Collimation and background in the pulsed neutron activation method for determination of water flow in pipes Online publication date: Tue, 13-Feb-2007
by Hakan Mattsson, Anders Nordlund, Berit Dahl
International Journal of Nuclear Energy Science and Technology (IJNEST), Vol. 3, No. 1, 2007
Abstract: In a Pulsed Neutron Activation (PNA) flowmeter, the water in a pipe is bombarded with neutron pulses, which introduce activity into the pipe. The activity is mixed with the flow, and gamma radiation emitted from the activity is measured with a detector downstream. The average velocity of the water is then calculated using the time-resolved detector signal. In this paper, the effect of collimation of the neutron radiation has been investigated. Such a collimation would increase the accuracy of the measurement, but the use of a collimator requires the distance between the pipe and the neutron source to be increased, with a corresponding loss in count rate. The results show that this loss makes neutron collimators in PNA of little use. In addition, a method to identify and subtract the background originating from stationary sources in a PNA measurement was developed.
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