Posted by Jannet on .
A radioactive isotope source has a mass of 120ug. If the isotope had a half life of 20s, what would be the mass if the isotope after 2 mins?

Radioactivity or science 
DrBob222,
k = 0.693/t_{1/2}
Then
ln(No/N) = kt
No = 120 ug
N = solve for this
k = from above
t = 120 sec.