Radioactive decay

A(t) = A0ekt = A0e(ln½/t½)t = A0(1/2)t/t½

Initial amount of radioactive substance (A0):
Half-life of substance (t½):     OR     k:

Time (t):     OR     Solve for t: Amount remaining (Ar):
             (If solving for t, the Time textbox must be empty.)

Pu-239 emits alpha particle to transmute into U-235.
C-14 undergoes beta decay, one proton becomes a neutron, becomes N-14. 1/trillion C's in air and body are C-14: ~4000 decays/second ionizing radiation but swamped by natural background radiation, medical imaging, radon, smoking, diet, and genetics as a cancer risk. C-14 used for radiocarbon dating.
Am-241 decays via alpha emission to Np-237. 0.29 micrograms in a smoke detector.