Precise determination of femtogram quantities of radium by thermal ionization mass spectrometry

Femtogram quantities of 226Ra (~ 3 x 106) atoms, or 4 x 10-5 Bq) have been determined in environmental materials, including seawater, mineral samples, and silicate rocks, by thermal ionization mass spectrometry. Chemical separation techniques suitable for all these materials are described here. Overall, these techniques enable the abundance of 226Ra to be determined in samples of both seawater and silicates which are some 103 times smaller than those required by conventional radioactive counting methods