NIST provides the national reference for the calibration of neutron radiation detectors used for personnel protection and for neutron personnel dosimeters.
The Neutron Physics Group performs calibrations of neutron radiation detectors used for personnel protection and irradiations of personnel dosimeters in standard neutron fields. The fields are produced by unmoderated 252Cf and 252Cf moderated with a D2O sphere (represented by the gray sphere near the center of the image). The spontaneous fission neutron energy spectrum of unmoderated 252Cf has been extensively studied and is an international standard reference field. The moderated spectrum, with an abundance of low and intermediate energy neutrons, is more characteristic of reactor working environments and is often preferred for that reason. Most personnel dosimeters are sensitive to neutrons scattered off the person wearing the dosimeter, so a frequent exposure configuration has dosimeters adjacent to an acrylic phantom. In all exposure geometries, corrections are made for air scatter and room return (neutrons scattered from the walls/ceiling/floor of the facility). Calibrations are performed in a large, mostly empty room as far from all walls as possible to minimize room return corrections. NIST periodically compares its calibration services to those of other national standards laboratories.
NIST is also able to provide calibrations to 241AmBe reference fields as a special test.