Study of the possibility of high accuracy flow measurements with the pulsed neutron activation method

The performance of water flow measurements with pulsed neutrons activation (PNA) have been investigated in the past few years. In this report the foll owing particular Problems were investigated: (a) the effect collimation on the time-resolved detector signals; (b) the behavior of the background sign al, in order to expedite optimum background elimination from the measured s ignals; and (c) the properties of water mixing, by measuring the geometrica l asymmetry of the activated volume as a function of distance from the sour ce as well as of flow velocity. It was seen that with the flow velocities a nd Reynolds numbers in the present experiments, the mixing is not perfect. Thus, in general, the PNA method will lead to an underestimation of the mas s flow due to the effect of the laminar layer close to the wall whose contr ibution to the total mass flow will be enhanced The investigations reported here contribute to the improvement. of the accuracy of the method.