Victor Hess Before making balloon ascents himself he

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 1913 - 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!

NUMBER Primary Cosmic “Rays” Largely protons (H, hydrogen nucleus) Energies peak ~ 300 Me. V (0. 3 Ge. V) 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

1 e. V e in TV picture tube CRT Ionize Atom Visible Light Photon 1 Ke. V 1000 e 1 Me. V million 1 Ge. V billion p Most Powerful Accelerator mp p a Charging Snail Fast-ish Cosmic “Rays” Gamma Rays Energy & e. V, Me. V, Ge. V stuff Mass energy 1 Te. V trillion

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

Muons /cm 2/sec Muon Flux at Surface (above some Energy) 0. 01 Less than 1 per minute In a square centimeter Muon Energy (Ge. V)

Relative Number # Muons Change with Angle off Vertical

Muon Rate vs Altitude(ft) Ct/min Feet Count Rate Increases ~ 100% over 10000 ft. So IF a straight line – expect 10 % increase in 1000 ft

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

10 X 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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