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22 Na as an Atmospheric Tracer and Radiochronometer Ian Hoffman, Royal Military College, Kingston & Health Canada, Ottawa Kurt Ungar, Health Canada Brent Lewis, Royal Military College Science and Technology Conference 2013 , Vienna Austria

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SLIDE 1

22Na as an Atmospheric

Tracer and Radiochronometer

Ian Hoffman, Royal Military College, Kingston & Health Canada, Ottawa Kurt Ungar, Health Canada Brent Lewis, Royal Military College Science and Technology Conference 2013, Vienna Austria June 21, 2013

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SLIDE 2

Acknowledgements

— Harry Toivonen, STUK (Radiation and Nuclear

Safety Authority, Finland) – Provided JMUFI software for use

— Andreas Pelikan – author of JMUFI software

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SLIDE 3

Contents

  • 1. Background
  • 2. Goals
  • 3. Theory and Method
  • a. Procedural Flowchart
  • b. Components
  • c. Spectroscopic Analysis
  • 4. Preliminary Results
  • 5. Future Work
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SLIDE 4

Background

Radionuclides have long been used as environmental tracers allowing examination of many physical phenomena

— 14C, U/Pb, 40K/40Ar, 147Sm/143Nd, 10Be

Measurements allow:

— Water or airborne transport pathway analysis

— Stratospheric-Tropospheric Exchange (STE), bulk air mass

transport

— Water flows and residence times

— Age of materials

— ice cores, sediments, bones, artifacts, etc. Provided:

— Initial conditions and any contamination effects are

known — Historical cosmic ray flux is important for cosmogenics

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SLIDE 5

Background

— Two factors influence the production of cosmogenic

radionuclides

— Cosmic ray intensity — Geomagnetic shielding

—

7Be is a commonly studied cosmogenic isotope produced

through spallation of isotopes of N, O, C and Ar

— High production rates and easy to measure at ground level

—

22Na is also cosmogenic but principally produced by

spallation of 40Ar

— Ar is rare (.9%) in the atmosphere

—

22Na is produced at about 1/1000 the rate of 7Be

— Difficult to measure – only under specific circumstances

Can 22Na be used as an atmospheric tracer?

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SLIDE 6

Background

For environmental aerosols considerable knowledge has been

  • btained. Consider 7Be (from [1]):

— Anti-correlated with

sunspot number and correlated with cosmic ray intensity —

22Na expected to behave

similarly as production process is similar

—

22Na has not been studied

very much due to lack of data

— The atmosphere plays a

strong role in observed concentrations

2800 3200 3600 4000 1972 1976 1980 1984 1989 1993 1997 2001 Cosmic ray intensity [Counts/hour]/100 Year

1000 2000 3000 4000

7Be [µBq/m3]

50 100 150 200 1972 1976 1980 1984 1989 1993 1997 2001 Sunspot number

23 22 21

Year

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SLIDE 7

Background

— The atmosphere has 3 major transport

circulation cells and 5 major layers

— The bottom two layers (troposphere and

stratosphere) are the active regions

— Production is

principally in stratosphere with a small amount in upper troposphere.

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SLIDE 8

Goals

This work was an attempt to:

— Provide the first global data set of 22Na activity

concentrations — Corrected for coincidence summation (1st time

performed for 22Na)

— Study the resulting statistical distributions of 22Na

activity concentrations and geographic influences (geomagnetic shielding) A spectral summation technique was applied to generate data. — Artificially increase air sample volumes at a cost of

temporal resolution

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SLIDE 9

Theory and Method - Model

— Jasiulionis and Wershofen[2]

modelled the behaviour of these nuclides vertically — Predicts ground-level 22Na

concentrations between 0.2 - 1.1 μBq/m3

— Predicts ground-level 7Be

concentrations that match what is observed in the IMS (~ 1- 8 mBq/m3)

— These low 22Na activity

concentration predictions are the reason special techniques are needed to measure this radionuclide

22 7

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SLIDE 10

Theory and Method -Spectral Summation

— One approach is to

perform spectral summation — Channel-by-channel

addition of raw MCA data

  • ver some time interval

— We can get a sense of

spectral summation by stacking spectra and viewing them from the “top”

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SLIDE 11

Theory and Method – Source Data

— The spectral data source are

the raw files from the Comprehensive Nuclear-Test- Ban Treaty (CTBT) International Monitoring System (IMS) from 2005 - 2011.

— 80 particulate stations at

completion well-distributed globally — Over 80% operational currently,

>50% during study period

— Daily high volume (> 20 000

m3) aerosol collection — MDC - 22Na ~ 0.2μBq/m3, 7Be

~ 0.8 μBq/m3

— 24 hour sample collection, 24

hour “cool-down”, 24 hour measurement

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SLIDE 12

Procedural Flowchart

  • Existing Software/New Software created for this work
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SLIDE 13

Components

— LINSSI – Database containing raw (1.1) and

processed spectra (2.2) from IMS.

Existing Software/New Software created for this work

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SLIDE 14
  • Components

— Pysum – Software that performs channel-by-channel

spectral summation over user defined interval

Existing Software/New Software created for this work

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SLIDE 15
  • Components

— AATAMI – gamma spec software used for energy

and resolution calibrations

Existing Software/New Software created for this work

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SLIDE 16
  • Components

— Calupdate – “Recommends” calibrations and

controls operation of JMUFI

Existing Software/New Software created for this work

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SLIDE 17
  • Components

— JMUFI – fast linear baseline template Gaussian

peak fitting

Existing Software/New Software created for this work

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SLIDE 18
  • Components

— Globalplot – Software that performs activity

calculus and data visualization

Existing Software/New Software created for this work

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SLIDE 19
  • Components

— Unisampo/Shaman – Provides an estimate of

coincidence summation correction factors for 22Na.

Existing Software/New Software created for this work

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SLIDE 20

Spectroscopic Analysis – some equations

JMUFI only provides peak area – some math is required to obtain activity concentrations, a. The activity, A, at the end of sample collection can be calculated by:

Where:

— G-B is the net peak area, or the Peak area, G, subtracted by the

background area, B

— e is the detector efficiency — tc is the live time of the detector — p is the emission probability of the radioisotope

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SLIDE 21

Spectroscopic Analysis – some equations

The activity concentration can then be calculated by:

a = A V

  • The Cx values are correction factors related to the operational

schedule, sampling (Cs), cool-down (Cw), measurement (Cc). Where V is the volume of air samples. However, there are a couple additional factors that need to be considered related to decays occurring during the sample and analysis process:

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SLIDE 22

Spectroscopic Analysis – some equations

The correction factors are:

  • Cs follows the same formulation as Cw (replace w by

s). Now let’s look at some results and problems with Pysum, the new spectral summation software.

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SLIDE 23

Preliminary Results

Several problems were discovered:

— Unstable energy

calibrations gives incorrect peak areas

— Resuspension of

radionuclides from the ground

2 4 6 8 10 12

7Be Activity Concentration (mBq/m3)

1 2 3 4 5 6 7

22Na Activity Concentration (µBq/m3) CAP00 ISP34 CAP17 FRP29 DEP33 GBP68 USP75 NZP47

Ratio Plot of 22Na/7Be (x1000) June 2006

22Na/7Be (µBq/mBq)

a=-0.540 b=3.497 2 4 6 8 10 12

7Be Activity Concentration (mBq/m3)

0.0 0.2 0.4 0.6 0.8 1.0

22Na Activity Concentration (µBq/m3) CAP00 CAP17 FRP29 DEP33 GBP68 USP75 NZP47

Ratio Plot of 22Na/7Be (x1000) June 2006

22Na/7Be (µBq/mBq)

a=0.152 b=-0.187

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SLIDE 24

Preliminary Results

200# 250# 300# 350# 400# 450# 500# 100000# 300000# 500000# 700000# 900000# 1100000# 1300000# 1500000# 12/26/05# 02/14/06# 04/05/06# 05/25/06# 07/14/06# 09/02/06# 10/22/06# 12/11/06# 01/30/07#

22Na$Peak$Area$ 7Be$Peak$Area$

Date$

St.$John's,$NFLD$7Be$and$22Na$(30$Day$Summa@on)$

Be.7# Na.22#

—

22Na and 7Be show good

correlation in terms of peak areas using St. John’s, NFLD and Schauinsland, Germany

— Activity calculus necessary

to intercompare different sites for long term trends and STE analysis.

200# 300# 400# 500# 600# 700# 800# 900# 1000# 1100# 1200# 400000# 600000# 800000# 1000000# 1200000# 1400000# 1600000# 11/06/05# 12/26/05# 02/14/06# 04/05/06# 05/25/06# 07/14/06# 09/02/06# 10/22/06# 12/11/06# 01/30/07#

22Na$Peak$Area$ 7Be$Peak$Area$

Date$

Schauinsland,$GER$7Be$and$22Na$(30$Day$Summa@on)$

Be/7# Na/22#

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SLIDE 25

Preliminary Results –Coincidence Correction

NZP47 TZP64 KIP39 MRP43 AUP10 FJP26 GBP67 GBP68 AUP04 AUP06 ARP03 CAP00 CKP23 RUP60 AUP08 ARP01 FRP30 CAP16 NZP46 CAP14 CAP17 NOP49 PAP50 PGP51 RUP58 RUP61 RUP59 PHP52 MNP45 RUP54 PTP53 MXP44 SEP63 FRP29 GBP66 ISP34 JPP37 USP80 USP74 DEP33 USP70 FRP28 KWP40 CLP19 CAP15 USP72 USP79 USP78 JPP38 USP75 USP76 USP77 USP71 USP73 Station 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Coincidence Correction Factor

— Factors were averaged from the monitoring history of station

using the Shaman software parameterized values — Missing values were “typical” values from other sites by host

country

— Factors varied from 1.3 – 2.7 depending on monitoring station — More accurate values could be generated via M-C simulation if

station geometries were confirmed

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SLIDE 26

Preliminary Results

2 4 6 8 10 12

7Be Activity Concentration (mBq/m3)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

22Na Activity Concentration (µBq/m3) GBP68 AUP08 FJP26 DEP33 SEP63 NZP47 AUP04

Ratio Plot of 22Na/7Be September 2006

22Na/7Be (µBq/mBq)

a=0.08 b=0.19 R2=0.64 1 2 3 4 5 6 7 8

7Be Activity Concentration (mBq/m3)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

22Na Activity Concentration (µBq/m3) AUP10 SEP63 NZP47 AUP08 FJP26 DEP33 CLP18 CLP19 GBP68 ARP01 USP72

Ratio Plot of 22Na/7Be March 2005

22Na/7Be (µBq/mBq)

a=0.13 b=-0.11 R2=0.79

STE occurring? Sweden – Spring/Autumn A new Python code, Globalplot, was written to perform data visualization and the activity calculus and apply all correction factors to the raw peak

  • areas. This allows for the identification of trends in:
  • absolute concentrations by location
  • Concentration with latitude or geomagnetic rigidity
  • ratio – potentially identifying STE events
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SLIDE 27

Preliminary Results

Feb 2005 Jun 2005 Oct 2005 Feb 2006 Jun 2006 Oct 2006 Feb 2007 Jun 2007 Oct 2007 Feb 2008 Jun 2008 Oct 2008 Feb 2009 Jun 2009 Oct 2009 Feb 2010 Jun 2010 Oct 2010 Feb 2011 Jun 2011

Month

−0.2 −0.1 0.0 0.1 0.2 0.3 0.4

Monthly 22Na Slope

Monthly Trending in Regression Fit

22Na 7Be

−1.0 −0.5 0.0 0.5 1.0 1.5

Monthly 7Be Slope

Anti-correlated with sunspot number as previously discovered.

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SLIDE 28

Future Work

— Incorporate production and transport model to

validate ground level observations

— Examine geographical effects on 22Na and compare

with other 7Be work.

  • Determine optimal

integration time and improve coincidence correction

  • Use advanced

measurement (γ-γ coincidence) techniques to improve sensitivity

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SLIDE 29

Applications

— Studies on STE

— Improvements in ATM (vertical modelling) — Indicates timing of atmospheric inversion

— Air mass composition (fractional amount of

stratospheric air in sample)

— Transit time of air masses (stratosphere-ground) — Spectral summation technique could be applied to

  • ther nuclides – surface Uranium mapping
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SLIDE 30

References

[1] A. Kulan, A. Aldahan, G. Possnert, and I. Vintersved. Distribution of 7Be in surface air of Europe. Atmospheric Environment, 40(21):3855–3868, 7 2006. [2] R. Jasiulionis and H. Wershofen. A study of the vertical diffusion of the cosmogenic radionuclides, 7Be and 22Na in the atmosphere. Journal of Environmental Radioactivity, 79(2):157–169, 2005.