1. ‘methane & climate change’ or ‘atom 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, 15 th -23 rd August 2009

2. Cosmogenic radionuclides Next is an AIRES simulation of what happens when a proton with 1Tev (=10 12 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.

4. 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), < 1% heavier elements and electrons. Energies > 10 20 eV, far higher than < 10 13 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.

5. energetic processes on the Sun Supernova unknown events in the farthest reaches of the visible universe. The origin of cosmic rays

6. Credit: JAXA/ Takaaki Tanaka/HESS 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 Supernova RXJ1713.7-3946 [Suzaku X-ray observatory]

7. Production rate modulation Cosmic ray flux Terrestrial magnetic field Heliosphere magnetic field

8. Cosmogenic radionuclides

9. C element symbol 4+ ion ised charge state (Z - number of electrons) 12 atomic mass, A (6 protons + 6 neutrons in nucleus) 6 atomic number, Z (number of protons in nucleus) radionuclide nomenclature

10. How do we measure cosmo-isotopes? ►By Accelerator Mass Spectrometry or ‘AMS’. Example: ‘radiocarbon’ or 14 C: Stable carbon isotopes: 12 C (98.90%) and 13 C (1.10%). Only 7.5kg of cosmogenic 14 C produced globally in the entire atmosphere per year: in equilibrium. Natural abundance: 14 C/ 12 C ~ 1.2 × 10 -12 : one in a trillion! 14 C oxidised to 14 CO 2 : 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.

11. Radiocarbon dating black square is carbon, mostly 12 C (99%) and 13 C (1%). yellow dots are 14 C atoms, initially 10 4 atoms. 14 C 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 14 C atoms remain. Modern natural carbon contains ~ 50 million per mg. credit: M. Blaauw 2007, chrono.qub.ac.uk/blaauw

12. The technique of accelerator mass spectrometry

13. ANSTO’s STAR accelerator: 2MV

14. Accelerator Mass Spectrometry at ANTARES Australian National Tandem for Applied RESearch. 10MV

19. advantages of tandem AMS over mass spectrometry: negative ions: elimination of 14 N isobar charge exchange: destruction of 12 CH 2 & 13 CH in terminal ionisation detector: E,M,Z  atom counting features: ultra-small samples ~ 0.1 mg rapid measurement ~ 20 min sensitivity: 1 in 10 15 accuracy ~ 0.5%, background ~ 50 ka

21. 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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23. Law Dome

24. W20k

25. 97/98 Law Dome firn air sampling

26. Law Dome DSS0506 thermal drilling

32. Gaseous components of the atmosphere.

33. Global warming in the anthropocene From ~1700 AD to 2005 AD, CO 2 has risen 36% from 280 ppm to 379 ppm, CH 4 has risen 153% from 700 ppb to 1,774 [IPCC4]

34. [assuming 300 ppm CO 2, 2 ppm CH 4 and 50 ppb CO and 100 mL of air per kg ice] quantity of air & ice needed for 14 C AMS

35. helping to determine the anthropogenic & natural sources of the important greenhouse gas - methane

36. A new highly interactive exhibition exploring the complex world of nuclear science, medicine and nuclear power. On display in the Museum’s 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.