Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
1
Spectrum if all energy is captured in detector.Allows identification of gamma energy.
• Large Detector (in depth?!).• Photo Peak or Full Energy Peak…?• Doppler.• Cost.• Crystal growth.
(with atoms, why??)
Photoelectric AbsorptionPhotoelectric Absorption.
Principles of Spectrometry
Auger
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
2
• Spectroscopy, energy deposition.• Consider what might escape.• Size and material of detector.• Shield lining.
Considerations for shields and detectors?shields and detectors?
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
3
HPGe
HW 15HW 15
Principles of Spectrometry
• “Probability” for photoelectric absorption:
• Strong Z dependence.• Considerations for shields and detectorsshields and detectors.
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
4
Practical
Theoretical
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
5
Efficiency considerations.Efficiency considerations.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
6
NaI or BGO
HPGe
Efficiency vs. ResolutionEfficiency vs. Resolution
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
7
Considerations for shields and detectors?
shields and detectors?
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
8
cos11 20
'
cmhh
h
20
21cmh
hEc
cos11
cos1
20
20'
cmhcmh
hhhEe
In the figure:• Photoelectric suppressed.• Single Compton (effect of crystal dimensions).• Below 1.022 MeV.
Compton ScatteringCompton Scattering.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
9
Reproduce the graph.
cos11 20
'
cmhh
h
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
10
• 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 16HW 16
20cm
h
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
11
Note tendency for forward Note tendency for forward scattering at high scattering at high
energies.energies.
Considerations for shields and detectors? Sources vs. accelerators???shields and detectors? Sources vs. accelerators???
HW 17HW 17 What is Thomson scattering.What is Thomson scattering.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
12
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.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
13
Single peak if electron and positron “kinetic” energies are captured by the
detector. But annihilation!2
02 cmhEEee
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. These photons may or may not be captured, causing single and double escape peaks in the spectrum (effect of crystal dimensions).
Pair ProductionPair Production.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
14
Low-energy gamma.Low-energy gamma. High-energy gamma.High-energy gamma.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
15
Probability of pair production.
Dependence on Z?
Recoil nucleus,Why?Why?
Effect of Effect of screening?screening?
HW 18HW 18
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
16
Principles of Spectrometry
Importance in Linacs?
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
17
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
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
18
Very small detectors. All secondary radiation, including Compton scattered gamma rays and annihilation photons, are not captured in detector volume (escaping).
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
19
A typical detector.
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011 (Saed Dababneh).
20
Effect of surrounding material. Detectors are normally shielded to minimize as much as possible the counting of ambient background radiation.
X-rays and
lining.
Principles of Spectrometry