Use of chemical etching of CR-39 foils at elevated temperature for fast neutron personnel monitoring in India

CR-39 Solid State Nuclear Track Detecting foils (SSNTD), along with 1 mm thick polyethylene radiator, sealed in triple laminated pouches, are used for country wide Fast Neutron Personnel Monitoring in India. With the present system of processing by elevated temperature electrochemical etching (ETECE) and evaluation using automatic image analysis, only 16 foils are processed at a time and it is useful over the dose equivalent range 0.2 mSv to 10 mSv. It has been reported that, by processing CR-39 of good detection efficiency by chemical etching at elevated temperature, more numbers of foils can be processed simultaneously. In the present study, CR-39 foils from Pershore Moulding (UK) have been chemically etched using 7 N KOH under various conditions of temperature and etching durations and evaluated using high magnification microscope. The duration of chemical etching, has been optimized at a constant temperature of 60°C for chemical etching process. The characteristics of the chemically etched CR-39 foils are compared with the characteristics of the CR-39 foils processed by the existing system of ETECE and the detailed results are presented in the full text of the paper. It has been observed that by chemical etching process, the dose equivalent range of CR-39 foils can be extended above 60 mSv.      

Thermionic emission characteristics of LC20M electrode material in open cycle MHD systems

The work function was measured in a vacuum of 10⁻⁵ Torr for magnesia incorporated lanthanum chromite based ceramic designated LC2OM. The results obtained are φ _R =2.75eV andA _R =0.11 A/cm² K² which ensure that LC2OM has favourable electron emission characteristics for MHD hot electrode material. The measurements have been carried out in the temperature range from ambient to 1700 K. Chemistry Division     

Discovering New Classes of <Emphasis Type="Italic">Brugia malayi</Emphasis> Asparaginyl-tRNA Synthetase Inhibitors and Relating Specificity to Conformational Change

SLIDE software, which models the flexibility of protein and ligand side chains while docking, was used to screen several large databases to identify inhibitors of Brugia malayi asparaginyl-tRNA synthetase (AsnRS), a target for anti-parasitic drug design. Seven classes of compounds identified by SLIDE were confirmed as micromolar inhibitors of the enzyme. Analogs of one of these classes of inhibitors, the long side-chain variolins, cannot bind to the adenosyl pocket of the closed conformation of AsnRS due to steric clashes, though the short side-chain variolins identified by SLIDE␣apparently bind isosterically with adenosine. We hypothesized that an open conformation of the motif 2 loop also permits the long side-chain variolins to bind in the adenosine pocket and that their selectivity for Brugia relative to human AsnRS can be explained by differences in the sequence and conformation of this loop. Loop flexibility sampling using Rigidity Optimized Conformational Kinetics (ROCK) confirms this possibility, while scoring of the relative affinities of the different ligands by SLIDE correlates well with the compounds’ ranks in inhibition assays. Combining ROCK and SLIDE provides a promising approach for exploiting conformational flexibility in structure-based screening and design of species selective inhibitors.     

Efficient Synthesis of N‐Oxide Derivatives: Substituted 2‐(2‐(Pyridyl‐N‐oxide)methylsulphinyl)benzimidazoles

Different substituted 2‐chloromethylpyridyl derivatives (6a–d) were oxidized with mCPBA to give the respective 2‐chloromethylpyridine‐N‐oxide derivatives (7a–d) at low temperature, which on condensation with 2‐mercapto‐1H‐benzimidazole (8a–c) in the presence of aprotic solvents give the 2‐[[(pyridin‐2‐yl‐1‐oxide)methyl]sulfanyl]‐1H‐benzimidazole (9a–d) in good yield. Finally, 9a–d oxidized with mCPBA in chlorinated solvent gives a mixture of 2‐[[(pyridin‐2‐yl‐1‐oxide)methyl]sulfonyl]‐1H‐benzimidazole (3a–d, 10%) and 2‐[[(pyridin‐2‐yl‐1‐oxide) methyl]sulfinyl]‐1H‐benzimidazole (4a–d, 90%) derivatives.     

Ordinary-wave Propagation in Mirror-Confined Plasmas

The non-relativistic dispersion relation for ordinary-waves propagating in a hot plasma confined by magnetic mirrors is derived under small gyroradius approximation. The hot electron velocity distribution is modelled by a bi-Maxwellian with a cutoff at the loss-cone boundary. The dispersion relation is analyzed from propagation point of view. It is seen that the presence of loss cones in the electron velocity distribution reduces the high temperature effects in the ordinary-wave propagation characteristics.     

Reduction of background in CR-39 SSNTD using chemical pre-etching methods

Presently, CR-39 Solid State Nuclear Track Detectors (SSNTD) is being used for Fast Neutron Personnel Monitoring in India. Individual detectors are cut manually from CR-39 sheets. Laser-cutting of the sheets will ensure precision and also save on the laborious efforts involved in sheet cutting. It was observed that there is a slight increase in background tracks due to laser-cutting. Studies were carried out on the effect of chemical pre-etching at higher temperatures in properties of CR-39 such as the background, sensitivity and minimum measurable dose. For this purpose a pre-etch step was included in the normal processing of the CR-39 foils in an elevated temperature electrochemical cell (ETECE cell) and the duration for pre-etch step at elevated temperature was optimized. Samples of CR-39 exposed to dose equivalents ranging from 1 mSv to 10 mSv using Am-Be neutron source were processed by both the methods, under normal processing using ECE cell and in the optimized chemical pre-etch followed by normal processing. The dose responses of CR-39 processed by both methods are compared in this paper.      

Excitation Temperature Measurement of Ar + N2 RF Plasma by Spectroscopic Method

The mixed gas (Ar + N₂) plasma has been generated by a 6 KW, 10.3 MHz radio frequency oscillator. The flame got extinguished if N₂ exceeded more than 20% of Ar. The Boltzmann plot using spectral intensities of Ar I and NI lines in the wavelength range 4000–4510 Å have been used to determine the excitation temperature. The results show that excitation equilibrium between two species exist since the temperatures are found to be nearly same for both species.