The amount left after 20 years = 154.15 mg
The atomic nucleus can experience decay into 2 particles or more due to the instability of its atomic nucleus. Â
Usually radioactive elements have an unstable atomic nucleus. Â
The main particles are emitted by radioactive elements so that they generally decay are alpha (α), beta (β) and gamma (γ) particles Â
The decay formula for isotope :
[tex]\tt \large{\boxed{\bold{A(t)=217e^{-0.0171t}}}[/tex]
Then for t=20 years, the amount left :
[tex]\tt A(t)=217e^{-0.0171\times 20}\\\\A(t)=154.15~mg[/tex]