wd ‘ - G3 - Unit of dose equivalent. When the appropriate modifying factors are used to calculate dose equivalent one rem is the quantity of any type of ionizing radiation which when absorbed in man produces an effect equivalent to the absorbtion of one rad of X- or gamma-radiation at the place of interest. Roentgen: . The guantity of X- or gamma-radiation such that the associated corpuscular emission per 0.001293 grams of air produces, in air ions carrying one electrostatic unit of electricity of either sign. For the purposes here, the roentgen is roughly equivalent to the rad. Specific activity: Total radicactivity of a given material (isotope, element, or compound) per gram of the material -- curies/gram. . Abbreviation for micron, which is onemillionth of a meter. Abbreviation for microcurie, which is one-millionth of a curie. Abbreviation for microgram, which is onemillionth of a gram.