Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of ¹²⁹I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable ¹²⁷I. The background ratios of ¹²⁹I/¹²⁷I of 10^-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10^-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 10⁰ and 10^-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure ¹²⁹I to below mBq concentrations. Therefore, where there are elevated concentrations of ¹²⁹I it is possible to use a combination of neutron activation techniques to determine ¹²⁹I/¹²⁷I ratios. This paper describes how NAA is used to measure ¹²⁹I/¹²⁷I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both ¹²⁹I and ¹²⁷I where the ratio is between 10⁰ and 10^-3. A radiochemical procedure is used to measure ¹²⁹I at ratios between 10^-3 and 10^-7, with a thermal neutron flux of 10¹⁶ m^-2·s^-1.     

Epithermal/Fast Neutron Cyclic Activation Analysis for the Determination of Fluorine in Environmental and Industrial Materials

Pseudocyclic activation analysis (12-second irradiation, 12-second count, 5 cycles, 25 minutes between cycles) is used to determine fluorine in plastic and rubber with detection limits in the range 15–40 mg/kg. The detection of fluorine in materials containing high concentrations of aluminum is improved using the ¹⁹F(n,p)¹⁹O reaction, induced by fast neutrons, (30-second irradiation, 30-second count, 25-minute decay between cycles). The method was applied to a biomonitoring survey in the vicinity of an aluminum smelter in the Årdal region, Norway. The fluorine concentration in the moss and soil samples could be determined in all samples above the detection limits of 50 and 100 mg/kg, respectively.     

Some cubic curves associated with a triangle

There are many interesting cubic curves which arise from the geometry of the triangle. In particular, those which are invariant under the operation of isogonal conjugacy have attracted much attention, and a class of these is here investigated by a variety of methods.     

Evidence for multiple band terminations in Pd

The level structure of ¹⁰²Pd has been investigated using data collected with the Eurogam 2 array. Several cascades of γ-rays have been established up to high spins. Termination of rotational bands has been observed at I^π = 28⁻ and 32⁺, and tentatively at I^π = 38⁺ and 42⁺. The nucleus ¹⁰²Pd is the first case where rotational bands built on valence space configurations are followed from spin close to zero up to termination and, at higher spins, a smooth rotational band which appears to terminate is built on core excited configurations.     

The biosynthesis of aristeromycin. Conversion of neplanocin A to aristeromycin by a novel enzymatic reduction

Partially purified cell-free extracts of the aristeromycin producer Streptomyces citricolor have been shown to catalyze the NADPH-dependent reduction of neplanocin A to aristeromycin. Stereochemical studies revealed that the reduction proceeds with anti geometry and involves transfer of the 4 pro-R hydrogen atom of NADPH to the 6′β position of aristeromycin.     

Standardized test mixture for the characterization of comprehensive two-dimensional gas chromatography columns: the Phillips mix

A novel column characterization test mixture is developed for use in comprehensive two-dimensional gas chromatography (GC x GC). This mixture has been named the "Phillips mix" in honor of the late professor John B. Phillips, the father of GC x GC. The mixture comprises a series of homologous compounds from structural groups that cover a volatility and polarity range that is similar to the Grob mix, and includes saturated hydrocarbons (alkanes), unsaturated hydrocarbons (alkenes and alkynes), carbonyls (ketones and aldehydes), primary alcohols, fatty acid methyl esters, alkyl ethers, carboxylic acids, aromatics, as well as other unique functional groups (such as amines, etc.). Similarly to the Grob mix in conventional one-dimensional GC, the Phillips mix can be used as a standardized test for performance characterization of GC x GC column sets. Unlike the Grob mix, however, the Phillips mix's most important use is as a practical guideline for column users. This paper addresses some qualitative aspects of the use of the Phillips mix through an investigation of the chromatographic fingerprints of two different GC x GC column combinations.     

Reorientational motions of substituted benzenes in the crystalline state. A consideration of the dielectric relaxation of appropriate site models having non-equivalent sites

A method is developed for solving the basic rate equations, and hence the dielectric behaviour, of C_N-type barrier systems. Both adjacent-jump (A–J) and multiple-jump (M-J) models are considered. It is shown that for certain six-fold barrier systems the active dielectric relaxation mode is characterized by a relaxatuion time τ which is, to a good approximation, inversely proportional to the transition probability κ₁₂ ≡ κ₁ = κ₀ exp(?W/κT) where W is the principal barriers height. The proportionality factor is either constant or is a slowly varying function of temperature when compared with that for κ₁.     

Implementation of symmetric Fabry-Perot quantum well electroabsorption modulators in symmetric self-electrooptic effect devices

We report results from a symmetric cavity electroabsorption modulator (SCEM) in GaAs/AlGaAs. A reflection change of 45% with an insertion loss of 1.3 dB is obtained under 7.5 V in the normally-off mode. We discuss the factors that affect the device performance and compare the attainable performance with that of the normally-off asymmetric Fabry-Perot modulator (AFPM). We also propose a new method for an improvement of the restricted tolerances of SCEMs. Finally, we demonstrate bistable operation using two SCEMs in the symmetric self-electrooptic effect device (S-SEED) configuration, and attempt to evaluate the potential of this type of modulator for SEED applications.