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.
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.
Rare-Earth Element (REE) concentrations in briny groundwaters are very low, and range from ppb to ppt levels. REE can be measured at these low levels using prechemistry to concentrate the REE, postchemistry as an REE group separation following neutron activation, and reactivation for chemical yields. The brine solutions appear to be stable with respect to trace elements (such as the REE) over the four years of sample storage. The brine REE patterns are highly fractionated from light REE to heavy REE, including a negative Eu anomaly. The REE patterns appear to be characteristic of each formation and its source region.
This paper describes the measurement of210Bi by Cerenkov counting in a commercial liquid scintillation counter. The counting efficiency in water is 0.17 counts per
second per Becquerel (17%). When the enhancers Triton X-100 (15% v/v) and sodium salicylate (1% m/v) are added to the solution
the counting efficiency for210Bi increases from 17% to 75%. The210Po daughter of210Bi causes interference of 0.85 counts per second per Becquerel in the presence of the enhancers but not in water. When210Bi and210Po are present in secular equilibrium the total counting efficiency is 160%. When210Bi and210Po are not in secular equilibrium the210Po can be removed immediately before counting by plating onto silver foil. The use of the enhancers gives a substantial increase
in counting efficiency compared to counting in water. Compared with solutions used in liquid scintillation counting the enhancer
solution is inexpensive and can be disposed of without environmental hazard.
Gamma-ray spectroscopy has been widely used in many areas of applied science. We have used the method to compare the137Cs contamination in fungi collected in central Sweden, Ukraine (Kiev region) and southern Ontario, Canada. Mean activities were comparable for Sweden and Ukraine, but were much lower in the North American samples. Many European mushroom species which are considered as prized edibles, contained unacceptably high levels of137Cs (1 kBq/kg) and should not be sold for human consumption. By contrast, no activity in mushrooms collected in Ontario or northern Michigan exceed 1 kBq/kg. The excessive contamination in European mushrooms is primarily due to the Chemobyl reactor accident of 1986. However, our observations suggest that about 20% of the137Cs contamination in the Ukraine is not due to this accident.
DSC can be used to quickly determine if a product labeled as butter is actually a recombined butter made without milk. Recombined
butter is manufactured from anhydrous milk fat, skim milk powder, water, salt, and lecithin. Melting profiles of tempered
samples of natural butter and recombined butter were alike, but DSC curves from 5 to 25°C of untempered refrigerated samples
revealed that the enthalpy of the melting transition around 17–20°C was much higher for natural butter than for recombined
butter. The procedure for differentiating the two products can be completed in less than 20 min.
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.
Radionuclide detection by mass spectrometric techniques offers inherent advantages over conventional radiation detection methods. Since radionuclides decay at variable rates (half-lives) and via various nuclear transformations (i.e. emission of alpha-, beta-, and/or gamma-radiation) their determination via radiation detection depends not only on decay systematics but also on detector technology. Radionuclide detection by directatom measurement, however, is dependent only on technique sensitivity and is indifferent to decay mode. Evaluation of inductively coupled plasma mass spectrometry (ICP/MS) indicates this method to be superior to conventional radiation detection techniques for many radionuclides. This work discusses factors which influence detection by both methods. Illustrative applications of ICP/MS to the ultra-trace determination of several radionuclides, including129I, are presented.
This paper examines the process of making a decision on the optimum technique for the measurement of low concentrations of226Ra in environmental materials. The available counting techniques are alpha spectrometry, high resolution gamma spectrometry and liquid scintillation counting. The properties of the analytical technique; sensitivity, lower limit of detection (LLD) and precision are considered. Method selection is also restricted by the available sample size and activity. The influence of procedure backgrounds, geometric efficiency, chemical recovery, counting time, sample size and activity on the precision and LLD are investigated. The process of method selection, applicable to a wide range of samples, is illustrated by reference to sediments, waters and tissues.