An Introduction to Cosmic Rays, Relativity, and MARIACHI

M. Marx

November 16, 2006

Radioactivity

• Radiactive material is classified according to its activity – the number of decays per second Ndecays = Npresent x x time interval

is the “lifetime” of the material

t1/2 or “half-life” = ln 2 = 0.6931471806

• Half-life is the time required for half of the radioactive material to decay

• We have identified particles and isotopes with half-lives ranging from

10-23 seconds (time it takes light to cross a nucleus)109 years (comparable to age of universe)

Puzzles

• Puzzle 1– There are lots of short lived radioactive isotopes that

can be found naturally on the surface of the earth– Deep underground (i.e. in mines) one only finds

isotopes whose half lives are comparable to the age of the Earth (109 years)

Where does the short lived stuff come from? Continuously replenished by radiation from

Outer Space!!

Puzzles

• Puzzle 2– Early researchers on radioactivity had great

difficulty in shielding their equipment from ubiquitous radiation

Where does it come from?

Outer Space!!

Discovery of cosmic radiationVictor Hess in 1914

• Electroscopes always discharge

• Radiation increases with altitude (balloon!)

– Varies with location and direction – Earth’s magnetic field!

– Led to discoveries of new particles

• Positron, muon, pion, strange particles….

– Good example of relativity in action!

Special Relativity (1905)

• Einstein’s postulates– Nothing can move faster than light in vacuum– Speed of light looks the same to all

independent of observer velocity

Special Relativity Consequences• Consequences:

– Moving objects look shorter L = Lo (1-v2/c2)1/2

– Moving clocks appear to run slower to = t (1-v2/c2)1/2

– Moving objects get more massive mo = m (1-v2/c2)1/2

• Mass and energy are interchangeable

E = mc2 = m0c2/ (1-v2/c2)1/2

• Velocity of light ( “c” )– 186,000 miles per second– 3 x 108 meters per second

• Effects of relativity are not noticeable in daily life

Consequences

v v/c (1-v2/c2)1/2 1/(1-v2/c2)1/2

28,000km/h 3 x 10-5 1 1 (Shuttle in orbit)

0.1 .99 1.0050.25 .96 1.03.99 .14 7.07.9999 .014 70.7

A particle traveling at 99% of speed of light has 7 times more mass, is 1/7 of its length, and lives 7 times as long!

Why Study Cosmic Rays?

• Cosmic rays are a tool to study phenomena at the extreme ends of sizes– Very small ==> fundamental particles (building blocks

of all matter)– Very large ==> window on energetic processes in the

universe (supernovae, black holes, colliding galaxies, and the unknown!)

• Early discoveries of fundamental particles before the era of accelerators (atom-smashers)

• Studies of ultra-high energy particles beyond the reach of man-made accelerators

Why Study Cosmic Rays?

• Cosmic rays are the prime source of natural background radiation– Short lifetime isotopes continuously replenished

• Cosmic radiation increases with altitude – the atmosphere shields us from most of it– Radiation dose doubles every 5000ft!– Deep rocks contain only long-lived isotopes

• Cosmic ray interactions with DNA of living cells may be prime (continuing) agent in evolution

Fundamental Particles- The Elements

The periodicity strongly suggests an underlying structure, i.e. allare composed of common building blocks

Now we know that these blocks are proton, neutron, and electron

Fundamental Particles – The Atom

All atoms are composed of nuclei surrounded by a cloud of electrons

The nuclei are composedof protons and neutrons

We know now that the protons and neutrons arethemselves composedof quarks and gluons

Fundamental Particles

Generation 1

Generation 2

Generation 3

ALL ordinary matter is composed solely of first generation particles – atoms have nuclei composed of protons (uud) and neutrons (udd) surrounded by clouds of electrons to make the atom electrically neutral.Second and third generation particles can be produced if there is sufficient energy available in a collision ( E = mc2), but all these particles decay eventually

into lower generations.

Introduction to Cosmic Rays

• What are cosmic rays?– Nuclei with composition similar to the solar system +

gammas, neutrinos – Interaction and decay products reach the ground– Rates at ground level are 1 per second per cm2

– Huge range of energies Mev – EeV ====>– Different energies come from various sources

• Low energies from sun (10 => 100 MeV typical)• Galactic sources – supernovae • Highest energies ( above 10 EeV) are a mystery

Cosmic Ray Energy Spectrum

Units

1 electron-Volt = 1 eVEnergy gain of a charged Particle ( q = 1e) accelerated thru 1V

2 – 4 eV visible light

Kev Xrays

Mev Binding of nucleons Mass electron * c2 = ½ MeV

GeV Mass*c2 of nucleons

EeV – (1018 eV) pitched baseball

GeV =====> EeV

Sun

1 particle/km2/century Origin Unknown - A dozen seen!

Extra-galactic

Our Galaxy

Cosmic RaysPrimary Cosmic Ray – Nucleus ( H ….Fe) strikes Atmospheric Molecule

Secondary particles – nucleons (p,n), pions (+, -, 0), Kaons……

Secondaries interact with atmospheric molecules

Charged pions decay

Neutral pions decay

Low energy muons decay

e

Gamma rays initiateElectromagnetic showers

e+e-

Shower debris reaches Earth – , e+,e- - very low energy fragments of

original showerhttp://www.auger.org/observatory/image_gallery_index.html

Cosmic Rays and Special Relativity• The primary cosmic ray collides with a molecule in the

atmosphere transferring much of its energy into a shower of secondary particles

• Lifetime of charged pions is ~ 10-8 sec and they all decay before reaching Earth (

• Lifetime of muons is ~ 10-6 sec• At close to speed of light would expect decays e S = vt = 3 x 108 m/s x 2.2 x 10-6 s = 660m• But most muons reach Earth (10km!!) because their clocks are

slowed by relativity! • From the muon’s perspective they see the distance to Earth shrunk

to < 660m they could move by their own clocks!

• Einstein was amazed by this practical proof of his theory

Shower Animations –1 Tev Proton Initiated Shower

Detection of Radiation/Particles• We have many ways at our disposal to detect the

passage of ionized (i.e. charged) particles – the particles themselves are not visible

• Uncharged particles can only be detected indirectly, either by their decay into charged particles, or by their interactions which produce charged particles.

• Charged particles disrupt the clouds of electrons surrounding the atoms in their path, exciting the electrons to higher energy states, or by knocking out an electron and ionizing the atom.

• The paths are marked by these disturbed electrons which can be collected and measured by several means.

Simplest Radiation DetectorX-rays are neutral and not detectable – however, theyknock out charged electronsionizing atoms in the film, creatinggrains that become visible oncedeveloped. The picture shows the intensity of X-raysreaching the film (negative!)

Film was the medium for Roentgen’s discovery of X-raysand radiation.

Film was originally and still is used for studies of cosmic rays throughstacks of emulsions. Many of the early discoveries were made with it

Nuclear Emulsions (Film)

Provides a Complete pictureOf an “event”

Excellent spatialresolution

Excellent energydensity givesidentification anddirections, speed

Provides no timeinformation

pion

muone - electronThis bubble

chamber pictureshows the decaychain

e +

This decay chain is very common in thedebris of a cosmic ray shower

From inspection of this picture one cantell the direction of the particles by theirionization (and the magnetic field confirms this!)

Measuring the curvaturedetermines the sign andmomentum of theparticles. There is notime information.

Bubble Chamber

1. Why are the neutrinos invisible?2. Why is the muon track so short?

Pierre Auger Observatory – Argentina

Surface Array 1600 detector

stations 1.5 km spacing 3000 km2

Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per

enclosure 24 Telescopes total

http://www.auger.org/observatory/animation.html

Cosmic ray

Distant TV station

TV signals

TV signal reflected by the cosmic rayInduced shower

TV antennas(radar)

Data acquisition system andcyberinfrastructure

GRID

datadata

Ground detectors(scintillators)

Three Key Pieces of

Radar detectors to find reflected TV signals from cosmic rays, meteors, & lightning

Scintillator detectors to confirm cosmic ray signals (and do correlations)

The “grid” – for data acquisition and analysis

Radar (EM wave) Reflections from an Ionized Plasma

• Radio (electromagnetic waves) are routinely reflected by metallic objects – “radar”

• They can also be reflected from areas where the ionization densities are high enough – exceeding the “plasma frequency” given by:

f (Hz) nee

2

me

ne = 8.98 (Hz)

ne is the ionization density

me is the electron mass

e is the electron charge

e

ep m

enf

2

Cosmic Ray Coverage

http://www-mariachi.physics.sunysb.edu/wiki/index.php/Ground_Array

The primitive Mariachi array we areimplementing now on Long Island covers an area of about

6000 km2

or twice the area of Auger!

Radar Echo Signals

Radar Echoes from Meteors

Typical echo from a meteor trail, with a weak echo from a second TV station.

Meteor data acquired from April 16th to April 26th showing the Lyrids meteor shower that peaked on April 22nd and a secondary minor shower that peaked on April 25th. The diurnal variation is due to the Earth's rotation.

Why Ground Arrays

• Mariachi hopes to exploit the new technique of Radio Cosmic Ray Scatter to detect and then study UHECR (and neutrinos!)

• We hope to identify a class of short duration radio echoes that are UHECR candidates

• To confirm their identity we need simultaneous detection by proven techniques – we use scintillator ground arrays for their simplicity and reliability.

• This also provides the opportunity to include in Mariachi the community of high school teachers and students, to learn about science and cyberinfrastucture, while contributing to the scientific goals of the project.

Charged particleVelocity ~ cTime D/c, 1ns/ft

Scintillation Counter•Doped plastic emits light• Light travels to ends by total internal reflection•Transit time ~ 2.5ns/ft

Photomultiplier Tube•Photon ejects electron by photo-electric effect•Electron guided to dynode ejectingseveral electrons•Process repeated many times•Electron cloud arrives at anode – negative pulse•Transit time ~ 100ns

Raw pulse fromPMT

DiscriminatorProvidesstandard height and width pulsewhenever inputpulse is over presetthreshold

Logic pulse

Scintillation Counters and Phototubes

D

31The final design

Scintillator

Light-tightstudent prooflockable case

See-throughPMT assembly

The MARIACHI Grid• The dream:

A transparent global network of computing resources available to all users uniformly. Like the World Wide Web via the Internet.

• User defines a “job”– An input file.– A program to run (installed or

provided).– A place to put the output file.– A set of constraints (CPU

speed, memory,etc.).• Users submit job.

– ...to chosen Grid sites (OSG) or the entire Grid (LCG) and await results.

Mariachi Wiki

• See our wiki based web site athttp://www-mariachi.physics.sunysb.edu/

• Opportunities to participate in this educational research for teachers and students at all levels!

High Energy Protons see High Energy Protons see Cosmic Microwave Background Cosmic Microwave Background as High Energy Gamma Rays!as High Energy Gamma Rays!

GZK CutoffGZK Cutoff-resonance

multi-pions

WMAP

p+cmb + p + 0

n + +

UHECR are too energetic to originate from known sources in our galaxy or nearby galaxies.

UHECR are too energetic to propagate through the microwave background from distant sources

Milky WayNeighboring Galaxies Galaxy

Clusters