The optimum irradiation, decay and counting times were calculated for single and double counting in the case of 3 isotopes.
Two different minimization functions were considered. The results, presented in graphical form, make possible the estimation
of the optimum times for the majority of practical cases. An important gain in sensitivity can be obtained by using a double
A new screening method is proposed for the determination of alpha-radioactivity in ground water. Natural alpha-emitters of Po, Ra, Th and U are precipitated from solution with sulphuric acid and ammonia. Ba2+ and Fe2+ are used as carriers. The overall yield for all emitters is greater than 80%. This method is faster than the evaporation technique, less dependent on the water composition and a better sensitivity can be achieved by using a large volume sample.
2000 analytical functions were fitted to the measured gamma-ray detection efficiencies of a Ge detector for a small irradiation vial located at the closest distance from the detector. Among these, the Pearson IV function, gave the best fit. The measured and calculated efficiencies were compared for 50 determinations (for energies which varied between 61 and 2754 keV) and a relative standard deviation of 8.3% was obtained.
The concentrations of 25 elements in 7 oil ash samples were determinedby computerized systematic instrumental absolute neutron activation analysis.In the oil ash samples, the following mean concentrations (in ppm) of elementswere found: Al: 39531, As: 109, Ba: 1391, Ca: 29701, Ce: 295, Co: 1294, Cr:1485, Cs: 7.9, Dy: 4.5, Eu: 1.2, Fe: 53094, Ga: 146, Hf: 2.2, La: 1534, Mn:547, Na: 40277, Sb: 360, Sc: 2.3, Sm: 21, Sr: 674, Ta: 15.8, V: 130548, W:4.1, Yb: 0.9 and Zn: 3125. These findings were compared with the concentrationsof elements found in coal ash samples. The concentrations of Co, Na and Vwere significantly higher in the oil ash samples, while the concentrationof Sc was lower. The purpose of this study has been to determine the backgroundlevels of different elements in oil ash, in order to evaluate its potentialimpact on the environment.
The median226Ra activity found in 216 drinking water samples in Quebec is 14 mBq/l. Only 6% of samples studied have an activity higher
than the Maximum Contaminant Level of 111 mBq/l. The detection limit of the method is 4 mBq/l.
Food samples were analyzed for uranium by neutron activation analysis. The concentration of U in 20 samples was above the
detection limit and it varied from 0.7 to 59 ppb. The lowest detection limit achievable with the method is 1 ppb.
Several two and three parameter analytical functions were fitted to the measured detection efficiencies () of a Ge detector for a Marinelli beaker filled with samples up to different heights (H). From these, the expression =308E–0.82/((H–6.1)2+107), gave the best fit. The measured and calculated efficiencies were compared and for 70 determinations, a relative standard deviation of only 7.6% was obtained.
A novel computing method has been developed to calculate the absolute photopeak efficiency of a Ge(Li) detector for Marinelli beakers of different heights and diameters and with variable density. For each point in the cylindrical sample the detection efficiency is calculated taking into account the distance from the detector and gamma-ray attenuation and the efficiency is integrated numerically over the volume of the sample. The detector is approximated as a point detector with an experimentally determined effective interaction depth. It is necessary to measure the absolute efficiency for a point source located on the detector axis and on a line beside the detector parallel to the axis. The computer program calculates the absolute counting efficiency for Marinelli beakers of any geometry and for any density. The measured and calculated values for three different densities give a good (–2.2%) overall agreement.
A modified version of the classical emanation method has been developed. It consists of emanation of radon from a 1 l water sample with argon, drying of the gas stream and counting of222Rn activity with a proportional counter. This method is very simple, reproducible, interference free and sensitive. The 3 detection limit obtained with a 100 min counting time is equal to 5 mBq l–1. Several bottled mineral waters were analyzed by using this method and the mean and the median concentration found were equal to 50 and 20 mBq l–1, respectively.