New developments in neutron counting chains for safeguards

Volume: 59, December 2019, pages 11-20,

Authors: Giovanni Varasano, Mahel Abousahl, Tatjana Bogucarska, Bent Pedersen

_{European Commission, Joint Research Centre}

Abstract:Standard neutron counting systems in nuclear safeguards typically use a thermal neutron absorber material in gas proportional counters embedded in a neutron moderator block, and surrounding the central sample cavity. Multiple detector tubes are normally connected to one electronics chain composed of a pre-amplifier, an amplifier, a single channel analyser and a digital signal mixer summing signals from multiple chains to produce a single pulse train representing the neutron detection events. This has typically been the design compromise considering factors such as the dead-time of the detection system, the reliability of the electronics, complexity and cost.

In this paper we describe the ongoing developments at JRC for modernizing the entire electronics chain, including all the individual components mentioned above as well as the digital signal analyser. A key element of this work concerns an in-house designed digitizer board capable of processing pre-amplifier outputs to identify neutron detection events. The board has multiple analogue inputs, a multichannel ADC, pulse processing in FPGA hardware and output of timestamps of neutron detection events. The benefits from this work are expected to be a reduced pulse processing time in the electronics, better pulse pair resolution, the elimination of the physical signal analyser and better systems diagnostics.

The new electronics developments are being assembled and tested in the JRC reference passive neutron counter, and will be ready for demonstration in the coming year. The reference counter is a cylindrical well-counter incorporating 126 3He neutron detector tubes.

Keywords: NDA; neutron counter; digitiser; list-mode; safeguards.

Reference guideline:

Varasano, G., Abousahl, M., Bogucarska, T., & Pedersen, B. (2019). New developments in neutron counting chains for safeguards. ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-proliferation, 59, 11-20. https://doi.org/10.3011/ESARDA.IJNSNP.2019.10