1.1 ,This test method covers the use of alpha spectrometry for determining the ²³⁸Pu isotopic abundance in plutonium samples. It is particularly useful for samples in which the ²³⁸Pu content is less than 1 ,% of the total plutonium content. For such samples, mass spectrometric results are vulnerable to bias because of potential interference from any ²³⁸U isobar remaining after ion exchange.