ANSI N42.35 requires 252Cf neutron sources encapsulated in 1 cm of steel with a fluence of 2x104 n/s ±20%.
NIST designed a compliant source. NIST acquired, calibrated and delivered several such sources for DOE laboratories, including the Nevada Test Site, and for the U.S. Navy. They are being used to evaluate potential neutron detectors for Homeland Security. Additional sources are being supplied as needed for new purposes and as old sources decay. The figure shows a reprentative energy spectrum from such sources.
During the last several years, NIST has responded to the national need of calibrated neutron sources. Calibrated sources were delivered to the Navy and DOE laboratories to perform equipment testing as required by DoD and ANSI standards.