Measurements, quantities and units Nuclear physics and elementary particles Rem (ber, rem), a non-SI unit of the equivalent dose of ionising radiation. 1 rem = 0.01 J/kg. Until 1963 the unit was defined as the biological equivalent of the roentgen (hence the Russian name, ber). Encyclopedia by letter A B C D E F G H I J K L M N O P Q R S T U V W Y Z