Radioactive Activity Calculator: Decay Rate and ...
Calculate the radioactive activity (in Becquerels or Curies) of any sample. Use the decay law to find activity at any time and understand units of radioactivity.
What is Radioactive Activity?
Radioactive activity (A) is the number of radioactive decays per second in a sample. Unlike the half-life (which is a fixed property of the isotope), activity depends on both the half-life and the number of atoms present. As atoms decay, the activity decreases over time following the same exponential law as the population.
☢️ Radioactive Activity Calculator
Free calculator for instant results.
📐 Formula
A = λN = A₀ × e^(−λt)
λ = decay constant = ln(2)/t½. A₀ = initial activity. N = number of radioactive atoms. Units: Becquerel (Bq) = 1 decay/s. Curie (Ci) = 3.7×10¹⁰ Bq.
📝 Worked Example
Iodine-131 (t½=8.02 days, A₀=1 μCi). Activity after 16 days (2 half-lives):
A = 1 × (½)² = 0.25 μCi = 9,250 Bq
📝 How to Use
❓ FAQ
Is 1 Curie a lot of radioactivity?
1 Ci = 37 billion decays/second — a very large activity. Typical medical procedures use microcuries (μCi) to millicuries (mCi). 1 Ci was originally defined as the activity of 1 gram of radium-226.
What is specific activity?
Activity per unit mass (Bq/g or Ci/g). Shorter half-life isotopes have higher specific activity for the same mass: shorter t½ → larger λ → more decays per second per gram.
Veer Kumavat
Founder & AuthorVeer is a 14-year-old student from Nashik, Maharashtra, who built SciFi Calculators to help students worldwide master STEM subjects. He is passionate about making complex science and math problems accessible through intuitive digital tools.