadecapole deformation parameter ${\ensuremath{\beta}}_{4}$ of the projectile was also discussed.

The fission decay probabilities of the $^{235}\mathrm{Pa}$ and $^{236}\mathrm{U}$ compound nuclei produced in a single experiment in $^{232}\mathrm{Th}$($^{7}\mathrm{Li}$, $\ensuremath{\alpha}f$)$^{235}\mathrm{Pa}$ and $^{232}\mathrm{Th}$($^{7}\mathrm{Li}$, $tf$)$^{236}\mathrm{U}$ transfer induced fission reaction channels, have been measured at ${E}_{\mathrm{lab}}=39.5$ MeV in the excitation energy range of 14--20 MeV. The $^{234}\mathrm{Pa}$(n, f) cross sections are then deduced from the measured fission decay probability ratios of $^{235}\mathrm{Pa}$ and $^{236}\mathrm{U}$ compound systems in the equivalent neutron energy range of 8--14 MeV within the framework of the hybrid surrogate ratio method, considering the well-measured $^{235}\mathrm{U}$(n, f) cross sections as the reference. The experimental data on $^{234}\mathrm{Pa}$(n, f) cross sections have been compared with the calculated fission cross sections using empire-3.1 code with the fission barrier height values obtained from barrier formula (BF) as well as ripl-3 [24]. The present experimental results are found to be in very good agreement with the empire-3.1 predictions for the fission barrier heights predicted by the BF.

The excitation functions have been measured for the {sup 12}C ({sup 12}C,{alpha}){sup 20}Ne and {sup 12}C({sup 12}C,{sup 8}Be){sup 16}O reactions leading to the excited states up to 25 MeV in {sup 20}Ne and 20 MeV in {sup 16}O, respectively, in the beam energy range E({sup 12}C)=48{endash}72 MeV. The region of excitation investigated was E{sub x}=38{endash}50 MeV in {sup 24}Mg which is well above the threshold for breakup into six alpha particles. In the {sup 8}Be channel leading to the 6{endash}7 MeV region of {sup 16}O, excitation functions were also measured for {sup 8}Be- {gamma} coincidences in {sup 12}C ({sup 12}C,{sup 8}Be){sup 16}O{sup *}{r_arrow}{gamma}+{sup 16}O{sub g.s.} particularly to distinguish between the otherwise unresolved 6.05 MeV, 0{sup +} and 6.13 MeV, 3{sup {minus}} states in {sup 16}O. It is observed that a cluster of resonances in the excitation region 39{endash}43 MeV in {sup 24}Mg decays via {alpha} and {sup 8}Be channels predominantly to the particle-hole states in {sup 20}Ne and {sup 16}O which are members of deformed bands. Another cluster of resonances in the region 44{endash}49 MeV (centered at E{sub c.m.}=32.5 MeV) decays predominantly to the 20.48 MeV state in {sup 20}Ne (which is above the 5{alpha} breakup threshold) and to amore » possible 4{alpha} linear chain band in {sup 16}O around 18 MeV, indicating their highly deformed nature. This latter cluster structure coincides in energy with the possible 6{alpha} linear chain resonance identified in the literature at E{sub c.m.}=32.5 MeV in the inelastic scattering channels {sup 12}C{sub 7.65,0{sup +}}+{sup 12}C{sub 7.65,0{sup +}} and {sup 12}C{sub 7.65,0{sup +}}+{sup 12}C{sub 9.64,3{sup {minus}}}. In this excitation energy region intermediate structures in the {sup 8}Be channel are found at E{sub c.m.}=31.5 and 33.5 MeV decaying to the 6.13 MeV, 3{sup {minus}} state and at E{sub c.m.}=32.5 MeV decaying to the 6.92/7.13 MeV states of {sup 16}O. (Abstract Truncated)« less

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.

An earlier measurement on the 4+ to 2+ radiative transition in 8Be 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 4He + 4He 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 ${}^{241}$Pu(n,f) cross sections have been determined by the surrogate ratio method in the equivalent neutron energy range 11.0--16.0 MeV by using ${}^{238}$U(${}^{6}$Li,$d$)${}^{242}$Pu and ${}^{232}$Th(${}^{6}$Li,$d$)${}^{236}$U transfer reactions at E${}_{\text{lab}}=39.6$ and 39.0 MeV, respectively. Results have been compared with direct measurement of ${}^{241}$Pu(n,f) cross-section data and predictions of statistical model code empire 3.1 for different sets of values of fission barrier heights from evaluated data libraries. The present ${}^{241}$Pu(n, f) cross-section data are observed to be consistent with the direct measurements, suggesting the applicability of surrogate methods. However, the empire 3.1 predictions are not in complete agreement with the experimental data in the neutron energy range 2.0--20.0 MeV for any set of the fission barrier data libraries. The consistency of experimental results on ${}^{241}$Pu(n,f) cross section data from direct and surrogate measurements suggests the need for fission barrier heights for Pu isotopes that are different from those used in standard libraries. The fission barrier heights for various Pu isotopes have been obtained for best fit to the experimental data in the neutron energy range 2.0--20.0 MeV.

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.

Fusion barrier distributions have been extracted from the quasi-elastic scattering excitation functions, measured at backward angle θlab = 160° in reactions of 6,7Li+209Bi. The present results have been compared with the barrier distributions obtained from the fusion excitation function measurements for the above mentioned systems. The fusion barrier distributions from the quasi-elastic scattering excitation functions have been analyzed with simplified Coupled Channels calculations using Fresco. Inclusions of resonant states for both 6,7Li projectiles improve the predictions to describe the measured quasi-elastic scattering excitation functions and barrier distributions. For both the reactions peak positions of fusion barrier distributions are shifted towards a lower energy side in comparison to that obtained from the fusion excitation function measurements. The observed discrepancy in peak positions of barrier distributions obtained from quasi-elastic scattering and fusion excitation function measurement...

Proton yields in the energy range of {similar_to}10--30 MeV have been measured in the reactions {sup 12}C+{sup 93}Nb at {ital E}({sup 12}C)=40, 45, 50, and 56 MeV and {sup 12}C+{sup 103}Rh at {ital E}({sup 12}C)=53 MeV at {theta}{sub lab}=125{degree} and 155{degree}. From these measurements the energy variation of the total nuclear level density has been extracted for {sup 104}Pd and {sup 114}Sn in the excitation-energy range of {similar_to}7--24 MeV and {similar_to}12--24 MeV, respectively. No sizable effect of the proton shell closure at {ital Z}=50 is seen at excitation energies beyond {similar_to}15 MeV though there is an indication of this effect becoming important at lower energies.

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 ã, has been made for the first time.

Evaporation-residue-gated high-energy gamma-ray spectra were measured in the ${}^{19}$F+${}^{27}$Al reaction at two beam energies of $\ensuremath{\sim}$75 and 125 MeV. The compound nuclear angular momenta populated at the higher energy should extend beyond the critical value for the Jacobi shape transition, while those at the lower energy should be mostly restricted below the critical value. A sharp low-energy (at $\ensuremath{\sim}$10 MeV) component has been observed in the gamma-ray strength function superimposed on a broad distribution. At the higher beam energy, the component becomes more prominent at higher angular momentum, whereas an opposite behavior is witnessed at the lower beam energy. The implication of these observations in connection with the occurrence of the Jacobi shape transition is discussed.

Elastic scattering angular distributions using the weakly bound projectile 7Li on medium-mass target 116Sn were measured for 10 different beam energies from much below to above the Coulomb barrier. Optical model (OM) analysis was carried out using the famous double folding Sao Paulo Potential (SPP) to investigate the energy dependence of the interacting polarizing potentials. The absence of the usual Threshold Anomaly (TA) is observed. Thus this unusual behavior of the interacting potentials indicates the coupling of the breakup channels with the elastic ones.

Elastic-scattering angular distributions of 7Li on 116Sn have been measured at different bombarding energies between 18 to 35 MeV. The effects of the weakly bound projectile breakup channel on the bombarding energy dependence of the interaction potential have been investigated. In this work we present the experimental results, along with the theoretical analysis using Woods-Saxon potential to investigate the energy dependence of the interacting polarizing potentials. Total reaction cross-sections are also presented and discussed.

We have measured the elastic scattering of the weakly bound $^{6}\mathrm{Li}$ on the $^{116,112}\mathrm{Sn}$ targets, at energies close to the Coulomb barrier. The energy dependence of the interaction potential has been investigated by two different methods and the presence of the breakup threshold anomaly is observed. We have also derived the total reaction cross sections for the above systems and compared them to those of other systems with halo, weakly bound, and tightly bound projectiles on targets with similar masses. The reaction cross sections are largest for systems with halo nuclei, then the systems with no-halo weakly bound nuclei, and the smallest cross sections are those for tightly bound systems.

Proton and {alpha}-particle spectra have been measured at backward angles in the {sup 12}C + {sup 93}Nb reaction at E({sup 12}C)=37.5-60 MeV and in the {sup 16}O+{sup 93}Nb reaction at E({sup 16}O)=54-75 MeV. The inclusive particle spectra generally are in good agreement with the statistical model calculations except for the {alpha} spectra in the {sup 12}C-induced reaction at beam energies of 37.5-42.5 MeV which are close to the Coulomb barrier in the entrance channel. In these cases the evaporation peak is up to 2 MeV lower than its expected position from the statistical model predictions. Gamma-multiplicity-gated {alpha} spectra, measured in the same reaction, also show the aforementioned discrepancy. These observations reveal that the conventional statistical model cannot explain the {alpha}-particle spectra in the {sup 12}C-induced reactions near the Coulomb barrier.

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 new hybrid surrogate ratio approach has been employed to determine neutron-induced fission cross sections of $^{233}\mathrm{Pa}$ in the energy range of 11.5 to 16.5 MeV for the first time. The fission probability of $^{234}\mathrm{Pa}$ and $^{236}\mathrm{U}$ compound nuclei produced in $^{232}\mathrm{Th}$($^{6}\mathrm{Li}$, $\ensuremath{\alpha}$)$^{234}\mathrm{Pa}$ and $^{232}\mathrm{Th}$($^{6}\mathrm{Li}$, $d$)$^{236}\mathrm{U}$ transfer reaction channels has been measured at ${E}_{\mathrm{lab}}=38.0$ MeV in the excitation energy range of 17.0 to 22.0 MeV within the framework of the absolute surrogate method. The $^{233}\mathrm{Pa}$$(n,f)$ cross sections are then deduced from the measured fission decay probability ratios of $^{234}\mathrm{Pa}$ and $^{236}\mathrm{U}$ compound nuclei using the surrogate ratio method. The $^{233}\mathrm{Pa}$$(n,f)$ cross section data from the present experiment along with the data from the literature, covering the neutron energy range of 1.0 to 16.5 MeV have been compared with the predictions of statistical model code EMPIRE-2.19. While the present data are consistent with the model predictions, there is a discrepancy between the earlier experimental data and EMPIRE-2.19 predictions in the neutron energy range of 7.0 to 10.0 MeV.

The measurement of the giant electric dipole resonance built on the isobaric analog state in the self-conjugate even-even nucleus $^{12}\mathrm{C}$ is reported covering a wide excitation energy range. This is done using the $^{11}\mathrm{B}$($p,\ensuremath{\gamma}$) reaction leading to the 15.1 MeV $T=1$ state in $^{12}\mathrm{C}$ over a proton energy range of 7 to 24.5 MeV. Two resonances of 1.3 and 2 MeV widths are observed at excitation energies of 24.4 and 28.8 MeV superimposed on a smoothly varying cross section. The \ensuremath{\gamma} transitions from both the resonances are assigned $E1$ multipolarity. The structured $T=0$ component of the $E1$ strength distribution is thus very different from that built on the first $T=1$ state in the neighboring nucleus $^{14}\mathrm{N}$ and those built on the ground states of $^{12}\mathrm{C}$ and $^{14}\mathrm{C}$.

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

The angular distributions of cross sections for the reaction $^{13}\mathrm{C}$${(}^{3}$He${,}^{4}$He${)}^{12}$C leading to ground state and first excited 4.44 MeV, ${2}^{+}$ state of $^{12}\mathrm{C}$ have been measured at sub-Coulomb energies of ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.}$=1.20 and 1.05 MeV. The angular distributions are asymmetric with respect to 90\ifmmode^\circ\else\textdegree\fi{} and anisotropies are also found to be much larger than those expected from compound nuclear processes. Analyses of the data, with assumptions of direct transfer processes, by exact finite range distorted wave Born approximation calculations show the presence of interference of two modes of direct transfer mechanisms of neutron transfer and $^{9}\mathrm{Be}$ cluster transfer from the target $^{13}\mathrm{C}$ to the projectile $^{3}\mathrm{He}$. These direct transfer calculations are in good agreement with the angular distributions and yield the value of the ratio of three nucleon spectroscopic strengths of first excited state to ground state of $^{12}\mathrm{C}$ in good agreement with the value predicted from structure calculations.

Coulomb effects during the interaction of light deformed projectile nuclei with a heavy collision partner have been predicted to modify the fusion barrier distribution leading to a hindrance in the sub-barrier fusion cross section. In order to verify this experimentally, we have determined the fusion barrier distributions from the measurement of quasielastic excitation functions for {sup 16}O(spherical)+{sup 115}In, {sup 28}Si(oblate)+ {sup 115}In, and {sup 30}Si(prolate)+ {sup 115}In systems. For {sup 16}O+{sup 115}In system, the fusion barrier distribution is single peaked, whereas for {sup 28}Si+{sup 115}In and {sup 30}Si+{sup 115}In systems, one observes broadening and well defined structures in fusion barrier distribution, which could be explained by coupled-channel calculations performed using the CCFULL code after including deformation and Coulomb effects on the projectile in the field of target nucleus.