A GAS SCINTILLATION MONITOR FOR TRITIUM GAS IN ARGON OR IN NITROGEN

For civilian purposes tritium is presently used in quantities of tens of PBq (MCi) in laboratories for the studies of tritium technology, at the Joint European Torus plant (Abingdon, Oxon, OX143A, UK) as fuel f or the process of nuclear fusion, and in the manufacture of radio-lumi nescent items. Given the extreme mobility of tritium in most materials , it is necessary to use systems for double containment, such as glove boxes or spaces between primary and secondary containers, in which in ert gas like argon or nitrogen flows. With these systems it is possibl e to recover tritium that escapes from the primary containment. Presen tly the gas flow is monitored continuously by means of ionization cham bers which may present problems in particular applications (''memory e ffect'' with high activity, strong dependence of the response on the p resence of impurity, etc.). The aim of the work here presented is to d etermine the prospects for the realization of a new type of monitor ma inly dedicated to the measurement of gas activity in isolation space o f the containing systems of the high activity tritium plants. This mon itor should have sufficient sensitivity, quick response, and should be easily decontaminated. As a detection technique we chose the scintill ation produced in the inert gas by radioactive decay. With the first p rototype, designed in cylindrical form, it was possible to observe gas eous scintillation events in mixture of tritium and argon or nitrogen. Following that, a spherical prototype was designed, of which we studi ed the performances and the dependence of the response varying the pre ssure, the concentration of tritium, the percentage of the impurity, a nd the gas flow rate. The results are satisfactory and suggest that th e monitor could be used in glove boxes and double containment systems. The future research program will include tests involving large quanti ties of tritium and a study of the ideal dimensions and geometry of th e detection chamber in order to optimize the detector response.