Neutron temperature

A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298.15K (25 C). An explanation of the y-axis label appears on the image page (click to see). Similar speed distributions are obtained for neutrons upon moderation.

The neutron temperature indicates a free neutron's kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature. The neutron energy distribution is then adopted to the Maxwellian distribution known for thermal motion. Qualitatively, the higher the temperature, the higher is the kinetic energy of the free neutron. Kinetic energy, speed and wavelength of the neutron are related through the De Broglie relation. Moderated and other, non-thermal neutron energy distributions or ranges are listed in the table below:

• Fast neutrons have an energy greater than 1 eV, 0.1 MeV or approximately 1 MeV, depending on the definition.
• Slow neutrons have an energy less than 1 eV.
• Epithermal neutrons have an energy from 0.025 to 1 eV.
• Hot neutrons have an average energy of about .2 eV.
• Thermal neutrons have an average energy of about 0.025 eV.
• Cold neutrons have an average energy from 5x10^{-5 eV to 0.025 eV.}
• Very cold neutrons have an energy from 2x10^{-7 eV to 5x10-5 eV.}
• Ultra cold neutrons have an energy less than 2x10^{-7 eV.}

• Continuum region neutrons have an energy from 0.01 MeV to 25 MeV.
• Resonance region neutrons have an energy from 1 eV to 0.01 MeV.
• Low energy region neutrons have an energy less than 1 eV.

References

• Language of the Nucleus