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.