Publications (34)84.12 Total impact
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ABSTRACT: Inclusive energy spectra of the complex fragments (3 $\leq$ Z $\leq$ 5) emitted in the reactions $^{12}$C (77 MeV)+ $^{28}$Si, $^{11}$B (64 MeV)+ $^{28}$Si and $^{12}$C (73 MeV)+ $^{27}$Al (all having the same excitation energy of $ \sim$ 67 MeV), have been measured in the angular range of 10$^\circ$ $\lesssim \theta_{lab} \lesssim$ 60$^\circ$. The fully energy damped (fusionfission) and the partially energy damped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energy damped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value.  [Show abstract] [Hide abstract]
ABSTRACT: The energy spectra of the α particles emitted in the reactions 16O (710 MeV/nucleon)+12C have been measured in the centerofmass angular range of 25∘≲θc.m.≲70∘. The experimental energy spectra have been compared with those obtained from the statistical model calculation with “deformability” parameters predicted by rotating liquid drop model (rldm) and also fitted the same with optimized deformability parameters, which are quite different from the respective rldm values. The data have also been found to be explained quite well using “frozen” deformation approximation, where the deformability parameters have been kept fixed at rldm values of the parent nucleus throughout the decay process. The effective radius in the latter case is smaller compared to that obtained using the optimized parameters; however, in both cases, the deformations (effective radii) are larger than the corresponding rldm values. So, considering the uncertainties in the estimation of actual compound nucleus deformations, it can, only qualitatively, be said that equilibrium orbiting, which is similar to particle evaporation in time scale, could also be one of the contributing factors for the observed deformation.  [Show abstract] [Hide abstract]
ABSTRACT: The 27Al(12C,11B)28Si reactions have been studied at 73, 81 and 85 MeV to extract spectroscopic factors for the ground (0+), first (2+) and second (4+) excited states of 28Si using a transfer reaction. The elastic scattering angular distributions have been fitted using the computer code ECIS94, and finite range distortedwave Born approximation calculations have been performed using DWUCK5. The extracted spectroscopic factors are compared with shell model calculations.  [Show abstract] [Hide abstract]
ABSTRACT: The high spin states in 195Bi were studied by γray spectroscopic method using the 181Ta(20Ne, 6n) fusionevaporation reaction at 130 MeV. The γγ coincidence data were taken using an array of eight clover highpurity germanium detectors. The spin and parity assignments of the excited states were made from the measured directional correlation from oriented states ratios and integrated polarization asymmetry ratios. The results show, for the first time, the evidence of a rotationallike band based on a 13/2+ bandhead in this nucleus, indicating the onset of deformation at the neutron number N=112 for the bismuth isotopes. The results obtained were found to be consistent with the prediction of the total Routhian surface calculations using the WoodsSaxon potential. The same calculations also predicted a change in shape from oblate to triaxial in 195Bi at high rotational frequency.  [Show abstract] [Hide abstract]
ABSTRACT: Inclusive energy spectra of the complex fragments (3 ≤ Z ≤ 5) emitted in the reactions 12C (77 MeV)+ 28Si, 11B (64 MeV)+ 28Si, and 12C (73 MeV)+ 27Al (all having the same excitation energy of ∼67 MeV), have been measured in the angular range of 10∘ ≲θlab≲ 60∘. The fully energydamped (fusionfission) and the partially energydamped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energydamped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value.  [Show abstract] [Hide abstract]
ABSTRACT: The 1p transfer channel in the $^{27}$Al($^{12}$C, $^{11}$B)$^{28}$Si reaction has been studied at E$_{lab}$ = 73, 81 and 85 MeV. The finite range distorted wave Born approximation calculations have been performed using phenomenological optical model potential to analyze the angular distributions for 3 transitions populating the 0.0, 1.78 and 4.62 MeV states of $^{28}$Si and 2 transitions populating the 2.12 and 4.44 MeV states of $^{11}$B via the $^{27}$Al($^{12}$C, $^{11}$B)$^{28}$Si reaction. The spectroscopic strengths as well as spectroscopic factors have been extracted for all the five states. The extracted strength values are compared with shell model calculations.  [Show abstract] [Hide abstract]
ABSTRACT: Direct observation of the survival of 199Au residues after 2n transfer in the system and the absence of the corresponding 67Cu in the system at various energies are reported. The measurements of the surprisingly large cross sections for 199Au, coupled with the integral cross sections for the various Au residues, is used to obtain the first modelindependent lower limits on the ratio of 2n to 1n transfer cross sections from 8He to a heavy target. A comparison of the transfer cross sections for 6,8He on these targets highlights the differences in the interactions of these Borromean nuclei. These measurements for the most neutronrich nuclei on different targets highlight the need to probe the reaction mechanism with various targets and represent an experimental advance towards understanding specific features of pairing in the dynamics of dilute nuclear systems.  [Show abstract] [Hide abstract]
ABSTRACT: Differential cross sections for elasticscattering and neutrontransfer reactions along with cross sections for fusion in the {sup 8}He+{sup 65}Cu system are reported at energies above the Coulomb barrier (E{sub lab}= 19.9 and 30.6 MeV). The present work demonstrates the feasibility of using inclusive measurements of characteristic inbeam {gamma} rays with lowintensity ({approx}10{sup 5} pps) radioactive ion beams to obtain the residue cross sections for fusion and neutron transfer. Exclusive measurements of {gamma} rays in coincidence with light charged particles have been used to further characterize the direct reactions induced by this doubleBorromean nucleus. Coupled reaction channels calculations are used to illustrate the important role played by the transfer channels and to help in understanding the influence of the structure of {sup 8}He on the reaction mechanism. 
Article: Extreme nuclear shapes examined via Giant Dipole Resonance lineshapes in hot light mass system
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ABSTRACT: The influence of alpha clustering on nuclear reaction dynamics is investigated using the giant dipole resonance (GDR) lineshape studies in the reactions 20Ne (Elab=145,160 MeV) + 12C and 20Ne (Elab=160 MeV) + 27Al, populating 32S and 47V, respectively. The GDR lineshapes from the two systems are remarkably different from each other. Whereas, the non alphalike 47V undergoes Jacobi shape transition and matches exceptionally well with the theoretical GDR lineshape estimated under the framework rotating liquid drop model (RLDM) and thermal shape fluctuation model (TSFM) signifying shape equilibration, for alpha cluster 32S an extended prolate kind of shape is observed. This unusual deformation, seen directly via decay for the first time, is predicted to be due to the formation of orbiting dinuclear configuration or molecular structure of 16O+ 16O in 32S superdeformed band.  [Show abstract] [Hide abstract]
ABSTRACT: Differential cross sections for elasticscattering and neutrontransfer reactions along with cross sections for fusion in the 8He+65Cu system are reported at energies above the Coulomb barrier (Elab = 19.9 and 30.6 MeV). The present work demonstrates the feasibility of using inclusive measurements of characteristic inbeam γ rays with lowintensity (∼105 pps) radioactive ion beams to obtain the residue cross sections for fusion and neutron transfer. Exclusive measurements of γ rays in coincidence with light charged particles have been used to further characterize the direct reactions induced by this doubleBorromean nucleus. Coupled reaction channels calculations are used to illustrate the important role played by the transfer channels and to help in understanding the influence of the structure of 8He on the reaction mechanism.  [Show abstract] [Hide abstract]
ABSTRACT: A systematic study of the variation of neutron detection characteristics (efficiency, pulse shape discrimination) and the intrinsic time resolution with the active volume of the detector has been carried out with liquid scintillator (BC501A)based neutron detectors of various dimensions designed and fabricated for this purpose. Energydependent neutron detection efficiency has been measured using associated particle technique and its dependence on detector dimension has been studied. The measured efficiencies have been compared with those obtained from GEANT4 simulations.  [Show abstract] [Hide abstract]
ABSTRACT: The inclusive energy distributions of the fragments (3 <= Z <= 5) emitted in the reaction O16+C12 have been measured in the angular range 9(degrees) to 29(degrees), at the energies 117, 125, 145, and 160 MeV, respectively. The centroids of the fragments energy distributions follow Viola systematics, which suggest that the fragments are emitted from a fully energy relaxed compositeas expected for both FF and orbiting processes. The center of mass angular distributions of the fragments B, Be, and Li obtained at all the bombarding energies follow 1/sin theta(c.m.) like variationwhich further corroborates the conjecture of emission from fully equilibrated composite. The average < Q > values for the fragments B, Be, and Li are found to be independent of the center of mass emission angles, which further suggest that at all angles, the fragments are emitted from completely equilibrated source at all incident energies considered here. The yields of the fragments Li and Be are in agreement with statisticalmodel predictions. The enhanced yields of entrance channel fragment B indicate the survival of orbitinglike process in O16+C12 system at these energies.  [Show abstract] [Hide abstract]
ABSTRACT: A comparison of various thermometric techniques used for the estimation of nuclear temperature has been made from the decay of hot composite {sup 32}S* produced in the reaction {sup 20}Ne (145 MeV) + {sup 12}C. It is shown that the temperatures estimated by different techniques, known to vary significantly in the Fermi energy domain, are consistent with each other within experimental limits for the system studied here.  [Show abstract] [Hide abstract]
ABSTRACT: Angular distributions for 1n and 2n transfer are reported for the 6He+65Cu system at E_{lab}=22.6 MeV. For the first time, triple coincidences between alpha particles, neutrons, and characteristic gamma rays from the targetlike residues were used to separate the contributions arising from 1n and 2n transfer. The differential cross sections for these channels, elastic scattering, and fusion were analyzed using a coupled reaction channels approach. The large measured ratio of the 2nto1n cross section and the strong influence of 2n transfer on other channels indicate that the dineutron configuration of 6He plays a dominant role in the reaction mechanism.  [Show abstract] [Hide abstract]
ABSTRACT: Inclusive energy distributions for light charged particles (p , d , t and a \alphahave been measured in the 20Ne (158, 170, 180, 200MeV) + 12C reactionsintheangularrange10 < sup > ° < /sup >10°   50 < sup > ° < /sup >50°.Exclusivelightchargedparticleenergydistributionmeasurementswerealsodoneforthesamesystemat158MeVbombardingenergybyin  planelightchargedparticle   fragmentcoincidence.Pre  equilibriumcomponentshavebeenseparatedoutfromprotonenergyspectrausingthemovingsourcemodelconsideringtwosources.ThedatahavebeencomparedwiththepredictionsofthestatisticalmodelcodeCASCADE.Ithasbeenobservedthatsignificantdeformationeffectswereneededtobeintroducedinthecompoundnucleusinordertoexplaintheshapeoftheevaporated< i > d < /i >d,< i > t < /i >tenergyspectra.Forprotons, evaporatedenergyspectrawereratherinsensitivetonucleardeformation, thoughangulardistributionscouldnotbeexplainedwithoutdeformation.Thedecaysequenceofthehot< sup > 32 < /sup > S32Snucleushasbeeninvestigatedthroughexclusivelight   charged  particlemeasurementsusingthe< sup > 20 < /sup > Ne20Ne(158MeV) + $12C reaction. Information on the sequential decay chain has been extracted through a comparison of the experimental data with the predictions of the statistical model. It is observed from the present analysis that exclusive lightchargedparticle data may be used as a powerful tool to probe the decay sequence of hot light compound systems. 



Article: First Measurement of the Giant Monopole and Quadrupole Resonances in a ShortLived Nucleus: Ni 56
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ABSTRACT: The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the 56Ni unstable nucleus by inducing the 56Ni(d,d') reaction at 50A MeV in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at 19.3+/0.5 MeV and 16.2+/0.5 MeV, respectively. The corresponding angular distributions are extracted from 3 degrees to 7 degrees . A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energyweighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediateenergy radioactive beam facilities. 
Article: Giant dipole resonance width in nuclei near Sn at low temperature and high angular momentum
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ABSTRACT: High energy γ rays in coincidence with low energy yrast γ rays have been measured from 113Sb, at excitation energies of 109 and 122 MeV, formed by bombarding 20Ne on 93Nb at projectile energies of 145 and 160 MeV, respectively, to study the role of angular momentum (J) and temperature (T) over giant dipole resonance (GDR) width (Γ). The maximum populated angular momenta for fusion were 67ℏ and 73ℏ, respectively, for the abovementioned beam energies. The high energy photons were detected using a Large Area Modular BaF2 Detector Array (LAMBDA) along with a 24element multiplicity filter. After preequilibrium corrections, the excitation energy E* was averaged over the decay steps of the compound nucleus (CN). The average values of temperature, angular momentum, CN mass, etc., have been calculated using the statistical model code CASCADE. Using those average values, results show the systematic increase of GDR width with T, which is consistent with Kusnezov parametrization and the thermal shape fluctuation model (TSFM). The rise of GDR width with temperature also supports the assumptions of adiabatic coupling in the TSFM. But the GDR widths and corresponding reduced plots with J are not consistent with those of the theoretical model at high spins.
Publication Stats
306  Citations  
84.12  Total Impact Points  
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Institutions

20082013

Bose Institute
 Center for Astroparticle Physics and Space Science
Kolkata, West Bengal, India 
Université ParisSud 11
Orsay, ÎledeFrance, France


20052012

Variable Energy Cyclotron Centre
 Physics Group
Kolkata, Bengal, India


20102011

Institut de Physique Nucléaire de Lyon
Lyons, RhôneAlpes, France


20072008

French National Centre for Scientific Research
Lutetia Parisorum, ÎledeFrance, France
