Victor Hess Before making balloon ascents himself, he determined the height at which ground radiation would stop producing ionization (about 500 meters) and designed instruments that would not be damaged by temperatures and pressure changes. He then made ten ascents (five at night) - two in 1911, seven in 1912, and one in and found that ionization soon ceased to fall off with height and began to increase rapidly, so that at a height of several miles it was many times greater than at the earth's surface. He concluded, therefore, that "a radiation of very high penetrating power enters our atmosphere from above." On one ascent, during an almost total eclipse of the sun, the radiation was not diminished. Hess therefore concluded that the rays could not be emitted by the sun. Hess was awarded the Nobel Prize in 1936 for this work (along with the discoverer of the Muon, Anderson).

PARTICLES!

Primary Cosmic “Rays” Largely protons (H, hydrogen nucleus) Energies peak ~ 300 MeV (0.3 GeV) Come from all directions From the galaxy, not the sun so much ~ 5000 particles /meter 2 /second Only the faster ones make “good” muons ~500 protons/meter 2 /second ENERGY NUMBER

Energy & eV, MeV, GeV stuff 1 eV1 KeV1 MeV 1 GeV1 TeV ep  1000millionbilliontrillion Ionize Atom p Most Powerful Accelerator e in TV picture tube CRT Charging Snail Gamma Rays Visible Light Photon Fast-ish Cosmic “Rays” Mass energy 

Cosmic Ray Essentials p (cosmic “ray”) Encounters air N or O nucleus around 15 km altitude  stuff other stuff  Gently slows down knocking off many (~million) air molecule’s electrons Muon may hit your sensor unless decays first eeeee pion produced pion decays into muon

Muon Flux at Surface (above some Energy) Muon Energy (GeV) Muons /cm 2 /sec 0.01 Less than 1 per minute In a square centimeter

# Muons Change with Angle Relative Number Angle off Vertical

Muon Rate vs Altitude(ft) Count Rate Increases ~ 100% over ft. So IF a straight line – expect 10 % increase in 1000 ft Feet Ct/min

How can this be? ~ 30% Difference from close locations

Muon Counting Headaches due to Statistics What is your best estimate of the average result if you did it a zillion times? How confident are you with the estimate? EXAMPLE: Count random “hits” over 30 seconds, multiple times - when the TRUE average rate is 1 per second.

One 30 Second Trial

Another 30 Second Trial

10X 30 Second Trials

Average -> TRUE with Trials

Uncertainty Reduced with Trials

Distribution for 1000 Trials

Is Result More for Test 1 or Test 2?

A Note of Caution from Professor Hess … discovered that up to about 700 meters the ionization rate decreased but then increased with altitude …

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