ISO 11483: 2005 describes three simple and fast procedures to prepare plutonium sources and a procedure to measure the activity ratio of 238Pu to (239Pu + 240Pu) by alpha spectrometry. The alpha spectrometry method is used for the determination of isotopic abundance of 238Pu in combination with mass spectrometry and eliminates the possible interferences of 238U in the latter method. It applies to the analysis of purified solutions of plutonium in 2 mol/l to 4 mol/l nitric acid containing 50 micrograms to 200 micrograms of plutonium per millilitre, as may result from the chemical treatment and purification preceding plutonium isotopic analysis by mass spectrometr