Cosmic Rays – A Thin Hard Rain from Space Roger Moses

Cosmic Rays –

A Thin Hard Rain from Space

Roger Moses

Cosmic Rays –


“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”

Cosmic Rays –


“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

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

Victor Hess

August 7, 1912, Austria

2½ hr flight to 16,000ft

3 gold-leaf electroscopes

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.)

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

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)

Can use the ionisation to

detect tracks in a variety

of detector systems

Photographic plate

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


Discovery of -meson (pion)

and its decay to a muon Bristol 1947


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

3.108Br = E/Z

3.108Br = E/Z r = E/3.108BZ

Z = +1, B = 2.4 tesla

E = 63 MeV = 6.3.107eV r = 0.0875 m

E = 23 MeV = 2.9.107eV r = 0.040 m

All highly relativistic, v/c = 1, = (1 - 2)-1/2

E = m0c2

Positron, electron m0 = 0.512 MeV

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.

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.

Charged particles (leave tracks of ionisation) of very high energy, moving close to speed of light c.



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

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/cm2s-1

87% Protons ( H nuclei )

12% Alpha particles ( He nuclei )

1% The Rest



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 106 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.



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 106 times those in low orbits.



Trapped Radiation


3.108Br = E/Z r = E/3.108 BZ

Z = +1, B = 10-4 tesla

E = 10 MeV = 107eV r = 333 m

Electrons and protons are trapped on the magnetic field lines of the Earth



Trapped Radiation


Electrons and protons are trapped on the magnetic field lines of the Earth

They leak into the atmosphere at high geomagnetic latitudes

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

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/cm2s-1

87% Protons ( H nuclei )

12% Alpha particles ( He nuclei )

1% The Rest

Galactic Cosmic radiation - Energetic particles incident on the top of the atmosphere at a rate of ~ 1 particle/cm2s-1

Composition

87% Protons

12% Alpha particles

1% The Rest

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!


Energy Spectrum


Energy Spectrum

For proton with 1020 ev

= 1011

Cf protons in

Large Hadron Collider

= 7.103

LHC

LHC

Galactic Cosmic radiation

For proton with 1020 ev

= 1011

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!



Thin - rare cf. photons

Hard – 1020 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?

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 1.83.10-5 Wm-2

Cf Sunlight 1.38.103 Wm-2

Cosmic rays don’t keep us warm!

Energy density = power/particle speed

= 6.1.10-14 Jm-2

= 3.81.105 eVm-3

Energy density = power/particle speed

= 6.1.10-14 Jm-2

= 3.81.105 eVm-3

But we are not in a typical place

In a typical place, well away from any star, the cosmic ray energy density doesn’t change, but starlight goes down by the

inverse Ɋ law, to 1.8.103 eVm-3, much less than CR

We can do the same sums for other components of the energy present

Energy densities in Interstellar Space

Cosmic Rays 3.8.105 eVm-3

Sunlight 1.8.103 eVm-3

Starlight = Sunlight x 100 1.8.105 eVm-3

Thermal Energy of Gas 1.3.105 eVm-3

Magnetic Field 2.5.106 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!

We can see cosmic ray type phenomena a long way away

Messier M1 Quasar 3C273

Crab Nebula Supernova Remnant


Messier M1 Crab 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


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

How do the very highest energy cosmic ray particles get their energy?

We don’t 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.


87% Protons

12% Alpha particles

1% The Rest

Surprisingly, the experiments we worked on looking at “the rest” 25-40 years ago are as good as it gets.It is instructive to ask why.

Can use the ionisation to

detect tracks in a variety

of detector systems

Photographic plate

Partial stack of photographic emulsion/dielectric detector

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

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


Ariel 6 1979


Ariel 6 1979


Ariel 6


Ariel 6

ApJ 1987


HEAO-C 1979

USA

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

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

Nothing much!

Nothing much!

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

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

Paul Mantsch Auger Project Manger

Building the Pierre Auger Observatory

The Design

The Observatory Plan

Surface Array 1600 detector stations 1.5 km spacing 3000 km2

Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per

enclosure 24 Telescopes total

The Surface Array Detector Station

Communications antenna

Electronics enclosure

3 – nine inchphotomultipliertubes

Solar panels

Plastic tank with 12 tons of water

Battery box

GPS antenna

The Fluorescence Detector

11 square meter segmented mirror

Aperture stop and optical filter

440 pixel camera

Deploying the First Surface Detectors

Official First Fluorescence Event

23 May 2001

First Surface Detector 4 – fold event – 12 August

2001

Example Hybrid Event

Θ~ 30º, ~ 8 EeV

A Tri-ocular Event!~20EeV

At the very highest energies, particle trajectories are distorted less and less by magnetic fields

3.108Br = E/Z, r = E/3.108BZ

Z = +1, B = 10-10 tesla probable galactic field

E = 1020eV r = 3.33.1021 m

This is now comparable to the distances separating galaxies 1 Mpc = 3.086.1022 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

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


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety


Mass extinctions


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.


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety




Radiation’s 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.


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety




The Earth’s 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.


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety


Carbon dating

Carbon dating

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 14C/12C isotope ratio enables us to estimate the age of biologically derived carbon compounds at the moment of death, in both organisms and artefacts.

Carbon datingCalibration by growth rings in ancient bristlecone pines indicate the method is generally accurate, but leads to a gradually increasing underestimate; about 6-700 yrs in 6000 years. This probably means that the CR intensity has increased over that period of time.


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety


Global Warming

Global Warming

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

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.

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.


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety


Astronaut safety

Astronaut safety

Astronaut safetyBiological Effects of Radiation - sparse and controversial data for humans, especially at low dose levels. 400 REM, delivered over a short time 50% fatalities in 30d

Gross failure of physiological systems 100 REM Can lead to sickness, falling blood cell count,

internal bleeding, susceptibility to infection, sometimes death

<50 REM No immediate effects Delayed effects - for several 100 REM over a period.Cancer, Cataract, SterilityReduction in life span (~ 2 days/REM ) Genetic effects - difficult to quantify, but 30-80 REM doubles the spontaneous mutation rate in cell culture.

Astronaut safetySPACE 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

Galactic Cosmic Ray

10~20 mrad/day No practical shielding

~3 300 mrem 16 rem Whole body

150 rad/flare Skin dose

(10 kgm-2) ave Whole body/3

Radiation Belts

5 rad/traverse ~1 10 rem 10 rem Whole body

I Week 1 Year

Remarks

Solar Flare ~1 20-300 rem 300 rem

RADIATION COMPONENT

DOSE RATE & SHIELDING

QUALITY FACTOR (QF)

INTEGRATED DOSE EQUIVALENT


Mass extinctions



Carbon dating

Global Warming

Astronaut safety

Aviation safety


Aviation safety

Aviation safety

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

Aviation safety

Protection of air crew from cosmic radiation: Guidance material

(Version 3.1 - May 2003)

1. Introduction

1.1 The Council of the European Union adopted Directive 96/29 Euratom[1] (the Directive) on 13 May 1996. 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 2000.

1.2 The Air Navigation Order (ANO) has been amended

What are Cosmic Rays? 8/10

Where do they come from? 5/10

How do they get their energy? 4/10

More work needed!

Thank you for your attention

Documents

Cosmic Rays – A Thin Hard Rain from Space Roger Moses