Nuclear Reactions: Types and Applications
1. Alpha Particle (?) Reaction
In 1919, Rutherford observed the first nuclear reaction. In his experiment, he bombarded nitrogen (N) gas with alpha (?) particles from a radioactive source. The products obtained were oxygen, hydrogen, and Q. Q represents the energy released or absorbed during the nuclear reaction.
- If Q is positive, energy is released, and the reaction is exoenergetic.
- If Q is negative, energy is absorbed, and the reaction is endoenergetic.
Q is also known as the decay energy and equals the mass difference between initial and final particles. The minimum energy required for the reaction to occur is called the threshold energy. A reaction where an alpha (?) particle interacts with a nucleus, forming a compound nucleus that immediately decays into a new nucleus by ejecting a proton, is termed an ?, p reaction.
2. Alpha Particle, Neutron (?, n) Reaction
This reaction involves bombarding a nucleus with alpha particles, followed by the emission of neutrons. It was the first reaction used to produce small neutron sources. A common laboratory neutron source is a mixture of radium and beryllium. The alpha particles emitted by radium bombard the beryllium nucleus, causing it to eject neutrons.
3. Proton Bombardment
Most reactions of this type involve capturing a proton and emitting a gamma ray (p, gamma reaction). Other possible reactions from proton bombardment include p, n; p, d; and p, ? types.
4. Deuteron Bombardment
A deuteron is a combination of a proton and a neutron. Bombardment with a deuteron can break this combination, resulting in a compound nucleus that emits either a proton or a neutron. One such reaction, the bombardment of deuterons with deuterons, is used as a source of high-energy neutrons.
5. Neutron Bombardment
Neutrons, having no charge, are very effective at penetrating the nucleus and inducing nuclear reactions. They do not require high energy for penetration. Slow or thermal neutrons, with energy equal to the thermal agitation energy of a material (approximately 0.025 eV at room temperature), are very effective. The most common process is the neutron capture reaction (n, gamma). The compound nucleus is raised to an excited state and returns to its normal state by emitting a gamma ray. The products of n, gamma reactions are often radioactive, emitting beta particles. Another type of neutron-induced reaction is the n, p reaction, which also often produces beta emitters. Whether a reaction occurs with slow or fast neutrons depends on the mass difference between the target nucleus and the desired product nucleus.
6. Photodisintegration
The interaction between a high-energy photon and an atomic nucleus can cause a nuclear reaction and the emission of one or more nucleons. In most cases, this results in the emission of neutrons from the nucleus. This reaction has a threshold, for example, of 10.86 MeV in a specific case. This threshold energy is calculated as the difference between the rest energy of the target nucleus and the residual nucleus plus the emitted nucleon(s). Because the rest energy of many nuclides is precisely known, photodisintegration is used to calibrate the energy of machines producing high-energy photons.