The (n-p) reaction, or (n,p) reaction, is an example of a nuclear reaction. It is the reaction which occurs when a neutron enters a nucleus and a proton leaves the nucleus simultaneously.
For example, sulfur-32 (<sup>32</sup>S) undergoes an (n,p) nuclear reaction when bombarded with neutrons, thus forming phosphorus-32 (<sup>32</sup>P).
The nuclide nitrogen-14 (<sup>14</sup>N) can also undergo an (n,p) nuclear reaction to produce carbon-14 (<sup>14</sup>C). This nuclear reaction <sup>14</sup>N (n,p) <sup>14</sup>C continually happens in the Earth's atmosphere, forming equilibrium amounts of the radionuclide <sup>14</sup>C.
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 <sup>14</sup>N (n,p) <sup>14</sup>C is an exception to this rule â it can take place at all incident neutron energies. The <sup>14</sup>N (n,p) <sup>14</sup>C nuclear reaction is responsible for most of the radiation dose delivered to the human body by thermal neutrons â these thermal neutrons are absorbed by the nitrogen <sup>14</sup>N 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.