• R K Bhowmik

      Articles written in Pramana – Journal of Physics

    • High spin states in 63Cu

      B Mukherjee S Muralithar R P Singh R Kumar K Rani S C Pancholi R K Bhowmik

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      Excited states of 63Cu were populated via the $^{52}{\rm Cr} + {}^{16}{\rm O}$ (65 MeV) reaction using the gamma detector array equipped with charged particle detector array for reaction channel separation. On the basis of $\gamma-\gamma$ coincidence relations and angular distribution ratios, a level scheme was constructed up to $E_{x} = 7$ MeV and $J^{\pi} = 23/2^{(+)}$. The decay scheme deduced was interpreted in terms of shell model calculations, with a restricted basis of the $f_{5/2}$, $p_{3/2}$, $p_{1/2}$, $g_{9/2}$ orbitals outside a $^{56}_{28}$Ni core.

    • Hybrid recoil mass analyzer at IUAC – First results using gas-filled mode and future plans

      N Madhavan S Nath T Varughese J Gehlot A Jhingan P Sugathan A K Sinha R Singh K M Varier M C Radhakrishna E Prasad S Kalkal G Mohanto J J Das Rakesh Kumar R P Singh S Muralithar R K Bhowmik A Roy Rajesh Kumar S K Suman A Mandal T S Datta J Chacko A Choudhury U G Naik A J Malyadri M Archunan J Zacharias S Rao Mukesh Kumar P Barua E T Subramanian K Rani B P Ajith Kumar K S Golda

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      Hybrid recoil mass analyzer (HYRA) is a unique, dual-mode spectrometer designed to carry out nuclear reaction and structure studies in heavy and medium-mass nuclei using gas-filled and vacuum modes, respectively and has the potential to address newer domains in nuclear physics accessible using high energy, heavy-ion beams from superconducting LINAC accelerator (being commissioned) and ECR-based high current injector system (planned) at IUAC. The first stage of HYRA is operational and initial experiments have been carried out using gas-filled mode for the detection of heavy evaporation residues and heavy quasielastic recoils in the direction of primary beam. Excellent primary beam rejection and transmission efficiency (comparable with other gas-filled separators) have been achieved using a smaller focal plane detection system. There are plans to couple HYRA to other detector arrays such as Indian national gamma array (INGA) and $4\pi$ spin spectrometer for ER tagged spectroscopic/spin distribution studies and for focal plane decay measurements.

    • Nuclear structure of 216Ra at high spin

      S Muralithar G Rodrigues R P Singh R K Bhowmik P Mukherjee B Sethi I Mukherjee

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      High-spin states of 216Ra $(Z = 88,N = 128)$ have been investigated through 209Bi(10B, 3n) reaction at an incident beam energy of 55 MeV and 209Bi(11B, 4n) reaction at incident beam energies ranging from 65 to 78 MeV. Based on $\gamma \gamma$ coincidence data, the level scheme for 216Ra has been considerably extended up to $\sim 33\hbar$ spin and 7.2 MeV excitation energy in the present experiment with placement of 28 new 𝛾-transitions over what has been reported earlier. Tentative spin-parity assignments are done for the newly proposed levels on the basis of the DCO ratios corresponding to strong gates. Empirical shell model calculations were carried out to provide an understanding of the underlying nuclear structure.

    • Probing of complete and incomplete fusion dynamics in heavy-ion collision

      D Singh Rahbar Ali M Afzal Ansari B S Tomar M H Rashid R Guin S K Das R Kumar R P Singh S Muralithar R K Bhowmik

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      Three different types of experiments have been performed to explore the complete and incomplete fusion dynamics in heavy-ion collisions. In this respect, first experiment for the measurement of excitation functions of the evaporation residues produced in the 20Ne+165Ho system at projectile energy ranges ≈2–8 MeV/nucleon has been done. Measured cumulative and direct crosssections have been compared with the theoretical model code PACE-2, which takes into account only the complete fusion process. It has been observed that, incomplete fusion fraction is sensitively dependent on projectile energy and mass asymmetry between the projectile and the target systems. Second experiment for measuring the forward recoil range distributions of the evaporation residues produced in the 20Ne+165Ho system at projectile energy ≈8MeV/nucleon has been done. It has been observed that, some evaporation residues have shown additional peaks in the measured forward recoil range distributions at cumulative thicknesses relatively smaller than the expected range of the residues produced via complete fusion. The results indicate the occurrence of incomplete fusion involving the breakup of 20Ne into 4He+16O and/or 8Be+12C followed by one of the fragments with target nucleus 165Ho. Third experiment for the measurement of spin distribution of the evaporation residues produced in the 16O+124Sn system at projectile energy ≈6 MeV/nucleon, showed that the residues produced as incomplete fusion products associated with fast 𝛼 and 2𝛼-emission channels observed in the forward cone, are found to be distinctly different from those of the residues produced as complete fusion products. The spin distribution of the evaporation residues also inferred that in incomplete fusion reaction channels input angular momentum ($J_0$) increases with fusion incompleteness when compared to complete fusion reaction channels. Present observation clearly shows that the production of fast forward 𝛼-particles arises from relatively larger angular momentum in the entrance channel leading to peripheral collision.

    • Neutron detector array at IUAC: Design features and instrumentation developments

      P Sugathan A Jhingan K S Golda T Varughese S Venkataramanan N Saneesh V V Satyanarayana S K Suman J Antony Ruby Shanti K Singh S K Saini A Gupta A Kothari P Barua Rajesh Kumar J Zacharias R P Singh B R Behera S K Mandal I M Govil R K Bhowmik

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      The characteristics and performance of the newly commissioned neutron detector array at IUAC are described. The array consists of 100 BC501 liquid scintillators mounted in a semispherical geometry and are kept at a distance of 175 cm from the reaction point. Each detector is a $5''\times 5''$ cylindrical cell coupled to $5''$ diameter photomultiplier tube (PMT). Signal processing is realized using custom-designed home-made integrated electronic modules which perform neutron–gamma discrimination using zero cross timing and time-of-flight (TOF) technique. Compact custom-built high voltage power supply developed using DC–DC converters are used to bias the detector. The neutrons are recorded in coincidence with fission fragments which are detected using multi-wire proportional counters mounted inside a 1m diameter SS target chamber. The detectors and electronics have been tested off-line using radioactive sources and the results are presented.

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