Radioactive Decay

Radioactive decay is:

• Spontaneous: it happens without any external trigger.
• Random: it is impossible to predict which particular nucleus will decay next.

Three types of nuclear radiation:

Type	Symbol	Charge	Mass	Penetrating power	Ionising power
Alpha	$\alpha$	+2	4	Stopped by paper	Strongest
Beta	$\beta^{-}$	$-1$	~0	Stopped by aluminium	Moderate
Gamma	$\gamma$	0	0	Reduced by lead/concrete	Weakest

Decay causes the nucleus to change its proton/nucleon numbers (except gamma, which only releases energy).