Absorbed Dose
The fundamental dosimetric quantity D is defined as:
D = dE /dm
where, ‘dE’ is the mean energy imparted by ionising radiation to the matter in a volume element and ‘dm’ is the mass of matter in the volume element. The energy can be averaged over any defined volume, the average dose being equal to the total energy imparted in the volume divided by the mass in the volume. The SI unit of absorbed dose is joule/kg (J.kg-1), termed the gray (Gy).
Activity
The quantity ‘A’ for an amount of radionuclide in a given energy state at a given time is defined as:
A(t)= dN/dt
where ‘dN’ is the expectation value of the number of spontaneous nuclear transformations from the given energy state in a time interval ‘dt’. The SI unit of activityis the reciprocal of second (s-1), termed the Becquerel (Bq).
Source: www.aerb.gov.in
