A NEW THERMAL NEUTRON FLUX DENSITY STANDARD
NATIONAL RESEARCH COUNCIL OF CANADA OTTAWA (ONTARIO) DIV OF APPLIED PHYSICS
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Six Am241-Bealpha,n neutron sources are arranged around the central circumfejence of a graphite cylinder 28 cm in diameter by 26.5 cm high. This assembly is surrounded by 10 cm of polyethylene. The graphite cylinder contains an accessible central cavity, 5 cm in diameter by 5 cm high, for the calibration of thermal neutron detectors. The thermal neutron flux density in the cavity is measured by 4 pi beta-gamma coincidence counting of irradiated gold foils. A flux density below cadmium cutoff of nthvo 8700sq cmsec 1.5 was found. The uniformity is shown to be constant within the cavity to better than 0.5 over a cylindrical volume 5 cm in diameter by 2 cm high.
- Fission Reactor Physics