عنوان مقاله [English]
To effective experimental implementation in a zero power reactor or more generally, critical assemblies, it is necessary to measure the absolute neutron flux to calibrate the reactor power.
The 4πβ-γ coincidence method via the activation of gold foil, is a well known standard method for absolute neutron flux measurements. The absolute neutron flux is obtained by measuring the absolute activity of the irradiated gold foil, ranged in 102-104 Bq. In this method, the gold foil is irradiated at the desired position. The beta, gamma and the coincidence rates are by using the 4πβ-γ coincidence system and the absolute activity of gold foil is then obtained. The β-γ rays emitted from the irradiated gold foil, are recorded in a very short time period (of the order 10-8 seconds). The advantage of this method is that the efficiency of either detector is directly to be dependent on the count rates. Changing the beta detector efficiency due the high voltage change, and then measuring the beta, gamma and coincidence count rates, the plot of beta count rates against the beta detector efficiencies can be represented. Extrapolating the efficiencies to the value 1, gives the absolute activity of the gold foil.