Activity is a measure of the radioactivity of a sample of a radionuclide.
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The activity (A) of an amount of a radioactive nuclide in a particular energy state at a given time is the quotient of dN by dt, where dN is the expectation value of the number of spontaneous nuclear transitions from that energy state in the time interval dt (i.e., the activity of a sample is the number of nuclear transitions - or -’disintegrations’ - per unit time).
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The SI unit of activity is s¹.
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The special unit of activity is the becquerel (Bq): ............1 Bq = 1 s¹
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The old special unit was the curie (Ci): ..........................1 Ci = 3.7 x 1010 s¹
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Hence ..............1 MBq = 27 pCi
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....and ..............1 mCi. = 37 MBq
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