Calibrations: Neutron Device Calibrations

Summary

NIST provides the national reference for the calibration of neutron radiation detectors used for personnel protection and for neutron personnel dosimeters.

Description

Low Scatter Neutron Calibration Facility. A neutron radiation detector (white sphere with attached tan readout meter) is positioned on a rolling cart at various distances from a D₂O-moderated ²⁵²Cf neutron source (gray sphere near the center of the image).  The readout meter is read by a video camera attached to the cart (not shown).

Credit: Rendering by: Neutron Physics Group

The Neutron Physics Group calibrates neutron radiation detectors used for personnel protection and irradiates 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 facility's walls/ceiling/floor). 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 can also provide calibrations to ²⁴¹AmBe reference fields as a special test.