A device for measuring the concentration of gaseous-phase fission products

970,368. Nuclear reactors. COMMISSARIAT A L'ENERGIE ATOMIQUE. June 1,1961 [June 2, 1960], No. 19813/61. Heading G6C. Apparatus for measuring the fission product content of a gas comprises an insulating cylinder to which gas to be tested can be admitted and provided with an annular repulsion electrode on its inner surface, a piston carrying an electrode on its centre portion and arranged to reciprocate inside the cylinder, and a scintillator detector arranged at one end of the cylinder. In Fig. 1 the insulating cylinder 1 is provided with a gas inlet pipe 8 and outlet pipe (not shown) and an annular electrode 2 is arranged on its inner surface. A scintillator 5 having a metalled surface is provided at one end of the cylinder adjacent a light guide 6 and photo-multiplier 7. An insulating piston 3 carrying an electrode 4 is integral with a rod 10 and is driven by a core 11 of ferromagnetic material. When a coil 12 surrounding the core 11 is excited the core is pulled on to the fixed armature 13 and a spring 14 is compressed; when the current in coil 12 is interrupted the spring 14 drives the piston to its upper position where electrode 4 abuts the scintillator 5, a dashpot 15 reducing any shocks at the end of the travel. In operation, gas to be monitored is passed into the cylinder when the piston is in its lower position and electrode 2 is maintained at a positive potential. Ions from decaying fission products are then collected on electrode 4 and on the metalled surface of scintillator 5. After the collection period the piston is moved to its upper position and the output of the scintillator is counted. Preferably two counts are made separated by an interval sufficient to allow an appreciable diminution of the short-lived ions which have been collected.