On measuring the neutron coherent scattering length with ultrahigh precision

We propose an order of magnitude improvement in the present five parts in 10⁵ precision of a nondispersive interferometric measurement of the neutron coherent scattering lengthb _c. For this purpose we make a judicious selection of the Bragg angle for the interferometer and the sample thickness. The precision is further improved by an optimal choice of the Bragg reflection (and a consequent neutron wavelength). By performing the experiment in vacuum, errors arising from possible variations in the pressure, composition or humidity of the ambient air can be eliminated. On attaining such precision, we ought to account for the neutron beam refraction at the sample-ambient interfaces, to infer the correctb _c from the observed phase. The formula for the phase used hitherto is approximate and would significantly overestimateb _c. The refractive index for neutrons can thus be determined to a phenomenal precision of a few parts in 10¹².     

Kinetic theory of interacting particles in dilute suspensions of mineral waste

A kinetic theory of interacting spherical particles in dilute suspension is developed which results in a Boltzmann transport equation. This equation is solved in the relaxation time approximation to calculate the settling velocity of fine particulates in the steady state. The theory is applied to the suspended Jamaican bauxite waste and kaolinite particles. The experimental settling velocity compares well with the calculated values at low concentrations. This treatment can form the basis for a more rigorous theory applicable to denser systems and non-spherical particulates.     

Synthesis and characterization of ammonium molybdophosphate–silica nano-composite (AMP–SiO2) as a prospective sorbent for the separation of 137Cs from nuclear waste

The ammonium molybdophosphate–silica (AMP–SiO₂) nano-composites were prepared by sol–gel method. The material synthesized was nanocrystalline, with average crystallite size of primary particles in the range of 10–25 nm. Small angle X-ray scattering showed presence of mass fractal aggregates made of small particles with rough pore boundaries. To realize the scope of using AMP–SiO₂ nano-composites sorbent for removal of ¹³⁷Cs from nuclear waste solutions, its adsorption characteristics for cesium were evaluated. It was found that the AMP–SiO₂ nanocomposites were amenable for column operation, have high affinity for Cs, and possess very high adsorption capacity for Cs. From the perspective of separation of ¹³⁷Cs from acidic radioactive waste solution, AMP–SiO₂ nanocomposite holds significant promise.     

Effect of planar oscillations on implanted distributions measured by low-angle He+ backscattering

Well-resolved planar oscillations within implanted Bi distributions in silicon have been observed in low-angle Rutherford backscattering measurements. Implications of such effects in atom location experiments are discussed.     

Optically transparent, superhydrophobic methyltrimethoxysilane based silica coatings without silylating reagent

The superhydrophobic surfaces have drawn lot of interest, in both academic and industries because of optically transparent, adherent and self-cleaning behavior. Surface chemical composition and morphology plays an important role in determining the superhydrophobic nature of coating surface. Such concert of non-wettability can be achieved, using surface modifying reagents or co-precursor method in sol-gel process. Attempts have been made to increase the hydrophobicity and optical transparency of methyltrimethoxysilane (MTMS) based silica coatings using polymethylmethacrylate (PMMA) instead of formal routes like surface modification using silylating reagents. The optically transparent, superhydrophobic uniform coatings were obtained by simple dip coating method. The molar ratio of MTMS:MeOH:H₂O was kept constant at 1:5.63:1.58, respectively with 0.5 M NH₄F as a catalyst and the weight percent of PMMA varied from 1 to 8. The hydrophobicity of silica coatings was analyzed by FTIR and contact angle measurements. These substrates exhibited 91% optical transmittance as compared to glass and water drop contact angle as high as 171 ± 1°. The effect of humidity on hydrophobic nature of coating has been studied by exposing these films at relative humidity of 90% at constant temperature of 30 °C for a period of 45 days. The micro-structural studies carried out by transmission electron microscopy (TEM).     

Effect of concentration of trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) silylating agents on surface free energy of silica aerogels

The surface free energy of a solid determines its surface and interfacial behavior in processes like wetting and adhesion which is crucial for silica aerogels in case of organic liquid absorption and transportation of chemicals at nano-scale for biotechnological applications. Here, we have demonstrated that the surface free energy of aerogels can be tuned in wide range from 5.5892 to 0.3073 mJ/m(2) by modifying their surface using TMCS and HMDZ silylating reagents. The alcogels were prepared by two step acid-base catalyzed process where the molar ratio of precursors Tetraethoxysilane (TEOS):Methanol (MeOH):Oxalic acid:NH(4)OH:NH(4)F was kept at optimal value of 1:2.7:0.18×10(-4):0.02:0.22×10(-3), respectively. To modify gel surfaces, TMCS and HMDZ concentration have been varied from 3% to 12% and such alcogels were dried at ambient pressure. It is observed from FTIR for aerogels that increase in concentration of silylating reagent resulted increase in hydrophobicity. This leads to increase in contact angle for water from 123° to 155° but leads to decrease in surface free energy from 5.5892 to 0.3073 mJ/m(2). As there is not direct method, we have used Neumann's equation of state to estimate surface energy of aerogels.     

Bonse-Hart angular profiles realized for multiply Bragg reflected neutrons

We have produced a monochromatic neutron beam with the sharpest angular profile to date. Multiple Bragg reflections from optimally designed channel-cut silicon single crystals have produced neutron beams with theoretical Darwin angular profiles. This experiment constitutes the first realization of the proposal made by Bonse and Hart 35 years ago and opens up avenues for ultrasmall angle neutron scattering studies down to wave vector transfers of 10(-5) A(-1).     

Thermal properties of amorphous materials at low temperatures

Recent investigations of X-ray diffraction and electron micrograph studies reveal high density clusters separated by density deficient regions (voids) in amorphous materials. The low temperature specific heat and the thermal conductivity anomalies are explained on the basis of such a structure for amorphous materials. It is a generalisation of Debye's theory applied to most of the amorphous solids in the temperature range from 0 to 10 K. The anharmonic effects lead to the observed temperature dependence of the sound velocity. The thermal conductivity between 0 and 2 K is due to thermal diffusion, the plateau observed between 2 and 20 K is a consequence of the decrease in thermal conductivity due to three phonon processes compensated by intercluster diffusion, while beyond this range it is due to excitations within a cluster limited by the size of a cluster. Further the model predicts the coefficient of expansion about 100 times that found in the corresponding crystalline solids. An experimental verification of this result can be a good test for the model.     

Small angle neutron scattering and small angle X-ray scattering studies of platinum-loaded carbon foams

The morphology of carbon nanofoam samples comprising platinum nanoparticles dispersed in the matrix was characterized by small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) techniques. Results show that the structure of pores of carbon matrix exhibits a mass (pore) fractal nature and the average radius of the platinum particles is about 2.5 nm. The fractal dimension as well as the size distribution parameters of platinum particles varies markedly with the platinum content and annealing temperature. Transmission electron micrographs of the samples corroborate the SANS and SAXS results.      

Discussion on a possible neutrino detector located in India

We have identified some important and worthwhile physics opportunities with a possible neutrino detector located in India. Particular emphasis is placed on the geographical advantage with a stress on the complimentary aspects with respect to other neutrino detectors already in operation.