Key concept 1: Nuclear decay reactions must obey the Law of Conservation of Mass.

Key concept 2: Nuclear decay reactions obey the Law of Conservation of Charge.

Put simply, this means the products have to add up to equal the decaying reactant (parent nuclide or isotope.) We need to pay attention to charges and to total mass.

It begins with the Nuclear Symbol


Atomic mass (protons + neutrons)


Atomic number (number of protons)

Radioactivity is the particles and energy emitted from an unstable nucleus to become stable. Sometimes it takes several steps.

Common radiation includes

alpha 42 He Helium nucleus
beta 0-1e electron from nucleus
gamma   ultra high energy photons
positron 0+1e positively charged electron
neutron 10n neutron ejected from nucleus

Examples of nuclear decay reactions

alpha decay

23592U ==> 42 He + 23190Th

beta decay

146C ==> 0-1e + 147N

positron decay

2211Na ==> 0+1e + 2210Ne

fusion reaction with neutron emission

21H + 31H ==> 42He + 10

Each of these reactions are also accompanied by the release of energy as gamma rays (high energy photons).