November 11, 1935 Explorer II, a 113,000 cubic foot helium balloon ascends to a record 22,066 m while collecting atmospheric and cosmic ray data.

May 11, 1950 A Naval Research Viking research rocket fired from the U.S.S. Norton Sound near Jarvis Island in the Pacific collects cosmic ray and pressure and temperature data.

1952-57 James A. Van Allen (The University of Iowa) reports the first high altitude survey of total

cosmic-ray intensity and latitude variation of heavy nuclei in primary cosmic

radiation, from his “Rockoon” (balloon-launched rocket).

July 31, 1961 NASA funds high-altitude balloon measurements of the proton and alpha-particle spectrum of primary cosmic radiation conducted by the University of Chicago above Uranium City, Saskatchewan, Canada.

July 1969 Apollo 11 astronauts trap cosmic ray particles on exposed aluminum foil, returned to earth for analysis of its elemental and isotopic composition. With no atmosphere or magnetic field of its own, the moon’s surface provides a constant bombardment of particles.

December 1972 Apollo 17’s lunar surface cosmic ray experiment measured the flux of low energy particles in space (foil detectors brought back to Earth for analysis..

October 26, 1973 IMP-8 launched. Continues today measuring cosmic rays, Earth’s magnetic field, and the near-Earth solar wind from a near-circular, 12-day orbit (half the distance to the moon).

October 1975 to the present GOES (Geostationary Orbiting Environmental Satellite) An early warning system which monitors the Sun's surface for flares.

1977 The Voyager 1 and 2 spacecraft are launched. Each will explore acceleration processes of charged particles to cosmic ray energies.

July 1992 SAMPEX (Solar Anomalous and Magnetospheric Particle Explorer) into polar orbit. By sampling interplanetary and magnetospheric particles, contributes to our understanding of nucleosynthesis and the acceleration of charged particles.

July 1992 IMAX (Isotope Matter-Antimatter eXperiment) balloon- borne superconducting magnetic spectrometer measured the galactic cosmic ray abundances of protons, anti-protons, hydrogen, and helium isotopes.

August 25, 1997 Advanced Composition Explorer (ACE) was launched!

Hydrogen (H) 1 1.00 640

Helium (He) 2 6.8 10-2 94

Lithium, beryllium, boron 2.6 10-9 1.5

Carbon, Nitrogen, Oxygen 1.2 10-3 6

Iron (Fe) 26 3.4 10-5 0.24

All heavier atoms 1.9 10-6 0.13

ElementAtomic

Number (Z)

Solar SystemComposition

(relative number of atoms)

PrimaryCosmic Ray

Flux(particles/m-2 sec)

50m

Cosmic ray strikes a nucleuswithin a layer of

photographicemulsion

Primary cosmic ray

Mostly photons, electrons and muons at Earth’s surface

A 1019 eV Extensive Air Shower

100 billion particles

at sea level

89% photons10% electrons~1% muons

12 km

6 km6 km

The Cosmic Ray Energy Spectrum

(1 particle per m2-sec)

(1 particle per m2-year)

(1 particle per km2-year)

Cosmic Ray Flux

Energy (eV)

Refrigerator cold CO2 bubble (887 mph)

0.02 eV

Room temperature nitrogen N2 (1160 mph)

0.03 eV

Atoms in sun’s MILLION DEGREE surface0.50 eV

Energy given to each single electron whenaccelerated by AA battery 1.5 eV

Electrons accelerated by your televisionpicture tube (traveling ~1/3 speed of light)

30,000 eV

Fermi National Lab’s high energy protons 1,000,000,000,000 eV

Superball bounced over your house 4 x 1017 eV

Pitched baseball 4 x 1020 eV

Slammed hockey puck 1 x 1021 eV

Recall: 1 joule = 6.2 x 1018 eV

The highest energy Cosmic Rays areSUBATOMIC particles carrying theenergy of MACROSCOPIC objects!

4 x 1021 eV = 60 joules

The Cosmic Ray Energy Spectrum

FERMILAB’s protonsFERMILAB’s protons

Bounced Superball

Bounced Superball

Pitched baseballPitched baseball

Hockey PuckHockey Puck

Energy (eV)

Two possible sources of cosmic rays

Colliding galaxies

Active galacticnucleus

GZK Cutoff

1966 - K. Greisen - G.T.Zatsepin & V.A.Kuz’min

showed the recently discovered cosmic microwave background radiation (CMBR)effectively makes the universe opaque tosufficiently high energy cosmic particles.

GZK Cutoff

For example:

p *+0 p

++ n

and similar resonances yield attenuation lengths mere 10s of Mega parsecs for cosmic ray protons with E>1019 eV.

Center of (our) Virgo supercluster is approximately 20 Mpc away

All E>1019 eV primaries must originate within 100 Mpc of the earth

1966 - K. Greisen - G.T.Zatsepin & V.A.Kuz’min

p

Energy [eV]

ICRC2001 news

AGASA: 717

HiRes: 7 2

events above 1020eV

AGASA