This model illustrates the different types of nuclear reactions. |
All nuclear reactions can be classified into three separate categories by the initial events that cause them:
- 1) change of a nucleon within the nucleus,
- 2) change of internal structure of the nucleus, and
- 3) rearrangement of nucleons between nuclei.
The first group of events includes the various types of beta decay that result in conversion of a neutron to a proton, or vice versa. The first and most frequent type of beta decay results in emission of an electron and an electron antineutrino. The second type of beta decay constitutes an emission of a positron and an electron neutrino, or capture of an electron from one of the inner electron shells, and an emission of an electron neutrino. Note that free protons cannot dissipate into neutrons, positrons and electron neutrinos, because this requires additional energy from the nucleus. Total energy value decreases in the process of beta-decay, resulting in a proton-to-neutron conversion. Since the number of protons decreases, so does the Coulomb repulsion force between the protons in the nucleus.
The second group involves gamma decay - emission of a gamma-quantum by an excited nucleus, which releases excess energy.
The third group includes alpha decay (emission of an alpha-particle), nuclear fission (neutron absorption by the nucleus followed by its disintegration into two lighter nuclei, and emission of several neutrons) and nuclear fusion (i.e. collision of two light nuclei resulting in one heavy nucleus and a lighter fission product; or a few protons and neutrons.)
Note that in the case of alpha decay, the nucleus undergoes a considerable shift in the direction that is opposite to the direction of the emitted alpha particle. Beta decay is a far weaker force, and its effects are imperceptible in this model, since the mass of an electron is several thousand times less than the mass of a nucleus.