Ghosts of Subatomic Particles

  • By Greg Kestin
  • Posted 03.19.15
  • NOVA

What do subatomic particles shooting through alcohol vapor look like? This footage beautifully reveals the smallest particles in the universe as they are ejected from a radioactive rod and as they fly down from space.

Running Time: 01:42



Produced, animated, and edited by
Greg Kestin
Demonstration and lighting technician:
Allen Crockett
Original Footage
© WGBH Educational Foundation 2015
Media Credits:
“Fresh and Bright” APM Music, Music


(main image: particle cloud chamber)
©WGBH Educational Foundation 2015



Watch this to learn where cosmic rays subatomic particles come from.

  • Subatomic particles include both elementary particles, such as electrons and muons, as well as nuclei such as protons or alpha particles. "The smallest particles in the universe" refers to the former.

  • The cosmic ray subatomic particles are independent of those ejected from the radioactive rod.

  • The “radioactive rod” in this video is thoriated tungsten, which is emitting alpha particles. Alpha particles are nuclei that include two protons and two neutrons (helium nuclei).

  • Here “cosmic ray subatomic particles” refer to secondary particles in “air showers” created by cosmic rays bombarding earth’s atmosphere.

  • The “cosmic rays subatomic particles” include muons, electrons, and positrons.

  • When a charged particle passes through the alcohol vapor, some of it is ionized (becomes electrically charged), and the neighboring vapor is attracted to the ions, forming visible droplets. This is the “disturbance” that muons or electrons create as they pass through the vapor.
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