A pre-irradiation group separation procedure for the quantification of 11 to 13 rare earth elements (REE) in geological materials by neutron activation analysis, with yield determination by mass spectrometry isotope dilution analysis of Sm and Nd, is described. Utilization of the shorterlived isotopes of the REE allow sufficient data for most geochemical studies to be obtained within one day of irradiation, although where necessary additional information may be obtained following a decay period of three to four weeks. Analysis of selected USGS rock standards shows the method to be both accurate and precise.
Several short-lived accelerator-produced radionuclides for medical applications have been routinely produced over the last
few years in Manchester, namely123I,81Rb−81mKr,111In,206Bi and191Pt. Nuclear reactions employed, target preparation and the radiochemical separation procedures used are briefly discussed.
Barium is estimated in biological material by thermal neutron activation analysis and measurement of139Ba by γ-counting. The biological material is digested with nitric acid and scavenged with ferric hydroxide. A special fluoride
precipitation removes calcium and strontium and the barium is recovered as the chromate. The method allows the analysis of
up to 40 samples per day and the sensitivity is 0.1 μg after irradiation for 85 mins at 4·1012n·cm−2·sec−1.
We have developed a sensitive method of determining enthalpy changes for gas-surface interactions: quartz microbalance microcalorimetry. We mount in an isoperibol environment both sample and reference combinations of a quartz crystal microbalance (QCM) in intimate thermal contact with a heat flow sensor. We coat the sample QCM with a thin (1 µm) polymer film. By exposing the film to ethanol vapor, we measure simultaneously the change in mass per unit area (to ±0.25 ng cm–2) and the resulting heat flows (to ±50 nW) when the polymer adsorbs or desorbs ethanol. The molar enthalpies of sorption of ethanol vapor in Tecoflex, an aliphatic polyurethane elastomer, are
adsorptionH= –53±8 kJ mol–1 and
desorptionH=52±3 kJ mol–1.
We investigated the neighbourhood-scale effect of weeding on native plants in Lance McCaskill Nature Reserve, Canterbury, New Zealand. The reserve is an unproductive basin of limestone debris. Originally set up to protect the Castle Hill buttercup,
, the reserve also offers protection for nationally endangered species:
. Our aim was to investigate whether removal of introduced plants increased the cover of remaining native species. We removed introduced plants, by hand, every year for 6 years from half of the plots. We used nonparametric multivariate analysis to compare overall species cover.The results suggest that weeding does benefit the native plants in this area. There was a significant difference in the mean of the overall native species cover between the weeded and the non-weeded plots. For the ten species measured, the mean area covered per square metre was higher in the weeded plots than in the non-weeded plots in most years of the study. There was considerable variation in the data and we discuss possible reasons for this.
Breakfast wheat-flake materials of different composition have been reconstituted as barshaped test pieces to reduce geometry and structure effects and allow better comparison of the matrix mechanical properties. The ground flakes comprised a control formulation and others in which components had been subtracted or substituted. The aim was to compare the mechanical properties of pressed specimens of multiple-component systems with those published for simpler one- and two-component materials. Sucrose or fructose, present in the ratio sugar∶wheat 1∶5.9–6.1, lowered the modulus of wheat-flake material, but by progressively lesser extent with decreasing water content below 22% (wet-weight basis, w.w.b), the difference becoming negligible at water contents of 7 to 10% (w.w.b). However, the energy to break wheat-flake samples and their fracture toughness were reduced more by fructose than sucrose addition to a control formulation sample at these water contents. The energy to break and fracture toughness increased markedly with increasing water content for all formulations.
Current techniques for determining low levels of dissolved thorium involve chemical separations, generally by coprecipitation with a carrier cation, purification by ion exchange procedures, electroplating and, finally, alpha counting by alpha spectrometry. Similarly, measurements of low228Ra and224Ra activities requires concentration, by coprecipitation with barium sulfate, followed by gamma counting. An improved method for determining radium and thorium from the232Th decay series has been developed which measures the activity of220Rn as an assay of its parents. Although some ingrowth corrections and minor separation procedures for Th are required, the results to date show that the dynamic counting of220Rn via de-emanation and alpha counting by the alpha-scintillation method is a preferable approach for determining these radium and thorium isotopes accurately and efficiently. The method for lower limit detection depends on the emanation rate, which depends on purge-gas flow rate and sample volume analyzed. Using 50-cc and 1000-cc bubblers, and maximum effective purge gas flow rate, a lower limit of detection of 0.4 and 0.06 pCi/L220Rn can be obtained, respectively.