Multielement Position Sensitive Proportional Counter for Measurement of Tritium Labeled Gas Movement

A multielement position sensitive proportional counter was developed for the measurement of ³H labeled gas movement in a pipe by internal counting. The counter consists of an outer cylindrical pipe with an inner diameter of 40 mm, seven resistive stainless steel anode wires with a diameter of 22 μm, and 24 cathode wires with a diameter of 120 μm. These wires divide the radial cross section of the pipe into seven regions. Since each region independently works as a position sensitive proportional counter and the seven resistive anode wires are connected in series through lump resistors, the region and the axial position where a β-decay event occurred can be known by a simple operation upon the charge signals obtained from two preamplifiers. The axial position resolution for ³H β-rays was 9 mm FWHM. Demonstrative experiments were performed for the flow and diffusion of ³H labeled ethane in the counter pipe.     

Measurement of Neutron Flux Distribution in Critical Assembly with Position-Sensitive Helium-3 Proportional Counter

Neutron flux distributions in the Kyoto University Critical Assembly were measured with a position-sensitive ³He proportional counter. The authors examined the results of the first attempt to apply the position-sensitive counter for such measurement in the critical assembly. Some problems to be solved were drawn from the present examination for the further development of this type of counters. The counter had a sensitive length of 118 cm and an outer diameter of 2.5 cm. The counting gas was a mixture of ³He (270 Pa) and CF₄ (3×10⁴Pa). The observed distribution was very similar to that measured with the conventional gold wire activation method. The position resolution was 2.7 cm in the experimental condition. The measurable neutron flux (at peak position) was limited to the order of 10⁴ n-cm^?2-s^?1 due to the pileup of signal pulses. The counter was a useful tool to quickly measure the flux distribution in the assembly.     

Dependence of Position Signal on Pressure of Counting Gas in Charge Division Type Position-Sensitive Proportional Counter

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 0.5×10⁵Pa to 4×10⁵Pa, the range of position signals for two position calibration sources became narrower by about 8% under 6 μs shaping time.