How do spontaneous nuclear fission processes occur?
Spontaneous nuclear fission can occur by the emission of alpha and beta particles. Other mechanisms involve positrons and gamma rays.
An alpha particle is a helium nucleus. The heavier elements usually decay by alpha emission. For example,
A beta particle is an electron. Nuclei that have too few protons can decay by converting a neutron to a proton and emitting a beta particle. For example,
A positron is the antimatter counterpart of an electron. Nuclei that have too many protons can decay by converting a proton to a neutron and emitting a positron. For example,
Gamma rays are high-energy photons. When a nucleus emits an alpha or beta particle, the new nucleus may have excess energy. It can release this excess energy by emitting gamma rays.
Thus, thorium-234 becomes more stable by releasing gamma rays and a beta particle.