Title: Collimation and background in the pulsed neutron activation method for determination of water flow in pipes

Authors: Hakan Mattsson, Anders Nordlund, Berit Dahl

Addresses: Department of Nuclear Engineering, Chalmers University of Technology, Fysikgrand 3, SE-412 96 Goteborg, Sweden. ' Department of Nuclear Engineering, Chalmers University of Technology, Fysikgrand 3, SE-412 96 Goteborg, Sweden. ' Department of Nuclear Engineering, Chalmers University of Technology, Fysikgrand 3, SE-412 96 Goteborg, Sweden

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.

Keywords: pulsed neutron activation; PNA flowmeters; pipe flow; water flow; collimation; neutron radiation.

DOI: 10.1504/IJNEST.2007.012438

International Journal of Nuclear Energy Science and Technology, 2007 Vol.3 No.1, pp.19 - 30

Published online: 13 Feb 2007 *

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