The detection limits of many nonnuclear methods for ultratrace (≤0.1 μg/g) elemental determinations lie well below the level
at which precise and accurate practical analysis can be executed routinely. Advances in analytical methodologies which are
rapidly eroding such disparities are reviewed. The applications of X-ray fluorescence, atomic absorption, stable isotope dilution
mass spectrometry, and laser intracavity absorption spectrophotometry to ultratrace analyses not amenable to solution by nuclear
methods are discussed.
Gamma-ray spectrometric survey analyses were used to screen raw materials available during the infancy of the optical waveguide
research program. Examinations of γ-ray spectra and semiquantitative survey analyses showed most samples to be insufficiently
pure for waveguide applications. Highly pure samples have been prepared successfully under carefully controlled conditions
when the purification process is adequately monitored by analyses. Radioisotope techniques and neutron activation analyses
were vital in the development of successful procedures for purifying various reagents from which glass could be subsequently
fabricated by melting techniques. Contamination sources during fiber production have also been detected by neutron activation
The distribution of nitrogen in plasma deposited silicon nitride films and in commercially produced, hot-pressed bulk material has been determined by the nuclear (proton) track image analysis technique. The nuclear track technique is shown to have the unique capability of sampling large areas (cm2) while providing distribution information on the micro scale (100 m2). Nitrogen over the range of 2 to 40% is determined quantitatively. Spatial distribution and topographical maps are plotted. The overall composition of the material is established by 14 MeV NAA through the determinations of silicon, nitrogen, and oxygen. An application in the micro electronic industry is described.
Un-hydrated Portland cement
consists of several anhydrous and reactive phases, that when mixed with water
react to form hydrates. The main hydration product of Portland cement is calcium
silicate hydrate (C–S–H). It is the main binding phase in a concrete
system, hence is important to construction chemists. The concrete engineer
measures the compressive strength of concrete after prescribed hydration periods,
typically 1, 3, 7, 28 days. It is often convenient to mimic these intervals
by stopping the hydration reaction at the same times. Several techniques can
be employed to stop this hydration reaction. One of which is solvent-based
and involves mixing a polar solvent such as acetone or isopropyl alcohol,
with the hydrated cement. This mixing should be vigorous enough to blend the
free water, in the partially hydrated cement system, with the polar solvent
without altering the cement system’s matrix. The solvent-water mixture
has a much lower boiling point and the mixture quickly evaporates out of the
system. This achieves two goals. It stops the hydration reaction at the moment
of solvent mixing, and it removes free water to prevent further hydration
from occurring. This procedure theoretically leaves behind a dry, chemically
unaltered, partially hydrated cement paste. In this way, pastes can be analyzed
after the prescribed 1, 3, 7 or 28 days of hydration. This paper uses thermogravimetric
analysis (TG) results to investigate the assumption that solvents have no
thermodynamic or chemical effect on the hydrated cement paste phases.
On mesure le cuivre 64 et le manganèse 56 dans du carbonate de sodium ultra pur par spectroscopie du rayonnement gamma après
élimination du24Na par passage sur colonnes de pentoxide d'antimoine hydraté (PAH); On a aussi déterminé le cobalt, le chrome et le fer par
détection spectrométrique non-destructive du rayonnement gamma du60Co,59Fe et51Cr. Dans le cas de CaCo3, après irradiation et dissolution, on a déterminé simultanément le64Cu et le56Mn, par une séparation radiochimique sélective à pH 3 à 4 avec un mélange de dithizone (H2D) et d'acide pynolidinedithiocarbamique (HPDC) dans CHCL3. L'interférence radioactive de47Sc et47Ca produits pendant 100 heures d'irradiation de CaCO3, étaient supprimées par extraction sélective de ce dernier en milieu HCl 5,0 M par l'oxyde de Tri-n-octylphosphine (TOPO)
0,1 M dans du cyclohexane. On a utilisé en mélange de 0,1 M Thenoyltrifluoroacetone (HTTA) 0,1 M et de TOPO 0,1 M dans du
cyclohexane pour enlever le47Ca à pH≥8.0. Après avoir éliminé l'activité des isotopes de la matrice, on mesure les pics photoélectriques de59Fe.60Co et51Cr pour doser ces impuretés.
A highly precise and selective method is described for the determination of traces of gold by substoichiometric extraction
from hydrochloric acid with tri-n-octylphosphine sulfide in cyclohexane following thermal neutron activation. Fundamental
aspects of the extraction system are discussed and results are reported for the determination of gold in an effluent from
a recovery process.
Stoichiometric, stable fluorides for comparison standards in neutron activation analysis were prepared by horizontal zone-refining
or sublimation in HF atmospheres. The fluorides of Na, Mg and Al were shown by thermogravimetry to be anhydrous and to remain
water-free after exposure to room air. Fluorine in the purified samples was separated by the pyrohydrolysis method and subsequently
measured by acid-base titrimetry or selective ion electrodes. Deviations from theoretical values were ±0.1, ±0.9 and ±2.8%
respectively for fluorides of Na, Mg and Al.
Authors:J. Mitchell, S. Yegnasubramanian, and L. Shepherd
Bulk and surface nitrogen levels of compression-molded samples of polyacrylonitrile, poly (styrene-co-acrylonitrile), poly(methacrylonitrile), polycaprolactam, polyimide, and a cured epoxy resin (EPON 828 — JEFFAMINE T-403, 100:50) were determined, respectively, by 14 MeV NAA (14N(n,2n)13N) and by analysis of proton tracks registered in cellulose nitrate detectors (CN85) as a result of their exposure to protons from the termal neutron induced reaction,14N(n,p)14C. Except for a few polymers, agreement of results obtained for nitrogen levels in the bulk and surface regions is within expected limits. Intrinsic limitations of the method for practical determinations of nitrogen are covered. The spatial homogeneity of materials consisting of nitrogen and non-nitrogen containing segments is easily determined by image analysis of proton track densities. These data are then used to construct nitrogen distribution plots and topographical maps. The potential ability of the proton track image analysis technique for distinguishing phase separation or immiscibility of nitrogen containing polymers is discussed.
Chromium, iron and copper were determined in niobium by radiochemical proton activation analysis (PAA). The main steps of
the technique involved the irradiation of the samples with 13 MeV protons, the post-irradiation decontamination of the sample
surface, a two-step separation procedure based on anion exchange from HF and HCl medium, and counting the separated indicator
radionuclides with a well-type NaI detector. For a 5-hr irradiation, limits of detection for chromium, iron, and copper were
0.2, 5.0, and 15 ppb respectively. The results obtained by this technique are compared with data obtained by radiochemical
neutron activation analysis (NAA) and atomic absorption spectrometry (AAS).
Authors:Laura J. Waters, S. A. Leharne, and J. C. Mitchell
Summary A novel method for the determination of the point of micellar saturation has been developed. To exemplify the theory a model system was considered, this being the saturation of two aqueous micellar solvents with dimethyl phthalate ester (DMP). Upon addition of a hydrophobic compound to an aqueous micellar system partitioning will occur. On further addition, the inner hydrophobic regions will eventually be unable to accommodate any more DMP and, at this specific concentration, the micelle is saturated. With a comparatively large enthalpy change upon partitioning the point of saturation can be determined by a corresponding significant reduction in enthalpy change.