Browsing by Author "P. Sugathan"

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A modular focal plane detector system for the heavy ion reaction analyzer at NSC, New Delhi
(Elsevier, 1996) D.O. Kataria; J.J. Das; N. Madhavan; P. Sugathan; A.K. Sinha; G. Dayanand; M.C. Radhakrishna; A.M. Vinodkumar; K.M. Varier; Mahendrajit Singh; N.V.S.V. Prasad
A detector system has been developed for the focal plane of the HIRA. It consists of two independent detectors, a low-pressure multiwire proportional counter (LP-MWPC) followed by a split-anode ionization detector. Details of the design and test results are presented. Using slow preamplifiers, the position resolution is ≥1 mm and the time resolution is estimated to be 1.5 ns for the LP-MWPC. The ionization detector gives 2.4% energy resolution for 150 MeV 28Si scattered off a gold target and the ΔZ/Z obtained for 28Si+27Al is 1/42 for Z=14. Some results for fusion and transfer studies for the 48Ti+58Ni and 28Si+68Zn systems, respectively, at energies around the Coulomb barrier, are presented to highlight the performance of the detector system.
Asymmetric fission around lead: The case of Po 198
(American Physical Society, 2019) Shilpi Gupta; C. Schmitt; K. Mahata; A. Shrivastava; P. Sugathan; A. Jhingan; K.S. Golda; N. Saneesh; M. Kumar; G. Kaur; L. Stuttgé; D. Arora; H. Arora; A. Chatterjee; K. Chauhan; S.K. Duggi; D.P. Kaur; V. Mishra; Prashant N. Patil; K. Rani
Asymmetric low-energy fission of neutron-deficient nuclei around lead is addressed with the measurement of fragment mass and total kinetic energy properties for the fissioning system Po198 produced in heavy-ion fusion. Interpretation of the measurement for such a transitional nucleus at finite excitation energy is challenging. The presence of asymmetric partitions is suggested by the observed weak dependence of the total kinetic energy on mass and by the nonmonotonic evolution of the fragment-mass distribution width with excitation energy. The interpretation is supported by microscopic model calculations as well as by the results of an advanced semiempirical code. Combined with previous experiments in the region, the present measurement contributes to establish the evolution of the fragment-mass distribution as a function of the fissioning system. The connection between the "new" and the "old" islands of asymmetric fission is discussed. © 2019 American Physical Society.
Fission dynamics and entrance-channel study in the Po 210 compound nucleus via light-particle multiplicities
(American Physical Society, 2023) Chetan Sharma; B.R. Behera; Shruti; Amit; Bharti Rohila; Amninderjeet Kaur; Subodh; Neha Dhanda; Ashok Kumar; P. Sugathan; A. Jhingan; K.S. Golda; N. Saneesh; Mohit Kumar; H. Arora; Divya Arora; H.P. Sharma
Neutron multiplicities, folding angle distribution, mass distribution, and mass-energy distribution are measured for the compound nucleus Po210 populated through the C12+Pt198 reaction at an excitation energy of 61.6 MeV. The measured neutron multiplicities are compared with the statistical model code joanne2 to extract total fission time for the Po210 compound nucleus. The total fission time (τtot) obtained for this system is (10±5)×10-21 s at 49 MeV and increases to (23±5)×10-21 at 61.8 MeV excitation energy indicating that dissipation increases with excitation energy. A comparison with τtot of the O18+Os192 reaction populating the same compound nucleus indicates the influence of entrance channel mass asymmetry on the fission time. Dynamical model calculations have been performed to understand the fusion dynamics for these reactions and it is observed that the formation time of the compound nucleus increases as we go from the asymmetric to the symmetric entrance channels. Also, these calculations predict that 93% of the total angular momentum lead to the formation of a fully equilibrated compound nucleus for the C12+Pt198 reaction whereas this percentage decreases to 84%, for the O18+Os192 reaction indicating a higher percentage of noncompound nuclear processes in the latter case. © 2023 American Physical Society.
Fission time scale from pre-scission neutron and α multiplicities in the O 16 + Pt 194 reaction
(American Physical Society, 2017) K. Kapoor; S. Verma; P. Sharma; R. Mahajan; N. Kaur; G. Kaur; B.R. Behera; K.P. Singh; A. Kumar; H. Singh; R. Dubey; N. Saneesh; A. Jhingan; P. Sugathan; G. Mohanto; B.K. Nayak; A. Saxena; H.P. Sharma; S.K. Chamoli; I. Mukul; V. Singh
Pre- and post-scission α-particle multiplicities have been measured for the reaction O16+Pt194 at 98.4 MeV forming Rn210 compound nucleus. α particles were measured at various angles in coincidence with the fission fragments. Moving source technique was used to extract the pre- and post-scission contributions to the particle multiplicity. Study of the fission mechanism using the different probes are helpful in understanding the detailed reaction dynamics. The neutron multiplicities for this reaction have been reported earlier. The multiplicities of neutrons and α particles were reproduced using standard statistical model code joanne2 by varying the transient (τtr) and saddle to scission (τssc) times. This code includes deformation dependent-particle transmission coefficients, binding energies and level densities. Fission time scales of the order of 50-65 ×10-21 s are required to reproduce the neutron and α-particle multiplicities. © 2017 American Physical Society.
High spin states in 70Ge
(2000) B. Mukherjee; S. Muralithar; G. Mukherjee; R.P. Singh; R. Kumar; J.J. Das; P. Sugathan; N. Madhavan; P.V. Madhusudanan Rao; A.K. Sinha; A.K. Pande; L. Chaturvedi; S.C. Pancholi; R.K. Bhowmik
High spin states in 70Ge nucleus have been studied in two different experiments using heavy ion fusion evaporation reaction. The Gamma Detector Array, comprising of eight Compton-suppressed High Purity Ge detectors, was used in conjunction with a recoil mass spectrometer - the HIRA - in order to identify and measure the transitions of this weakly populated nucleus. The level scheme is extended up to an excitation energy of 13 MeV for spin-parity 21- with several newly observed transitions placed in it. A rotational like band is also observed in this nucleus for the first time.
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.
Indian National Gamma Array at Inter University Accelerator Centre, New Delhi
(2010) S. Muralithar; K. Rani; R. Kumar; R.P. Singh; J.J. Das; J. Gehlot; K.S. Golda; A. Jhingan; N. Madhavan; S. Nath; P. Sugathan; T. Varughese; M. Archunan; P. Barua; A. Gupta; M. Jain; A. Kothari; B.P.A. Kumar; A.J. Malyadri; U.G. Naik; Raj Kumar; Rajesh Kumar; J. Zacharias; S. Rao; S.K. Saini; S.K. Suman; M. Kumar; E.T. Subramaniam; S. Venkataramanan; A. Dhal; G. Jnaneswari; D. Negi; M.K. Raju; T. Trivedi; R.K. Bhowmik
A 4π multi-detector gamma-ray spectrometer named the Indian National Gamma Array (INGA) has been set up at the Inter University Accelerator Centre, New Delhi, for nuclear structure studies. The array is designed to incorporate twenty four Compton-suppressed Clover germanium detectors with a total photopeak efficiency ∼5%. The spectrometer along with sub-systems developed in-house like, mechanical support structure, high voltage power supplies, automatic liquid nitrogen filling system, front-end electronics and data acquisition system are described. The mechanical support structure facilitates the use of the Clover Germanium array with a recoil mass separator. The array has been used in a number of nuclear spectroscopic investigations. The in-beam and off-beam performance of the array are reported. © 2010 Elsevier B.V.
Indian National Gamma Array at IUAC
(Institute of Physics Publishing, 2011) S. Muralithar; K. Rani; R.P. Singh; R. Kumar; J.J. Das; J. Gehlot; K.S. Golda; A. Jhingan; N. Madhavan; S. Nath; P. Sugathan; T. Varughese; M. Archunan; P. Barua; A. Gupta; M. Jain; A. Kothari; B.P.A. Kumar; A.J. Malyadri; U.G. Naik; Raj Kumar; Rajesh Kumar; J. Zacharias; S. Rao; S.K. Saini; S.K. Suman; M. Kumar; E.T. Subramaniam; S. Venkataramanan; A. Dhal; G. Jnaneswari; D. Negi; M.K. Raju; T. Trivedi; R.K. Bhowmik
Indian National Gamma Array (INGA) is a 4π multi-detector gamma-ray spectrometer based on twenty four Compton-suppressed Clover Germanium detectors with a total photo peak efficiency ∼ 5 %. INGA was designed to perform high resolution gamma-ray spectroscopy to study nuclear structure at high spins with stable ion beams at Inter University Accelerator Centre (IUAC). Description of the facility and performance of the array are presented in this paper. Since its commissioning, a number of nuclear spectroscopic investigations have been carried out using the array.
Inference on fission timescale from neutron multiplicity measurement in 18O + 184W
(IOP Publishing Ltd, 2022) N.K. Rai; A. Gandhi; M T Senthil Kannan; S.K. Roy; N. Saneesh; M. Kumar; G. Kaur; D. Arora; K.S. Golda; A. Jhingan; P. Sugathan; T.K. Ghosh; Jhilam Sadhukhan; B.K. Nayak; Nabendu K Deb; Saumyajit Biswas; A. Chakraborty; A. Parihari; Ajay Kumar
The pre-scission and post-scission neutron multiplicities are measured for the 18O + 184W reaction in the excitation energy range of 67.23-76.37 MeV. Langevin dynamical calculations are performed to infer the energy dependence of fission decay time in compliance with the measured neutron multiplicities. Different models for nuclear dissipation are employed for this purpose. Fission process is usually expected to be faster at a higher beam energy. However, we found an enhancement in the average fission time as the incident beam energy increases. It happens because a higher excitation energy helps more neutrons to evaporate that eventually stabilizes the system against fission. The competition between fission and neutron evaporation delicately depends on the available excitation energy and it is explained here with the help of the partial fission yields contributed by the different isotopes of the primary compound nucleus. © 2022 IOP Publishing Ltd.
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.
Measurement of neutron multiplicity to investigate the role of entrance channel parameters on the nuclear dissipation
(American Physical Society, 2019) N.K. Rai; A. Gandhi; Ajay Kumar; N. Saneesh; M. Kumar; G. Kaur; A. Parihari; D. Arora; K.S. Golda; A. Jhingan; P. Sugathan; T.K. Ghosh; Jhilam Sadhukhan; B.K. Nayak; Nabendu K. Deb; S. Biswas; A. Chakraborty
In the present work, the pre- and post-scission neutron multiplicities were measured for the reaction O18+W186 at different excitation energies populating the compound nucleus Pb204, using the National Array of Neutron Detectors (NAND) facility at IUAC, New Delhi, India. Here, we investigated the entrance channel effect on the nuclear dissipation involved in the heavy ion fusion-fission dynamics. The statistical model analysis was performed using the code vecstat. The prescribed reaction O18+W186 had similar value of the mass asymmetry as the system O16+Ta181 studied earlier, populating the compound nucleus Tl197. Specifically, we observed the similar behavior from both the systems against the nuclear dissipation, with the similar value of the mass asymmetry. The role of the entrance channel parameters on the nuclear dissipation was also discussed in the present work. © 2019 American Physical Society.
Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV Si8+-Ar collisions
(Springer New York, 1998) M.J. Singh; S.K. Goel; R. Shanker; D.O. Kataria; N. Madhavan; P. Sugathan; J.J. Das; D.K. Avasthi; A.K. Sinha
Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV Si8+ ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of "optimized parameters" of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for Ar+ to 4.02 eV for Ar10+. These values are compared with the results reported by earlier workers and are shown to follow a g2-behaviour up to a charge state q = 8+ of the recoil ions. © EDP Sciences Springer-Verlag 1998.
Role of nuclear dissipation and entrance channel mass asymmetry in pre-scission neutron multiplicity enhancement in fusion-fission reactions
(American Physical Society, 2008) Hardev Singh; K.S. Golda; Santanu Pal; Ranjeet; Rohit Sandal; Bivash R. Behera; Gulzar Singh; Akhil Jhingan; R.P. Singh; P. Sugathan; M.B. Chatterjee; S.K. Datta; Ajay Kumar; G. Viesti; I.M. Govil
Pre-scission neutron multiplicities are measured for 12C+204Pb and 19F+197Au reactions at laboratory energies of 75-95 MeV for the C12 beam and 98-118 MeV for the F19 beam. The chosen projectile-target combinations in the present study lie on either side of the Businaro-Gallone mass asymmetry (αBG) and populate the Ra216 compound nucleus. The dissipation strength is deduced after comparing the experimentally measured neutron yield with the statistical model predictions which contains the nuclear viscosity as a free parameter. Present results demonstrate the combined effects of entrance channel mass asymmetry and the dissipative property of nuclear matter on the pre-scission neutron multiplicity in fusion-fission reactions. © 2008 The American Physical Society.
Role of viscosity in fusion-fission dynamics via simultaneously measured neutron and α -particle multiplicities
(American Physical Society, 2019) K. Kapoor; N. Bansal; Chetan Sharma; S. Verma; K. Rani; R. Mahajan; B.R. Behera; K.P. Singh; A. Kumar; H. Singh; R. Dubey; N. Saneesh; M. Kumar; A. Yadav; A. Jhingan; P. Sugathan; B.K. Nayak; A. Saxena; H.P. Sharma; S.K. Chamoli
The multiplicities of α particles and neutrons have been measured simultaneously for the reaction O16+Pt196 forming Rn212 compound nucleus at excitation energies of 56 MeV, 61 MeV, and 68 MeV. Neutrons and α particles were detected at various angles in coincidence with the fission fragments. To extract the contribution of pre- and postmultiplicities using the total α-particle and neutron spectra, moving source formalism was implemented. In the case of α particle, near scission contribution has also been extracted. Study of the fission mechanism using light particle emissions are helpful in understanding the detailed fusion-fission reaction dynamics. The statistical model code joanne2, which includes deformation-dependent particle transmission coefficients, binding energies and level densities, has been used to reproduce the measured multiplicities of neutrons and α particles by varying the transient (τtr) and saddle to scission (τssc) times. It is found that the fission time scales of the order of 50-70×10-21 sec are required to reproduce the neutron and α-particles multiplicities simultaneously. The fission time scales are the measure of the nuclear viscosity, which is responsible for the dynamic hindrance of the fission process. © 2019 American Physical Society.
SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi
(Indian Academy of Sciences, 1997) M.J. Singh; S.K. Goel; R. Shanker; D.O. Kataria; N. Madhavan; P. Sugathan; J.J. Das; D.K. Avasthi; A.K. Sinha
An on-line facility to measure coincidences between the recoil ions and the scattered projectiles (SCORPION) has been designed, fabricated and commissioned at Nuclear Science Centre (NSC), New Delhi. The facility consists of a four jaw slit assembly, a time of flight (TOF) spectrometer, a parallel plate electrostatic charge analyser and a one dimensional position sensitive parallel plate avalanche counter (PPAC). Details of the design and working principles of various components and the test results obtained for the Siq+-Ar collision system are presented to highlight the performance of the system. A multiple loss of up to four electrons has been observed for 60 MeV Si4+ ions colliding with argon atoms in a single collision condition. Spectra of recoil ions detected in coincidence with a particular charge state of the scattered projectile show a bell shaped distribution as a function of the recoil charge state (r) for the electron loss events. However, the yield of recoil ions drops as r increases for the direct ionization channel. Also for electron loss, the peak of the recoil ion distribution is seen to shift to a higher recoil charge state as the number of lost electrons from the projectile increases.
Shape coexistence and high spin states in Cr52
(2007) Rajesh Kumar; S.K. Chamoli; I.M. Govil; A. Dhal; R.K. Sinha; L. Chaturvedi; Z. Naik; C.R. Praharaj; S. Muralithar; R.P. Singh; N. Madhavan; P. Sugathan; J.J. Das; R.K. Bhowmik
High spin states in Cr52 have been populated by means of the reaction Al27(Si28,3p)Cr52 at a beam energy of 70 MeV and studied with an array, consisting of eight Compton-suppressed clover germanium detectors. Eleven new γ rays have been assigned to Cr52 and placed in the level scheme. The level structure of Cr52 has been extended up to Ex 10 MeV. Spins and parities have been assigned to many of the levels on the basis of directional correlations and linear polarization measurements. The band structures are discussed in the framework of cranked Woods-Saxon and deformed Hartree-Fock (HF) models. Both the oblate and prolate orbits are considered for J projection in the HF model. The K=0+ band is properly understood if we consider the J projection from both prolate and oblate orbits and collectivity shown by the K=4+ band to be accounted for by taking the J projection from prolate HF configurations. Thus there is prolate and oblate shape coexistence in Cr52. © 2007 The American Physical Society.
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.
Study of nuclear fusion-fission dynamics in 16O+194Pt reaction
(American Institute of Physics Inc., 2017) K. Kapoor; S. Verma; P. Sharma; R. Mahajan; N. Kaur; G. Kaur; B.R. Behera; K.P. Singh; H. Singh; R. Dubey; N. Saneesh; A. Jhingan; P. Sugathan; G. Mohanto; B.K. Nayak; A. Saxena; H.P. Sharma; S.K. Chamoli; I. Mukul; A. Kumar
Pre- and post-scission α-particle multiplicities have been measured for the reaction 16O + 194Pt at 98.4 MeV forming compound nucleus 210Rn. The α-particle's yield has been measured in coincidence with the fission fragments at various angles. The moving source analysis was performed to extract the alpha particle multiplicity which yielded the contribution of pre- and post- scission components. The pre-scission α-particle multiplicity has been compared with JOANNE2 statistical model code predictions to extract fission time scale and which is observed to be around 55zs (1zs=10-21s). © 2017 Author(s).