1. Subatomic Particles and Quantum Theory
Atomic Physics

2. Subatomic Particle Tracks
Were originally detected by Charles Thompson Rees in 1910 using a cloud chamber
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 particles that have a charge create tracks of condensed liquid in the cloud chamber

5. 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.

6. Bubble Chamber Contains a liquefied 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 of bubbles.

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

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

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

10. Eg) A charged particle traveling at 2
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.

11. 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.

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

13. q/m

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

15. 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.

16. Antimatter
early 1900’s, 3 fundamental particles: electrons, protons, and neutron
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 mass of an electron but 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

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

18. Eg) PET (positron emission topography)
Electron - positron annihilation
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

19. Quantum Theory
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

20. Relative Strength for Protons in a Nucleus Mediating Particle
4 Fundamental Forces
Range
Relative Strength for Protons in a Nucleus
Mediating Particle
Electromag- netic
Infinite
10-2
Photon
Weak Nuclear
< fm (x10-15)
10-6
W+,W-, Z0
Strong Nuclear
<1 fm 1
Gluons ?
Gravitational
10-39
Gravitron ?
Physicists believe (hope?) they will eventually show that these are all different manifestations of single fundamental force (aka Grand Unified Theory or GUT).

21. 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

22. 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

23. 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).
CERN on Wikipedia

24. 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

25. 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

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

27. Proton