Performance of HPGe gamma spectrometry system for the measurement of low level radioactivity

Comprehensive quality assurance/quality control procedure is very much necessary to obtain accurate and precise analytical measurement result. This paper discusses the quality control aspects of the High-Purity Germanium (HPGe) based gamma spectrometry system, which has been used for the measurement of low-level radioactivity in environmental samples. The gamma spectrometry system consisting of coaxial n-type HPGe detector having 50% relative efficiency with respect to 7.62 cm x 7.62 cm NaI (Tl), Nuclear Instrumentation Module (NIM) based pulse processing electronic accessories and 8 k MCA. To reduce the background contribution, 7.5 cm thick lead has been placed surrounding the detector. The minimum detectable activities (MDA) with 95% confidence level (for 300 g soil sample and 100,000 s counting time) for important radionuclides such as ²³⁸U, ²²⁶Ra, ²³²Th, ⁴⁰K, and ¹³⁷Cs are 10.4, 4.3, 4.1, 16.9 and 0.1 Bq kg^?1, respectively. The Quality control (X bar R) charts were plotted using ¹³⁷Cs and ⁴⁰K background counts observed periodically, which showed that the fluctuation is well within the confidence limit and confirms the stability of the system. The laboratory has been participating in the proficiency tests (PTs) of the International Atomic Energy Agency (IAEA). In recently concluded PTs, the samples include soil, spiked standard solution, spinach, phosphogypsum and spiked air filter were analysed for the natural, fission and activation products radionuclides. The performance evaluation of the IAEA PTs showed that the laboratory results were in good agreement with the target value, which confirms the reliability and traceability of the gamma spectrometric measurement result of the laboratory.     

Intricate packing in the hydrophobic core of barstar through a CH–π interaction

Identification of specific packing interactions within in the hydrophobic core of proteins is important for understanding the integrity of protein structure. Finding such interactions is challenging because few tools allow monitoring of a specific interaction in the presence of several non‐specific forces that hold proteins together. It is important to understand how and when such interactions develop during protein folding. In this study, we have used the intrinsic tryptophan residue, Trp53, as an ultraviolet resonance Raman probe to elucidate the packing interactions in the hydrophobic core of the protein barstar. Barstar is extensively studied for its folding, unfolding and aggregation properties. The Trp53 residue is known to be completely buried in the hydrophobic core of the protein and is used extensively as an intrinsic probe to monitor the folding and unfolding reactions of barstar. A comparison of the resonance Raman cross sections of some bands of Trp53 with those observed for N‐acetyl‐tryptophanoamide in water suggests that Trp53 in barstar is indeed isolated from water. Intensity ratio of the Fermi doublet suggests that Trp53 is surrounded by several aliphatic amino acid residues in corroboration with the crystal structure of barstar. Importantly, we show that the side chain of Trp53 is involved in a unique CH–π interaction with CH groups of Phe56 as well as a steric interaction with the methyl group of Ile5. Copyright © 2014 John Wiley & Sons, Ltd.     

Study of uranium isotopic composition in groundwater and deviation from secular equilibrium condition

Uranium concentration in groundwater reflect both redox conditions and uranium content in host rock. In the present study an attempt has been made to study the uranium concentration and activity ratios of uranium isotopes to present the geochemical conditions of the groundwater in Malwa region of Punjab state, India and the reason for high uranium levels and variation of activity ratios from secular equilibrium conditions. Uranium concentration in groundwater samples was found to be in the range of 13.9 ± 1.2 to 172.8 ± 12.3 μg/l with an average value of 72.9 μg/l which is higher than the national and international guideline values. On the basis of uranium concentration, the groundwater of the study region may be classified as oxidized aquifer on normal uranium content strata (20 %) or oxidized aquifer on enhanced uranium content strata (80 %). The ²³⁸U, ²³⁵U and ²³⁴U isotopic concentration in groundwater samples was found to be in the range of 89.2–1534.5, 4.4–68.5, and 76.4–1386.2 mBq/l, respectively. Activity ratios of ²³⁴U/²³⁸U varies from 0.94 to 1.85 with a mean value of 1.11 which is close to unity that shows secular equilibrium condition. High value of ²³⁴U isotope than ²³⁸U may be due to alpha recoil phenomenon. The plot of AR of ²³⁴U/²³⁸U against the total uranium content in log scale reveals that the groundwaters of the study region either belongs to stable accumulation or normal oxidized aquifer.     

Dielectric relaxation studies of aqueous N,N-dimethylformamide using a picosecond time domain technique

The dielectric relaxation studies of N,N-dimethylformamide at thirteen concentration in aqueous solutions have been carried out using a time domain reflectometry technique in the frequency range 10 MHz to 10 GHz. The dielectric parameters and excess dielectric properties have also been determined from 5 to 40°C. The Luzar theory was applied to compute the cross correlation terms for the mixture. It adequately reproduces the experimental values of the static dielectric constants. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.     

Use of the Pictet-Spengler reaction for the synthesis of 1,4-disubstituted-1,2,3,4-tetrahydro-β-carbolines and 1,4-disubstituted-β-carbolines: formation of γ-carbolines

Microwave-assisted conjugate addition of indole on nitro-olefins furnished nitro compounds, which were reduced to tryptamines. Further, by using Pictet-Spengler condensation, new 1,4-disubstituted-1,2,3,4-tetrahydro-β-carbolines were synthesized in diastereoselective manner. Dehydrogenation of the tetrahydro-β-carbolines produced new 1,4-disubstituted-β-carbolines. As a new observation, in some of the cases, Pictet-Spengler condensation and dehydrogenation gave two products, namely 1,4-disubstituted-β-carbolines and 1,4-disubstituted-γ-carbolines. A mechanism is proposed for this observation.     

Synthesis of five and six membered aminocyclitols: stereoselective Michael and Henry reaction approach with d-glucose derived α,β-unsaturated ester

The stereoselective intermolecular Michael addition of nitromethane to d-glucose derived α,β-unsaturated ester 7 afforded l-ido-configurated nitroester 8 as the only product that on reduction of the ester functionality, cleavage of 1,2-acetonide and the intramolecular Henry reaction afforded exclusively muco-nitroinositol 9. While reduction of the ester functionality in 8, deprotection of 1,2-acetonide, oxidative cleavage with NaIO₄ and the intramolecular Henry reaction afforded nitrocyclopentitol 13. Nitrocyclitols 9 and 13 were converted to the hydroxyethyl substituted aminocyclohexitol 5 and aminocyclopentitol 6, respectively.     

Differential Distortion of Purine Substrates by Human and Plasmodium falciparum Hypoxanthine‐Guanine Phosphoribosyltransferase to Catalyse the Formation of Mononucleotides

Plasmodium falciparum (Pf) hypoxanthine‐guanine phosphoribosyltransferase (HGPRT) is a potential therapeutic target. Compared to structurally homologous human enzymes, it has expanded substrate specificity. In this study, 9‐deazapurines are used as in situ probes of the active sites of human and Pf HGPRTs. Through the use of these probes it is found that non‐covalent interactions stabilise the pre‐transition state of the HGPRT‐catalysed reaction. Vibrational spectra reveal that the bound substrates are extensively distorted, the carbonyl bond of nucleobase moiety is weakened and the substrate is destabilised along the reaction coordinate. Raman shifts of the human and Pf enzymes are used to quantify the differing degrees of hydrogen bonding in the homologues. A decreased Raman cross‐section in enzyme‐bound 9‐deazaguanine (9DAG) shows that the phenylalanine residue (Phe186 in human and Phe197 in Pf) of HGPRT stacks with the nucleobase. Differential loss of the Raman cross‐section suggests that the active site is more compact in human HGPRT as compared to the Pf enzyme, and is more so in the phosphoribosyl pyrophosphate (PRPP) complex 9DAG–PRPP–HGPRT than in 9‐deazahypoxanthine (9DAH)–PRPP–HGPRT.     

Effects of wall conduction and rarefaction on shock propagation in a micro-channel

A Direct Simulation Monte Carlo code is coupled with a continuum unsteady conduction finite volume code to study the effects of wall conduction on shock propagation in a micro-channel. In addition, the effects of rarefaction and wall accommodation are also investigated. Wall accommodation is seen to influence the shock attenuation more significantly than wall conduction. The results indicate that both the shock front Mach number and shock strength are comparatively higher in case of adiabatic wall condition as there is no loss of energy from the shocked region. At higher rarefaction, the effect of wall accommodation as well as that of wall conduction are seen to become more noticeable. The simulation results show that it is not necessary to exactly model the wall conduction heat transfer for studying shock attenuation, and the two limiting situations of isothermal and adiabatic approximations are satisfactory as the thermal wall boundary conditions.     

Phytochemical Investigation of Artemisia pallens

Two new eudesmanolides, pallensin ( 1 ) and 4‐epipallensin ( 2 ), along with a known eudesmanolide, santonin, and a known flavone, 4‐epivalgarin, have been isolated from the aerial part of A. pallens. Their structures were established by detailed spectral studies (1D and 2D) and by comparison of their spectroscopic data with those of known compounds.