Principles of Spectrometry
• Efficiency and resolution.
• Summing effects.
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
1
Principles of Spectrometry
Resolution
HPGe
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
2
Principles of Spectrometry
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
3
Principles of Spectrometry
What is this?
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
4
Principles of Spectrometry
Deconvolution.
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
5
Principles of Spectrometry
Energy and efficiency calibration.
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
6
Principles of Spectrometry
.
Select events
Compton suppression.
“Anti-coincidences”.
What if cascades are present?
► Coincidences.
By software or by
hardware.
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
7
Advanced background reduction
Cascade
selection
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
8
Principles of Spectrometry
Compton spectrometer.
Another example for
coincidences.
h
1  cos  
2
m0 c
Ee  h  h '  h
h
1  cos  
1
2
m0 c
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
9
Principles of Spectrometry
• Peak area determination.
• Peak-to-total ratio.
• Attenuation coefficient.
• Peak-to-Compton ratio.
• Mass attenuation coefficient.
• Relative efficiency.
• Mean-free path.
• Intrinsic efficiency.
• Absolute efficiency.
• Total efficiency.
• Solid angle.
• Energy Resolution (effect of number of charge carriers).
• Dead time.
• Resolving time.
• Anti-coincidences.
• Coincidences.
• Summation effects and true coincidences.
• Random coincidences.
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
10
Principles of Spectrometry
Mass thickness
I  I 0e
 t
 I 0e
 (  /  ) t
Linear attenuation coefficient
  t (photoelectric) + s(Compton) + k (pair production)
Mass attenuation coefficient

Mean free path  
 xe
0

e
0
 x
 x
 is independent of density and physical state.
HW 19
dx

dx

1

Compounds and mixtures??
Give examples.
Refer to XCOM.
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
11
Principles of Spectrometry
Photon Attenuation
I  I 0 e  t
Not realistic…!!
Self-Absorption
Valid for parallel
photon paths
or far geometries.
 t
HW 20
1 e
I  I0

t
1
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).


12
Principles of Spectrometry
1  e  t
I  I0
t
Solutions to self
absorption at
close
geometries?
MC
Isotropic Photon
Emission
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
13
Principles of Spectrometry
Geometric correction factor
THINKING QUIZ
Point
Source
Detector
Detector
Extended
Source
Radiation Detection and Measurement, JU, First Semester, 2010-2011
(Saed Dababneh).
14