Research Pursuits of the Nuclear Physics


The research interests of the Nuclear Physics Group at the Kolkata Centre of Consortium incorporate a wide vista of endeavours, centered around the studies using heavy-ion induced fusion evaporation reactions. Following is a succinct summary of the same



The group is one of the first to have embarked on a programme to investigate the structure of the A~30 nuclei, at the interface of the sd and fp shells, using heavy-ion induced fusion-evaporation reactions.

A set of experiments have been carried out using the Indian National Gamma Array (INGA), as the detection system, during the campaigns of the spectrometer at different accelerator centers (IUAC, TIFR) in the country.

Neutron-rich 18O target, available in the form of thick Ta2O5 layer on a Ta foil, has been used in the measurements while the chosen heavy-ion beam has been 18O or 16O or 13C, depending on the particular system of interest.

Analysis of the acquired data has been carried out using programs developed and/or extensively modified by the group. These investigations have facilitated a systematic perspective on the structure of these transitional nuclei between the valley of stability and the "island of inversion".

The thesis of Ritwika Chakraborty is based on these investigations


Development of a Modified Approach for Lifetime Measurements using DSAM

Measurement of nuclear level lifetimes is one of the key components in nuclear structure research. The Doppler Shift Attenuation Method (DSAM) is one that is wielded to determine lifetimes in the range of few tens of fs to few ps. The method is based on analysis of the Doppler shaped / shifted gamma-ray transitions emitted from de-exciting nuclei, produced in a nuclear reaction, as they slow down in the target and the backing medium.

Conventionally DSAM is carried out with a thin target, wherein the production of residue occurs, on a thick high-Z elemental backing that principally contributes to the stopping process. Simulation of the latter is understandably one of the crucial inputs in DSAM analysis and is also identified as one of the principal sources of uncertainty on the resulting lifetimes.

The LINESHAPE package [J.C. Wells et al. (1991)] is one of the codes which is extensively used across the globe fo r the analysis of DSAM data.. However, the code, in its original form, allows only elemental target and backing, to be used for stopping simulations, and models the stopping powers based on old alpha and proton stopping data.  

Modification of the LINESHAPE code has been one of the recent thrust areas for our group. These endeavours have been primarily intended to

  • incorporate molecular stopping media,
  • updated stopping powers and
  • thick target setup in DSAM analysis.



One of the major modificative exercises has been to include the stopping powers calculated by the SRIM software directly into the lifetime analysis. The stopping power is believed to be one of the principal sources of uncertainty in lifetime determination and the same calculated using a contemporary, updated and benchmarked code, like SRIM, is understandably a much desired approach .

Further extension of the code has been implemented to embody DSAM setup with a thick target that provides for both the target and the backing. The effect of changing beam energy as it traverses the thickness of the target and the consequent change in the cross section for the residue of interest has been assimilated in the modified code.



The exercise was initiated in the light of the aforesaid spectroscopic investigations of sd-pf nuclei with thick molecular target, unconventional in DSAM measurements, but eventually comprehended to be of relevance even in typical setups.

Stopping powers calculated using the prescriptions indicated in the legend.

Incorporation of cross section dependence on the changing beam energy as the latter traverses the thickness of the target

The thesis of Smt Rajarshi Bhattacharjee is based on these investigations

In a further stride towards ameliorating the stopping calculations in DSAM analysis, Monte Carlo simulations of the stopping histories, carried out by the SRIM (TRIM) program, have been directly incorporated in the LINESHAPE package, by rendering them into a format compatible with the LINESHAPE operations.

The simulations for DSAM analysis would require trajectories distributed over the thickness of the target and, for compatibility with the LINESHAPE operation, should have the trajectory information at uniform time steps.

Further, these results have to be folded in with the nusances of reaction kinetics, before being finally used in the LINESHAPE analysis.

Incorporation of nuances of nuclear reations in LINESHAPE analysis

These developments are detailed in the doctoral thesis of Shri Soumya kanti Das


Spectroscopy of transitional nuclei at the interface of the sd-pf shells.
The nuclei at the interface of the sd-pf orbitals present us with a unique scenario wherein the level structure of these nuclei could be explained on the basis of the spherical shell model and at the same time they have sufficient number of valence nucleons to favour the observation of deformed states.

This motivated us to revisit the level structures of nuclei such as 26Mg, 29Si, 41Ca, using heavy-ion fusion evaporation reactions and a state of the art contemporary detecion system, viz. INGA.

The present investigation establishes the possibility to interpret the observed sequences in these transitional nuclei along with the deformation characteristics within the shell model framework. Choice of an appropriate model space and the associated effective interactions along with a judicious truncation scheme remain the crucial inputs for such an exercise.

Level scheme of 26Mg as deduced from the prresent work.

The thesis of Shri Soumendu Shekar Bhattacharjee is based on these investigations


Exploring the Level Structures Around the Doubly Magic 56Ni Core
Nuclear structure pursuits in nuclei in the vicinity of shell closures have been motivated by the quest for observation of either deformed structures (resulting from collectivity) or structures involving the excitation of nucleons across the shell gaps (single particle excitations). With few nucleons outside the 56Nicore, the low-spin domain of these nuclei exhibit complex irregular excitation patterns, typical of shell-model configurations, based on the occupation of the p3/2, f5/2, p1/2, and g9/2 orbitals. At higher excitations, availability of high-spin orbitals may lead to observation of deformed rotational bands, based on multi-quasiparticle excitations across the N = Z = 28 closure.

The level structute of 64Cu and 61Ni is expected to be dominated by single particle excitations at low spins, with a possibility that at higher excitations availability of high-spin orbitals may lead to observation of deformed structures.

The nuclei were populated using the 7Li beam (obtained from the Pelletron LINAC Facility at TIFR, Mumbai) at an incident energy of 22–24 MeV on a 59Co target (on a Ta backing).

The level structure was deduced following the detailed analysis of both the angle dependent (for determination of the electromagnetic nature and multipolarity of the gamma rays) and angle independent data-set (for determination of the genetic relation of the gamma ray of interest in the level scheme) based on the observed coincidence information

Level scheme for 61Ni as deduced from present investigations.

These investigations constitute the doctoral research for Shri Saradindu Samanta

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