Radioactivity and radiation protection

Unit of activity = becquerel (curie): 1 Bq = 1 disintegration s–1 [= 1/(3.7 × 1010) Ci] Unit of absorbed dose = gray (rad): 1 Gy = 1 J kg–1 (= 104 erg g–1 = 100 rad) = 6.24 × 1012 MeV kg–1 deposited energy Unit of exposure, the quantity of xor γ-radiation at a point in space integrated over time, in terms of charge of either sign produced by showering electrons in a small volume of air about the point: = 1 C kg–1 of air (roentgen; 1 R = 2.58 × 10–4 C kg–1) = 1 esu cm–3 (= 87.8 erg released energy per g of air) Implicit in the definition is the assumption that the small test volume is embedded in a sufficiently large uniformly irradiated volume that the number of secondary electrons entering the volume equals the number leaving. Unit of equivalent dose for biological damage = sievert. 1 Sv = 100 rem (roentgen equivalent for man). The equivalent dose in Sv = absorbed dose in grays × wR, where wR is the radiation weighting factor (formerly the quality factor Q), which depends upon the type of radiation and other factors, as shown in Table 5-3. The equivalent dose expresses the long-term risk (primarily due to cancer and leukemia) from low-level chronic exposure.