Measurement of the neutron current and its use for the localisation of a neutron source

It was suggested recently [Pلzsit, Ann. Nucl. Energy 24 (1997) 1257] that in addition to the traditionally measured scalar neutron flux, the information contained in the higher angular moments of the neutron flux, such as the neutron current or the flux gradient, could be used for monitoring and diagnostics of reactor cores. To explore this possibility, a detector was constructed with which vector components of the partial currents, and thus also components of the net current vector, can be measured. The two-dimensional current vector was measured in an experimental system containing a neutron source in a water tank, and was compared with calculated values. As one simple application, it was shown how the position of the source can be determined from measuring the scalar flux and the neutron current in one single spatial point. The experiments demonstrate both the suitability of the detector construction for the measurement of the neutron current vector and the use of the current in diagnostics and monitoring.