Preparation and certification of plutonium standards

The Commissariat a l'Energie Atomique has prepared plutonium metal reference samples of guaranteed mass, ranging from 300 to 900 mg, and plutonium content (99.977%). Purification then fragmentization into beads were performed by electrorefining in fused salt baths. The high-precision weighings in a glove box required special equipment and extemely careful handling to achieve a +- 42 μg dubiousness on the mass determination of each sample. Packaging in glass ampoules was carried out under secondary vacuum. Many of the residual impurities were detected by spark mass spectrometry while carbon, nitrogen, hydrogen, oxygen and americium were determined by specific methods. The discovery of an americium segregation necessitated a γ spectrometric sorting to eliminate samples containing abnormal amounts of the element. The plutonium content was determined from the results of direct analyses carried out in five laboratories by five different methods. An extensive statistical treatment guarantees the plutonium mass in each sample with a maximum dubiousness of +- 0.052 % at the probability level 0.95. A certificate of guarantee gives instructions for use of the standards