1833-47
Workshop on Understanding and Evaluating Radioanalytical
Measurement Uncertainty
5 - 16 November 2007
Uncertainty in Alpha Spectrometry
Paul MARTIN
International Atomic Energy Agency IAEA
Agency's Laboratories Seibersdorf
Chemistry Unit, A-2444 Seibersdorf
AUSTRIA
Alpha Spectrometry:
Sources of Uncertainty
Paul Martin
IAEA Laboratories Seibersdorf
ICTP Workshop November 2007
General procedure
Sample collection
and preparation
Addition of tracer
Sample dissolution
Chemical separation
Deposition onto
counting disc
Count in an
alpha spectrometer
Calculation of
tracer recovery
& sample activity
Sources of uncertainty
Sample collection
and preparation
Appropriate preparation method
Addition of tracer
Tracer activity
Sample dissolution
Isotopic equilibration
Chemical separation
Complete separation
Deposition onto
counting disc
Count in an
alpha spectrometer
Calculation of
tracer recovery
& sample activity
Source quality
Counting statistics, tailing
Correct calculation, decay corrections
Plus: background, blank
Can all sources of uncertainty be
estimated statistically?
These can be estimated statistically
Sample collection
and preparation
Appropriate preparation method
Addition of tracer
Tracer activity
Sample dissolution
Isotopic equilibration
Chemical separation
Complete separation
Deposition onto
counting disc
Count in an
alpha spectrometer
Calculation of
tracer recovery
& sample activity
Source quality
Counting statistics, tailing
Correct calculation, decay corrections
Plus: background, blank
Looking at spectra: Thorium
300
232
Counts/channel
250
Th
228
Th
200
230
150
Th
229
Th
100
50
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Looking at spectra: Thorium + Po-210
300
232
Counts/channel
250
Th
228
Th
Thorium spectrum
Po-210 spectrum
200
230
150
Th
229
Th
100
50
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Looking at spectra: Th + U
300
232
Counts/channel
250
Th
228
Th
Thorium spectrum
Uranium spectrum
200
230
150
Th
229
Th
100
50
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Exercise 1
Identify as many peaks as you can in the
spectra provided
Polonium
1000
Counts/channel
800
600
400
200
0
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Polonium
1000
209
Po
Counts/channel
800
600
400
210
200
209
Po
Po
0
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Polonium – log scale
Counts/channel
1000
100
10
1
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Americium
140
Counts/channel
120
100
80
60
40
20
0
4.5
5.0
5.5
Eα (MeV)
6.0
Americium
140
241
Counts/channel
120
Am
100
80
243
60
Am
40
20
0
4.5
5.0
5.5
Eα (MeV)
6.0
Americium : effect of tailing
Counts/channel
300
241
Am
200
243
Am
100
0
4.5
5.0
5.5
Eα (MeV)
6.0
Plutonium
80
Counts/channel
60
40
20
0
4.0
4.5
5.0
Eα (MeV)
5.5
6.0
Plutonium
80
242
Pu
Counts/channel
60
40
20
239,240
Pu
238
Pu
0
4.0
4.5
5.0
Eα (MeV)
5.5
6.0
Uranium
250
Counts/channel
200
150
100
50
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Uranium
250
232
U (+ 228Th)
Counts/channel
200
238
150
234
U
U
100
228
50
Th
224
Ra
212
Bi
220
Rn
216
Po
235
U
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Thorium
300
Counts/channel
250
200
150
100
50
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Thorium
300
232
Counts/channel
250
Th
228
Th (+224Ra +225Ac)
200
230
150
225
Ac
+ Bi
Th
213
229
Th
212
224
100
221
Bi
Ra
Fr
220
216
Rn
Po
50
0
3.5
4.0
4.5
5.0
5.5
Eα (MeV)
6.0
6.5
7.0
Exercise 2
Calculate the activity concentration of 210Po in
a sample for the date of chemical
separation, including the uncertainty.
Polonium
1000
209
Po
Counts/channel
800
600
400
210
200
209
Po
Po
0
4.0
4.5
5.0
Eα (MeV)
5.5
6.0
Alpha Spectrometry:
Sources of Uncertainty
Paul Martin
IAEA Laboratories Seibersdorf
ICTP Workshop November 2007