Calibrations: Californium Neutron Irradiation Facility

Summary

NIST maintains the Californium Neutron irradiation Facility (CNIF), which is an exposure facility providing fast neutrons for irradiations requiring high neutron fluence. The facility provides Cf-252 and monoenergetic (2.5 MeV and 14 MeV) neutrons that can be used for detector calibration, sample irradiation, and other similar activities.

Description

A photograph of a rig for mouting samples inside the Californium Neutron Irradiation Facility.

Credit: Neutron Physics Group

A high-activity Cf-252 source (~10¹⁰ neutrons/s as of May 2024) is housed in a large (approximately 15 m x 10 m x 10 m high) room with concrete walls, floor, and ceiling (see photograph) at a depth of 10 meters-water-equivalent. In addition, there are two monoenergetic neutron generators for 2.5 MeV and 14 MeV neutrons that produce neutron emission rates of order 10⁶/s and 10⁸/s, respectively. Inside the concrete is a 5.4 cm thick shell (5.3 m x 5.3 m x 5.9 m high) of anhydrous borax, which prevents neutrons scattered by the concrete from returning to the source. Typical irradiations include detector and dosimeter calibrations, neutron transport studies, sample activation experiments, electronic damage studies, and other special tests requiring high neutron fluence and a low-room-scatter environment. Calibrated fission monitors allow neutron fluence to be determined to high accuracy and can be traceable to NBS-1. Closed-circuit TV coverage of the experimental area is provided, and experiments requiring active monitoring may be reached with approximately 25 m of cable. Recent customers include the Georgetown University Medical Center, Sandia National Laboratory, Global Resonance Technologies, and various internal NIST projects including tests of alanine dosimeter response to neutrons and studies of chlorine content in concrete. NIST provides reference high-intensity Cf-252 neutron exposures in support of US nuclear programs.