Neutron Emission

Neutron emission is a type of radioactive decay in which an unstable atomic nucleus releases a neutron. This process typically occurs when the nucleus has an excess of neutrons, making it unstable, or when it is excited to a higher energy state due to previous reactions. In such cases, emitting a neutron allows the nucleus to achieve a more stable energy state.

Since the neutron is electrically neutral, it does not ionize atoms directly but can interact with nearby nuclei, sometimes inducing further reactions and potentially leading to chain reactions. This trait is very different from other types of radioactive decay, such as alpha and beta decay, where charged particles are emitted.

Sources of Neutron Emission

Neutron emission typically occurs in heavy isotopes – forms of elements with an unusually high neutron-to-proton ratio in their nuclei. These isotopes are less stable because the excess neutrons disrupt the delicate balance of nuclear forces that hold the nucleus together. Heavy isotopes can occur naturally, such as uranium-238, which has 146 neutrons compared to 92 protons. They can also be artificially created in environments like nuclear reactors and particle accelerators.

In some cases, neutron emission is not a primary process but occurs as a secondary effect of nuclear reactions. For instance, during fission, the splitting of a heavy nucleus into lighter nuclei releases free neutrons, which may go on to initiate further reactions. These secondary processes play a crucial role in chain reactions and are vital in both energy production and scientific research.

Examples

1. Nitrogen – 24 transforms into nitrogen – 23 while releasing one neutron.

\[ _{7}^{24}\text{N} \rightarrow _{7}^{23}\text{N} + _{0}^{1}\text{n} \]

2. Iodine – 137 transforms into iodine – 136 while releasing one neutron.

\[ _{53}^{137}\text{I} \rightarrow _{53}^{136}\text{I} + _{0}^{1}\text{n} \]

3. During spontaneous fission, Californium-252 decays into Tellurium-137 and Palladium-107, emitting 8 free neutrons in the process.

Cf-252 → Te-137 + Pd-107 + 8n

4. Uranium-235 absorbs a neutron and splits into Barium-141 and Krypton-92, along with the emission of 3 neutrons, which can further sustain the chain reaction in a nuclear reactor.

U-235 + n → Ba-141 + Kr-92 + 3n

5. Plutonium-239 absorbs a neutron and splits into Cesium-144 and Rubidium-94, emitting 3 neutrons in the process.

Pu-239 + n → Cs-144 + Rb-94 + 3n

Applications

Nuclear Energy: Neutron emission is essential in sustaining chain reactions in nuclear reactors, where it drives the fission process to generate electricity.
Environmental Monitoring and Archaeology: Emitted neutrons are used to identify and quantify trace elements in various materials, aiding in fields like environmental monitoring and archaeology.
Medical Treatments: Neutron beams from neutron-emitting sources are used in boron neutron capture therapy (BNCT) to target and destroy cancer cells more precisely than traditional radiation therapy.

References
- 1. Nuclear Decay Pathways – Chem.libretexts.org
  2. Neutron Decay – Neutron Emission – Nuclear-power.com
  3. Radioactive Decay | Formula, Types & Examples – Arpansa.gov.au
  4. Radioactive Decay Types – Khanacademy.org
  5. Neutron Emission & Capture – Chemteam.info