SCATTERED NEUTRON REFERENCE FIELDS PRODUCED BY RADIONUCLIDE SOURCES

Realistic fields similar to those occurring in practice can be approxi mately realised using the ISO-recommended radionuclide sources if the neutrons scattered by the concrete walls of a medium sized irradiation room are used. At the PTB, such fields were established at the irradi ation facility with radionuclide reference neutron sources. In order t o determine the spectral fluence rate at the point of test as the basi s of calibrations, the different spectra were calculated using the MCN P code, and measured by means of a Bonner sphere spectrometer. The mea sured count rates were unfolded using different codes. The total fluen ce rate can be determined with a relative standard uncertainty of abou t 4%. The relative standard uncertainty of the ambient dose equivalent is found to be about 5%.