The Background in Flow Measurement using Pulsed Neutron Activation

In flow measurement with Pulsed Neutron Activation (PNA), water flowing in a pipe is activated with 14 MeV neutrons, producing the radioactive nuclide sup 1 sup 6 N. The gamma radiation emitted from this radionuclide will produce a characteristic peak in a time spectrum from a detector downstream. Experiments have shown that the peak is superimposed on a background distribution, which can affect the measurement. As it is necessary to correct for the background, different subtraction methods have been used in the past, although the origin of the background has not been known. In this work the source of the background has been investigated. It has been found that there are two components of the background: one time dependent and one time independent. The time-dependent component is shown to be caused by stationary sup 1 sup 6 N in the surroundings. A method for subtracting the background in a reproducible way has been developed. This was done by fitting the peak with an empirical function consisting of several Taylor distributions