The number of neutrons released by each fission event is dependent on the substance.Typically photons begin to produce neutrons on interaction with normal matter at energies of about 7 to 40 Me V, which means that megavoltage photon radiotherapy facilities may produce neutron radiation as well, and require special shielding for it.However, for drill sites with very low accumulation rates, sites where hiati exist, or at greater depth where stratigraphical methods become more uncertain due to layer thinning, "The sharp dependence on energy of the cadmium cross section for neutrons of energies near 0.35 e V [slow neutrons] has been used to investigate the energy distribution of 0.35-ev neutrons scattered through 90° by lead, aluminum, diamond, and graphite." J or 2.4 MJ/kg, hence a speed of 2.2 km/s), which is the most probable energy at a temperature of 290 K (17 °C or 62 °F), the mode of the Maxwell–Boltzmann distribution for this temperature.After a number of collisions with nuclei (scattering) in a medium (neutron moderator) at this temperature, neutrons arrive at about this energy level, provided that they are not absorbed.The background radiation dose received by an average person in the United States is approximately 3.5 milli Sv/year.Conversely, an exposure of 1 Sv can result in radiation poisoning and a dose of five Sv will result in death in 50 percent of exposed individuals.Moderated and other, non-thermal neutron energy distributions or ranges are "Significant in situ production of radiocarbon by fast neutrons is restricted to the first ~15 m of firn, while the pore closure at this site occurs at 71 m depth .
Neutrons (so-called photoneutrons) are produced when photons above the nuclear binding energy of a substance are incident on that substance, causing it to undergo giant dipole resonance after which it either emits a neutron (photodisintegration) or undergoes fission (photofission).Thermal neutrons have a different and sometimes much larger effective neutron absorption cross-section for a given nuclide than fast neutrons, and can therefore often be absorbed more easily by an atomic nucleus, creating a heavier, often unstable isotope of the chemical element as a result (neutron activation).Neutrons are produced when alpha particles impinge upon any of several low atomic weight isotopes including isotopes of lithium, beryllium, carbon and oxygen.Qualitatively, the higher the temperature, the higher the kinetic energy is of the free neutron.Kinetic energy, speed and wavelength of the neutron are related through the De Broglie relation.Gamma radiation with an energy exceeding the neutron binding energy of a nucleus can eject a neutron.Two examples and their decay products: Traditional particle accelerators with hydrogen (H), deuterium (D), or tritium (T) ion sources may be used to produce neutrons using targets of deuterium, tritium, lithium, beryllium, and other low-Z materials.The average dose-equivalent rate observed through the BBND investigation is 3.9 micro Sv/hour, or about ten times the average US surface rate.The highest rate, 96 micro Sv/hour was observed in the SAA region." The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts.The neutron emission process itself is controlled by the nuclear force and therefore is extremely fast, sometimes referred to as "nearly instantaneous." The ejection of the neutron may be as a product of the movement of many nucleons, but it is ultimately mediated by the repulsive action of the nuclear force that exists at extremely short-range distances between nucleons.The life time of an ejected neutron inside the nucleus before it is emitted is usually comparable to the flight time of a typical neutron before it leaves the small nuclear "potential well," or about 10 A synonym for such neutron emission is "prompt neutron" production, of the type that is best known to occur simultaneously with induced nuclear fission.