A prototype BF3 based neutron multiplicity counter for nuclear safeguards

Neutron coincidence counting and neutron multiplicity counting are standard techniques for mass determination of fissile materials in nuclear safeguards applications. The preferred neutron detector layout incorporates 3He gas proportional counters in a cylindrical polyethylene moderator block with a central sample cavity. The detector tubes are embedded in the polyethylene in a ring shape approximating a 4 geometry. This standard layout has been adopted in several detector designs such as the High Level Neutron Coincidence Counter (HLNCC-II). The recent worldwide shortage of 3He gas has prompted research into alternative detection technologies for neutrons. An obvious candidate from a physics point of view is 10B due to the high thermal neutron cross section and the inexpensive enrichment process of the 10B isotope. An important advantage includes the fact that when in form of boron trifluoride gas this neutron detector the can replace 3He gas tubes while maintaining other standard counter materials, the well counter design, and even the detector electronics. The toxicity of the BF3 gas however has been mentioned as a potential problem for using this neutron detector is large size neutron coincidence or multiplicity counters in nuclear facilities. The paper describes the newly developed prototype well counter based on BF3 detector tubes including a discussion of results of test bed experiments and Monte Carlo simulations carried out to reach the final design. The objective to build a working counter with same cavity dimensions as the standard HLNCC but with neutron detection efficiency high enough to allow neutron multiplicity counting in practical applications was achieved. The paper shows initial results of measurements with the counter as well as the measured assay parameters. The paper also shows how the issue of the toxicity of the gas has been addressed in the design of the new counter.

PEDERSEN Bent;  CROCHEMORE Jean-Michel;  MOSCONI Marita;  MAYOROV Valeriy;  TAGZIRIA Hamid;  OCHERASHVILI Aharon;  ROESGEN Eric;  SCHWALBACH Peter; 

2016-01-21

Publications Office of the European Union

JRC95683

978-92-79-49495-6,   

1831-9424 (online),   

https://publications.jrc.ec.europa.eu/repository/handle/JRC95683,   

10.2789/099293,