Beta decay operates at the subnucleon level: it involves a transition between different quarks. This is reflected at the nuclear level as the transition of neutron to proton or vice versa. Beta decay shapes the nuclear landscape: it is the prime mechanism by which nuclei reach the line of stability. Many isotopes used for medical and industrial uses are beta emitters, as are isotopes of importance in radioactive dating. But perhaps the most visible manifestation of beta decay is its role in the burning of hydrogen to helium in the Sun.
The weakness of the weak interaction results from the mass of the W
boson. Beta (minus) decay can be described (in a cartoonish way), for
instance, as the
decay of a virtual 
boson into an electron and antineutrino, after
being emitted in the transition of a down quark into an up quark.
The 80 GeV mass of the W results in a range of the interaction of
fm. The strength of the interaction
is given by a coupling constant of the order of 
where
is of the same order of strength as the
electromagnetic interaction. In fact, the Standard Model of particle
physics sees these interactions as the `electroweak interaction'.
The study of beta decay has been a wonderful source of new physics. The invention and subsequent discovery 25 years later, and the discovery of non-conservation of parity are but two examples.