Nuclear energy - measurement of radioactivity in the environment - water - part 2 : measurement of strontium 90 activity in water - organic solvent extraction of yttrium 90 and measurement of beta activity 核能.环境中放射性的测量.水.第2部分:水中锶90放射性测定.钇90的有机溶剂萃取和放射性的测量