Full set of Notes with Fill-Ins - San Jose State University

Chem 155 Unit 5 Page 109 of 316Noise in PMT’s and Single Photon Counting:Two major sources:Thermal:Individual electrons are ‘thermionically’emitted from photocathode or one of thedynodes.Cosmic Ray Background:Energetic particles (α and β particles, γ-raysetc. from space) strike photocathode ordynodes and cause a large current spike.current / microamperestime / sReject: cosmicray – e- cascade.Accept: photonelectronfromphotocathodeReject:Thermal e - fromdynodesMuon: created by very high energy cosmic ray interaction with upper atmosphere, similar toelectron (-1 charge, spin 1/2) but about 200 times heavier.About 10,000 muons reach every square meter of the earth's surface a minute; these chargedparticles form as by-products of cosmic rays colliding with molecules in the upper atmosphere.Traveling at relativistic speeds, muons can penetrate tens of meters into rocks and other matterbefore attenuating as a result of absorption or deflection by other atoms.—Mark Wolvertron, science writer, Scientific American magazine, September 2007, page 26 "Muons forPeace"Page 109 of 316