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Cosmic Rays – A Thin Hard Rain from Space Roger Moses.

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Presentation on theme: "Cosmic Rays – A Thin Hard Rain from Space Roger Moses."— Presentation transcript:

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2 Cosmic Rays – A Thin Hard Rain from Space Roger Moses

3 Cosmic Rays – A Thin Hard Rain from Space Coming out of space and incident on the high atmosphere, there is a thin rain of high energy particles known as the primary cosmic radiation

4 Cosmic Rays – A Thin Hard Rain from Space Coming out of space and incident on the high atmosphere, there is a thin rain of high energy particles known as the primary cosmic radiation Nobel Physics Prize Lecture 1950 Cecil Powell, University of Bristol

5 What are Cosmic Rays? Natural Ionising Radiation Background Radioactive decay - discovered in 1896 by Becquerel Natural ionising radiation similar to recently discovered X- rays Alpha Emission of He nucleus Beta Emission of high energy electron Gamma Emission of high energy photon Spontaneous fission Split into two parts

6 Victor Hess August 7, 1912, Austria 2½ hr flight to 16,000ft 3 gold-leaf electroscopes

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10 Cloud chamber track of the positron, discovered by Carl Anderson. Use of a strong magnetic field caused charged particles to follow curved paths. The positron entered the chamber at the lower left and travelled up, through the lead plate across the middle of the chamber. The positive charge is inferred from the direction of curvature. This discovery of the first anti-particle, predicted by Paul Dirac, was the beginning of particle physics. (From Phys.Rev 43 [1933]: 491; courtesy of the Archives, California Institute of Technology.)

11 Cosmic Ray Summary 1935 Charged particles (leave tracks of ionisation) of very high energy, moving close to speed of light c. Used as tool to do high energy particle physics Deflected by magnetic fields Produce showers of secondaries in atmosphere, which reach the ground The next 30 years fill out this picture

12 Charged particles (leave tracks of ionisation) of very high energy Can use the ionisation to detect tracks in a variety of detector systems Luminescent screen (scintillator) Cloud chamber Photographic plate Electronic detector (ionisation chamber, spark gap)

13 Can use the ionisation to detect tracks in a variety of detector systems Photographic plate

14 Charged particles (leave tracks of ionisation) of very high energy Can measure the energy by measuring energy lost in ionisation until it stops, or interpose matter e.g. lead, or by curvature in magnetic field

15 Used as tool to do high energy particle physics Discovery of -meson (pion) and its decay to a muonBristol 1947

16 Deflected by magnetic fields Magnetic Rigidity - For a particle with electric charge Z, energy E eV (electron volts) in a magnetic field strength B tesla, the radius of its circular track will be r metres Br = E/Z

17 Br = E/Z r = E/ BZ Z = +1, B = 2.4 tesla E = 63 MeV = eV r = m E = 23 MeV = eV r = m All highly relativistic, v/c = 1, = (1 - 2 ) -1/2 E = m 0 c 2 Positron, electron m 0 = MeV

18 Produce showers of secondaries in atmosphere, which reach the ground. The peak ionisation is reached a height between the original collision of the primary with a nucleus in the atmosphere, and the ground. This generates the Pfotzer maximum at 18km.

19 Produce showers of secondaries in atmosphere, which reach the ground. The peak ionisation is reached a height between the original collision of the primary with a nucleus in the atmosphere, and the ground. This generates the Pfotzer maximum at 18km.

20 Charged particles (leave tracks of ionisation) of very high energy, moving close to speed of light c. Used as tool to do high energy particle physics Deflected by magnetic fields Produce showers of secondaries in atmosphere, which reach the ground The next 30 years fill out this picture The basic knowledge and tools outlined above has enabled us to investigate the cosmic radiation in great depth

21 Galactic Cosmic Radiation Solar Flare Particles Trapped Radiation Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 87%Protons ( H nuclei ) 12%Alpha particles ( He nuclei ) 1%The Rest

22 Galactic Cosmic Radiation Solar Flare Particles Trapped Radiation Solar particles (largely protons) with energies > 100 MeV are produced by solar flares in periods of solar activity. They can exceed G.C.R. by 10 6 for a short time. Advance warning of solar flare particles is provided by prompt electromagnetic radiation (visible, U.V., X-ray). The X-ray and hard U.V. photons have ionising properties and are themselves a hazard, although easy to shield against.

23 Galactic Cosmic Radiation Solar Flare Particles Trapped Radiation The Earth's magnetic field - Acts as a partial barrier to high energy charged particles from outside, Stores solar particle radiation for long periods (years) in the VAN ALLEN trapped radiation belts, which provide a major radiation hazard to both manned and unmanned space vehicles, since the trapped charged particles, both electrons and protons may attain space densities in excess of 10 6 times those in low orbits.

24 Galactic Cosmic Radiation Solar Flare Particles Trapped Radiation The Earth's magnetic field Br = E/Z r = E/ BZ Z = +1, B = tesla E = 10 MeV = 10 7 eV r = 333 m Electrons and protons are trapped on the magnetic field lines of the Earth

25 Galactic Cosmic Radiation Solar Flare Particles Trapped Radiation The Earth's magnetic field - Electrons and protons are trapped on the magnetic field lines of the Earth They leak into the atmosphere at high geomagnetic latitudes

26 Electrons and protons are trapped on the magnetic field lines of the Earth, and leak into the atmosphere at high geomagnetic latitudes

27 I will concentrate on the Galactic Cosmic Radiation – Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 87%Protons ( H nuclei ) 12%Alpha particles ( He nuclei ) 1%The Rest

28 Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 Composition 87%Protons 12%Alpha particles 1%The Rest

29 Galactic Cosmic radiation Composition 87%Protons 12%Alpha particles 1%The Rest ALL the lithium, beryllium and boron on earth was produced in collisions between cosmic ray primaries moving at the speed of light and nuclei in the interstellar medium!

30 Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 Energy Spectrum

31 Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 Energy Spectrum For proton with ev = Cf protons in Large Hadron Collider = LHC

32 Galactic Cosmic radiation For proton with ev = Protons with these energies experience the passage of time slower by the above factor; they cross the visible universe in about a month! They have sufficient energy to boil a small cup of water!

33 Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 A Thin Hard Rain from Space Thin - rare cf. photons Hard – ev is enough energy in one particle to boil a cup of water Rain – Random, sounds like rain, magnetic fields have completely scrambled directional information and age We have established what Cosmic Rays are, so Where do they come from?, and How do they get their energy?

34 Where do they come from?, and How do they get their energy? Firstly, do they matter, are they an important bit of astrophysics, or just an interesting minor topic? The power input from CR is Wm -2 Cf Sunlight Wm -2 Cosmic rays dont keep us warm! Energy density = power/particle speed = Jm -2 = eVm -3

35 Energy density = power/particle speed = Jm -2 = eVm -3 But we are not in a typical place In a typical place, well away from any star, the cosmic ray energy density doesnt change, but starlight goes down by the inverse law, to eVm -3, much less than CR We can do the same sums for other components of the energy present

36 Energy densities in Interstellar Space Cosmic Rays eVm -3 Sunlight eVm -3 Starlight = Sunlight x eVm -3 Thermal Energy of Gas eVm -3 Magnetic Field eVm -3 All these are broadly comparable, is there some principle of equipartition at work. The main problem of the Cosmic Rays is sheer Energy Supply!

37 We can see cosmic ray type phenomena a long way away Messier M1 Quasar 3C273 Crab Nebula Supernova Remnant

38 We can see cosmic ray type phenomena a long way away Messier M1Crab Nebula Supernova Remnant The galactic supernovae can supply the heavy element enriched material we see, and accelerate it in the magnetospheres of the central pulsars, rotating neutron stars, to cosmic ray energies (but not the highest). There is still no direct link between this likely source and what we observe at Earth

39 We can see cosmic ray type phenomena a long way away Quasar 3C273 Energetic galactic nuclei are supplying relativistic electrons with cosmic ray energies (but again not the highest detected) in these jets. We see them by the synchrotron radiation they produce in the galactic magnetic fields Again there is still no direct link between this likely source and what we observe at Earth

40 How do the very highest energy cosmic ray particles get their energy? We dont know in detail, but an old idea of Enrico Fermi gives us a conceptual route to a solution, but the detailed mechanisms are not clear Individual particles collide with the magnetic fields of interstellar gas clouds, and eventually will attain the KE of an average gas cloud by equipartition. This is sufficient to explain the very highest energies, though there are competing loss processes.

41 Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm 2 s -1 87%Protons 12%Alpha particles 1%The Rest Surprisingly, the experiments we worked on looking at the rest years ago are as good as it gets. It is instructive to ask why.

42 Can use the ionisation to detect tracks in a variety of detector systems Photographic plate

43 Partial stack of photographic emulsion/dielectric detector

44 Stack of photographic emulsion/dielectric detector on its way to 140,000ft. Cost approx. £100,000 (1970) It is as easy to count atomies as resolve the propositions of a lover Celia, As You Like It

45 The only way to improve on this is to put experiments on satellites

46 Ariel

47 The only way to improve on this is to put experiments on satellites Ariel

48 The only way to improve on this is to put experiments on satellites Ariel 6

49 The only way to improve on this is to put experiments on satellites Ariel 6 ApJ 1987

50 The only way to improve on this is to put experiments on satellites HEAO-C 1979 USA

51 So what has been done in this field in the last 20 years?

52 Nothing much!

53 The problem is statistics To do an experiment 10x better than Ariel 6 or HEAO-C We would need 100x exposure in space i.e. 100x area, a detector 10x as big Still economically impossible, as are the other good things we could do along the same lines e.g. Chemical composition vs. energy Anti-matter nuclei

54 Nothing much! However the same constraints do not apply to ground based observatories, looking at air showers and the very high energy particles that generate them There is one exciting new development current, The Pierre Auger Observatory

55 Paul Mantsch Auger Project Manger Building the Pierre Auger Observatory

56 The Design

57 The Observatory Plan Surface Array 1600 detector stations 1.5 km spacing 3000 km 2 Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total

58 The Surface Array Detector Station Communications antenna Electronics enclosure 3 – nine inch photomultiplier tubes Solar panels Plastic tank with 12 tons of water Battery box GPS antenna

59 The Fluorescence Detector 11 square meter segmented mirror Aperture stop and optical filter 440 pixel camera

60 Deploying the First Surface Detectors

61 Official First Fluorescence Event 23 May 2001

62 First Surface Detector 4 – fold event – 12 August 2001

63 Example Hybrid Event Θ~ 30º, ~ 8 EeV

64 A Tri-ocular Event! ~20EeV

65 At the very highest energies, particle trajectories are distorted less and less by magnetic fields Br = E/Z, r = E/ BZ Z = +1, B = tesla probable galactic field E = eV r = m This is now comparable to the distances separating galaxies 1 Mpc = m The cosmic rays will come from a direction in the sky related to where the source actually is. Experiments like the Pierre Auger Observatory give us a chance of identifying high energy sources, and the physics going on in them producing and accelerating the particles

66 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Astronaut safety Aviation safety Global Warming

67 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

68 How do Cosmic Rays affect us? Mass extinctions

69 How do Cosmic Rays affect us? Mass extinctions If a supernova (SN) occurred sufficiently close to the solar system (nearer than about 10 parsecs), it could disrupt life on Earth. Two phenomena resulting from such a nearby SN would severely deplete the Earth's ozone layer allowing more harmful radiation to reach the Earth's surface. First, there would be an initial burst of gamma-rays from the SN (lasting about three months). Second, since cosmic rays are thought to be accelerated in the shock wave of a SN (the supernova remnant), there would be an increase in cosmic ray activity on Earth lasting from 1,000 to 10,000 years. Such an event, could explain a few of the mass extinctions which have occurred through Earth's history.

70 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

71 How do Cosmic Rays affect us? Source of random mutation for genetic diversity

72 Radiations effect on life is not always negative; for evolution to work, it is necessary to have a natural cause for genetic mutation. The cosmic rays are a major component of the background radiation, which is an important cause of mutation.

73 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

74 How do Cosmic Rays affect us? Magnetic field reversals

75 The Earths magnetic dipole switches polarity in an irregular fashion, every few hundred thousand years, as seen in the field reversals in the spreading mid-ocean ridges, as the cooling lava cools below its Curie temperature, and records the magnetic field polarity at that instant. As it goes through zero, life on Earth is exposed to the full radiation intensity of the cosmic rays.

76 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

77 How do Cosmic Rays affect us? Carbon dating

78 The Carbon 14 produced by CR irradiation of Nitrogen 14 has a half life of 5730 years. Its decay and the consequent change in the 14 C/ 12 C isotope ratio enables us to estimate the age of biologically derived carbon compounds at the moment of death, in both organisms and artefacts.

79 Carbon dating Calibration by growth rings in ancient bristlecone pines indicate the method is generally accurate, but leads to a gradually increasing underestimate; about yrs in 6000 years. This probably means that the CR intensity has increased over that period of time.

80 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

81 How do Cosmic Rays affect us? Global Warming

82 A recent hypothesis is that cosmic rays from the sun increase during periods of solar activity, as at present; the extra ionisation produced in the atmosphere increases nucleation centres for water condensation, and hence increases cloud cover, reflecting back the earths heat radiation, producing global warming

83 Global Warming Whether this happens, or if it produces the opposite effect, is not clear to me. Solar activity increases ionisation high in the atmosphere produced by lower energy solar cosmic rays, but decreases ionisation lower in the atmosphere produced by high energy galactic cosmic rays as these are deflected by increased solar magnetic field. The net effect on cloud cover is unclear, and increased cloud cover can lead to warming or cooling, dependent on where it is produced.

84 Global Warming It is certainly true that solar activity as manifested by sunspot number has clear climatic effects, but whether this is due to cosmic rays is dubious. Solar terrestrial phenomena are clearly potential climate modifiers, but mechanisms are poorly understood, and this idea seems to not be verifiable at the moment.

85 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

86 How do Cosmic Rays affect us? Astronaut safety

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88 Biological Effects of Radiation - sparse and controversial data for humans, especially at low dose levels. 400 REM, delivered over a short time50% fatalities in 30d Gross failure of physiological systems 100 REMCan lead to sickness, falling blood cell count, internal bleeding, susceptibility to infection, sometimes death <50 REMNo immediate effects Delayed effects - for several 100 REM over a period. Cancer, Cataract, Sterility Reduction in life span (~ 2 days/REM ) Genetic effects - difficult to quantify, but REM doubles the spontaneous mutation rate in cell culture.

89 Astronaut safety SPACE RADIATION EXPOSURE SUMMARY This makes a 2.5 year minimum mission to Mars look decidedly hazardous SPACE RADIATION EXPOSURE SUMMARY This makes a 2.5 year minimum mission to Mars look decidedly hazardous

90 How do Cosmic Rays affect us? Mass extinctions Source of random mutation for genetic diversity Magnetic field reversals Carbon dating Global Warming Astronaut safety Aviation safety

91 How do Cosmic Rays affect us? Aviation safety

92 Concorde was/is the only civil airliner with a cosmic-ray detector as standard fit – flies at the Pfotzer maximum

93 Aviation safety Protection of air crew from cosmic radiation: Guidance material (Version May 2003) 1. Introduction 1.1 The Council of the European Union adopted Directive 96/29 Euratom[1] (the Directive) on 13 May Article 42 of the Directive imposes requirements relating to the assessment and limitation of air crew members' exposure to cosmic radiation and the provision of information on the effect of cosmic radiation. Member States were required to implement the Directive by 13 May The Air Navigation Order (ANO) has been amended

94 What are Cosmic Rays?8/10 Where do they come from?5/10 How do they get their energy?4/10 More work needed!

95 Thank you for your attention

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