Which particle decomposes to produce beta radiation?

The particle that decomposes to produce beta radiation is NEUTRON.

The neutron decays (udd) into a proton (uud), an electron and an anti-neutrino. This process is known as neutron beta decay and here is how it happens.

The neutron that has a charge of zero is made up of up and two down quarks. One of the down quarks is transformed into an up quark. Since the down quark has a -1/3 charge and the up quarks has a positive charge of 2/3, it immediately follows that this process is mediated by a virtual W particle which carries away a negative charge. The new up quark rebounds away from the emitted W-. Then comes the formation of a proton. An electron and antineutrino them emerge from the virtual W-boson. The proton, electron, and antineutrino will finally move away from one another,