Download LHCC

Interaction of particles
with matter
M. Cobal, PIF 2006/2007
Particle detection
M. Cobal, PIF 2006/2007
M. Cobal, PIF 2006/2007
Heavy charged particles
M. Cobal, PIF 2006/2007
M. Cobal, PIF 2006/2007
Mass thickness
M. Cobal, PIF 2006/2007
Energy loss by ionization:
Bethe-Bloch formula
M. Cobal, PIF 2006/2007
Bethe-Bloch
M. Cobal, PIF 2006/2007
Penetration Depth
M. Cobal, PIF 2006/2007
Range
M. Cobal, PIF 2006/2007
Tracking Detectors
Fitted Track
M. Cobal, PIF 2006/2007
Fast electrons
M. Cobal, PIF 2006/2007
Interactions of fast electrons:
Bremsstrahlung
M. Cobal, PIF 2006/2007
Energy loss by radiation
M. Cobal, PIF 2006/2007
Bremsstrahlung
M. Cobal, PIF 2006/2007
Interactions of photons
with matter
M. Cobal, PIF 2006/2007
Photon properties
Relation between particle and wave properties of light
E  h
Energy and frequency
Also have relation between momentum and wavelength
E  p c m c
Relativistic formula relating
energy and momentum
For light
2
E  pc
and
2 2
2 4
c  
h
p 

c
h
Also commonly write these as
E 
M. Cobal, PIF 2006/2007
p k
  2
angular frequency
wavevector
k
2

h

2
hbar
Photoelectric Effect
When UV light is shot on a metal plate in a
vacuum, it emits charged particles (Hertz 1887),
which were later shown to be electrons by J.J.
Thomson (1899).
Hertz
J.J. Thomson
Classical expectations
Light, frequency ν
Vacuum
chamber
Collecting
plate
Metal
plate
Electric field E of light exerts force F=eE on electrons. As intensity of light
increases, force increases, so KE of
ejected electrons should increase.
Electrons should be emitted whatever
the frequency ν of the light, so long as
E is sufficiently large
I
Ammeter
Potentiostat
M. Cobal, PIF 2006/2007
For very low intensities, expect a time
lag between light exposure and
emission, while electrons absorb enough
energy to escape from material
Einstein
Actual results:
Maximum KE of ejected electrons is
independent of intensity, but dependent
on ν
For ν<ν0 (i.e. for frequencies below a
cut-off frequency) no electrons are
emitted
There is no time lag. However, rate
of ejection of electrons depends on
light intensity.
Einstein’s interpretation
(1905):
Light comes in packets of
energy (photons)
E  h
Millikan
An electron absorbs
a single photon to
leave the material
The maximum KE of an emitted electron is then
K max  h  W
Planck constant: universal
constant of nature
h  6.63 1034 Js
M. Cobal, PIF 2006/2007
Work function: minimum
energy needed for electron to
escape from metal (depends
on material, but usually 2-5eV)
Verified in detail
through
subsequent
experiments by
Millikan
Compton Scattering
Compton
Compton (1923) measured intensity of
scattered X-rays from solid target, as function
of wavelength for different angles. He won
the 1927 Nobel prize.
X-ray source
Collimator
(selects angle)
Crystal
(selects
wavelength)
θ
Target
Result: peak in scattered radiation
shifts to longer wavelength than source.
Amount depends on θ (but not on the
target material).
M. Cobal, PIF 2006/2007
Detector
A.H. Compton, Phys. Rev. 22 409 (1923)
Classical picture: oscillating electromagnetic field causes
oscillations in positions of charged particles, which re-radiate in all
directions at same frequency and wavelength as incident radiation.
Change in wavelength of scattered light is completely
unexpected classically
Incident light wave
Oscillating electron
Emitted light wave
Compton’s explanation: “billiard ball” collisions between
particles of light (X-ray photons) and electrons in the material
Before
After
p 
scattered photon
Incoming photon
p
M. Cobal, PIF 2006/2007
θ
Electron
pe
scattered electron
Before
After
p 
scattered photon
Incoming photon
θ
p
Electron
pe
Conservation of energy
h  me c  h    p c  m c
2
2 2
e

2 4 1/ 2
e
scattered electron
Conservation of momentum
hˆ
p  i  p   p e

From this Compton derived the change in wavelength
h
   
1  cos 
me c
 c 1  cos    0
h
c  Compton wavelength 
 2.4  1012 m
me c
M. Cobal, PIF 2006/2007
Pair production
M. Cobal, PIF 2006/2007
A collider experiment
M. Cobal, PIF 2006/2007
Z  e e 
Z   
Z  qq
M. Cobal, PIF 2006/2007