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methane climate changeoratom counting
reveals secrets of Earth past climate

• Dr Andrew Smith
• Australian Nuclear Science and Technology
  Organisation

Climate change reflecting back, looking
forward 10 days of science National Science Week,
15th -23rd August 2009
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Cosmogenic radionuclides

• Next is an AIRES simulation of what happens when
  a proton with 1Tev (1012 electron volts energy)
  hits the atmosphere about 20km above the ground.
  The shower is in a 20km x 5km x 5km box
  superimposed on a scale map of Chicago's
  lakefront. Different kinds of particles are
  coloured differently electrons and positrons are
  green, muons are red, and gamma rays are cyan.

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Cosmic rays (discovered 1912)

• Cosmic rays are energetic particles from outer
  space that impinge on Earth's atmosphere.
• Ray a misnomer cosmic particles arrive
  individually, not as a ray or beam of particles.
• 90 are protons, 10 are helium nuclei (alpha
  particles), lt 1 heavier elements and electrons.
• Energies gt 1020 eV, far higher than lt 1013 eV
  man-made particle accelerators can produce.
• Cosmic rays incessantly bombard Earth, smashing
  atoms and molecules high in the atmosphere,
  producing cascades of secondary particles that
  reach the surface.

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The origin of cosmic rays

• energetic processes on the Sun
• Supernova
• unknown events in the farthest reaches of the
  visible universe.

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Supernova RXJ1713.7-3946Suzaku X-ray
observatory

• This supernova remnant is the gaseous remnant of
  a massive star that exploded about 1,600 years
  ago
• The contour lines show where gamma-ray intensity
  is highest

Credit JAXA/ Takaaki Tanaka/HESS
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Production rate modulation

• Cosmic ray flux
• Terrestrial magnetic field
• Heliosphere magnetic field

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Cosmogenic radionuclides
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radionuclide nomenclature
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How do we measure cosmo-isotopes?

• By Accelerator Mass Spectrometry or AMS.
• Example radiocarbon or 14C
• Stable carbon isotopes 12C (98.90) and 13C
  (1.10).
• Only 7.5kg of cosmogenic 14C produced globally in
  the entire atmosphere per year in equilibrium.
• Natural abundance 14C/12C 1.2 10-12 one in
  a trillion!
• 14C oxidised to 14CO2 radiocarbon dioxide
• Photosynthesis living organisms in equilibrium
  with atmosphere.
• Radiocarbon dating the clock starts on death
  limit 10-16 (50ka).
• Carbon from sample chemically prepared as
  graphite.

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Radiocarbon dating

• black square is carbon, mostly 12C (99) and 13C
  (1).
• yellow dots are 14C atoms, initially 104 atoms.
• 14C atoms are radioactive and disintegrate with
  a half-life of 5,730 years.
• When? It cannot be predicted for a given atom.
• Dating old samples is difficult few 14C atoms
  remain.
• Modern natural carbon contains 50 million per
  mg.

credit M. Blaauw 2007, chrono.qub.ac.uk/blaauw
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The technique of accelerator mass spectrometry
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ANSTOs STAR accelerator 2MV
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Accelerator Mass Spectrometry at ANTARES
Australian National Tandem for Applied RESearch. 1
0MV
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advantages of tandem AMS over mass
spectrometry negative ions elimination of 14N
isobar charge exchange destruction of 12CH2
13CH in terminal ionisation detector E,M,Z ?
atom counting
features ultra-small samples 0.1 mg rapid
measurement 20 min sensitivity 1 in
1015 accuracy 0.5, background 50 ka
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Isotopes and climate science

• Stable and radioactive isotopes
• Isotopes of atoms provide valuable information
  about past climates. and factors which have
  forced climate change.
• Natural radioisotopes provide additional, and
  often unique, data.
• Archives for cosmogenic radionuclides
• tree rings, rocks, coral, speliothems,
  sediments, ice cores
• Applications include
• Past atmospheric composition.
• Timing of past climate change.
• Atmospheric circulation transport.

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climate signals recorded in polar ice sheets
Snowfall traps traces of atmospheric gas and
impurities...
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Law Dome
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W20k
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97/98 Law Dome firn air sampling
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Law Dome DSS0506 thermal drilling
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Gaseous components of the atmosphere.
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Global warming in the anthropocene
From 1700 AD to 2005 AD, CO2 has risen 36 from
280 ppm to 379 ppm, CH4 has risen 153 from 700
ppb to 1,774 IPCC4
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quantity of air ice needed for 14C AMS
assuming 300 ppm CO2, 2 ppm CH4 and 50 ppb CO
and 100 mL of air per kg ice
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helping to determine the anthropogenic natural
sources of the important greenhouse gas - methane
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A new highly interactive exhibition exploring the
complex world of nuclear science, medicine and
nuclear power. On display in the Museums
Experimentations gallery where different areas of
science are explained, Nuclear matters aims to
provide a greater public understanding of what
nuclear science is and how it plays a big part in
our everyday lives.
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