Establishment of a procedure for calibrating neutron monitors at the Physics Institute of the University of Sao Paulo, Brazil

A facility for neutron irradiation was designed and built in order to apply the ISO draft procedures for calibrating and determining the response of neutron measuring devices to Brazilian neutron monitors and dosemeters used for radiation protection. As a test for the system, the three methods proposed by the draft were applied. A calibrated Am-Be source, a Li(Eu) sensor, a Bonner multisphere detector, and three shadow cones were used. Based on the data from the Bonner spheres, the free field fluence response, the fractional room scattering contribution at unit calibration distance, and the source detector characteristic constant were determined. The unfolded neutron spectrum was also determined and the corresponding fluence, dose equivalent, and mean energy were calculated. All of them proved to be in good agreement with values expected from the spectrum of the neutron source. (author)