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A high pressure tiny pump operatable in a range of (0.5-5) x 105 Pa was needed for gas circulation in the newly developed direct measurement method of radioactivities of gaseous samples, yet, such a pump was not commercially available. A tiny air bubbling pump of electromagnetic vibrating-reed type for small fish raising was remodeled by putting it inside a high pressure stainless steel vessel and vibrating the reed with an electromagnet being set outside the vessel wall. Gas flow rate (Pa • m3/s) was measured at atmospheric pressure both by a method using a measuring-cylinder and by radioisotope (RI) tracer method , and at other pressures by RI tracer method. The flow rate decreased with increasing pressure and viscosity of the gas. The pump was very useful for the present purpose. Details of remodeling and characteristics of the pump are described.

In the absolute radioactivity measurement of radioisotope gaseous samples with newly developed position-sensitive proportional counter (PSPC) method, it is necessary to change the counting gas pressure for the correction of the wall effect. The position signal was found to drift depending on the pressure. Theoretical explanation was given for this drift. Rise time of output pulses varies with gas pressure, which leads to a change of ballistic deficit. Consequently, the ballistic deficit differs between pulses from both the ends of the PSPC, which causes the change of position signals. Increasing the pressure of the counting gas from 0.5 x 106Pa to 4x106Pa, the range of position signals for two position calibration sources became narrower by about 8% under 6 p s shaping time.