Radon monitoring in the Kamioka mine Guillaume Pronost Kamioka Observatory, ICRR, University of Tokyo TAUP conference, 2019 September 10th, Toyama (Supported by KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas 26104008)
Why monitor the radon concentration in Kamioka Mine? Radon is a radioactive gas which tend to accumulate indoors → Accumulation in the Kamioka Mine ◮ Radioactivity from Radon can lead to health issue in case of high exposure. ◮ Radioactivity from Radon is a background for high precision experiments looking for low energy physics, like the ones present in the Kamioka mine. → Monitoring the Radon concentration allows to protect the health of the researchers and technicians working in the mine, as well as, to control the background coming from Radon. We use the US recommendation for indoor radon concentration: 4 pCi/L → 148 Bq/m 3 TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 2/17
Radon detection method: electrostatic collection N α Count α α P 1600 4 3 α α amp. 5.407 MeV 7.833 MeV 21 X Po + 2 Th 1400 6.115 MeV 8.954 MeV -120V 1200 1000 800 218 Po + 600 400 222 Rn 200 � Mesh 0 Filter 0 50 100 150 200 250 bin Black cover Air ◮ Collection of positive ions from 222 Rn decay chain on the PN photo-diode: β β α 1 → 218 Po + α 2 222 Rn → 214 Pb + → 214 Bi + → 214 Po + − − − − β β 214 Po + α 3 → 210 Po + α 4 → 210 Pb + → 210 Bi + → 206 Pb + − − − − ◮ Concentration = α 3 counts × Calibration Factor(Humidity, ∆t data taking ) TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 3/17
Calibration 20 )] 3 Po/day)/(Bq/m 18 16 14 12 214 10 Calibration Factor[( 8 χ χ χ 2 2 2 / ndf / ndf / ndf 2.84 / 2 2.84 / 2 2.84 / 2 6 ± ± ± p0 p0 p0 12.86 12.86 12.86 0.40 0.40 0.40 4 ± ± ± p1 p1 p1 1.66 1.66 1.66 0.19 0.19 0.19 2 0 -1 10 1 10 3 Absolute Humidity [g/m ] ◮ Radon measurement has a humidity dependence (ion neutralization) → humidity dependence calibration taken into account − TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 4/17
Data acquisition system ◮ We developed a Raspberry Pi based data acquisition (DAQ) system. → Compatible with all Raspberry Pi B types using 17 × or 8 × GPIO connections ◮ This DAQ board is able to handle input rate > 20 kHz, much more than what we need for Rn monitoring. 17 × GPIO (RP B+ and later) ◮ We integrate all the decays occurring in 10 minutes. Event by event recording is also possible at low rate, but this is not needed for Rn monitoring. ◮ Stable operation: used for more than 3 years in the Kamioka mine without trouble (some in high humidity / high temperature environment). 8 × GPIO (RP B) TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 5/17
1L radon detectors in the mine USB Humidity sensor 1L detector � � -120V H.V. inside the box ± 12V signal input Raspberry Pi ADC ◮ 1L detector able to measure Rn concentration between 0.4 Bq/m 3 and > 250 MBq/m 3 . TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 6/17
Radon detectors map in Kamioka mine KamLAND LAB-A SK CANDLES A t o XMASS t s u t u n LAB-E n e l ( ∼ 2 k m ) Rn Hut LAB-G LAB-1 LAB-B ◮ 29 Rn detectors used to monitor the radon in the mine (15 in SK areas) ◮ with 26 using the Raspberry Pi electronics TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 7/17
Radon monitoring in the tunnel Radon monitoring in the tunnel KamLAND LAB-A SK CANDLES A t o XMASS t s u t u LAB-E n n e l ( ∼ 2 k m ) Rn Hut LAB-G LAB-1 LAB-B TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 8/17
Radon monitoring in the tunnel: Seasonal fluctuation ) 3 3500 Radon concentration in Tunne (Bq/m July 2016 - August 2019 3000 2 10 2500 2000 10 1500 1000 500 1 0 − − − 0.3 0.2 0.1 0 0.1 0.2 0.3 0.4 0.5 Wind speed in Tunnel (m/s) ◮ Very high concentration, visible seasonal fluctuation ◮ Since July 2016, we have access to the data of the wind sensor in this tunnel → Observation of correlations between wind direction and Rn concentration − TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 9/17
Radon monitoring in the tunnel: Seasonal fluctuation 35 Temperature outside the mine (deg.C) Feb. 2018 - August 2019 30 2 10 25 20 10 15 10 5 1 0 − − − 0.3 0.2 0.1 0 0.1 0.2 0.3 0.4 0.5 Wind speed in Tunnel (m/s) ◮ Very high concentration, visible seasonal fluctuation ◮ Since February 2018, we record the temperature outside the mine → Observation of correlations between wind direction and temperature − → When the outside temperature passes 10 . 4 ± 2 . 3 ℃ the direction of wind − (and the Rn concentration) changes. TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 10/17
Radon monitoring of the fresh air Radon monitoring of the fresh air KamLAND LAB-A SK CANDLES A t o XMASS t s u t u LAB-E n n e l ( ∼ 2 k m ) Rn Hut LAB-G LAB-1 LAB-B TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 11/17
Radon monitoring of the fresh air SK Dome US Hut ◮ Low radon concentration over year ◮ This fresh air is distributed in all experimental areas for the breathing air of the workers. (Radon free air ( < 10 mBq/m 3 is used for the experiments) TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 12/17
Radon monitoring in experimental areas Radon monitoring in experimental areas KamLAND LAB-A SK CANDLES A t o XMASS t s u t u LAB-E n n e l ( ∼ 2 k m ) Rn Hut LAB-G LAB-1 LAB-B TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 13/17
Radon monitoring in Super-K areas: Dome 200 3 Concentration Bq/m SK tank 180 openning 160 Dome LAB-A side 140 120 100 Dome Center 80 Dome Tunnel side 60 40 20 2016-01-01 2016-12-01 2017-11-01 2018-02-21 2016-02-26 2016-04-22 2016-06-17 2016-08-12 2016-10-07 2017-01-26 2017-03-23 2017-05-18 2017-07-13 2017-09-07 2017-12-27 2018-04-18 2018-06-13 2018-08-08 2018-10-02 2018-11-27 2019-01-22 2019-03-19 2019-05-14 2019-07-09 2019-09-02 ◮ Usually low Rn concentration ◮ During the SK tank opening period (Summer 2018), the Rn concentration was very high, due to the need of additional air circulation and trouble to get the doors closed. ◮ The current high concentration on LAB-A side is being investigated. TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 14/17
TAUP conference, 2019 September 10th, Toyama ◮ Low Rn concentration is ensured via the fresh air input. ◮ More typical Rn concentration in an experimental area in the Kamioka Mine. 3 Concentration Bq/m 100 120 140 160 20 40 60 80 0 2016-10-15 2016-11-28 2017-01-11 2017-02-24 2017-04-09 2017-05-23 Radon monitoring in LAB-E 2017-07-05 2017-08-18 2017-10-01 2017-11-14 2017-12-28 15/17 2018-02-10 2018-03-25 2018-05-08 2018-06-21 2018-08-04 2018-09-17 2018-10-31 2018-12-13 2019-01-26 2019-03-11 2019-04-24 2019-06-07 pronost@km.icrr.u-tokyo.ac.jp 2019-07-21 2019-09-02
Summary ◮ In the Kamioka mine we are using 29 1-L Radon detectors, 26 with a custom Raspberry Pi based ADC board [1]. ◮ There is a strong seasonal fluctuations of the Rn concentration in the mine, with high value during Summer, and low value during winter. ◮ Radon-less air is distributed in the experimental areas, allowing them to keep low radon concentrations. ◮ The experimental areas are relatively safe for workers, and we are trying to keep the Rn concentration below 148 Bq/m 3 in all these area. [1] More details available in: G. Pronost et al., “Development of new radon monitoring systems in the Kamioka mine”, 10.1093/ptep/pty091 (2018) TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 16/17
Radon monitoring in the tunnel - fluctuations ◮ Fluctuations occur with a one day high, one day low pattern, changing at fix time every 24h, over the whole year, the high concentration period is correlated with an increase of the temperature measured near the detector. ◮ This is due to the activation of the air conditioning pumps near the detector. The displacement of water by the pump causes a degasification of the high radon concentrated water these pumps are using. TAUP conference, 2019 September 10th, Toyama pronost@km.icrr.u-tokyo.ac.jp 17/17
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