Model of BF3 neutron proportional Geiger counter

Model of BF3 neutron proportional Geiger counter, made by staff at 20th Century Electronics in 1954. In January 1953, the UKAEA at Harwell wanted 20th Century Electronics to produce a range of Geiger-Muller tubes to detect neutrons. The proposed tubes were different from ordinary GM tubes in that they had to be filled with a gas that would absorb neutrons - boron trifluoride, which was very dangerous to handle. 20th Century produced the tube commercially (they were the only people manufacturing such a type) and it sold widely all over the world.