"\"Radioactivity\" means the number of radioactive decays of a material per second. \"Radioactivity concentration\" means radioactivity per unit volume of the medium. \"U\" means the element \"uranium\" and \"231U\" is the isotope \"uranium-231\" with a half-life of 4.29e+00 days."@en . "SDN:P07::03NKJYIC" . "radioactivity_concentration_of_231U_in_air"@en . . . . "SDN:P07::03NKJYIC" . . "1" . "1" . . "SDN:P07::03NKJYIC" . "2018-02-12 16:53:18.0" . "" . . "accepted"@en . "false" . "2018-02-12 16:53:18.0" .