The (n-p) reaction, or (n,p) reaction, is an example of a
nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a t ...
. It is the reaction which occurs when a
neutron
The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...
enters a
nucleus and a
proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
leaves the nucleus simultaneously.
For example,
sulfur-32 (
32S) undergoes an (n,p) nuclear reaction when
bombarded with neutrons, thus forming
phosphorus-32
Phosphorus-32 (32P) is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31. Phosphorus-32 only exists in small quantiti ...
(
32P).
The nuclide
nitrogen-14
Natural nitrogen (7N) consists of two stable isotopes: the vast majority (99.6%) of naturally occurring nitrogen is nitrogen-14, with the remainder being nitrogen-15. Thirteen radioisotopes are also known, with atomic masses ranging from 9 to 23, ...
(
14N) can also undergo an (n,p) nuclear reaction to produce
carbon-14
Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
(
14C). This nuclear reaction
14N (n,p)
14C continually happens in the Earth's atmosphere, forming equilibrium amounts of the radionuclide
14C.
Most (n,p) reactions have threshold neutron energies below which the reaction cannot take place as a result of the charged particle in the exit channel requiring energy (usually more than a MeV) to overcome the
Coulomb barrier experienced by the emitted proton. The (n,p) nuclear reaction
14N (n,p)
14C is an exception to this rule – it can take place at all incident neutron energies. The
14N (n,p)
14C nuclear reaction is responsible for most of the radiation dose delivered to the human body by thermal neutrons – these thermal neutrons are absorbed by the nitrogen
14N in proteins, causing a proton to be emitted; the emitted proton deposits its kinetic energy over a very short distance in the body tissue, thereby depositing radiation dose.
References
Nucleosynthesis
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