S. K. Pal

Coherent bremsstrahlung and GDR width from 252Cf cold fission

Abstract The energy spectrum of the high energy γ-rays in coincidence with the prompt γ-rays has been measured for the spontaneous fission of 252Cf. The nucleus–nucleus coherent bremsstrahlung of the accelerating fission fragments is observed and the result has been substantiated with a theoretical calculation based on the Coulomb acceleration model. The width of the giant dipole resonance (GDR) decay from the excited fission fragments has been extracted for the first time and compared with the thermal shape fluctuation model (TSFM) in the liquid drop formalism. The extracted GDR width is significantly smaller than the predictions of TSFM.

Extreme nuclear shapes examined via giant dipole resonance lineshapes in hot light-mass systems

The influence of alpha clustering on nuclear reaction dynamics is investigated using the giant dipole resonance (GDR) lineshape studies in the reactions {sup 20}Ne (E{sub lab}=145,160 MeV) + {sup 12}C and {sup 20}Ne (E{sub lab}=160 MeV) + {sup 27}Al, populating {sup 32}S and {sup 47}V, respectively. The GDR lineshapes from the two systems are remarkably different from each other. Whereas, the non-alpha-like {sup 47}V 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 the alpha cluster {sup 32}S an extended prolate kind of shape is observed. This unusual deformation, seen directly via gamma decay for the first time, is predicted to be due to the formation of orbiting dinuclear configuration or molecular structure of {sup 16}O + {sup 16}O in the {sup 32}S superdeformed band.

Critical behavior in the variation of GDR width at low temperature

Abstract We present the first experimental giant dipole resonance (GDR) width systematics, in the temperature region 0.8–1.2 MeV for 201 Tl, a near Pb nucleus, to investigate the evolution of the GDR width in shell effect and pairing dominated region. The extracted GDR widths are well below the predictions of shell effect corrected thermal shape fluctuation model (TSFM) and thermal pairing included phonon damping model. A similar behavior of the GDR width is also observed for 63 Cu measured in the present work and 119 Sb, measured earlier. This discrepancy is attributed to the GDR induced quadrupole moment leading to a critical point in the increase of the GDR width with temperature. We incorporate this novel idea in the phenomenological description based on the TSFM for a better understanding of the GDR width systematics for the entire range of mass, spin and temperature.

Measurement of giant dipole resonance width at low temperature: A new experimental perspective

Abstract The systematic evolution of the giant dipole resonance (GDR) width in the temperature region of 0.9 – 1.4 MeV has been measured experimentally for 119 Sb using alpha induced fusion reaction and employing the LAMBDA high energy photon spectrometer. The temperatures have been precisely determined by simultaneously extracting the vital level density parameter from the neutron evaporation spectrum and the angular momentum from gamma multiplicity filter using a realistic approach. The systematic trend of the data seems to disagree with the thermal shape fluctuation model (TSFM). The model predicts the gradual increase of GDR width from its ground state value whereas the measured GDR widths appear to remain constant at the ground state value till T ∼ 1 MeV and increase thereafter, indicating towards a failure of the adiabatic assumption of the model at low temperature.

The STAR Photon Multiplicity Detector

Abstract Details concerning the design, fabrication and performance of STAR Photon Multiplicity Detector (PMD) are presented. The PMD will cover the forward region, within the pseudorapidity range 2.3–3.5, behind the forward time projection chamber. It will measure the spatial distribution of photons in order to study collective flow, fluctuation and chiral symmetry restoration.

A honeycomb proportional counter for photon multiplicity measurement in the ALICE experiment

Abstract A honeycomb detector consisting of a matrix of 96 closely packed hexagonal cells, each working as a proportional counter with a wire readout, was fabricated and tested at the CERN PS. The cell depth and the radial dimensions of the cell were small, in the range 5– 10 mm . The appropriate cell design was arrived at using GARFIELD simulations. Two geometries are described illustrating the effect of field shaping. The charged particle detection efficiency and the preshower characteristics have been studied using pion and electron beams. Average charged particle detection efficiency was found to be 98%, which is almost uniform within the cell volume and also within the array. The preshower data show that the transverse size of the shower is in close agreement with the results of simulations for a range of energies and converter thicknesses.

Probing the critical behavior in the evolution of GDR width at very low temperatures in A∼100 mass region

Article history: The influence of giant dipole resonance (GDR) induced quadrupole moment on GDR width at low temperatures is investigated experimentally by measuring GDR width systematically in the unexplored temperature range T = 0.8-1.5 MeV, for the first time, in A ∼ 100 mass region. The measured GDR widths, using alpha induced fusion reaction, for 97

Scaling of the giant dipole resonance widths in hot rotating nuclei from the ground state values

The system atics ofthe giant dipole resonance (GDR) widths in hot and rotating nucleiare studied in term softem peratureT,angularm om entum J and m assA.Thedierentexperim ental datain thetem peraturerangeof1-2M eV havebeen com pared with thetherm alshapeuctuation m odel(TSFM ) in the liquid drop form alism using a m odied approach to estim ate the average values ofT,J and A in the decay ofthe com pound nucleus. The values ofthe ground state GDR widthshave been extracted from theTSFM param etrization in theliquid drop lim itforthe corrected T,Jand A foragiven system and com pared with thecorrespondingavailablesystem atics ofthe experim entally m easured ground state GDR widthsfor a range ofnucleifrom A = 45 to 194. Am azingly, the nature of the theoretically extracted ground state GDR widths m atches rem arkably well,though 1.5 tim essm aller,with the experim entally m easured ground state GDR widthsconsistently overa widerangeofnuclei.

Experimental Determination of η / s for Finite Nuclear Matter

We present, for the first time, simultaneous determination of shear viscosity (η) and entropy density (s) and thus, η/s for equilibrated nuclear systems from A∼30 to A∼208 at different temperatures. At finite temperature, η is estimated by utilizing the γ decay of the isovector giant dipole resonance populated via fusion evaporation reaction, while s is evaluated from the nuclear level density parameter (a) and nuclear temperature (T), determined precisely by the simultaneous measurements of the evaporated neutron energy spectra and the compound nuclear angular momenta. The transport parameter η and the thermodynamic parameter s both increase with temperature, resulting in a mild decrease of η/s with temperature. The extracted η/s is also found to be independent of the neutron-proton asymmetry at a given temperature. Interestingly, the measured η/s values are comparable to that of the high-temperature quark-gluon plasma, pointing towards the fact that strong fluidity may be the universal feature of the strong interaction of many-body quantum systems.

Examination of level density prescriptions for the interpretation of high-energy γ -ray spectra

High-energy