(4) Aktiivsus (A) on mingis kindlas energiaseisundis oleva radionukliidi koguse aktiivsus etteantud ajal: A = dN /dt, kus dN on sellest energiaseisundist toimuvate spontaansete tuumasiirete arvu ootev, (4) Activity (A) is the activity per quantity of a radionuclide in a specific energy state at a given time: A = dN / dt, where dN is the expectation value of the number of spontaneous nuclear transfor, defineeritakse kõikide Eesti õigusaktide ulatuses, defined within the scope of all Estonian legal instruments