ISO 31-10 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to nuclear reactions and ionizing radiations. It gives names and symbols for 70 quantities and units. Where appropriate, conversion factors are also given.
Its definitions include:
|activity||A||Expectation value of the number of spontaneous nuclear transitions from a particular energy state occurring in an amount of radionuclide in a small time interval, divided by that time interval||becquerel||Bq||1 Bq = 1/s||The becquerel is a special name for second to the power minus one, to be used as the SI unit of activity.
1 Ci = 3.7×1010 Bq (exactly)
|absorbed dose||D||For any ionizing radiation, the mean energy imparted to an element of irradiated matter divided by the mass of this element||grey||Gy||1 Gy = 1 J/kg||The grey is a special name for joule per kilogram, to be used as the SI unit for absorbed dose.
1 rad = 0.01 Gy
|dose equivalent||H||Product of D, Q and N, at the point of interest in tissue, where D is the absorbed dose, Q is the quality factor and N is the product of any other modifying factors
H = D · Q · N
For Q and N, see CIPM, 1984, Recommendation 1  and ICRU Report 33 (1980) 
|sievert||Sv||1 Sv = 1 J/kg||The sievert is a special name for joule per kilogram, to be used as the SI unit for dose equivalent.
1 rem = 0.01 Sv