Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Revealing the Nano‐Level Molecular Packing in Chitosan–NiO Nanocomposite by Using Positron Annihilation Spectroscopy and Small‐Angle X‐ray Scattering

Chitosan–NiO nanocomposite (CNC) is shown to be a potential dielectric material with promising properties. CNCs containing NiO nanoparticles (0.2, 0.6, 1, 2, 5 wt %) are prepared through chemical methods. The inclusion of NiO nanoparticles in the chitosan matrix is confirmed by scanning electron microscopy (SEM) and X‐ray diffraction. The morphology of the NiO nanoparticles and the nanocomposites is investigated by transmission electron microscopy and SEM, respectively. Positron annihilation lifetime spectroscopy (PALS) and the coincidence Doppler broadening (CDB) technique are used to quantify the free volume and molecular packing in the nanocomposites. The triplet‐state positronium lifetime and the corresponding intensity show the changes in nanohole size, density, and size distribution as a function of NiO loading. Small‐angle X‐ray scattering indicates that the NiO aggregates are identical in all the CNCs. The momentum density distribution obtained from CDB measurements excludes the possibility of a contribution of vacant spaces (pores) available in NiO aggregates to the free volume of nanocomposites upon determination by using PALS. The results show systematic variation in free‐volume properties and nano‐level molecular packing as a function of NiO loading, which is presumed to play a vital role in determining the various properties of the nanocomposites.     

Synthetic studies on taxanes: A domino-enyne metathesis/Diels-Alder approach to the AB-ring

A domino enyne cross-metathesis/intramolecular Diels-Alder reaction has been successfully used to synthesize a bicyclo[5.3.1] undecene, corresponding to AB-ring of taxol without the gem dimethyl group.     

X-ray scattering measurements of particle orientation in a sheared polymer/clay dispersion

We report steady and transient measurements of particle orientation in a clay dispersion subjected to shear flow. An organically modified clay is dispersed in a Newtonian polymer matrix at a volume fraction of 0.02, using methods previously reported by Mobuchon et al. (Rheol Acta 46: 1045, 2007). In accord with prior studies, mechanical rheometry shows yield stress-like behavior in steady shear, while time dependent growth of modulus is observed following flow cessation. Measurements of flow-induced orientation in the flow-gradient plane of simple shear flow using small-angle and wide-angle X-ray scattering (SAXS and WAXS) are reported. Both SAXS and WAXS reveal increasing particle orientation as shear rate is increased. Partial relaxation of nanoparticle orientation upon flow cessation is well correlated with time-dependent changes in complex modulus. SAXS and WAXS data provide qualitatively similar results; however, some quantitative differences are attributed to differences in the length scales probed by these techniques.     

Hydrogelation and spontaneous fiber formation of 8-aza-7-deazaadenine nucleoside ‘click’ conjugates

Nucleoside hydrogels based on benzyl azide ‘click’ conjugates of 8-aza-7-deaza-2′-deoxyadenosine bearing 7-ethynyl, 7-octa-(1,7-diynyl), and 7-tri-prop-2-ynyl-amine side chains were synthesized (1, 3, 4). The cycloaddition adduct with the shortest linker (1) yields the most powerful hydrogelator forming stable gels at a concentration of 0.3 wt % of 1 in water. One molecule of 1 catches 7500 water molecules. Cycloaddition of the 8-aza-7-deaza-7-azido-2′-deoxyadenosine (9) and 3-phenyl-1-propyne (10) leads to the isomeric conjugate 2, with a C-N connectivity between the nucleobase and triazole moiety. This gel is less stable than that of the adduct 1. Both gels show a similar stability over a wide pH range (4.0-10.0). Xerogels of 1 and 2 studied by scanning electron microscopy (SEM) reveal that both click adducts (1 and 2) form long fibers spontaneously.     

Modification of microstructure of the surface and the bulk in ion-irradiated membrane studied using positron annihilation spectroscopy

The effect of ion irradiation and etching on the microstructure of polyethyleneterephthalate (PET) membrane has been studied using positron annihilation spectroscopy. PET membrane of 25 μm thickness was irradiated by 100 MeV ³⁵Cl beam (7×10⁷ ions/cm²) and then etched with NaOH for 45 min. The modification in the microstructure at the surface of the membrane was probed by depth-dependent Doppler-broadened S-parameter and positronium 3γ–2γ annihilation ratio using a slow positron beam, while the free volume properties in the bulk of the membrane were studied using the conventional positron lifetime technique. Positron annihilation parameters were found to be very sensitive to the microstructural changes occurring in the polymer at such a low fluence. It was observed that on ion-irradiation, the surface of the membrane is modified in a different way than the bulk. While the ion-irradiation produces large fraction of excess free volumes at the surface of the membrane due to chain scission, the free volumes are reduced in the bulk of the membrane due to cross-linking. FTIR and XRD measurements were also carried out to investigate the changes occurring in the chemical structure and crystallinity of the polymer samples on ion-irradiation and etching.     

Optical and microstructural studies on electron irradiated PMMA: A positron annihilation study

The effect of electron irradiation on the free volume related microstructural and optical properties of Poly(methyl methacrylate) have been studied using Positron Annihilation and other techniques. The FTIR spectral study on the irradiated films suggests the existence of CC group and is understood by invoking the carbonaceous clusters as a consequence of chain scission in PMMA. Using UV-Visible absorption spectra the optical parameters like optical energy bandgap and activation energy were determined and the variation of these parameters suggests the existence of defects within the irradiated sample. Following Robertson’s theory, the carbonaceous cluster size is estimated and it increases with increase in electron dose. The XRD study indicates the enhancement of amorphous nature of the film due to chain scission by irradiation. The Positron annihilation result shows that electron irradiation affects the free volume related microstructure and the carbonaceous clusters may act as positron scattering centers.     

Observation of self-amplified spontaneous emission and exponential growth at 530 nm

Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator.     

Simultaneous determination of low Z elements in barium borosilicate glass samples by in situ current normalized particle induced gamma-ray emission methods

Particle induced gamma-ray emission (PIGE) method using 4 MeV proton beam was utilized to analyze two types of barium borosilicate glass (BaBSG) samples for quantification of concentrations of low Z elements. The in situ current normalization method was applied in the analysis of eight samples containing varying concentration of F along with Si, B and Na. Charge normalized PIGE method was applied to determine concentrations of above low Z elements including Li and Al in samples having simulated nuclear waste from reprocessing of thoria spent fuel. Synthetic samples and NIST SRMs were used for method validation.     

Measurement of free-volume hole size distribution in Nafion-117 using positron annihilation spectroscopy

We report a new result of free-volume hole size distribution in water and ethanol-swollen Nafion-117 polymer. With the increase in water content, free-volume hole size decreases, but overall the volume fraction increases. The hole size distribution in dry polymer is seen to be distinctly different from hydrated membranes. The narrow and symmetric distribution in hydrated membrane as compared to dry membrane is believed to be a consequence of crosslinking due to cluster formation. In alcohol-swollen membranes, on the other hand, not only are the free-volume size and fraction seen to be higher, the hole size distribution is seen to be broader compared to dry or hydrated membranes, indicating the effect of penetration of alcohol into the hydrophobic backbone region. We have also examined our results vis-a-vis reported gas diffusion studies in Nafion in the framework of existing free-volume model. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 983–989, 1998