Ar-37, Be-7 and Xe-133 in the atmosphere

Transcription

1 Ar-37, Be-7 and Xe-133 in the atmosphere Roland Purtschert1, Martin Kalinowski2, Pierre Bourgouin2, Elisabeth Wieslander2, Xavier Blanchard2, Robin Riedmann2, Lauren Raghoo1, Jolanta Kusmierczyk-Michulec2, Abdelhakim Gheddou2, Clemens Schlosser3, Yutaka Tomita4 1 University of Bern, Bern, Switzerland 2 CTBTO Preparatory Commission, Vienna, Austria 3Bundesamt für Strahlenschutz, Germany 4 Japan Atomic Energy Agency, Japan page 1

2 Objectives Ar-37 in soil air is included in the OSI verification regime Ar-37 measurements in the atmosphere at locations close to IMS stations can provide information of Ar-37 concentrations in atmospheric air (both background & elevated) give insights of possible seasonal effects be correlated with simultaneous Xe-133 measurements in the atmosphere with its 35 day half-life provides information about atmospheric circulation pattern on timescales between Pb212 (10.6 h) and Be-7 (53.3 days) page 2

3 Natural atmospheric Ar-37 level in low troposphere (Bern) T1/2: 35d Stratosphere Cosmic rays Atmosphere 40Ar + n 37Ar + 4n 36Ar + n 37Ar + g Loosli, 1972 Background low troposphere: mbq/m3air 40Ca + n 37Ar + a Lithosphere page 3

4 Sampling at site of the IMS Radionuclide Station, Takasaki Takasaki station Acknowledgment: Sampling carried out Yutaka Tomita (IMS Radionuclide Station) On-Site Inspection (OSI) noble gas (NG) sampling equipment was used to collect atmospheric gas samples for Ar-37 Sample bags were shipped to Low-Level Counting laboratory at University of Bern, Switzerland for activity measurements page 4

5 Low Level Counting Laboratory, Bern 35 m 40 m (70 mwe) Sample size Shipping time Measuring time Counter volume MDC L 1-2 weeks week cm mbq/m3air Counting arrangement Sample ISS 2011, Viennabag in separation laboratory page 5

6 Takasaki Ar-37 Results (Jan 2016-May 2017) o 1-2 samples per month 10 3 Ar-37 mbq/mair 9 o Samples cover a full seasonal cycle MDA MDC 8 o Most values close or below MDA 37 3 Ar (mbq/m air) 7 o No activities above 9 mbq/m3 including periods after the two DPRK tests in Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun DPRK Tests page 6

7 Statistics and Comparison with Bern No of samples Bern Observation period Mean Median Std Deviation 30 counts Ar-37 (mbqair) Takasaki Observation period counts Ar-37 (mbqair) page 7

8 Possible sources for observed variations A In-flow of stratospheric air masses B Outgassing of soil air C Emissions from nuclear installations Cosmic rays Stratosphère A Tropopause Lower Troposphere C Sampling location B Lithosphere page 8

9 Sources and Indicators A In-flow of stratospheric air masses B Outgassing of soil air Emissions from nuclear installations C Cosmic rays Stratosphère A Be-7 (T1/2: 53.3 d ) B Pb-212 (T1/2: 10.6 h ) C Xe-133 (T1/2:5.2 d) O, N Be-7, Be-10, Ar-37 A Tropopause Lower Troposphere C Be-7 Xe-133 Ar-37 Rn-220 Pb-212 B Ca Ar-37 Lithosphere Th-232 Ra-224 Rn-220 page 9

10 Ar-37 in the stratosphere: Theory Ar-37 (mbq/m3) Machta et al, 1972 page 10

11 Ar-37 in the stratosphere: Measurements Ar-37 (mbq/m air ) % Stratospheric air Data Low Troposphere ( ) Lal and Peters 1962, Loosli 1980 et al., Machta 1973 Loosli 1980 et al., Currie 1980 page 11

12 Stratospheric vertical transport: Supporting weather conditions Surface pressure pattern leading to the high concentration observed on 2 February Idealized vertical motions associated with a well-developed cyclonic (low pressure) system Low activity situation High activity situation page 12

13 Correlation with weather situation Ar-37 < 2 mbq/m3air Date 12 Feb Feb Feb Feb Mar Mar Avr May Jun Oct Jan Feb Feb Mar 2017 Ar-37 (mbq/m3) 0.33/ / / / Avr Weather Pattern Strong anticyclonic system Strong anticyclonic system Anticyclonic system Anticyclonic system Strong anticyclonic system Anticyclonic system Weak weather pattern Anticyclonic system Weak anticyclonic system Anticyclonic system Strong anticyclonic system Strong anticyclonic system Strong anticyclonic system Deep cyclonic system south of Japan anticyclonic system strong Weak, moderate cyclonic system strong Weak, moderate Strong anticyclonic system Ar-37 > 3 mbq/m3air Date 02 Feb 2016 Ar-37 (mbq/m3) Sep Sep Dec Mar 2017 SnT CTBTO May Weather Pattern A cyclonic system with a trough crossing the area over a period of several days A cyclonic system with a trough crossing the area over a period of several days, typhoon over East China Sea Ridge of high pressure, typhoon over East China Sea Vigorous trough over the area, typhoon far over South China Sea Sharp trough moving out of Japan early in the day Sharp trough moving out of Japan early in the day page 13

14 Exhalation of gasses from soil column: Extreme scenario Guillon et al, m 500 mbq/m3air 15 mbq/m3air 10 m 500 mbq/m3air Porosity 30% page 14

15 Emissions from Nuclear Power Plants Power (MW) 37Ar at stack (Bq/m3Luft) 37Ar/power (Bq/m3Luft/GW) Air stream (m3/h) Emission rate BWR ±3 PWR ±3 ~70 ~ ~8 MBq/h ~8 MBq/h (Joint Uni Bern BfS Ar-37 Project for Noble Gas Measurements) from Stack Samples Sampling at stack page 15

16 Emissions from Nuclear Power Plants Power (MW) 37Ar at stack (Bq/m3Luft) 37Ar/power m3/h with 25 Bq/m3 ~8 MBq/h (Bq/m3Luft/GW) Air stream (m3/h) Emssion rate BWR ±3 PWR ±3 ~70 ~ ~8 MBq/h ~8 MBq/h Dilution factor (1/m3) 1.00E E E E-15 Ar-37 (mbq/m3air) page 16

17 Wind direction 8 7 Ar-37 mbq/m3air wind direction Not conclusive page 17

18 Temporal pattern of potential indicators (monthly means) Be-7 (mbq/m3) Xe-133 (mbq/m3) Pb-212 (mbq/m3) 14 Ar-37 (mbq/m3) page 18 Apr May Mär Feb Jan Dez Nov Okt Sep Aug Jul Jun Mai Apr Feb Mär Jan 0

19 Correlations? Measurements from Takasaki (Jan May 2017) Pb-112, Be-7 (ubq/m3) Xe-133, Ar-37 mbq/m3) page 19

20 Conclusions The first time a long and extensive record of tropospheric Ar-37 activity concentrations at the location of an IMS station was measured All values measured range between 1-10 mbq/m3air in agreement with numbers found elsewhere Three potential sources for slightly elevated background values were discussed Influence of stratospheric vertical transport Emanation of gases from soils Emissions from power plants Source strengths are likely low for all three scenarios, which is also demonstrated by the missing correlation with all source indicators Be-7, Pb212 and Xe-133 More investigations are needed in particular for the characterisation of emissions from nuclear installations ( next talk Heise et al) The absence of activity concentrations significantly above the natural background demonstrate the potential of Ar-37 as an conclusive source discriminator in high background areas ( talk Bowyer) CTBTO SnT2017 page 20