Nuclear Makeup

Z: number of protons, N: number of neutrons, A: mass number

Nuclear Reaction

m < mo: nuclear reaction releases energy

m < mo: nuclear reaction absorbs energy

Radioactive Decay

No: initial amount of active substance, N: quantity that still remains and has not yet decayed after a time t, ΔN: amount of decayed substance, mo: initial mass, m: mass of remaining, λ: decay constant, t: time, T: half life

Half Life of some elements

ElementHalf Life-T
Radon (Rn-219)4 seconds
Oxygen (O-15)122 seconds
Iodine (I-131)8 days
Polonium (Po-210)138.4 days
Radium (Ra-226)1600 years
Carbon (C-14)5730years
Uranium (U-235)7.108

Amount Of Radioactivity

Ho: initial amount of radioactivity, H: amount of radioactivity at time t