A summary of the results from some tests concerning the investigation of the influence of measuring conditions on the results of radon measurements using high voltage accumulation of Po-218-ions on alpha detector. The used detector preamplifier unit is described in „Bauanleitung Allg. und Verstärker“ (in German).

Remarks:

The aim of the release of the results of Rn-222-measurements using HV accumulation of Po-218-ions carried out by myself is to indicate some difficulties in using this method.

My apologies for a bad English of the text; I’m not perfect in English language and have not the possibility for a professional correction of the text. I hope that the content is readable and can be understand also from native speaking reader.

The measurements carried out are not traceable calibrated but the basis of the results is the comparison of measurements at different conditions and therefore the conclusions are valid.

The documentation of my measurements is not a Peer-reviewed article for a scientific publication but I hope that it can be helpful for a critical assessment of results from Rn-222-measurements using HV accumulation of Po-218-ions. 

Furthermore I hope some scientists can be motivated to investigate neutralization rates and neutralization processes of Po-218 at different conditions to improve this method for Rn-222-measurements.

Abstract

The aim of experiments was to check the influence of humidity and radon activity concentration on the calibration factor of a measuring chamber and to estimate rates of neutralisation of Po-218 ions as well. The chamber consists of a cylinder with 3.6 l volume. Experiments were carried out in flow through mode. For reference measurements a scintillation chamber (lucas chamber) was used. To change the humidity a CaCl2 dryer column in bypass to the air stream was used. It was found that the calibration factor increased significantly with increasing humidity as suggested. The increase of calibration factor depends of activity concentration. In the range from dry air up to absolute  humidity of a.H. =10 g/kg (dry air) the calibration factor changes of about factor 3.5 at low activity concentrations (< 2.5 Bq/l) and about factor 1.9 for higher activity concentrations.

At low absolute humidity (< 2.5 g/kg) no influence of the Rn-222-activity concentration on calibration factor was found. 

Additionally the measured results were taken to calculate neutralisation rates of Po-218-ions. Using a spherical model of the electrical field the neutralisation rates were calculated for low and high humidity. Values of neutralisation rate n of about n= 5 s-1 for dry air and about n= 20 s-1 for an absolute humidity of about 10 g/kg (dry air) was found.

Estimation of Neutralisation rates