Interaction of charged particles in matter today electrons Introductory remarks • Electrons ‚feel‘ electro-magnetic and weak interaction • Electrons couple to photons and W- and Z-Boson of weak interaction • Electrons ‚talk‘ easily to photons, remember pair creation and Bremsstrahlung • Electron and photon detection are entangled, e.g. electro-magnetic shower detection at high energies Relevance of electrons in nuclear and particle physics some examples: - beta decays - conversion electrons (complementary to g-spectroscopy) - electron beams for electron-nucleon-scattering (structure functions) - electron-positron collisions at high energies provide clean source for particle production and new discoveries - electron is most abundant reaction product, often source of unwanted and tremendous back ground 2 2 2 2 ) / ( mc e r e
19
Embed
Interaction of charged particles in matter today electrons · 2018-06-06 · Interaction of charged particles in matter today electrons Introductory remarks •Electrons ‚feel‘
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Interaction of charged particles in matter
today electrons
Introductory remarks
• Electrons ‚feel‘ electro-magnetic and weak interaction
• Electrons couple to photons and W- and Z-Boson of weak interaction
• Electrons ‚talk‘ easily to photons, remember pair creation and
Bremsstrahlung
• Electron and photon detection are entangled, e.g. electro-magnetic
shower detection at high energies
Relevance of electrons in nuclear and particle physics some examples:
- beta decays
- conversion electrons (complementary to g-spectroscopy)
- electron beams for electron-nucleon-scattering (structure functions)
- electron-positron collisions at high energies provide clean source for
particle production and new discoveries
- electron is most abundant reaction product, often source of unwanted
and tremendous back ground
2222)/( mcere
Consider moving particle of charge ze passing by with v the stationary charge Zeze
vb
Ze
r q
y
Assumptions:
• momentum approximation: short inter-
action, only transversal moment. transfer
• target remains non-relativistic
Interaction of heavy charged
particles in matter
Bethe-Bloch
energies)(low correction shell :
energies)ic relativist (at correctiondensity : terms correction two
collision single in transferenergy max. : matter abs. of massatomic :
potential ionisation averaged :I matter abs. of number charge :
v/c : mass electron :
particle incoming of charge : cm10 x 2.81 radius electron class. :
matter absorbing ofdensity : mol10 x 6.022 constant Avogadro
13-
1- 23
C
WA
Z
m
zr
N
Z
C
I
Wvmz
A
ZcmrN
dx
dE
e
e
a
eeea
gg
g
max
2
2
2
max
22
2
222
1/1,
:
222
ln2
Energy loss of electrons and positrons via collisions with electrons on atoms and
electro-magnetic radiation (Bremsstrahlung)
collradtot dx
dE
dx
dE
dx
dE
Modified calculation of energy loss
- large scattering angle of incoming particle
- scattering of identical particles -> Q.M. interference
positrons electrons
of units inenergy kinetic
...)23(12
2ln2)(...1)(:)(
:
2)()/(2
)2(ln
12
22
2
22
2
2
22
FFF
cm
Z
CF
cmIA
ZcmrN
dx
dE
e
e
eea
coll
Collisional energy loss:
Interaction of electrons and positrons
Bremsstrahlung loss and ionisation loss for electrons and protons in copper
electron
2-4 MeV proton
> 3 GeV
Comparison of interactions
crit. energy
24 MeV
Variation in range and energy loss caused by statistics of absorbing collisions.
Energy loss distribution
- average energy loss –(dE/dx)
- energy loss straggling
- range straggling
heavy charged particle electrons
Range and energy loss
Electron range fluctuates considerably due to
multiple scattering.
Large energy transfer via collisions is possible.
Range distribution is smeared out .
Transmission of electrons in aluminium [1 g/cm2 = 3.7 mm]
Electron range
Polyethylene [1 g/cm2 = 9.0 mm]
Aluminium [1 g/cm2 = 3.7 mm]
Lead [1 g/cm2 = 0.88 mm]
Range variation below critical energy is
very energy dependent.
Electron range: low energies
– decay of 185W
185W -> 185Re + - + n
Q = 433 keV, T1/2 = 75.1 d
Neutrinos cause continuous electron
spectrum
Folding of electron energy spectrum and
range in matter shows exponential
attenuation
I = I0 exp(-mx)
– attenuation coefficient m
Exponential attenuation is not valid in
general, only for simple –decay
scheme.
Absorption of electrons from185W - decay
Absorption of -electron
Scattering cause large deflection, even
Backward angles and small energy losses.
Depending on incident angle!
Electrons leave matter in most cases even
below the detection threshold.
Reduced detection efficiency!
Strongly dependent on:
-Electron energy
- at low energies highest impact
- charge number Z of absorbing matter
Electron back scattering
h is backscattering coefficient, given for perpendicular incidence