arXiv subjects

Balaram Dey

Publications and source records attributed to Balaram Dey.

At least 19 recordsLinked to original sources

arXiv2025

Unraveling the anomaly in the production of $^{60}$Fe nucleus in massive stars

The production of $^{60}$Fe is crucial for nucleosynthesis in massive stars and supernovae. In this work, by using the microscopic EP+IPM (exact pairing plus the independent-particle model) for the nuclear level density (NLD) and extended EP+PDM (exact pairing plus phonon damping model) for the $\gamma$-ray strength function (gSF), we re-evaluate the substantial enhancement of $^{60}$Fe production recently reported in {\it A. Spyrou et al., Nat. Comm. {\bf 15}, 9608 (2024)}, which was attributed to an unexpectedly large Maxwellian-averaged cross section (MACS). Our analysis demonstrates that this enhancement indeed originates from the choice of NLD, which, despite being constrained to reproduce the total NLD and gSF data, lacks a reliable spin dependence, a critical input for Hauser-Feshbach calculations of nuclear reaction rate. In contrast, our predictions yield a significantly lower MACS, calling the claimed enhancement into question. In particular, our approach highlights the microscopic nature of the low-energy enhancement of the gSF, the so-called upbend resonance, which arises from strong particle-particle ($pp$) and hole-hole ($hh$) excitations that emerge only at finite temperature, thereby further reinsisting on the invalidity of the Brink-Axel hypothesis in this low-energy region. Overall, our study reopens the question on the long-standing problem of $^{60}$Fe production in massive stars.

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arXiv2025

Analysis of (p,$\gamma$) capture cross-sections relevant to p-process using TALYS for A=75-110

The proton capture (p, $\gamma$) cross-sections for eight different atomic nuclei in the mass region A=75-110 were calculated within the nuclear reaction model code TALYS. For all the reactions, we tested different combinations of inputs for level density (l.d) parameter and gamma strength function ($\gamma_{sf}$). Finally, it was observed that application of hybrid input in TALYS (macroscopic l.d and microscopic or semi-microscopic $\gamma_{sf}$ or in abbreviation mac-mic) resulted successful agreement of theoretical prediction with the existing experimental data. Isospin correction was also incorporated in a few cases which improved the matching if the centre of mass energy reaches the threshold energy of the opening of (p,n) channel. The corresponding thermonuclear reaction rates were calculated for all the nuclei and some discrepancies were found with the prediction of the NON-SMOKER code. Using the particular mac-mic input combination, the cross-section and reaction rate for the nuclei $^{92}$Nb and $^{92}$Mo are calculated within TALYS. These two nuclei lack experimental data but are highly important for understanding early solar system processes. This is a rare attempt to explain the p-capture cross-section of different p-nuclei (A=75-110 range) with similar set of input combinations in TALYS, which may help to remove the uncertainty generated due to the variation of input parameters within nuclear statistical model code

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arXiv2023

Measurement of the Hoyle State Radiative Transition Width

The radiative decay of the Hoyle state is the doorway to the production of heavier elements in stellar environment. Here we report, an exclusive measurement of electric quadruple (E$_2$) transitions of the Hoyle state to the ground state of $^{12}$C through the $^{12}$C(p, p$^\prime$$\gamma$$\gamma$)$^{12}$C reaction. Triple coincidence measurement yields a value of radiative branching ratio $\Gamma_{rad}$/$\Gamma$ = 4.01 (30) $\times$ 10$^{-4}$. The result has been corroborated by an independent experiment based on the complete kinematical measurement $via.$ $^{12}$C(p, p$^\prime$)$^{12}$C reaction ($\Gamma_{rad}$/$\Gamma$ = 4.04 (30) $\times$ 10$^{-4}$). Using our results together with the currently adopted values of $\Gamma_{\pi}$(E$_0$)/$\Gamma$ and $\Gamma_{\pi}$($E_0$), the radiative width of the Hoyle state is found to be 3.75 (40) $\times$ 10$^{-3}$ eV. We emphasize here that our result is not in agreement with 34 $\%$ increase in the radiative decay width of the Hoyle state measured recently but consistent with the currently adopted value.

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arXiv2022

Collective enhancement in nuclear level density of $^{72}$Ga and its effect on $^{71}$Ga(n, $γ$)$^{72}$Ga capture cross-section

The $γ$-gated proton spectra measured in the reactions $^{64}$Ni($^{9}$Be, p2n)$^{70}$Ga and $^{64}$Ni($^{9}$Be, pn)$^{71}$Ga, have been utilized to obtain the nuclear level density (NLD) of $^{71}$Ga and $^{72}$Ga nuclei by using the statistical model (SM) calculations. It is seen that the $γ$-gated proton spectrum are reasonably explained by using the large value of the inverse level density parameter ($k$ = 11.2 MeV) in the NLD prescription of the Fermi gas (FG) model. The large value of $k$ is indicative of the rotational enhancement, which is consistent with the earlier results in other mass regions. Furthermore, a rotational enhancement factor has been included in the NLD and used in the SM calculation keeping the systematic value of $k$=8.6 MeV and it explains the $γ$-gated proton spectrum nicely. The result clearly indicates the presence of collective enhancement in NLD. Subsequently, the NLD with collective enhancement has been utilized in the TALYS calculation, for the first time, to calculate the $^{71}$Ga(n, $γ$)$^{72}$Ga capture cross-section. It is observed that, while the FG model without the collective enhancement in the NLD for $^{72}$Ga under predicts the capture data, with the rotational enhancement correction the FG model over predicts the data by similar amount at higher energies. However, in the energy range of 0.01 MeV to 0.1 MeV, the FG model corrected for rotational enhancement describes the data quite well. Thus, the present work indicates that collective enhancement, whenever required, should be taken into account fro proper description of low energy capture cross section data.

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arXiv2021

Enhanced symmetry energy bears universality of the r-process

The abundance of about half of the stable nuclei heavier than iron via the rapid neutron capture process or $r$-process is intimately related to the competition between neutron capture and $β$-decay rates, which ultimately depends on the binding energy of neutron-rich nuclei. The well-known Bethe-Weizsäcker semi-empirical mass formula\cite{weiz,bethe} describes the binding energy of ground states -- i.e. nuclei with temperatures of $T\approx0$ MeV -- with the symmetry energy parameter converging between $23-27$ MeV for heavy nuclei. Here we find an unexpected enhancement of the symmetry energy at higher temperatures, $T\approx0.7-1.0$ MeV, from the available data of giant dipole resonances built on excited states. Although these are likely the temperatures where seed elements are created -- during the cooling down of the ejecta following neutron-star mergers\cite{mergersnucleo} or collapsars\cite{collapsar} -- the fact that the symmetry energy remains constant between $T\approx0.7-1.0$ MeV, suggests a similar trend down to $T\approx0.5$ MeV, where neutron-capture may start occurring. Calculations using this relatively larger symmetry energy yield a reduction of the binding energy per nucleon for heavy neutron-rich nuclei and inhibits radiative neutron-capture rates. This results in a substantial close in of the neutron dripline -- where nuclei become unbound -- which elucidates the long sought universality of heavy-element abundances through the $r$-process; as inferred from the similar abundances found in extremely metal-poor stars and the Sun.

astro-ph.HE↗

arXiv2021

Study evolution of fragment energy spectrum in compound and elemental absorber with thickness via effective charge correction

The energy loss behaviour of fission fragments (FF) from $^{252}$Cf(sf) in thin Mylar ($H_8 C_{10} O_4$) and Aluminium absorber foils have been revisited. The aim is to investigate the observed change in the well known asymmetric energy of spontaneous fission of $^{252}$Cf as the fragments pass through increasingly thick absorber foils. Two different types of absorbers have been used: one elemental and the other an organic compound. The stopping powers have been determined as a function of energy for three fragment mass groups with average masses with $ $ = 106.5, 141.8, 125.8 corresponding to light, heavy and symmetric fragment of $^{252}$Cf. Using the effective charge (Z$_{eff}$) in the stopping power relation in the classical Bohr theory best describes the stopping power data. Spectrum shape parameters, subsequently have been extracted from the energy spectra of fission fragments for different foil thickness. The effective charge (Z$_{eff}$) correction term determined from the stopping power data is then used in the simulation for the absorber thickness dependence of the shape parameters of the energy spectrum. The present simulation results are compared with the TRIM prediction. The trends of the absorber thickness dependence of the spectrum shape parameters, for both Mylar and Aluminium are well reproduced with the present simulation.

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arXiv2020

Nuclear level density of $^{69}$Zn from gamma gated particle spectrum and its implication on $^{68}$Zn(n, $γ$)$^{69}$Zn capture cross-section

Evaporated $α$-spectra have been measured in coincidence with low energy discrete $γ$-rays from residual nucleus $^{68}$Zn populated in the reaction $^{64}$Ni($^9$Be,$α$n)$^{68}$Zn at $E(^9$Be) = 30 MeV producing $^{73}$Ge compound nucleus. Low energy $γ$-gated $α$-particle spectra, for the first time, have been used to extract the nuclear level density (NLD) for the intermediate $^{69}$Zn nucleus in the excitation energy range of E $\approx$ 5-20 MeV. The slope of NLD as a function of excitation energy for $^{69}$Zn matches nicely with the slope determined from RIPL estimates for NLD at low energies and the NLD from neutron resonance data. Extracted inverse NLD parameter (k = A/$\widetilde{a}$) has been used to determine the nuclear level density parameter value $a$ at neutron separation energy $S_n$ for $^{69}$Zn. Total cross-section of $^{68}$Zn(n,$γ$) capture reaction as a function of neutron energy is then estimated employing the derived $a(S_n)$ in the reaction code TALYS. It is found that the estimated neutron capture cross-section agrees well with the available experimental data without any normalization. The present result indicates that experimentally derived nuclear level density parameter can constrain the statistical model description of astrophysical capture cross-section and optimize the uncertainties associated with the astrophysical reaction rate

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arXiv2019

Characterization of an electrically cooled BEGe detector till E$_γ\sim7$ MeV

An electrically cooled Broad Energy Germanium (BEGe) detector has been characterized in the energy range E$_γ$ $\sim$ 0.122 - 7 MeV by utilizing the $γ$- rays emitted by a short-lived resonance state in $^{15}$O populated through $^{14}$N(p,$γ$) reaction and standard radioactive source ($^{152}$Eu). The experimental results have been reproduced through simulations with GEANT4 code, including vendor specified detector geometry along with the detailed construction of the target holder flange, to delineate the effects of the holder at various energies and detector position. Later the efficiency with a bare point source has been simulated. It has been found that the electrically cooled BEGe detector is suitable for usage in the $γ$-ray spectroscopy as well as for the study of resonance phenomena in nuclear astrophysics.

physics.ins-det↗

arXiv2019

Study of radioactivity built-up and decay with singles time-stamped data

Time-stamped data have been used to estimate the decay half-lives of radioactive 118mSb and 64,66,68Ga nuclei. These nuclei are populated through the reaction 4He (Elab = 32 MeV) + nat In and p (Elab = 10 MeV) + natZn, respectively. The g -rays emitted by the excited daughter nuclei are detected by a single high purity germanium (HPGe) detector and the data are acquired using a CAEN 5780M desktop digitizer. Half-lives of different orders of magnitudes for the above mentioned nuclei are obtained from both the decay of parent and the growth of daughter nuclei. It is observed that the half-lives obtained from both these techniques match fairly well and also are consistent with the reported values. It is demonstrated that the time-stamped data can be useful while studying certain half-lives which are too long for measurement using in-beam electronic technique and too short for decay studies in off-beam methods. The data also have a special relevance for constant monitoring of beam current and beam-tuning.

physics.ins-det↗

arXiv2018

Experimental signature of collective enhancement in nuclear level density

We present a probable experimental signature of collective enhancement in the nuclear level density (NLD) by measuring the neutron and the giant dipole resonance (GDR) $γ$ rays emitted from the rare earth $^{169}$Tm compound nucleus populated at 26.1 MeV excitation energy. An enhanced yield is observed in both neutron and $γ$ ray spectra corresponding to the same excitation energy in the daughter nuclei. The enhancement could only be reproduced by including a collective enhancement factor in the Fermi gas model of NLD to explain the neutron and GDR spectra simultaneously. The experimental results show that the relative enhancement factor is of the order of 10 and the fadeout occurs at $\sim$ 14 MeV excitation energy, much before the commonly accepted transition from deformed to spherical shape. We also explain how the collective enhancement contribution changes the inverse level density parameter ($k$) from 8 to 9.5 MeV observed recently in several deformed nuclei.

nucl-ex↗

arXiv2017

Neutron response of PARIS phoswich detector

We have studied neutron response of PARIS phoswich [LaBr$_3$(Ce)-NaI(Tl)] detector which is being developed for measuring the high energy (E$_γ$ = 5 - 30 MeV) $γ$ rays emitted from the decay of highly collective states in atomic nuclei. The relative neutron detection efficiency of LaBr$_3$(Ce) and NaI(Tl) crystal of the phoswich detector has been measured using the time-of-flight (TOF) and pulse shape discrimination (PSD) technique in the energy range of E$_n$ = 1 - 9 MeV and compared with the GEANT4 based simulations. It has been found that for E$_n$ $>$ 3 MeV, $\sim$ 95 \% of neutrons have the primary interaction in the LaBr$_3$(Ce) crystal, indicating that a clear n-$γ$ separation can be achieved even at $\sim$15 cm flight path.

physics.ins-det↗

arXiv2017

Search for Jacobi shape transition in A $\sim30$ nuclei

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

nucl-ex↗

arXiv2017

Experimental Determination of $η$/$s$ for Finite Nuclear Matter

We present, for the first time, simultaneous determination of shear viscosity ($η$) and entropy density ($s$) and thus, $η/s$ for equilibrated nuclear systems from $A$ $\sim$ 30 to $A$ $\sim$ 208 at different temperatures. At finite temperature, $η$ is estimated by utilizing the $γ$ decay of the isovector giant dipole resonance populated via fusion evaporation reaction, while $s$ is evaluated from the nuclear level density parameter (${a}$) and nuclear temperature ($T$), determined precisely by the simultaneous measurements of the evaporated neutron energy spectra and the compound nuclear angular momenta. The transport parameter $η$ and the thermodynamic parameter $s$ both increase with temperature resulting in a mild decrease of $η$/$s$ with temperature. The extracted $η$/$s$ is also found to be independent of the neutron-proton asymmetry at a given temperature. Interestingly, the measured $η$/$s$ values are comparable to that of the high-temperature quark-gluon plasma, pointing towards the fact that strong fluidity may be the universal feature of the strong interaction of many-body quantum systems.

nucl-ex↗

arXiv2017

Giant Dipole Resonance studies in Ba isotopes at $\textbf{ E/A}\sim$ 5 MeV

Exclusive measurements of high energy $γ$-rays are performed in $\rm ^{124}Ba$ and $\rm ^{136}Ba$ at the same excitation energy ($\sim$ 49 MeV), to study properties of the giant dipole resonance (GDR) over a wider $N/Z$ range. The high energy $γ$-rays are measured in coincidence with the multiplicity of low energy $γ$-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 $γ$-ray spectra of $\rm ^{124}Ba$ can be explained with prolate deformation, whereas a single component Lorentzian function which corresponds to a spherical shape could explain the $γ$-ray spectra from $\rm ^{136}Ba$. The observed GDR width in $\rm ^{136}Ba$ is narrower compared to that of $\rm ^{124}Ba$. The statistical model best fit GDR cross sections are found to be in good 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--1.7MeV.

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arXiv2017

Signature of clustering in quantum many body systems probed by the giant dipole resonance

The present experimental study illustrates how large deformations attained by nuclei due to cluster formation are perceived through the giant dipole resonance (GDR) strength function. The high energy GDR $γ$-rays have been measured from $^{32}$S at different angular momenta ($J$) but similar temperatures in the reactions $^{4}$He(E$_{lab}$=45MeV) + $^{28}$Si and $^{20}$Ne(E$_{lab}$=145MeV) + $^{12}$C. The experimental data at lower J ($\sim$ 10$\hbar$) suggests a normal deformation, similar to the ground state value, showing no potential signature of clustering. However, it is found that the GDR lineshape is fragmented into two prominent peaks at high J ($\sim$ 20$\hbar$) providing a direct measurement of the large deformation developed in the nucleus. The observed lineshape is also completely different from the ones seen for Jacobi shape transition at high $J$ pointing towards the formation of cluster structure in super-deformed states of $^{32}$S at such high spin. Thus, the GDR can be regarded as a unique tool to study cluster formation at high excitation energies and angular momenta.

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arXiv2015

Experimental investigation on the temperature dependence of the nuclear level density parameter

The effect of temperature (T) and angular momentum (J) on the inverse level density parameter (k) has been studied by populating the compound nucleus $^{97}$Tc in the reaction $^{4}$He + $^{93}$Nb at four incident beam energies of 28, 35, 42 and 50 MeV. For all the four energies, the value of k decreases with increasing J. The T dependence of k has been compared for two angular momentum windows with different theoretical predictions as well as with FTBCS1 calculation which takes into account the quasiparticle-number fluctuations in the pairing field. Interestingly, the experimental data are in good agreement with the theoretical calculations at higher J but deviate from all the calculations at lower J.

nucl-ex↗

arXiv2014

Examination of level density prescriptions in the interpretation of high energy gamma-ray spectra

High energy $γ$-ray spectra measured by our group involving the compound nuclei (CN) $^{63}$Cu at excitation energy ($E^*$) $\sim$ 36 MeV with average angular momentum ($J$) = 12 - 17 $\hbar$, $^{97}$Tc at $E^* \sim$ 29 - 50 MeV with $J$ = 12 - 14 $\hbar$, $^{113}$Sb at $E^*$ = 109 MeV and 121 MeV with $J$ = 49 - 59 $\hbar$ and $^{201}$Tl at $E^*$ = 39.5, 47.5 MeV with $J$ = 18 - 24 $\hbar$ have been analyzed utilizing the level density prescriptions of (i)Ignatyuk, Smirenkin and Tishin (IST), (ii)Budtz-Jorgensen and Knitter (BJK), and (iii) Kataria, Ramamurthy and Kapoor (KRK). These three prescriptions have been tested for correct statistical model description of high energy $γ$-rays in the light of extracting the giant dipole resonance (GDR) parameters at low excitation energy and spin where shell effects might play an important role as well as at high excitation energy where shell effects have melted. Interestingly, only the IST level density prescription could explain the high energy $γ$-ray spectra with reasonable GDR parameters for all the four nuclei.

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arXiv2014

Probing the critical behavior in the evolution of GDR width at very low temperatures in A~100 mass region

The influence of giant dipole resonance (GDR) induced quadrupole moment on GDR width at low temperatures is investigated experimentally by measuring GDR width systematically in the unexplored temperature range $T$=0.8-1.5 MeV, for the first time, in $A$ $\sim$ 100 mass region. The measured GDR widths, using alpha induced fusion reaction, for $^{97}$Tc confirm that the GDR width remains constant at the ground state value up to a critical temperature and increases sharply thereafter with increase in $T$. The data have been compared with the adiabatic Thermal Shape Fluctuation Model (TSFM), phenomenological Critical Temperature Fluctuation Model (CTFM) and microscopic Phonon Damping Model (PDM). Interestingly, CTFM and PDM give similar results and agree with the data, whereas the TSFM differs significantly even after incorporating the shell effects.

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