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Subatomic Particles and Quantum Theory

Subatomic Particles and Quantum Theory. Atomic Physics. Subatomic Particles. A cloud chamber is a confined space super saturated with water or alcohol vapour high energy particles moving though them condense the droplets and produce a vapour trail. Charged Particles.

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Subatomic Particles and Quantum Theory

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  1. Subatomic Particles and Quantum Theory Atomic Physics

  2. Subatomic Particles • A cloud chamber is a confined space super saturated with water or alcohol vapour • high energy particles moving though them condense the droplets and produce a vapour trail

  3. Charged Particles • Only charged particles and ionizing radiation or photons create tracks in the cloud chamber • http://www.youtube.com/watch?v=mLDASjzbxlA&feature=related • http://www.youtube.com/watch?v=kuzWNOUqLmQ&feature=related

  4. Uses • One of the earliest ways of detecting the path of charged particles. • Could be placed in magnetic fields to study path. • Principle tool of particle physics for 50 years.

  5. Bubble Chamber • Contains a liquified gas (ie. H2, He, Xe) • Lowering the pressure reduces the boiling pt to just below actual temperature. • Charged particles passing through cause liquid to boil, leaving a trail. http://www.youtube.com/watch?v=qcUwLH8L5AU

  6. Interpreting Cloud and bubble chambers do not detect neutral particles (neutral particles do not form ions).

  7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B directed out of the plane of the page -q +q Right hand rule In a bubble chamber, these particles create a series of bubbles in the trail • Particle tracks are used to determine the radius of the path of a charged particle or q/m ratio

  8. Spiral Tracks • The spiral results from the charged particle slowing in • the bubble chamber. r decreases as v decreases

  9. Eg) A charged particle traveling at 2.50 x 107 m/s enters a magnetic field of 2.44 x 10-3T and travels in a circular path with a radius of 5.82cm. Determine the q/m ratio for the particle.

  10. Analyzing • If initial v of this particle is 0.10c, initial r of spiral is 5.7 mm and B = 30 mT (into page), find q/m for the particle. • Determine the particle’s charge and its identity.

  11. Charge • B: into page • v: to top of page • F: toward centre Left or right hand? Left. Charge is negative.

  12. q/m

  13. Identify • Particle appears to be an e¯ (evidence consistent with of charge and q/m for an e¯)

  14. Collisions • Collisions can be seen when two tracks emerge from one. • Collisions with a neutral particle (that leave no track) appear to emerge from nowhere. • This is something different.

  15. early 1900’s, scientists thought there were 3 fundamental particles: electrons, protons, and neutrons • fundamental particle – particle that cannot be split or divided into smaller pieces • Carl Anderson, 1923, discovered antimatter where a particle track in a cloud chamber had the mass of an electron but the opposite charge • the collision of a particle (e-) and antiparticle (e+) can annihilate both particles and create a pair of high energy gamma rays traveling in opposite directions

  16. Interaction of Electron and Positron • Neutral particles – neutron n • antineutron - place a bar over the symbol for matter to represent antimatter

  17. Eg) PET (positron emission topography) • Electron - positron • fluorine-18 emits positrons as it decays, these collide with electrons in body cells and the gamma rays are detected showing the concentration of the radioactive tracer element injected into the body

  18. Quantum theory describes mediating particles that exist to indicate that fundamental forces act on particles over some distance • Particles that mediate forces for a brief time are virtual particles, energy, mass, momentum, etc. are not the same as real particles

  19. Physicists believe (hope?) they will eventually show that these are all different manifestations of single fundamental force (aka Grand Unified Theory or GUT).

  20. strong nuclear force is very large over a short distance (x10-8m) which is the size of a nucleus - to separate the parts of the nucleus, scientists need very large energies • cosmic rays – energies of 102 – 1014 MeV • - are EM photons protons, - antiprotons, electrons positrons, alpha particles

  21. Subatomic Particles ( ~ 300) • Muons – unstable particles having similar properties to electrons but 207 x the mass of the electron • Pion – unstable particle – 270 x mass of the electron

  22. The Large Hadron Collider at CERN can accelerate protons to an energy of about 7 TeV (7 x 1012 eV) each, or lead nuclei to • about 574 TeV per nucleus. • Beams of protons, moving in opposite directions, will be collided (each beam moving very close to c). http://www.youtube.com/watch?v=j50ZssEojtM • CERN on Wikipedia

  23. Two Separate Families • Leptons – subatomic particles that do not interact by means of a strong nuclear force eg) electrons, neutrinos, muons • Hadrons – subatomic particles that do interact by means of a strong nuclear force eg) protons and neutrons

  24. Hadrons are divided into 2 groups based upon spin 1. Mesons – hadron with an integer spin eg(0, 1, or 2) eg) pion 2. Baryons- hadron with a half integer spin eg (1/2, 3/2) eg) proton or neutron Text: p. 842 – 843 tables • *Fermion – a particle with a half integer spin – all leptons and baryons • Boson – a particle with an integer spin

  25. Masses of subatomic particles are expressed in MeV/c2 • Eg) electron

  26. Proton

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