Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
1
Radiation Interaction - Detection• Radiation detection requires that radiation interacts with detector material.• Energy deposition (not all detectors…!).• Charged particles continuously transfer their energy to the medium.http://www.srim.org
• Gammas and X-rays interact (if they do) catastrophically.http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html
• Photon interactions produce secondary electrons.• Neutron interactions produce secondary heavy charged particles.
I0 I Usually corresponds to net area under the full energy peak.
If not, then
build-up.Good or
bad geometry.
and shielding!!
Collimation.
Could be secondary gamma, but for shielding.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
2
Charged particles.
Gamma.
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
3
• Partial or complete transfer of photon energy to electrons.• Many types of interactions, but three (or four) are important.
Interaction of gammasInteraction of gammas
• Attenuation Attenuation coefficient and coefficient and
mass attenuation mass attenuation coefficient.coefficient.
• Compare to Compare to macroscopic cross macroscopic cross
section section for for neutrons.neutrons.
What is coherent scattering.What is coherent scattering.
xeII 0
HW 11HW 11
Radiation Interaction - Detection
Buildup Factor
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
4
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
5
Spectrum if all energy is captured in detector.Allows identification of gamma energy.
Radiation Interaction - Detection
• Large Detector.• Photo Peak or Full Energy Peak…?• Doppler.• Cost.• Crystal growth.
(with atoms, why??):Photoelectric AbsorptionPhotoelectric Absorption.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
6
• Spectroscopy, energy deposition.• Consider what might escape.• Size and material of detector.• Shield lining.
Considerations for shields and detectors?shields and detectors?
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
7
HPGe
HW 12HW 12
Radiation Interaction - Detection
• “Probability” for photoelectric absorption
• Strong Z dependence.• Considerations for shields and detectorsshields and detectors.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
8
Practical Theoretical
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
9
Radiation Interaction - DetectionEfficiency considerations.Efficiency considerations.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
10
Radiation Interaction - DetectionNaI or BGO
HPGe
Efficiency vs. ResolutionEfficiency vs. Resolution
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
11
Considerations for shields and detectors?
shields and detectors?
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
12
cos11 20
'
cmh
hh
20
21cm
hh
Ec
cos11
cos1
20
20'
cmhcm
h
hhhEe
In the figure:• Photoelectric suppressed.• Single Compton (effect of crystal dimensions).• Below 1.022 MeV.
Radiation Interaction - DetectionCompton ScatteringCompton Scattering.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
13
Reproduce the graph.
Radiation Interaction - Detection
cos11 20
'
cmh
hh
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
14
• Compton scattering is predominant for energies typical of radioisotope sources.
• “Probability” per atom increases linearly with Z (Why).• Electron density.• Effect of binding energy.• Effect of polarized photons.• Compton fraction.
Klein-Nishina formulaKlein-Nishina formula
Let the recoil electron be emitted at an angle , calculate cot() as a function of tan(/2).
HW 13HW 13
20cm
h
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
15
Note tendency for Note tendency for forward scattering forward scattering at high energies.at high energies.
Considerations for shields and detectors?shields and detectors?
HW 14HW 14 What is Thomson scattering.What is Thomson scattering.
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
16
If you need to measure gamma ray yield from nuclear reactions (using particle accelerators), the photon energies could be as high as 10 MeV. What is the typical Ge detector to be used?
Prepared with Monte Carlo simulations.
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
17
Single peak if electron and positron “kinetic” energies
are captured by the detector.
202 cmhEE
ee
Rest mass of electron and positron. Gamma must have 1.022 MeV
minimum energy for PP to occur.
Two annihilation photons are then created when positron recombines with an electron. This photon may or may not be captured, causing single and double escape peaks in the spectrum (effect of crystal dimensions).
Radiation Interaction - DetectionPair ProductionPair Production.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
18
Low-energy gamma.Low-energy gamma. High-energy gamma.High-energy gamma.
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
19
Probability of pair production.
Recoil nucleus,Why?Why?
Effect of Effect of screening?screening?
HW 15HW 15
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
20
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
21
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
22
HPGeHPGe
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
23
Very large detector. All secondary radiation, including Compton scattered gamma rays, Bremsstrahlung, x-rays and annihilation photons, are captured in detector volume
Large photofraction (fraction of full energy events) is desired in any detector
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
24
Very small detectors. All secondary radiation, including Compton scattered gamma rays and annihilation photons, are not captured in detector volume (escaping).
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
25
A typical detector.
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
26
Effect of surrounding material. Detectors are normally shielded to minimize as much as possible the counting of ambient background radiation.
Radiation Interaction - Detection
X-rays and
lining.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
27
• Peak area determination.• Peak-to-total ratio.• Peak-to-Compton ratio.• Relative efficiency.• Absolute efficiency.• Total efficiency.• Solid angle.• Energy Resolution (effect of number of charge carriers).• Dead time.• Resolving time.• Anti-coincidences.• Coincidences.• Summation effects.• True coincidences.• Random coincidences.
• Attenuation coefficient.• Mass attenuation coefficient.• Mean-free path.
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
28
Compton suppression.“Anti-coincidences”.
What if cascades are present?Coincidences.
Radiation Interaction - DetectionSelect events.
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
29
Radiation Interaction - Detection
Cascade Cascade selectionselection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
30
Compton spectrometerCompton spectrometer
Radiation Interaction - Detection
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
31
Linear attenuation coefficientLinear attenuation coefficient(photoelectric) + (Compton) + (pair production)
1
0
0
dxe
dxxe
x
x
Mean free path
Mass attenuation coefficient Mass attenuation coefficient is independent of density and physical state.
Compounds and mixtures??Compounds and mixtures??Give examples.Give examples.Refer to XCOM.Refer to XCOM.
tt eIeII )/(00
Mass thicknessMass thickness
Radiation Interaction - Detection
HW 16HW 16
THINKING QUIZTHINKING QUIZProbability of interaction or of
no-interaction?
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
32
Self-AbsorptionSelf-Absorption
Photon AttenuationPhoton Attenuation
Valid for parallelphoton paths
or far geometries.
Radiation Interaction - Detection
HW 17HW 17
t
eII
t
10
Build-upteII 0
teEtBII
),(0
Solutions to buildup problem?Solutions to buildup problem?
1
Not realistic…!!Not realistic…!!
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
33
Isotropic PhotonEmission
Radiation Interaction - Detection
Solutions to self Solutions to self absorption at close absorption at close
geometries?geometries?
t
eII
t
10
MCMC
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
34
Radiation Interaction - Detection
Geometric correction factorGeometric correction factor
PointSource
Detector
ExtendedSource
Detector
THINKING QUIZTHINKING QUIZ
Radiation Detection and Measurement, JU, 1st Semester, 2008-2009 (Saed Dababneh).
35
N
Neutron Interaction
• Secondary radiation is different from that for gammas, it is mainly heavy charged particles (or gammas).• Utilize them for neutron detection (Chapters 14 and 15).• Slow neutrons: Thermalized through scattering then detected through reactions.• Fast neutrons: Recoil nuclei (elastic) and probable gammas (inelastic). (Shielding vs. detection).(Shielding vs. detection).
Macroscopic cross section
Nuclei per unit volume
...
0
absorptionscattertotal
ttotaleIIMean free path?Neutron flux?
Radiation Interaction - Detection
Cd cutoff energy.Cd cutoff energy.
• Later in this courseLater in this course We will discuss neutron detection. neutron detection.
Top Related