R&D Activities of the Nuclear Physics Group at the

UGC-DAE CSR, Kolkata Centre

(Updated on February, 2015)

 

Group Members

 

Dr. A.K. Sinha

Dr. S.S. Ghugre

Dr. R. Raut

Mr. K. Basu

 

Mrs. R. Bhattacharjee

Mr. S.S. Bhattacharjee

Mr. S.K. Das

Mr. S. Samanta

 

 

 

The research interests of the Nuclear Physics Group at the Kolkata Centre of the UGC-DAE CSR incorporate a wide vista of endeavours. Following is a succinct summary of the same.

Nuclear structure studies using heavy-ion induced fusion-evaporation reactions

Spectroscopy of Nuclei at the sd-fp Interface

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.

 

 

Production of 32P in a transfer reaction

[EPJA 29, 151 (2006)]

Production of 32P in fusion-evaporation reaction

[Phys. Rev C 80, 034326 (2009)]

Fusion reaction has resulted in the considerable population of higher angular momentum states in 32P

 

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".

 

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 and is carried out using a wide range of techniques, depending on the range of lifetimes being addressed. 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. Several codes are available for analysis of the DSAM data and the LINESHAPE package [J.C. Wells et al. (1991)] is one that is extensively used across the globe. 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. 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.

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.

 

Stopping powers calculated using the prescriptions indicated in the legend. The difference between the SRIM calculated stopping powers with the existing prescriptions in the DECHIST is to be noted.

 

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.

 

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

 

Incorporating TRIM Monte Carlo Simulations for Lifetime Analysis

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, thus dispensing the simulations carried out within the latter. The inclusion of TRIM simulations in the LINESHAPE operation requires a substantial amount of intermediate processing. This is owing to the fundamental differences between the objectives of the TRIM package, dedicated for investigation of ion transport in matter, and the Monte Carlo processes carried out as a part of the Doppler shape analysis. The former assigns a common starting point for all the trajectories and dumps the same at definite energy intervals. 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, the output of the TRIM simulations may contain unfinished trajectories that require to be eliminated in DSAM analysis. A series of programs have thus been developed to cater to the processing of the TRIM results for application into lifetime analysis. These endeavours have eventuated into a developed tool for Doppler shape analysis with an unprecedented flexibility in the choice of the target and the backing that can now be faithfully represented in the DSAM analysis using LINESHAPE code.

We welcome sharing and usage of these codes in the community and shall be happy to be of help in any relevant endeavour. Communications pertaining to the same may please be directed to Dr. A.K. Sinha (aks@delta.iuc.res.in) or Dr. S.S. Ghugre (ssg@alpha.iuc.res.in) or Dr. R. Raut (rraut@alpha.iuc.res.in).

Large Basis Shell Model Calculations

Our group has been actively pursuing large basis shell model calculations using the code NuShell and NuShellX@MSU [Alex Brown et al.], particularly in the domain of sd-pf nuclei. Improved computational infrastructure for these calculations is now available at the Centre with a High Performance Computing machine facilitated with 80-cores on 10 nodes and 576 GB memory. The setup has facilitated calculation of negative parity states in the sd-pf domain, as a maiden instance in some of the nuclei. These states represent cross-shell excitations and are indicative of the sd-pf shell gap, thus providing a critical input to the model calculations in this regime.

Anyone interested in using the computing facility at the Kolkata Centre may kindly communicate with Dr. S.S. Ghugre (ssg@alpha.iuc.res.in).

Details of the activities in the domain of nuclear structure research can be found in the following recent publications.

1.Level lifetimes in 32P obtained using the Doppler-shift attenuation method with thick molecular targets. R. Bhattacharjee, S.S. Bhattacharjee, K. Basu, P.V. Rajesh, R. Raut, S.S. Ghugre, D. Das, A.K. Sinha et al. [Physical Review C89, 024324(2014)]

 

 2. Nuclear structure study of 26Mg following heavy-ion-induced fusion-evaporation reaction. S.S. Bhattacharjee, R. Bhattacharjee, R. Chakrabarti, R. Raut, S.S. Ghugre, A.K. Sinha et al. [Physical Review C89, 024324(2014)]

 

3. Structure of 32P at high spins. R. Chakrabarti, S. Mukhopadhyay, R. Bhattacharjee, S.S. Ghugre, A.K. Sinha et al. [Physical Review C84, 054325(2011)]

 

4. Experimental study of nuclei in the vicinity of the island of inversion through the fusion-evaporation reaction. R. Chakrabarti, S. Mukhopadhyay, Krishichayan, A. Chakraborty, A. Ghosh, S. Ray, S.S. Ghugre, A.K. Sinha et al. [Physical Review C80, 034326(2009)]

 

Investigations in the domain of nuclear dynamics

The group, under the guidance of Dr. A.K. Sinha, has recently embarked on studies pertaining to various facets of nuclear reactions research. The two principal problems being pursued are as follows.

 

Fission survivality across N=126 shell closure

 

Lack of stabilizing effect of N=126 against fission has been reported in literature and is in sharp contrast to the predictions of the statistical model calculations using the intrinsic level densities. The dichotomy has been interpreted in the light of the Collective Enhancement in the Level Density (CELD) wherein it has been implied that the CELD is essentially the same at the saddle point deformation (fission channel) for all nuclei, but differs substantially in the ground-state deformation of an evaporation channel depending upon the magicity of the neutron number. The lack of shell stabilization against fission observed for the N = 126 shell is expected to impact the production cross sections of spherical superheavy nuclei around magic neutron no. N = 184 and necessitates a closer investigation that can unambiguously confirm the influence of CELD. It is proposed to pursue the probe through reactions producing compound nuclei across the N = 126 shell closure through asymmetric combinations of target and projectile, asymmetries being more than the respective Bussinaro-Gallone (typically represented by aBG) parameter, in order to ascertain the pure compound nucleus process and restrict the possibility of non-compound fission plaguing the acquired results.

 

The proposal has been presented at the Accelerator Users Workshop at IUAC, New Delhi and has been approved for a beam time at the Pelletron facility.

 

Energy and angular momentum dependence of heavy-ion fusion potential

 

Heavy-ion fusion reactions around the barrier exhibit nuclear structure effects owing to the channel couplings. Description based on optical model indicates a relatively rapidly changing energy dependent attractive real potential near the barrier. However, it has been established [Mohanty et al. Phys. Rev. Lett. 65, 1096(1990)] that, apart from the energy dependence, the angular momentum dependence of the barrier also needs to be considered. The group is pursuing calculations, based on this model proposed by Mohanty et al., for energy and angular momentum dependent barriers with a new algorithm wherein the barrier heights are not a priori parameterized but the fusion cross-section data are inverted to extract the same. A code has been developed for the purpose, that accepts the charge and mass of the projectile and the target, the curvature and the radius of the barrier, the centre-of-mass energy and the corresponding fusion cross section, in order to output the barrier height as a function of energy.

 

 

DSP based pulse processing and data acquisition system for nuclear spectroscopy

 

The recent campaign of INGA at TIFR has witnessed a radical transformation in the methodology adopted for pulse processing and data acquisition associated with the spectrometer. This was the maiden instance in the decade long history of the facility that the associated electronics and acquisition system have been based on digitizers, being opted at detector arrays across the globe, primarily owing to their compactness and superior processing speed that befits the increased data rates expected from the large arrays.

 

Our group has been one of the key participants of the INGA campaigns and has actively contributed in the installation of the same at different accelerator centers. Following the implementation of the new digitizer based processing and acquisition system at the TIFR campaign, the group has been working on development of codes to probe the quality of the acquired data as well as programs to simulate performance of the pulse processing algorithms adopted in the digitizers. The simulation of digitizer performance has been carried out using contemporary computational toolkits like MATLABŪ and ROOT and has been part of some of the M.E. thesis projects of the School of Nuclear Studies and Applications (Jadavpur University), carried out at the Kolkata Centre. Part of these activities have been reported in,

 

1. Digital Pulse Processing Simulations in MATLAB & OCTAVE for Nuclear Spectroscopy.  A. K. Tiwari, R. Raut, K. Basu, S. S. Ghugre, A. Dutta, A. K. Sinha [Proceedings of DAE-BRNS Symposium on Nuclear Physics 57, 944(2012)]

 

2. Development of Zero Cost Digitizer based Data Acquisition System. A. Jana, S. Singh, A. Gupta, S. Das, K. Basu, R. Raut, S.S. Ghugre, A.K. Sinha. [Proceedings of DAE-BRNS Symposium on Nuclear Physics 59, 970(2014)]

 

The probe into the data acquired from the TIFR campaign, using the programs developed by the group, has helped identifying the avenues for optimization of the digitizer based system for the subsequent INGA campaigns. In the light of this understanding, a pulse processing and data acquisition system based on digitizers has been envisaged and procured by our group for implementation in the INGA setup scheduled to be hosted at VECC. The system and the operating firmware have resulted from an elaborate technical discussion within the group and with the interested manufacturers. The primary impetus has been to acquire a system characterized with features identical, in all feasible aspects, to the existing NIM / CAMAC based systems that are being dispensed with. The digitizer system is currently being tested offline at the Centre.

 

 

Detector simulation using GEANT4

 

Our group has been working on the simulation of the Clover detector, being used in INGA, with an impetus to envision the performance of the array at hitherto experimentally unexplored domains. At the heart of this exercise is a simplistic representation of the complex Clover geometry that has been adopted to simulate the detector characteristics (efficiency, hit pattern, addback factor etc.) and compare the same with available experimental data. The simulations have been carried out for conventional as well as segmented (two and four folds) Clovers. The efforts have been / are being extended to the development of Doppler correction algorithms and calculation of Doppler shape for a gamma transition de-exciting a level with a known lifetime. Part of these developments are being reported in the manuscript,

 

Simplistic Simulations for the Performance of a Clover Detector. S.S. Bhattacharjee, R. Bhattacherjee, R. Raut, S.S. Ghugre, A.K. Sinha, Z. Elekes  (Under preparation)

 

 

Clover geometry and energy dependence of the addback factor from the simulations by our group.

 

 

Collaborations

Our group members have been / are part of several national and international collaborations and have participated in the related efforts, as summarized here.

1. Search for wobbling band in 135Pr (Notre Dame University, USA). The wobbling phenomenon has been identified as one of the signatures of Triaxiality in the nuclei and has been zealously pursued in the recent years. The present measurements have been carried out at the GAMMASPHERE (Argonne National Laboratory, USA) and the INGA setup stationed at TIFR. The results have been accepted for publication in the Physical Review Letters.

(i) Transverse wobbling in 135Pr. J. T. Matta, U. Garg, A. D. Ayangeakaa, S. Frauendorf, D. Patel, and K. W. Schlax, R. Palit, S. Saha, J. Sethi, and T. Trivedi, S. S. Ghugre, R. Raut, and A. K. Sinha et al. (Accepted in Phys. Rev. Lett.)

2. Nuclear structure studies in the A~140 region (SINP, Kolkata). Experiments pertaining to the structural investigation of nuclei in the mass 140 region have been carried out at the INGA campaigns in IUAC (New Delhi) and TIFR (Mumbai). Some of the publications from these studies are,

(i) Shape co-existence in the near-spherical 142Sm nucleus. S. Rajbanshi, Abhijit Bisoi, Somnath Nag, S. Saha, J. Sethi, T. Trivedi, T. Bhattacharjee, S. Bhattacharyya, S. Chattopadhyay, G. Gangopadhyay, G. Mukherjee, R. Palit, R. Raut, M. Saha Sarkar, A.K. Singh, A. Goswami [Physical Review C89, 014315(2014)]

 

(ii) Multiple magnetic rotational bands based on proton alignment in 143Eu. S. Rajbanshi, Abhijit Bisoi, Somnath Nag, S. Saha, J. Sethi, T. Bhattacharjee, S. Bhattacharyya, S. Chattopadhyay, G. Gangopadhyay, G. Mukherjee, R. Palit, R. Raut, M. Saha Sarkar, A.K. Singh, T. Trivedi, A. Goswami [Physical Review C90, 024318(2014)]

 

3. Cross-section measurements using gamma-ray beams (Triangle Universities Nuclear Laboratory, USA). Cross-section measurements of significance in nuclear astrophysics and other domains have been carried out using the High Intensity Gamma-ray Source (HIGS) facility at the Triangle Universities Nuclear Laboratory (TUNL), USA. Some of the recent publications from these studies are as follows.

(i) Cross-Section Measurements of 86Kr(g,n) Reaction to Probe the s-Process Branching at 85Kr. R. Raut, A.P. Tonchev et al. [Physical Review Letters 111, 112501(2013)]

 

(ii) Photodisintegration Cross Section of the Reaction 4He(g,p)3H between 22 and 30 MeV. R. Raut, W. Tornow et al. [Physical Review Letters 108, 042502(2012)]

4. INGA Collaboration. Our group has been one of the key participants of the INGA collaboration and has substantially contributed to the resources and the man power in installation and operation of the array at the accelerator centers across the country. Further, in compliance with the mandate of the Consortium, our group has actively supported the experimental endeavours of the University users at the INGA campaigns in VECC, Kolkata and TIFR, Mumbai. The in-house activities of the group, based on the INGA facility, have been detailed in the preceding text. In recent years, the group has also been instrumental in organizing workshops, of relevance to the community, pertaining to the logistics and the experimental proposals for the next campaign at VECC (May, 2012 and February, 2014, VECC) or review of the progress of the array through the decade or subsequent upgrade of the facility as the next generation tool for gamma spectroscopy efforts in the country (March, 2013, TIFR and February, 2014, VECC).  The upgrade of the facility is being actively deliberated by the group and has been presented in the aforesaid events.

 

 

 

Outlook

Our group has several proposals approved for beam times at different accelerator centers in the country. These proposals pertain to a panorama of interests ranging from probing the structural aspects of nuclei in the A~60, ~150 and A~210 region to investigation of reaction dynamics through heavy-ion induced fission studies.

With the current activities in progress and proposals that are expected to be implemented in near future, we are looking forward to a prolific time in nuclear physics research ahead of us.