Calculate activity in Becquerels or Curies, decay constant, mean lifetime and remaining atoms from any radioactive source.
Activity is the rate at which a radioactive sample decays — specifically, the number of disintegrations per second. It's measured in Becquerels (1 Bq = 1 decay/second) or Curies (1 Ci = 3.7 × 10¹⁰ decays/second). The Curie was originally defined based on the activity of one gram of Radium-226.
If you know the mass of a sample in grams and its atomic mass number, the number of atoms is N = (mass / atomic_mass) × Avogadro's number, where Avogadro's number is 6.022 × 10²³. For example, 1 gram of U-238 contains about 2.53 × 10²¹ atoms.
Activity decreases exponentially, just like the number of atoms. After time t, the activity is A(t) = A₀ × e^(−λt), where A₀ is the initial activity. This is important for radiation safety, medical dosimetry, and managing radioactive waste.