Q.What are alpha, beta and gamma decays?

[!TLDR] Alpha decay emits a helium nucleus (2p+2n); beta decay converts a neutron to a proton (emitting an electron) or a proton to a neutron (emitting a positron); gamma decay emits a high-energy photon as an already-formed nucleus drops between nuclear energy levels, with no change in Z or A. [!ANSWER] Alpha = emission of a $_2^4He$ nucleus; beta = a nucl …

In alpha decay, the parent nucleus ejects an alpha particle (a helium-4 nucleus, i.e. two protons and two neutrons bound together), so the daughter nucleus has its atomic number reduced by 2 and its mass number reduced by 4: $_Z^AX\rightarrow\,_{Z-2}^{A-4}Y+\,_2^4He$; this mode is typical of very heavy nuclei (A > 210). In beta decay, one of the nucleons itself changes type: in $\beta^-$ decay a neutron converts to a proton, emitting an electron and an antineutrino, so Z increases by one with A unchanged; in $\beta^+$ decay a proton (bound in the nucleus) converts to a neutron, emitting a positron and a neutrino, so Z decreases by one with A unchanged. In gamma decay, no nucleon changes type at all -- the nucleus's Z and A stay exactly the same -- instead, the nucleus (usually already left in an excited state by a preceding alpha or beta decay …

State the particle emitted and the resulting change (or lack of change) in Z and …

Describing beta decay as simply 'electron emission' without mentioning that the underlying process is a neutron converting to a proton (or vice versa for $ …