Abstract
In thermal nuclear reactors, most of the power is generated by thermal neutron induced fission. Therefore, fission chambers with targets that respond directly to slow neutrons are of great interest for thermal neutron flux measurements due to relatively low sensitivity to gamma radiation. However, the extreme conditions associated with experiments at very low cross section demand highly possible thermal neutron flux, leading often to substantial design changes. In this paper we report design of a fission chamber for wide range (from 10 to 1012 n/cm2 sec) measurement of thermal neutron flux. Test experiments were performed at the first beam of IBR2 pulsed reactor using digital pulse processing (DPP) technique with modern waveform digitizers (WFD). The neutron pulses detected by the fission chamber in each burst (5 Hz repetition rate) of the reactor were digitized and recorded to PC memory for further on-line and off-line analysis. New method is suggested to make link between the pulse counting, the current mode and the Campbell technique.
Highlights
Experimental Setup and ResultsIn recent decade digital pulse processing (DPP) is considered as very powerful alternative to traditional analogue pulse processing (APP) in experimental nuclear physics research
In this work we demonstrated the power of DPP implemented in thermal neutron counting with fission chamber (FC) in the various modes developed in the reactor instrumentation, namely the counting, the current and the Campbelling techniques
We demonstrated how to implement DPP making direct link between the counting and the current mode measurement with the thermal neutron sensor based on gas filled detectors
Summary
In recent decade digital pulse processing (DPP) is considered as very powerful alternative to traditional analogue pulse processing (APP) in experimental nuclear physics research. In this work we demonstrated the power of DPP implemented in thermal neutron counting with fission chamber (FC) in the various modes developed in the reactor instrumentation, namely the counting, the current and the Campbelling techniques. We demonstrated how to implement DPP making direct link between the counting and the current mode measurement with the thermal neutron sensor based on gas filled detectors. Fission chamber was located at distance 27 m from the pulsed nuclear reactor IBR2 with the following main parameters: average power 1.8 MW, fast neutron pulse duration 200 us, the pulse repetition rate 5Hz, the thermal neutron intensity at the target position was about 10 6 n/cm 2 per. For each reactor burst we measured the number of detected neutrons, which was fluctuating from burst to burst making distribution presented in Fig..
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