Subatomic Particles and Quantum Theory
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Transcript of 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
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
Charged Particles
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.
Uses
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.
Bubble Chamber
http://www.youtube.com/watch?v=qcUwLH8L5AU
Interpreting
Cloud and bubble chambers do not detect neutral particles (neutral particles do not form ions).
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
-q
+q
. . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Right hand rule
B directed out of the plane of the page
The spiral results from the charged particle slowing in
the bubble chamber.
Spiral Tracks11
11
1.8 10 /
1.76 10 /e
e
q C kgmq
C kgm
2
c mF F
mv qv BrmvrqB
r decreases as v decreases
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.
2
7
3
11
2.50 10 /(2.44 10 / )(0.0582 )
1.76 10 /
c mF F
mv qvBrq vm Brq m sm Ns Cm mq C kgm
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.
Analyzing
B: into page v: to top of page F: toward centre
Left or right hand?
Left. Charge is negative.
Charge
q/m
2
8
11
0.10 3.00 10 /0.030 0.0057
1.8 10 /
c mF F
mv qv Brq vm Br
m sT mC kg
Particle appears to be an e¯ (evidence consistent with of charge and q/m for an e¯)
Identify11
11
1.8 10 /
1.76 10 /e
e
q C kgmq
C kgm
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.
Collisions
• 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
Neutral particles – neutron n antineutron - place a bar over the symbol for
matter to represent antimatter
Interaction of Electron and Positron
2e e
e e
n
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
Eg) PET (positron emission topography)
annihilation produces gamma rays
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
4 Fundamental Forces
Range Relative Strength for Protons in a Nucleus
Mediating Particle
Electromag-netic
Infinite 10-2 Photon
Weak Nuclear
< 0.003 fm (x10-15)
10-6 W+,W-, Z0
Strong Nuclear
<1 fm 1 Gluons ?
Gravitational Infinite 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).
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
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
Subatomic Particles ( ~ 300)
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
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
Two Separate Families
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
Hadrons are divided into 2 groups based upon spin
, , ,e e v v
Eg) electron
Masses of subatomic particles are expressed in MeV/c2
2
2 2
2 2 2 2 2 2 2
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// / /
1.7827 10
E mc
E J Nm kgm sm kgc m s m s m seVm kgc
31 4 29.11 10 5.4858 10 0.5110 /m kg u MeV c
Proton27 21.6726 10 1.0073 938.23 /m kg u MeV c