Browsing by Author "Krishichayan"

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Alignment effects in the medium-spin level structure of Se 78
(American Physical Society, 2022) K. Mandal; A. Chakraborty; A.K. Mondal; U.S. Ghosh; Aniruddha Dey; Saumyajit Biswas; B. Mukherjee; S. Rai; S. Chatterjee; S.K. Das; S. Samanta; R. Raut; S.S. Ghugre; S. Bhattacharyya; S. Nandi; S. Bhattacharya; G. Mukherjee; S. Ali; A. Goswami; S. Mukhopadhyay; Krishichayan; R. Banik; R. Chakrabarti; V. Kumar; A. Kumar
The excited states of Se78 were populated using the Ge76(α,2n) fusion evaporation reaction. The deexcited gamma rays were detected using the Indian National Gamma Array (INGA) spectrometer comprising clover and low-energy photon spectrometer (LEPS) detectors. The ground state band of Se78 has been extended up to Ex = 8.5 MeV and J = 16â ; this excitation regime is very close to the π(1g9/22) crossing frequency. Several newly observed in-band and intraband transitions belonging to the other bands of Se78 have also been placed in the level scheme based on their coincidence relationships. From the newly identified E1 transitions, an enhancement in the B(E1)/B(E2) values with spin has been observed which indicates the onset of octupole correlations in the band structure built on the 3-, 2508-keV state. Persistence of triaxial shape up to the highest observed spin of the ground state band has been observed and the feature of successive 1g9/22 quasiparticle alignments due to protons and neutrons has been unveiled. The consequences arising due to the occurrence of the neutron 1g9/2 quasiparticle alignments in the other observed correlated band structures are also presented. The results are interpreted in terms of total Routhian surface (TRS) calculations and the level structure systematic of the neighboring nuclei. © 2022 American Physical Society.
High spin states in Pm139
(American Physical Society, 2009) A. Dhal; R.K. Sinha; L. Chaturvedi; P. Agarwal; S. Kumar; A.K. Jain; R. Kumar; I.M. Govil; S. Mukhopadhyay; A. Chakraborty; Krishichayan; S. Ray; S.S. Ghugre; A.K. Sinha; R. Kumar; R.P. Singh; S. Muralithar; R.K. Bhowmik; S.C. Pancholi; J.B. Gupta
The odd mass nucleus Pm139 has been studied to high spins through the Cd116(Al27,4n)Pm139 reaction at an incident beam energy of 120 MeV. The de-exciting γ-rays were detected using an array of 12 Compton suppressed Ge detectors. A total of 46 new levels have been proposed in the present work as a result of the observation of 60 new γ-rays. Four new bands including a ΔJ=1 sequence have been identified and all the earlier reported bands, other than the yrast band, have been extended to higher spins and excitation energy. The spin assignments for most of the newly reported levels have been made using the observed coincidence angular anisotropy. Tilted axis cranking calculations support the interpretation of two of the observed magnetic dipole sequences as examples of magnetic rotational bands. © 2009 The American Physical Society.
High-spin states in the odd-odd nucleus146Tb
(American Physical Society, 2004) Krishichayan; A. Chakraborty; S.S. Ghugre; R. Goswami; S. Mukhopadhyay; N.S. Pattabiraman; S. Ray; A.K. Sinha; S. Sarkar; P.V. Madhusudhana Rao; U. Garg; S.K. Basu; B.K. Yogi; L. Chaturvedi; A. Dhal; R.K. Sinha; M. Saha Sarkar; S. Saha; R. Singh; R.K. Bhowmik; A. Jhingan; N. Madhavan; S. Muralithar; S. Nath; R.P. Singh; P. Sugathan
The odd-odd 146Tb nucleus has been investigated using the 115In(34S,3n) reaction at 140 MeV incident energy using an array of eight Compton-suppressed Clover detectors. Based on the observed γ- γ coincidences, the level structure of 146Tb has been extended up to Ex∼ 10 MeV. Linear polarization measurements have been combined with angular correlations of the observed γ rays to assign the electromagnetic nature to the transitions. Probable origin of a cascade of M1 transitions observed around 8 MeV excitation energy has been discussed.
Investigation of different possible excitation modes in neutron-rich As 78
(American Physical Society, 2020) A.K. Mondal; A. Chakraborty; K. Mandal; U.S. Ghosh; Aniruddha Dey; Saumyajit Biswas; B. Mukherjee; S. Rai; Krishichayan; S. Chatterjee; S.K. Das; S. Samanta; R. Raut; S.S. Ghugre; S. Rajbanshi; R. Banik; S. Bhattacharyya; S. Nandi; S. Bhattacharya; G. Mukherjee; S. Ali; A. Goswami; R. Chakrabarti; S. Mukhopadhyay; A.K. Sinha; V. Kumar; A. Kumar
The yrast and nonyrast level structure of the odd-odd As78 nucleus has been investigated using the standard ? ray spectroscopic techniques. The excited states of As78 were populated through Ge76(a,pn) fusion evaporation reaction at the incident beam energies of 30, 35, and 40 MeV. The deexciting gamma rays were detected with the Indian National Gamma Array spectrometer composed of Clover and low-energy photon spectrometer detectors. In addition to the extension of the previously known yrast positive-parity band up to Ex ˜ 2.7 MeV with J=11?, an excited dipole band-like structure based on the 7(-), 1243-keV state has also newly been established. Several weak transitions feeding the low-lying nonyrast states have newly been identified and placed in the level scheme. A highly irregular sequence of levels has been observed at the low-excitation regime suggesting the dominance of single-particle excitations. The experimental results have been compared with the predicted results from the large-scale shell-model calculations. The calculated results indicate an enhanced contribution from the intruder p(1g9/2) orbital to the wave function of the positive-parity yrast excited states with J=7?. This enhanced contribution is supposed to provide subsequent mild collectivity for the concerned states. The nature of collectivity has been extracted from the total Routhian surface calculations. Evidences for the possible persistence of the stapler like mechanism prevailing in the positive- and negative-parity level sequences are presented. © 2020 American Physical Society.
Investigation of the low- and medium-spin level structure in As 77
(American Physical Society, 2023) A.K. Mondal; A. Chakraborty; K. Mandal; U.S. Ghosh; Aniruddha Dey; Saumyajit Biswas; B. Mukherjee; Krishichayan; S. Chatteerjee; S.K. Das; S. Samanta; R. Raut; S.S. Ghugre; S. Mukhopadhyay; S. Rajbanshi; R. Banik; S. Bhattacharyya; S. Nandi; S. Chakraborty; S. Bhattacharya; G. Mukherjee; S. Ali; A. Goswami; R. Chakrabarti; A. Kumar; R. Goswami
The low- and medium-spin level structure of As77 nucleus has been investigated using the Ge76(α,p2n) fusion evaporation reaction and the standard in-beam γ ray spectroscopic technique. The deexciting γ rays were detected with the Indian National Gamma Array spectrometer comprising Clover and LEPS detectors. The previously known 9/2+ yrast positive-parity band, based on the π(g9/2) configuration, has been extended to the excitation energy of Ex≈7.5 MeV with Jπ=(33/2+). An extension of the high-lying negative-parity band, based on the π[(g9/2)] - ν[(g9/2)(fp)] configuration, has been made up to Ex≈5.1 MeV, Jπ=(25/2-). The yrast positive-parity α=-1/2 signature partner band has newly been identified and the occurrence of large signature splitting associated with the partner bands have been observed. A quasi-γ vibrational band structure built on the nonyrast 13/2+ state has also newly been established. The experimental findings have been interpreted on the basis of the predicted results from the total Routhian surface, particle plus triaxial-rotor model, and shell-model calculations. The band crossing phenomena correlated to the ν(g9/2) alignment and the perseverance of triaxial shape up to the highest observed excitation regime of the 9/2+ yrast positive-parity band have been discussed. The evidence for the possible onset of the stapler-like mechanism prevailing in the high-lying negative-parity band structure are presented. © 2023 American Physical Society.
Lifetime measurements of microsecond isomers in the N=48 nuclei 88Zr and90Mo using recoil-isomer tagging
(American Physical Society, 2004) A. Chakraborty; Krishichayan; S.S. Ghugre; R. Goswami; S. Mukhopadhyay; N.S. Pattabiraman; S. Ray; A.K. Sinha; S. Sarkar; P.V. Madhusudhana Rao; U. Garg; S.K. Basu; L. Chaturvedi; A. Dhal; R.K. Sinha; I.M. Govil; M.B. Chatterjee; M. Saha Sarkar; R.K. Bhowmik; A. Jhingan; N. Madhavan; S. Muralithar; S. Nath; R.P. Singh; P. Sugathan
The recoil-isomer tagging technique has been used to study the isomeric states of nuclei in the vicinity of the N=50 shell closure. The nuclei of interest were separated from the projectilelike nuclei and other evaporation residues and transported to the focal plane of a recoil separator. The decay of the tagged isomer was studied at the focal plane using a high-purity Ge detector. The prompt transitions feeding the isomer were detected in an array of Clover Ge detectors placed around the target. The measured half-lives of the 8+ isomers in 88Zr and 90Mo are 1.41 (-0.09)(+0.12) μs and 1.17(-0.07) (+0.19), respectively. The corresponding transition probabilities are in reasonable agreement with the predictions of shell model calculations. The systematics of effective charges (ep and en) for N=48 nuclei are qualitatively understood in these calculations.
Spectroscopy of Nb90 at high spin
(2005) A. Chakraborty; Krishichayan; S.S. Ghugre; R. Goswami; S. Mukhopadhyay; N.S. Pattabiraman; S. Ray; A.K. Sinha; S. Sarkar; P. V. Madhusudhana Rao; U. Garg; S.K. Basu; M.B. Chaterjee; M. Saha Sarkar; L. Chaturvedi; A. Dhal; R.K. Sinha; I.M. Govil; R.K. Bhowmik; A. Jhingan; N. Madhavan; S. Muralithar; S. Nath; R.P. Singh; P. Sugathan
Excited states of Nb90 were investigated via prompt and delayed γ decays and the recoil-isomer tagging technique. The level scheme of Nb90 has been extended up to J=19 and Ex=8.4 MeV. Half-lives of the 11- and 17/2- isomeric levels in Nb90,91 were measured to be 0.47±0.01 and 3.3±0.4 μs, respectively. The results are compared with the predictions of large-basis shell model calculations. The effects of truncation of the valence model space on the calculated results are discussed. © 2005 The American Physical Society.
Spin-parity measurements in the neutron-rich N ∼ 20 34P and 36S nuclei
(2006) Krishichayan; A. Chakraborty; S. Mukhopadhyay; S. Ray; N.S. Pattabiraman; S.S. Ghugre; R. Goswami; A.K. Sinha; S. Sarkar; U. Garg; P.V. Madhusudhana Rao; S.K. Basu; B.K. Yogi; L. Chaturvedi; A. Dhal; R.K. Sinha; M. Saha Sarkar; S. Saha; R. Singh; R.K. Bhowmik; A. Jhingan; N. Madhavan; S. Muralithar; S. Nath; R.P. Singh; P. Sugathan
Yrast and near-yrast energy levels in the neutron-rich N ∼ 20 nuclei 34P, 36S were populated using transfer/deep-inelastic processes following the 34S + 115In reaction at an incident energy of 140MeV. The use of a multi-clover array has facilitated polarization measurements of the observed γ-rays and necessitated some changes in the previously known level scheme. The observation of the negative-parity levels in these nuclei on the periphery of the "island of inversion" is indicative of the influence of the intruder orbitals on the level structure at low spins. Shell-model calculations indicate that the inclusion of the orbitals from the upper pf shell is important even for the low-lying positive-parity states.
Triaxial shape coexistence and new aligned band in Os178
(American Physical Society, 2009) Rajesh Kumar; I.M. Govil; A. Dhal; L. Chaturvedi; C.R. Praharaj; A.K. Rath; G. Kiran Kumar; S.K. Basu; A. Chakraborty; Krishichayan; S. Mukhopadhyay; N.S. Pattabiraman; S.S. Ghugre; A.K. Sinha
High spin states in Os178 were studied by means of Ho165(Ne20,p6n)Os178 fusion evaporation reaction at a beam energy of 150MeV, using a clover detector array. Several new transitions belonging to Os178 were placed in a level scheme and a new aligned rotational band was observed in addition to earlier known bands. Spin-parity assignments for most of the proposed levels were made using the deduced directional correlation orientation and polarization measurements for the de-exciting transitions. Experimental results are compared with the projected angular momentum deformed Hartree-Fock model calculations and cranked Woods-Saxon model calculations. This nucleus is predicted to be prolate deformed in the ground state but the γ-softness at higher excitation is revealed by the cranked Woods-Saxon model and the geometrical asymmetric model calculations. © 2009 The American Physical Society.