S. B. Manohar

Validation of a neutron activation analysis method using k0-standardization

A neutron activation analysis method using k0-standardization has been adopted for multielement analysis using our research reactors. Gold has been used as the comparator. The input parameters, used for calculation of elemental concentration, such as subcadmium to epithermal neutron flux ratio (f), the epithermal neutron flux shape factor (alpha), and the absolute efficiency of the detector (epsilon) have been determined. The values of k0-factors and Q0 (the ratio of resonance integral to thermal neutron cross section) have been taken from the literature. The validity of applying this method in our laboratory is evaluated by analyzing the elemental concentrations with respect to the certified values in eight reference materials of different origin obtained from USGS, IAEA and NIST. The percent deviation of the measured elemental concentrations are found to be within +/- 15% to that of the certified values whereas the percent relative standard deviation ranged from 2% to 10% for most of the elements analyzed.

Probing the microstructure of Nafion‐117 using positron annihilation spectroscopy

We report a new result on positron annihilation studies in acid- and cation-neutralized (Li+, Na+, K+, Rb+, Cs+, UO22+, Ni2+) Nafion membranes using positron lifetime and Doppler-broadened annihilation radiation (DBAR) measurements. The free-volume structure is characterized using a simple quantum mechanical model of positronium (Ps) in a spherical well. Our studies indicate that formation and expansion of clusters is always associated with a change in free-volume structure resulting in smaller free-volume holes.

MULTIELEMENT ANALYSIS OF NATURAL RUBY SAMPLES BY NEUTRON ACTIVATION USING THE SINGLE COMPARATOR METHOD

Multielement analysis was carried out in two samples of natural rubies obtained from Kenya and Tanzania and a synthetic ruby obtained locally. The trace element profile was used to characterise the ruby samples. Instrumental Neutron Activation Analysis (INAA) by the single comparator (K0 method) was used to determine the concentrations of 22 elements with gold as the comparator. High resolution γ-ray spectrometry was employed for radiometric assay of the activation products. The accuracy and precision were evaluated by analysing standard reference materials such as USGS-W-1 and AGV-1 and were found to be satisfactory.

Multielement analysis in cereals and pulses by k0 instrumental neutron activation analysis

The concentrations of some elements in a few varieties of cereals and pulses are determined by Instrumental Neutron Activation Analysis using a single comparator method (k0-standardised NAA method). A total of 15 elements are measured. The method was validated by analysing the Standard Reference Material (SRM-1571) of NIST; the results are within +/-10% of the reported values for the majority of the elements. The measured concentrations of major and minor elements are analysed in terms of the average intake of mineral content and the role of these elements in terms of the nutritional value.

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.

Complete and incomplete fusion reactions in the 12 C +169 Tm

Abstract Excitation functions of evaporation residues produced in 12 C + 169 Tm reaction have been measured at several beam energies in the range of 60–84 MeV using recoil catcher technique followed by off-line gamma-ray spectrometry. Comparison of the experimental excitation functions with those calculated using the statistical model code PACE2 revealed dominance of incomplete fusion in the cross section of alpha-emission products. Measurement of recoil-range distributions of evaporation residues at 84 MeV beam energy corroborated these observations. Analysis of the cross sections of incomplete fusion products showed that these reactions are associated with peripheral collisions. Comparison of the present data with similar data on 16 O + 165 Ho system revealed that incomplete fusion probability is more in a mass asymmetric system than in a mass symmetric system.

Determination of Essential Elements in Ayurvedic Medicinal Leaves by k0 Standardized Instrumental Neutron Activation Analysis

Elemental concentrations of a few medicinal leaves are determined by instrumental neutron activation analysis using the single comparator (k0) method. Data obtained for neem leaves, collected from two different places, have been used to see the effect of soil condition. The applicability of the method particularly for the simultaneous determination of Ca, Mg, V and Al in biological matrices has been evaluated in terms of the detection limit, precision and accuracy. The method was validated by analysing the NIST Standard Reference Material (SRM-1571) and it was found that the elemental concentrations measured in SRM-1571 are within ±10% of the reported values.

Backscattering spectrometry studies on metal ion distribution in polymer inclusion membranes

Abstract Polymer inclusion membranes based on cellulose triacetate polymer, containing 2-nitrophenyloctyl ether as plasticizer and dinonyl napthalene sulfonic acid as cation exchanger were loaded with Cs+ and Ag+ and were studied by backscattering spectrometry technique to measure the distribution of the metal ions across the membrane using a proton beam. The study showed that the distribution of the metal ions across the membrane is uniform, thereby suggesting the uniform distribution of the cation exchanger. This indicates that the hydrophilic nature of the sulfonic acid group in the cation exchanger does not significantly influence its distribution in the predominantly hydrophobic matrix of cellulose triacetate. However, the microstructure of the membrane, obtained by atomic force microscopy, shows the formation of blobs on the surface of the PIM indicating the inhomogeneity at the sub-micron scale.

Preparation of thin osmium targets by electrodeposition

Abstract An electrodeposition method for preparation of thin metallic targets of osmium, suitable for nuclear physics experiments, is reported. Electrodeposition was carried out from aqueous solution of osmium. A tracer technique was used to obtain the deposition efficiency, which was found to be about 80%.

Heavy metal concentration and distribution in a dated sediment core of Nainital Lake in the Himalayan region

The concentrations and distribution of the elements, including heavy metals such as As, Ba, Br, Co, Cr, Cs, Fe, Ga, K, Mn, Na, Rb, Sc, Sr, Th and Zn, were investigated in dated sediment cores of Nainital Lake located in the Himalayan region, in Uttar Pradesh state of India, which is considered as a remote background area. The concentrations of the elements were measured by instrumental neutron activation analysis using the k0 method. The International Atomic Energy Agency certified reference material SL-3 was used to evaluate the accuracy of the method. The normalized data for a series of elements were used to understand the source of loading. Elements like Br, Co, Cr, Fe, K, Mn and Zn show a negative correlation with increasing depth whereas elements like As, Ba, Cs, Na and Rb show a positive correlation with increasing depth. By considering the concentration for the bottom segments of the core as close to the baseline concentration, recent flux values for different elements were calculated. An increase in the flux value was observed for Br, Cr, Fe, K, Mn and Zn, which can be attributed to anthropogenic contribution in recent years.