The long-term stability of a proportional counter filled with CO2

The long-term stability of two proportional counters was studied by compiling oxalic acid data over a period of several years. For each period of several months to about one year the mean values were used for age calculations assuming no correction for variation in the filling pressure save that of the working voltage determined via the muons and that of the amount of radioactive gas. When filling pressure was changed from one period to another the mean values calculated were seen to vary significantly although variations during such a period were accepted from the statistical point of view. The long series over years indicated that an additional correction should be incorporated in the computer program unless variations of filling pressure were kept small. (author)