Physics

$ΔtΔN ∝N$

or $ΔtΔN =λN$

where $λ$ is called the radioactive decay constant or disintegration constant.

$NdN =−λdt$

Integrating both sides,

$∫_{N_{0}}NdN =−λ∫_{t_{0}}dt$

$ln(N_{0}N )=−λt$

$N=N_{0}e_{−λt}$

This is the law of radioactive decay

1 curie = 1 Ci = 3.7 10^{10} Bq (decays per second)