A helium flash occurs because the core of the star is in what is known as a "degenerate" state. This means that the core has contracted so much that the pressure of the electron shells of the atoms...
Nuclear fusion occurs when two nuclei fuse together. This is frequently nuclei of deuterium and tritium (both hydrogen isotopes), which form a helium nucleus plus a neutron.
The ionizing radiation that is similar in structure to the helium nucleus is the Alpha Particle. The Alpha consists of two neutrons and two protons (but no electron shell) traveling with sufficient...