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Victor Hess

Victor Hess.

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Victor Hess

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  1. 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).


  3. Primary Cosmic “Rays” NUMBER 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 /meter2/second Only the faster ones make “good” muons ~500 protons/meter2/second ENERGY

  4. Energy & eV, MeV, GeV stuff Fast-ish Cosmic “Rays” Charging Snail p Most Powerful Accelerator e in TV picture tube CRT Visible Light Photon Gamma Rays Ionize Atom m a e p p Mass energy 1 eV 1 KeV 1 MeV 1 GeV 1 TeV 1000 million billion trillion

  5. e e e e e Cosmic Ray Essentials p (cosmic “ray”) Encounters air Nor Onucleus around 15 km altitude pion produced p stuff pion decays intomuon m other stuff Gently slows down knocking off many (~million) air molecule’s electrons Muon may hit your sensor unless decays first

  6. Muon Flux at Surface (above some Energy) 0.01 Less than 1 per minute In a square centimeter Muons /cm2/sec Muon Energy (GeV)

  7. # Muons Change with Angle Relative Number Angle off Vertical

  8. 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

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

  10. Muon Counting Headachesdue 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.

  11. One 30 Second Trial

  12. Another 30 Second Trial

  13. 10X 30 Second Trials

  14. Average -> TRUE with Trials

  15. Uncertainty Reduced with Trials

  16. Distribution for 1000 Trials

  17. Is Result More for Test 1 or Test 2?

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

  19. Get Beyond Flapping

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