A Simple Detector for Measuring the Density of Air Using an α-Ray Source

Abstract

The IR pulsed photoacoustic method was used to investigate rotational relaxation processes in MPA. We have examined the bulk rotational relaxation times (t R ) and the bulk rotational relaxation cross sections (σ R ), related to R-R and R-T relaxation mechanisms. The saturation intensities for SF 6 gas molecules have been measured in the gas mixtures with CH 4 (buffer) molecules, at constant SF 6 gas pressure (0.47 mbar) and variable CH 4 gas pressure (1-140 mbar), using the 10P(16) CO 2 laser line in the fluences range 0.1-0.7 J cm −2 . It has been found that for proper investigation of the rotational relaxation processes, the buffer gas pressure range must be divided into two parts: the low pressure range (0-20 mbar) and the high pressure range (20-140 mbar), according to the behaviour of the saturation intensities versus buffer gas pressure. Consequently, two different sets of values for rotational relaxation parameters are obtained. The found step-function behaviour for σ R shows that the rotational hole-filling effect during MPA only dominates at low buffer gas pressure (p CH 4 20 mbar). At higher buffer gas pressures (between 20-140 mbar) collisional deactivation takes place. We also derive the enhanced absorption cross sections for absorbing SF 6 gas molecules from the measured saturation intensities data (at zero buffer gas pressure) confirming the expectation that the enhanced absorbing cross sections are not only a function of laser fluence and buffer gas pressure, but are very strongly dependent on laser beam parameters, too.