Development of a working standard of thermal neutron flux on the basis of the Ph-1 reactor

The results of investigations aimed at developing a Ph-1 reactor base facility for reproduction of the thermal neutron flux unit in the range from 1010 to 7 x 1014 neutrons/m2x c are presented. The Ph-1 reactor is a research natural uranium-graphite reactor . Activation detectors were used to measure spatial and angular distributions of the neutron field. The spectral parameters were determined using methods of cadmium ratios and spectral indeces. The total error of reproducing the effective neutron flux is not greater than +- 2% for a reliability probability of 0.99. The results show that the working thermal neutron flux standard is in line with the state metrology system specifications