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Transcript
Atomic Physics – Part 3
Ongoing Theory Development
To accompany Pearson Physics
PowerPoint presentation by R. Schultz
robert.schulz@ei.educ.ab.ca
17.1 Detecting and Measuring Subatomic Particles
Tools
Cloud Chamber: supersaturated vapour
condenses along track of particle
Bubble Chamber: Liquid gas near its boiling
point boils along track of particle
Recall analysis of alpha, beta, and gamma for
charge and relative mass
17.1 Detecting and Measuring Subatomic Particles
More tools:
Particle accelerators: use high energy particles
to probe matter
High energy “probe particles” required to
overcome the strong nuclear force
Types: cyclotron, linear accelerator,
synchotron, Van de Graaff, CERN’s LHC
17.1 Detecting and Measuring Subatomic Particles
Check and Reflect, page 835, question 5
Note: particle notation uses lines on top for
antiparticles, e.g. n = neutron, n = antineutron
17.2 Quantum Theory and the Discovery of New
Particles
Antimatter
Positrons postulated by Dirac, verified by
Anderson
Matter/anti-matter collision
e+ + ephotons?
2γ
annihilation
Why must there be 2 gamma
17.2 Quantum Theory and the Discovery of New
Particles
At this point in time, theory has predicted and
evidence has supported existence of over 300
subatomic particles
Subatomic masses are communicated for
convenience in units of eV
c
2
Einstein’s equation E  mc 2 can be rewritten as
E
m 2
c
17.2 Quantum Theory and the Discovery of New
Particles
eV and MeV are units of energy, therefore
eV
1
eV
c
2
c2
and
MeV
c2
are units of mass
= 1.7827 x 10-36 kg (you don’t need to know this!)
Your formula sheet records masses of all first
generation “fermions” this way
17.4 Quarks and the Standard Model
Moving to the Standard Model:
Read Pearson Physics pages 836-8 and 842-3
Read SNAP pages 366-9
17.4 Quarks and the Standard Model
Standard Model: (1963 originally with many updates)
Fermions (make up
matter)
leptons
e
μ
τ
(+ anti of
νe
each)
νμ
ντ
Bosons (mediating
particles)
quarks
1st gen
u
d
s (+ anti of
c each)
b
t
make up hadrons
baryons
(3 quarks)
including
proton uud
neutron udd
mesons
(2 quarks)
1 reg, 1 anti
17.2 Quantum Theory and the Discovery of New
Particles
Further: hadrons interact by the strong nuclear
force (e.g. protons and neutrons)
Leptons do not (e.g. electrons)
Bosons are virtual particles that mediate forces
W+, W-, Z mediate weak nuclear force
existence
photons mediate electromagnetic force
confirmed
gluons mediate strong nuclear force
gravitons mediate gravitational force
unconfirmed
17.2 Quantum Theory and the Discovery of New
Particles
Formula sheet chart:
Keep this chart in front of
you for the next section
17.4 Quarks and the Standard Model
Beta decay
You already learned that in beta negative
decay, a neutron becomes a proton
How can we understand this in terms of quarks
and mediating particles?
17.4 Quarks and the Standard Model
(hadron)
(hadron)
(lepton)
(lepton)
neutron → proton + beta negative + antineutrino

udd → uud
+
e+
1
2

e
 e
3 1 3
 e
3
charge = 0
1
2

e
 e
3 2 3
 e
3
charge = +1e
to make this occur, a d quark has
turned into a u quark by the
following process:
d → u + [W-]
[W-] → e- +

boson mediating
weak nuclear force
very short lifetime
17.4 Quarks and the Standard Model
Beta positive decay:
(hadron)
(hadron)
(lepton)
(lepton)
proton → neutron + beta positive + neutrino
uud → udd
+
e+
+
ν
1
2

e
 e
3 2 3
 e
3
1
2

e
 e
3 1 3
 e
3
charge = +1e charge = 0
to make this occur, a u quark has
turned into a d quark by the
following process:
u → d + [W+]
[W+] → e- + ν
boson mediating
weak nuclear force
very short lifetime
17.4 Quantum Theory and the Discovery of New
Particles
Standard Model Summary:
• All matter composed of 12 fundamental
particles and their antiparticles ……..
• electromagnetic force and weak nuclear
force are different aspects of the same force
• electromagnetic and nuclear forces mediated
by virtual particles called bosons
We are done!!!
17.4 Quarks and the Standard Model