Field testing of collection and measurement of radioxenon for the Comprehensive Test Ban Treaty

Pacific Northwest National Laboratory, with guidance and support from the U.S. Department of Energy's NN-20 Comprehensive Test Ban Treaty (CTBT) Research and Development program, has developed and demonstrated a fully automatic sampler-analyzer (ARSA) for the collection and quantitative measurement of the four xenon radionuclides,^131mXe (11.9 d),^133mXe (2.19 d),¹³³Xe (5.24 d), and¹³⁵Xe (9.10 h), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a CTBT, and may have applications in stack monitoring and other areas where xenon radionuclides are present. The activity ratios between certain of these radionuclides permit discrimination between radioxenon originating from nuclear detonations and that from nuclear reactor operations, nuclear fuel reprocessing, or from medical isotope production and usage. With the ARSA system, xenon is continuously and automatically separated from the atmosphere at flow rates of about 100 lpm by sorption-bed techniques. Samples collected in 8 hours are automatically analyzed by electron-photon coincidence spectrometry to provide detection sensitivities as low as 100 μBq/m³ of air. This sensitivity is about 10-fold better than achieved with reported laboratory-based procedures¹ for the short time collection intervals of interest. Gamma-ray energy spectra and gas analysis data are automatically collected.     

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

连续波锁模P_r~（3＋）：YLF激光器

本文报导了采用氩离子激光器来泵浦Ｒｒ￣（３＋）：ＹＬＦ晶体，应用声光调制器实现了主动锁模；同时应用振动─高反射平面镜也实现了被动锁模，两种锁模均得到了ｐｓ光脉冲。据作者了解这是这种晶体材料的第一次锁模运转。     

Applications of electron spin resonance in the analytical chemistry of transition metal ions: Part 3. Determination of Chromium(III) in Aqueous Solution [1]

Chromium(III) can be determined in aqueous solution at pH 1.5– 2.5 by electron spin resonance techniques. The analytical range is 2.0 x 10^-1–2.0 x 10^-6 mol dm^-3 ; the precision is± 0.3%. The effects of instrumental variables are discussed. Few commonly occurring species up to a concentration of 1.0 x 10^-1 mol dm^-3 interfered with the determination. The characteristic g value of 1.98 for chromium(III) suggests that the method may also be used to identify chromium(III).     

Structure and composition of adsorbed layers formed by sequential exposure of Pt(100) and Pt(111) to pairs of compounds: Solvents and electrolytic substances

Studies are reported of the interaction of vapor of typical polar solvents and electrolytes at electrodes having Pt(111) or Pt(100) single-crystal surfaces: water, pyridine, acetonitrile, dimethyl-sulfoxide, hydrogen bromide, iodine, sulfur dioxide, acrylic acid, and ammonia. Exposure was extended from low pressures (about 10^?5 Torr) to pressures approaching the vapor pressure of the pure liquid. The results indicate that these typical electrochemical materials adsorb strongly to the clean Pt surface but once adsorbed tend not to react with each other. However, analysis of LEED patterns and Auger intensities suggests that exposure of an adsorbed layer of solvents such as dimethylsulfoxide to iodine results in adsorption of the halogen and molecular re-orientation of the adsorbed solvent.     

Optimum control of bobsled steering

Minimum-time and smooth-steering control algorithms are developed for bobsled optimal control. Numerical solutions are obtained both for one-curve optimal control and whole-course piecewise optimal control with application to realistic three-dimensional track surface shapes. Specific results are calculated for the Lillehammer Olympic Track.     

Medium effects upon the kinetics of formation of nickel(II) and cobalt(II) pyridine 2-azo-p-dimethylaniline

Summary The kinetics of formation of the Ni^II and Co^II complexes of pyridine 2-azo-p-dimethylaniline have been studied in aqueous ethylene glycol, aqueous glycerol and in moderate (up to 2.5 mol dm^–3) concentrations of NaCl at 298.2K.Mole fractions of 0.24 and 0.12 respectively for ethylene glycol and glycerol effect a lowering of the formation rate constant K_f of Ni(PADA)²⁺ to about 50% of the value in water. A concentration of 2.0 mol dm^–3 NaCl doubles k_f for both the Ni and Co complexes. These findings are discussed within the framework of the dissociative interchange mechanism; the possible effects upon each step of the mechanistic pathway are considered.     

Transfer chemical potentials for iron(II)-diimine complexes from water into aqueous methanol

Summary Solubilities of perchlorate and thiocyanate salts of several iron(II)-diimine complexes of Schiff base ligands in methanolwater mixtures are reported. From these results and published values for transfer chemical potentials of the perchlorate and thiocyanate anions, transfer chemical potentials for the complex cations are calculated. Trends with solvent composition suggest that preferential solvation varies from negligible to very strongly by methanol, depending on the size and hydrophilic-hydrophobic character of the complex.On leave from the Faculty of Science, Sohag, Egypt.