On the techniques for primary calibration of electronic radon detectors

Conclusions 1Successful calibrations were conducted at PTB and LNHB with primary radon activity standards with uncertainties < 1.5 % at 300 Bq/m3,< 1.7 % at 130 Bq/m3and < 2.5 % at 55 Bq/m3. The uncertainty using an AlphaGUARD was < 3.5 % at 55 Bq/m3(Table 1, Fig. 2a). 2The dynamic mode (activity decay or build-up) proved unsuitable for calibration of user-grade electronic detectors in this activity range (Fig.2b). 3The linearity of RadonEye +2 in the range 50 Bq/m3300 Bq/m3was demonstrated (Fig.2a). Dynamic background correction, universal for nonspectrometric detectors, was applied (Fig.3). 4The unknown pulse-processing algorithm of RadonEyes +2 distorts the Poisson distribution of the signal and increases statistical variation (Fig.4). On the techniques for primary calibration of electronic radon detectors K. Mitev1, B. Sabot2, V. Todorov1, S. Georgiev1, S. Pierre2, S. Röttger3, B. Krastev1,4, I. Dimitrova1,* 1 Sofia University “St. Kliment Ohridski” (SU), Bulgaria 2 Université Paris-Saclay, CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), France 3 Physikalisch-Technische Bundesanstalt (PTB), Germany 4 Department of Radiotherapy, University Oncology Hospital “Prof. Ivan Chernozemski”, Bulgaria Acknowledgements: This work is supported by the project RadonNET (23IND07), which received funding from the European Partnership on Metrology (ID: 10.13039/100019599), co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States. This work is supported by the European Union NextGenerationEU, through the National Recovery and Resilience Plan of the Republic of Bulgaria, project No BG-RRP-2.004-0008-C01. *[email protected] Source Uncertainty (k=1) Referent activity Rn standard rel. unc. Primary : LNHB: 0.8 % - 1 %; PTB - IRSD: 1 % - 1.2 % Secondary (AlphaGUARD) - 2.5 % Volume rel. unc . Primary : due to inactive volume of detectors: LNHB: 0.8 %; PTB: 0.15 % Secondary : N/A Decay correction Hermetic volume: negligible; Non -hermetic: 1.5 % - 7 % depending on time and decrease rate unc. Stat. unc. Primary : N/A ; Secondary: ~ 1 % av. st. dev. at 55 Bq/m3for 15 days RadonEye Stat. Unc Dynamic mode: fit slope unc.: 0.5 % - 1 %; Static mode (rel. st. dev. of average): <1 % at 300 Bq/m3 for 6 days, <2 % at 55 Bq/m3for 15 days Channel cross - talk abs. unc, Bq/m3 1 Bq/m3 RadonEye background abs . unc., Bq/m 3 Due to stat. unc. and build-up correction: 0.1 Bq/m30.6 Bq/m3; Due to channel cross-talk: 1 Bq/m3 Total Interval 50 Bq/m3-2000 Bq/m3: 1 % - 2 % (LNHB, primary ) At 300 Bq/m3: 1.3 % - 1.4 % (LNHB, primary);3.7 % (LNHB, secondary ) At 130 Bq/m3: 1.6 %- 1.7 % (PTB, primary); 2.8 % (PTB, secondary ) At 55 Bq/m3: 2.3 % - 2.4 % (PTB, primary); 3.4 % (PTB, secondary) IntroDUCTION Experimental Results Calibrations and tests of user-grade electronic radon detectors at low activity concentrations (≤ 300 Bq/m3) are needed when using them to test compliancy with the reference levels indoor or for outdoor monitoring. Exposures of electronic radon detectors (RadonEye +2) at radon activity concentrations down to 50 Bq/m3were conducted at PTB and LNHB. Fig.1. (a) The exposure system at PTB; (b) The exposure chamber with the RadonEye +2 and AlphaGUARD; (c) Data from the IRSD of PTB; (d) Radon activity concentrations during the 3 exposure sessions - the last at 55.56(60) Bq/m3was maintained for more than 3 months. Exposures at PTB:Mode 1: Build-up of 222Rn activity; Mode 2: Constant activity at plateau after 25 days of build-up. Primary standard: absolute radon emanation rate measurement in time by IRSD source.AlphaGUARD included. Exposures at LNHB: Mode 1: Decaying activity certified by the primary defined solid angle 222Rn standard; Mode 2: Constant activity in open system secured by mass-flow controller and source emanation rate traceable to the primary thoron standard.AlphaGUARD included as secondary standard. Fig.3. (a) Increase of RadonEye +2 background (dots) between exposure sessions due to previous exposure (red line) and 210Po contribution. Dynamic background correction (blue line) applied by estimating 210Pb build-up; (b) 210Pb decay data by Nucléide – Lara used in the Bateman equations. ab c d Table 1. Uncertainty budget in calibrations of electronic radon detectors. Fig.2. (a) Calibration factors (measured to referent value) determined at low activity exposures at constant activity at PTB by IRSD primary standard and AlphaGUARD. (b) Radon activity concentration at decay mode and its statistical variations (>10 % below 100 Bq/m3; >20 % below 50 Bq/m3). Fig.4. Distribution of RadonEye +2 signal distorted by rounding and unknown processing algorithm. The small sensitivity of compact user-grade detectors leads to gaps. The dots mark the Poisson distribution of deduced counts. ab ab