Precise determination of nanogram quantities of europium by the combination of gravimetric sample preparation and neutron activation gamma-ray spectrometry

The precision of the determination of nanogram quantities of europium was increased greatly through the gravimetric sampling of standard and sample solutions. About 3 mg(≈0.003 ml) of europium solutions (1100 μg-Eu/ml) was weighed out by means of a polyethylene pycnometer (Fig. 1) and spottes on a piese of filter paper (0.5 cm in diameter). The filter paper was dried at room temperature and sealed in a polyethylene pouch.The sample was irradiated, together with a standard in a pneumatic tube of JRR-2 at a neutron flux of 7.0×1013 neutron·cm-2·sec-1 for 1 minute. 151Eu (natural abundance 47.77%) is nuclearly trasformed through 151Eu(n, γ) 152mEu to 152Eu, which decays as152mEu β-, γ(0.842 MeV, 0.961 MeV)→T1/2:9.2h152Eu β-, γ→T1/2:12.7 years 152GdThe radioactivity of 152mEu was measured by a high resolution Ge(Li)-detector and 1024 channel pulse height analyzer.The repeatability precision of the method was 0.418% in terms of coefficient of variation for 4ng of europium, this value being higher than theoretical precision calculated from statistical fluctuation. The corresponding values were 2.3% and 5.20%, when a 1-ml pipette and a 10-μl microsyringe were used, respectively, for the sampling. The adoption of the gravimetric sampling and activation γ-ray spectrometry allowed the determination of nanogram quantities of europium with an error of 0.5% or less.The procedure was applied to the test of local distribution of europium in red phosphors (europiumdoped yttrium oxide).About 0.5 mg of the sample powder was weighed by a semi-micro balance, transfered to the weighed "weighing vial", then dissolved in 5 ml of 2 M HNO3, and the weight of the solution was determined.About 1 ml of the solution was introduced into a pycnometer, and europium was determined according to the above-described procedure. This experiment revealed that the doped europium was not uniformly distributed in commercial red phosphors from a microscopic point of view.