Erwin O. Flückiger Physikalisches Institut University of Bern erwin.flueckiger@space.unibe.ch

1. Cosmic Rays and Neutron Monitors -A training course in science and applicationsSeptember 14-19, 2009Athens, Greece Cosmic Ray Interaction with the Earth‘s Atmosphere and Environment / Part I Erwin O. Flückiger Physikalisches Institut University of Bern erwin.flueckiger@space.unibe.ch

2. Ionisation * Ionisation Rate * Ion Concentration * Global Electric Circuit - Commmunication - E-Fields, Lightnings, Thunderclouds - Air Conductivity - Hurricanes * Catalytic Reactions - Ozone - Nitrates * Weather and Climate - Mesosphere – lower Thermosphere Dynamics - Temperature - Rain - Lightning - CR and Clouds Nuclear Interactions * Particle Fluxes, Spectra * Cosmogenic Isotopes Radiation Effects Epidemic Flu Genetic Mutations CR as Diagnostic Tool

3. Cosmic Rays in the Earth‘s Atmosphere

4. Cosmic Ray Cascade in the Earth‘s Atmosphere The „standard picture“

5. Cosmic Ray Cascade in the Earth‘s Atmosphere An alternative representation…

6. The Earth‘s Atmosphere I

7. h Hg The Earth‘s Atmosphere II Atmospheric Thickness / Atmospheric Depth Top of atmosphere 0 g·cm-2 Sea level ~1033 g·cm-2 Sea level Atmospheric pressure in units of mm Mercury (Hg)= heigth of mercury column in barometer: h = 760 mm = 76 cm Density of Mercury (Hg): ρ = 13.534 g·cm−3 Atmospheric thickness / depth:ρ x h=13.534 g·cm−3 x 76 cm ≈ 1030 g·cm-2

8. The Earth‘s Atmosphere III Chemical Composition Nitrogen ~ 78 % (by Volume) Oxygen ~ 21 % Argon ~ 1 % …..

9. Cosmic Ray Cascade in the Earth‘s Atmosphere What most people are interested in: • Flux • Omnidirectional or Integrated Intensity • Differential Energy Spectrum • Integral Energy Spectrum • for all species of secondaries, and • as a function of • atmospheric depth • zenith angle (where appropriate) • cutoff rigidity • solar activity • - ….

10. Cosmic Ray Cascade in the Earth‘s Atmosphere Present solution to the problem: cascade programs e.g. PLANETOCOSMICS (GEANT4 application) http://cosray.unibe.ch/~laurent/planetocosmics/ Technique: 1) calculate i.e. the number of secondaries of type k, in energy interval Ei + ΔEi , in zenith angle interval θj+ Δ θj , produced on average at atmospheric depth h by a primary particle of type k0 , penetrating the Earth‘s atmosphere with rigidity R0 under a zenith angle θ0 2) take into account cutoff information 3) integrate over respective primary particle spectrum (solar activity)

11. Simulation of the Cascades in the Atmoshere PLANETOCOSMICS GEANT4 Application Interaction of cosmic rays with Planet Atmospheres and Soils http://cosray.unibe.ch/~laurent/planetocosmicshttp://cosray.unibe.ch/~laurent/magnetocosmics Atmospheric cascade initiated by a 1 GeV proton Laurent Desorgher

12. Cosmic Ray Cascade in the Earth‘s Atmosphere Here: basic physics background „interaction of particles and radiation with matter“

13. Nuclear Interactions I

14. Nuclear Interactions II

15. protons & neutrons i Nuclear Interactions III The hadronic interaction mean free path λi (g cm-2)

16. target Nuclear Interactions IV The hadronic interaction mean free path λi (g cm-2) Fragmentation of heavy primaries in first nuclear interaction

17. Nuclear Interactions V Energy Transport A hadron having an initial energy E0, undergoing n interactions with a mean inelasticity, <k>, will retain on average an energy, E, of E = E0 (1 - <k>)n typically <k> ≈ 0.5 „leading particle effect“

18. Of all the secondaries, pions (π+, π-, π0) are the most abundant Mass π0: 134.97 MeV/c2 π±: 139.57 MeV/c2 Very short mean life times:π0: τ ≈ 10-16 s π0⇒ γ+γ π± : τ ≈ 2.6 x 10-8 s π+ ⇒ μ+ + νμ π- ⇒ μ- + νμ Decay within meters! Interaction mean free path in air: ~ 120 g cm-2 Production of Pions & Muons I

19. Mass: mμ = 105.658 MeV/c2 Mean lifetime: τ ≈ 2.197 x 10−6 s Although their lifetime without relativistic effects would allow a half-survival distance of only about 0.66 km at most, the time dilation effect of special relativity allows cosmic ray secondary muons to survive the flight to the earth's surface. Production of Pions & Muons II

20. Muons

21. The Differential Proton Spectra I

22. The Differential Proton Spectra II Examples of the differential vertical proton spectra for mean solar activity

23. The Neutron Spectra(still considerable uncertainties!) Hagmann et al., 2007

24. The Vertical Development IPfotzer Maximum

25. The Vertical Development IIDifferent Species

26. The Attenuation of Protons in the Atmosphere Attenuation length for GCR-induced secondary protons (and neutrons): ~ 127 g cm-2 Attenuation length for SCR-induced secondary protons (and neutrons): ~ 145 g cm-2 ⇒ attenuation length defines barometric coefficient of NMs! Attenuation of vertical proton intensity > 1GeV

27. The Baromteric Coefficientfor Neutron Monitors Neutron Monitor counting rate: N(t, p0) = N(t, p) x exp {α·(p(t) – p0)} where t: time p: atmospheric pressure at time t p0: reference pressure Barometric coefficient α≈ - 0.96 % / (mm Hg)

28. Zenith Angle Dependence Zenith angle dependence of proton radiation at sea level

29. This explains why we can use „vertical cutoff rigidities“ in many applications! Debrunner & Flückiger, 1972 Dependence on Primary Zenith Angle Dependence of the total neutron monitor count rate on the zenith angle of the primary cosmic radiation at the top of the atmosphere

30. GCR SCR Magnetospheric Particles Geomagnetic Storms Electromagnetic Radiation Radioactive Constituents Lightnings Ion Production in the Earth‘s Atmosphere The energy flux of Galactic Cosmic Rays (GCR) falling on the Earth‘s atmosphere is about 108 times smaller in comparison with solar electromagnetic irradiation But: at altitudes h ~3 to 35 km in the atmosphere, Cosmic Rays are the main ionizing agent

31. Ion Production and Ion Concentration in the Earth‘sAtmosphere Ion production rate q q = I ρσ / M where I = I (h, Rc, Φ) cosmic ray flux ρ air density σ effective ionisation cross section  2 x 10-18 cm2 at h ≤ 20 km M average mass of air atom Ion concentration n q = α n2α 3D recombination coefficient Stozhkov, 2003 q(h) = β(h) n(h) β(h) linear recombination coefficient

32. Rule of thumb: 2 MeV / g cm-2 Ionization

33. Cosmic Ray induced Ionization

34. Europe - COST Action 724: “Developing the scientific basis for monitoring, modeling and predicting Space Weather” (COST = European Cooperation in the field of Scientific and Technical Research) Oulu Model Sofia Model Bern Model Paper 916, Velinov & Mishev Paper 433, Usoskin & Kovaltsov

35. Ionization by GCR Monthly averaged fluxes of ionizing particles in the atmosphere over Murmansk region as measured by an omnidirectional Geiger counter Bazilevskaya et al., 2007

36. Ionization by SCR Bern Model: http://cosray.unibe.ch/~laurent/planetocosmics Desorgher et al., AOGS 2004

37. Cerenkov Radiation I slow electron fast electron in dielectric medium

38. Cerenkov Radiation II The geometry of the Cerenkov radiation (shown for the ideal case of no dispersion)

39. Cerenkov Radiation III

40. Air Showers Cosmic ray air shower created by a 1TeV proton hitting the atmosphere 20 km above the Earth. The shower was simulated using the AIRES package.

41. Cosmic Rays and Neutron Monitors -A training course in science and applicationsSeptember 14-19, 2009Athens, Greece Cosmic Ray Interaction with the Earth‘s Atmosphere and Environment End of Part I

43. Test Questions 1) What is the minimum energy required for a proton to produce an effect at flight altitude? (assumption: mimimum ionizing particle, no nuclear interactions) 2) Energetic primary protons undergo on average how many nuclear inter-actions along a vertical trajectory through the atmosphere down to sea level? 3) What is the most abundant species of secondary CR at sea level? 4) How many muons hit your body approximately per second? 5) What is the relation between the barometric coefficient of a NM and the attenuation length of nucleons in the atmosphere? 6) What is the Pfotzer maximum? 7) Why do muons survive to sea level (and underground)? 8) Why is it justified in many NM applications to use the „vertical cutoff rigidity“?