Q value
= Q value
{c}
{title2=$Q=E_{\mathrm{rest},i}-E_{\mathrm{rest},f}$}
The <Q value> of a reaction or <particle decay> is the initial total rest <energy> minus the final total rest <energy>. Positive $Q$ releases <kinetic energy>; a negative $Q$ requires energy supplied by incident motion or another source. Atomic and bare nuclear <mass> conventions must be distinguished when counting <Electrons> in <beta decay>.