Radon monitoring in the Kamioka mine Guillaume Pronost Kamioka - - PowerPoint PPT Presentation
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
Kamioka Observatory, ICRR, University of Tokyo
TAUP conference, 2019 September 10th, Toyama
(Supported by KAKENHI Grant-in-Aid for Scientific Research
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/m3
TAUP conference, 2019 September 10th, Toyama 2/17 pronost@km.icrr.u-tokyo.ac.jp
Radon detection method: electrostatic collection
amp.
222Rn 218Po+
Air Mesh Filter Black cover
21XPo+
α N P
bin
50 100 150 200 250
Count
200 400 600 800 1000 1200 1400 1600
4
α 5.407 MeV
2
α 6.115 MeV
3
α 7.833 MeV
Th
α 8.954 MeV
◮ Collection of positive ions from 222Rn decay chain on the PN photo-diode:
222Rn α1
β
β
214Po+ α3
β
β
◮ Concentration = α3 counts × Calibration Factor(Humidity, ∆tdata taking)
TAUP conference, 2019 September 10th, Toyama 3/17 pronost@km.icrr.u-tokyo.ac.jp
Calibration
]
3
Absolute Humidity [g/m
10 1 10 )]
3
Po/day)/(Bq/m
214
Calibration Factor[( 2 4 6 8 10 12 14 16 18 20 / ndf
2
χ 2.84 / 2 p0 0.40 ± 12.86 p1 0.19 ± 1.66 / ndf
2
χ 2.84 / 2 p0 0.40 ± 12.86 p1 0.19 ± 1.66 / ndf
2
χ 2.84 / 2 p0 0.40 ± 12.86 p1 0.19 ± 1.66
◮ Radon measurement has a humidity dependence (ion neutralization) − → humidity dependence calibration taken into account
TAUP conference, 2019 September 10th, Toyama 4/17 pronost@km.icrr.u-tokyo.ac.jp
Data acquisition system
17 × GPIO (RP B+ and later) 8 × GPIO (RP B)
◮ 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. ◮ 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).
TAUP conference, 2019 September 10th, Toyama 5/17 pronost@km.icrr.u-tokyo.ac.jp
1L radon detectors in the mine
USB Humidity sensor 1L detector
±12V signal input Raspberry Pi ADC
◮ 1L detector able to measure Rn concentration between 0.4 Bq/m3 and >250 MBq/m3.
TAUP conference, 2019 September 10th, Toyama 6/17 pronost@km.icrr.u-tokyo.ac.jp
Radon detectors map in Kamioka mine
A t
s u t u n n e l ( ∼ 2 k m ) Rn Hut XMASS CANDLES LAB-1 KamLAND SK LAB-A LAB-B LAB-E LAB-G
◮ 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 7/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring in the tunnel
A t
s u t u n n e l ( ∼ 2 k m ) Rn Hut XMASS CANDLES LAB-1 KamLAND SK LAB-A LAB-B LAB-E LAB-G
TAUP conference, 2019 September 10th, Toyama 8/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring in the tunnel: Seasonal fluctuation
0.3 − 0.2 − 0.1 − 0.1 0.2 0.3 0.4 0.5
Wind speed in Tunnel (m/s)
500 1000 1500 2000 2500 3000 3500
)
3
Radon concentration in Tunne (Bq/m 1 10
2
10
July 2016 - August 2019
◮ 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 9/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring in the tunnel: Seasonal fluctuation
0.3 − 0.2 − 0.1 − 0.1 0.2 0.3 0.4 0.5
Wind speed in Tunnel (m/s)
5 10 15 20 25 30 35
Temperature outside the mine (deg.C) 1 10
2
10
◮ 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 10/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring of the fresh air
A t
s u t u n n e l ( ∼ 2 k m ) Rn Hut XMASS CANDLES LAB-1 KamLAND SK LAB-A LAB-B LAB-E LAB-G
TAUP conference, 2019 September 10th, Toyama 11/17 pronost@km.icrr.u-tokyo.ac.jp
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
(Radon free air (< 10 mBq/m3 is used for the experiments)
TAUP conference, 2019 September 10th, Toyama 12/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring in experimental areas
A t
s u t u n n e l ( ∼ 2 k m ) Rn Hut XMASS CANDLES LAB-1 KamLAND SK LAB-A LAB-B LAB-E LAB-G
TAUP conference, 2019 September 10th, Toyama 13/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring in Super-K areas: Dome
2016-01-01 2016-02-26 2016-04-22 2016-06-17 2016-08-12 2016-10-07 2016-12-01 2017-01-26 2017-03-23 2017-05-18 2017-07-13 2017-09-07 2017-11-01 2017-12-27 2018-02-21 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 20 40 60 80 100 120 140 160 180 200
3
Concentration Bq/m
SK tank
Dome Tunnel side Dome Center Dome LAB-A side
◮ 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 14/17 pronost@km.icrr.u-tokyo.ac.jp
Radon monitoring in LAB-E
2016-10-15 2016-11-28 2017-01-11 2017-02-24 2017-04-09 2017-05-23 2017-07-05 2017-08-18 2017-10-01 2017-11-14 2017-12-28 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 2019-07-21 2019-09-02 20 40 60 80 100 120 140 160
3
Concentration Bq/m
◮ More typical Rn concentration in an experimental area in the Kamioka Mine. ◮ Low Rn concentration is ensured via the fresh air input.
TAUP conference, 2019 September 10th, Toyama 15/17 pronost@km.icrr.u-tokyo.ac.jp
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/m3 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 16/17 pronost@km.icrr.u-tokyo.ac.jp
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 17/17 pronost@km.icrr.u-tokyo.ac.jp