the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Nov 2023
Full characterization and calibration of a transfer standard monitor for atmospheric radon and thoron measurements
Abstract. In this work a full characterization of the new user-friendly version of the Atmospheric Radon MONitor (ARMON), used to measure very low activity concentrations of the radioactive radon gas in the outdoor atmosphere, is carried out. The ARMON is based on the electrostatic collection of 218Po+ particles on a semiconductor detector surface. A main advantage of this instrument is offering high resolution alpha energy spectra which will allow to separate radon progeny (210Po, 218Po and 214Po). The monitor feature may also allow measurements of thoron (220Rn) by collection of 216Po+.
In this work the physical principle, the hardware configuration and the software development of the automatic and remotely controlled ARMON, conceived and constructed within the MAR2EA and the traceRadon projects, are described. The monitor efficiency and its linearity over a wide spam of radon concentration activities has been here evaluated and tested using theoretical as well as experimental approaches. Finally, a complete budget analysis of the total uncertainty of the monitor was also achieved.
Results from the application of a simplified theoretical approach shows a detection efficiency for 218Po+ of about 0.0075 (Bq m‑3)-1 s-1. The experimental approach, consisting of exposing the ARMON at controlled radon concentrations between few hundreds to few thousands of Bq m-3, gives a detection efficiency for 218Po+ of 0.0057 ± 0.0002 (Bq m-3) s-1. This last value and its independence from the radon levels was also confirmed thanks to a new calibration method which allows, using low emanation sources, to obtain controlled radon levels of few tens of Bq m‑3.
The total uncertainty of the ARMON detection efficiency obtained for hourly radon concentration above 5 Bq m-3 was lower than 10 % (k=1). The characteristics limits of the ARMON were also calculated, being those dependent on the presence of thoron in the sampled air, and a value of 0.132 Bq m-3 was estimated in thoron absence. Current results may allow to confirm that the ARMON is suitable to measure low-level radon activity concentration (1 Bq m‑3 – 100 Bq m‑3) and to be used as transfer standard to calibrate secondary atmospheric radon monitors.
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CC1: 'Comment on egusphere-2023-2680', Scott Chambers, 28 Nov 2023
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AC1: 'Reply on CC1', Roger Curcoll Masanes, 20 Dec 2023
Dea Scott Chambers
Thanks for your Community comment.
Please find in the attached file a point by point answer to your comments.
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CC2: 'Reply on AC1', Scott Chambers, 22 Dec 2023
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AC2: 'Reply on CC2', Roger Curcoll Masanes, 12 Jan 2024
Dear Scott Chambers
Thanks for your Community comment.
Please find in the attached file a point by point answer to your comments.
-
CC3: 'Reply on AC2', Scott Chambers, 18 Jan 2024
Dear Roger (et al.),
Thank you for the responses. If the laboratory calibrations of the ARMON v2 at PTB have indeed been finalised, and all contributions to uncertainties included as you say, then there should be no reason to expect a substantial difference in reported ARMON v2 performance characteristics between this study and the field-based intercomparison study.
Regarding your comment about deconvolution: if the response time correction (deconvolution) algorithm used for the ANSTO monitors resulted in a substantial change to the physical signal aggregated to hourly temporal resolution, this would show up in a comparison of signal power spectra between the radon and corresponding meteorological data at that height. There is little evidence of a difference between these power spectra for the Saclay ANSTO radon monitor, indicating that "rapid changes" in radon concentration (at the agreed hourly temporal resolution) are quite faithfully represented by the response time corrected signal.
Lastly, I expect that if there were leaks in the ARMON sampling line during the period of measurements shown, bearing in mind the 100m sampling height and proximity to the ground of potential leak sites (1-3 m?), this would manifest as prolonged periods of higher observed radon concentration by the ARMON compared with the ANSTO detector at Saclay, and this bias would likely have a pronounced diurnal variability (given that nocturnal radon concentrations at 15m agl at Saclay typically reach 15 – 25 Bq/m3 and median concentrations at 100m are only 2.5 Bq/m3). This does not appear to be the case, but as you reiterated, these observations have yet to be finalised, so I have no further comments.
Regards,
Scott
Citation: https://doi.org/10.5194/egusphere-2023-2680-CC3
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CC3: 'Reply on AC2', Scott Chambers, 18 Jan 2024
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AC2: 'Reply on CC2', Roger Curcoll Masanes, 12 Jan 2024
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CC2: 'Reply on AC1', Scott Chambers, 22 Dec 2023
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AC1: 'Reply on CC1', Roger Curcoll Masanes, 20 Dec 2023
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RC1: 'Comment on egusphere-2023-2680', Anonymous Referee #1, 25 Jan 2024
The manuscript describes an instrument sensitive to radon and thoron in concentrations frequently found in near-surface air above continents. Characterisation and calibration of the instrument were thorough, though only for radon and not for thoron (lines 114-115). Hence, the manuscript title requires modification. The instrument can help to make sure that radon concentrations measured at different stations within a monitoring network are real and unaffected by differences between instruments' performance, their individual calibration, or differences in data processing.
There is little I can add to the earlier discussion between Scott Chambers and the Authors. The main additional issue I would like to raise is the long-term stability of the instrument's calibration. Is the instrument assumed to maintain its current calibration throughout its lifetime, even when travelling frequently and extensively? Or, is regular re-calibration foreseen? If so, how often? Lines 496 to 499 hint at a calibration unit for "...very short calibration or recalibration [...] under field conditions..." The next sentence states this issue "...will be the object of a future paper." There are two further papers announced, one on a field intercomparison with an ANSTO detector (lines 499 to 501) and another one on the "full calibration procedures" (last line in AC2). Is it really necessary to distribute the outcome of this enterprise among four (!) papers? From my point of view, the mobile calibration unit definitively has to be included in the present manuscript, as should be more details about the air dryer and the thoron delay volume that will go with the instrument once it will be 'on the road' as a travelling standard instrument. Please add these items also to Figures 1 and A2. In addition, please show in the schematic diagram of Fig. 1 the position of the air pump.
At the end of AC1 you state that "... air inside the sphere is at atmospheric pressure because it is an open circuit." This presumption cannot be correct. If air pressure inside the sphere would be exactly the same as outside, there would be no air flowing through the sphere. Yet, the sphere is continuously flushed with 2 L/min. Upstream of the sphere a filter, downstream a flow meter (Fig. 1). Both restrict flow in addition to the tubing connecting the sphere with the outside. It may not be necessary to continuously monitor pressure inside the sphere, but I would suggest to determine once the pressure difference between inside and outside the sphere and add the offset to the pressure reading from the atmospheric station. Even if the correction is small, it should be included because not doing so introduces a perhaps small but systematic error.
3.) Perhaps tell the reader already in line 139 that the detection volume is 20 L.
4.) Line 445: The humidity was < 150 ppm, so why Eq. 2 and not Eq. 13?
Citation: https://doi.org/10.5194/egusphere-2023-2680-RC1 - AC3: 'Reply on RC1', Roger Curcoll Masanes, 11 Mar 2024
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RC2: 'Comment on egusphere-2023-2680', Anonymous Referee #2, 12 Feb 2024
The authors present a detailed description of the new version of the ARMON detector, including its metrological characterization. In particular, I appreciate the carefully done uncertainty budget.
The ms. is well structured and written, motivation and conclusions are clear.
Att. the commented ms. pdf. Most comments are trivial linguisting suggestions which the authors are free to accept or not. One perhaps more serious comment pertains to the simulation technique in sec. 3.1 / fig. 2b.
Overall a very interesting paper!
- AC4: 'Reply on RC2', Roger Curcoll Masanes, 11 Mar 2024
Status: closed
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CC1: 'Comment on egusphere-2023-2680', Scott Chambers, 28 Nov 2023
-
AC1: 'Reply on CC1', Roger Curcoll Masanes, 20 Dec 2023
Dea Scott Chambers
Thanks for your Community comment.
Please find in the attached file a point by point answer to your comments.
-
CC2: 'Reply on AC1', Scott Chambers, 22 Dec 2023
-
AC2: 'Reply on CC2', Roger Curcoll Masanes, 12 Jan 2024
Dear Scott Chambers
Thanks for your Community comment.
Please find in the attached file a point by point answer to your comments.
-
CC3: 'Reply on AC2', Scott Chambers, 18 Jan 2024
Dear Roger (et al.),
Thank you for the responses. If the laboratory calibrations of the ARMON v2 at PTB have indeed been finalised, and all contributions to uncertainties included as you say, then there should be no reason to expect a substantial difference in reported ARMON v2 performance characteristics between this study and the field-based intercomparison study.
Regarding your comment about deconvolution: if the response time correction (deconvolution) algorithm used for the ANSTO monitors resulted in a substantial change to the physical signal aggregated to hourly temporal resolution, this would show up in a comparison of signal power spectra between the radon and corresponding meteorological data at that height. There is little evidence of a difference between these power spectra for the Saclay ANSTO radon monitor, indicating that "rapid changes" in radon concentration (at the agreed hourly temporal resolution) are quite faithfully represented by the response time corrected signal.
Lastly, I expect that if there were leaks in the ARMON sampling line during the period of measurements shown, bearing in mind the 100m sampling height and proximity to the ground of potential leak sites (1-3 m?), this would manifest as prolonged periods of higher observed radon concentration by the ARMON compared with the ANSTO detector at Saclay, and this bias would likely have a pronounced diurnal variability (given that nocturnal radon concentrations at 15m agl at Saclay typically reach 15 – 25 Bq/m3 and median concentrations at 100m are only 2.5 Bq/m3). This does not appear to be the case, but as you reiterated, these observations have yet to be finalised, so I have no further comments.
Regards,
Scott
Citation: https://doi.org/10.5194/egusphere-2023-2680-CC3
-
CC3: 'Reply on AC2', Scott Chambers, 18 Jan 2024
-
AC2: 'Reply on CC2', Roger Curcoll Masanes, 12 Jan 2024
-
CC2: 'Reply on AC1', Scott Chambers, 22 Dec 2023
-
AC1: 'Reply on CC1', Roger Curcoll Masanes, 20 Dec 2023
-
RC1: 'Comment on egusphere-2023-2680', Anonymous Referee #1, 25 Jan 2024
The manuscript describes an instrument sensitive to radon and thoron in concentrations frequently found in near-surface air above continents. Characterisation and calibration of the instrument were thorough, though only for radon and not for thoron (lines 114-115). Hence, the manuscript title requires modification. The instrument can help to make sure that radon concentrations measured at different stations within a monitoring network are real and unaffected by differences between instruments' performance, their individual calibration, or differences in data processing.
There is little I can add to the earlier discussion between Scott Chambers and the Authors. The main additional issue I would like to raise is the long-term stability of the instrument's calibration. Is the instrument assumed to maintain its current calibration throughout its lifetime, even when travelling frequently and extensively? Or, is regular re-calibration foreseen? If so, how often? Lines 496 to 499 hint at a calibration unit for "...very short calibration or recalibration [...] under field conditions..." The next sentence states this issue "...will be the object of a future paper." There are two further papers announced, one on a field intercomparison with an ANSTO detector (lines 499 to 501) and another one on the "full calibration procedures" (last line in AC2). Is it really necessary to distribute the outcome of this enterprise among four (!) papers? From my point of view, the mobile calibration unit definitively has to be included in the present manuscript, as should be more details about the air dryer and the thoron delay volume that will go with the instrument once it will be 'on the road' as a travelling standard instrument. Please add these items also to Figures 1 and A2. In addition, please show in the schematic diagram of Fig. 1 the position of the air pump.
At the end of AC1 you state that "... air inside the sphere is at atmospheric pressure because it is an open circuit." This presumption cannot be correct. If air pressure inside the sphere would be exactly the same as outside, there would be no air flowing through the sphere. Yet, the sphere is continuously flushed with 2 L/min. Upstream of the sphere a filter, downstream a flow meter (Fig. 1). Both restrict flow in addition to the tubing connecting the sphere with the outside. It may not be necessary to continuously monitor pressure inside the sphere, but I would suggest to determine once the pressure difference between inside and outside the sphere and add the offset to the pressure reading from the atmospheric station. Even if the correction is small, it should be included because not doing so introduces a perhaps small but systematic error.
3.) Perhaps tell the reader already in line 139 that the detection volume is 20 L.
4.) Line 445: The humidity was < 150 ppm, so why Eq. 2 and not Eq. 13?
Citation: https://doi.org/10.5194/egusphere-2023-2680-RC1 - AC3: 'Reply on RC1', Roger Curcoll Masanes, 11 Mar 2024
-
RC2: 'Comment on egusphere-2023-2680', Anonymous Referee #2, 12 Feb 2024
The authors present a detailed description of the new version of the ARMON detector, including its metrological characterization. In particular, I appreciate the carefully done uncertainty budget.
The ms. is well structured and written, motivation and conclusions are clear.
Att. the commented ms. pdf. Most comments are trivial linguisting suggestions which the authors are free to accept or not. One perhaps more serious comment pertains to the simulation technique in sec. 3.1 / fig. 2b.
Overall a very interesting paper!
- AC4: 'Reply on RC2', Roger Curcoll Masanes, 11 Mar 2024
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