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Principles of
Operation
Prompt Gamma Neutron Activation Analysis, What is it?
 Elemental Analysis Technique
 Bulk Analysis Method
• Penetrating Technology
 Non-Destructive Analysis Tool
2
The PGNAA Process
 Neutron source 252Cf emits
neutrons.
 Thermal neutrons are
absorbed and cause gamma
ray emissions
 Each element reacts differently
 When the gamma ray strikes
the NaI crystal a photon of light
is emitted.
 Gamma ray detection system
converts counts into an energy
spectrum
 High speed digital electronics
and sophisticated software
convert the spectra into
elemental composition
3
PGNAA Detection
Electronics enclosure
Detector Assembly
PreAmp
Detector PMT
10
A/D
Converter
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
Pulse
Processor
(DSP)
4
x 10
9
16
8
14
7
12
6
10
5
8
4
6
3
4
2
2
1
0
0
100
200
300
400
500
600
700
800
900
1000
0
0
100
200
300
400
500
600
700
800
900
0
1000
0
5
10
15
20
25
0
150
OpCon
Data
Processing
4
200
250
300
350
400
450
500
Typical PGNAA Gamma Ray Spectrum for Coal
5
2
x 10
1.8
1.6
1.4
Counts
1.2
1
Counts
0.8
0.6
0.4
0.2
0
100
0
100
150
200
200
300
Channel
5
250
300
Channel
400
350
400
450
500
500
600
Method of Spectral Analysis
6
14
The measured
spectrum
x 10
12
10
8
6
4
2
0
100
150
S
250
300
350
400
Si
x 10
5
450
500
Fe
6
6
3
200
C
5
x 10
18
4.5
6
x 10
3.5
x 10
16
3
2.5
4
14
2.5
3.5
12
2
+
1.5
+
3
2.5
+
10
8
2
1.5
2
6
1
1.5
1
4
1
0.5
0.5
2
0.5
0
0
50
100
150
200
×1
250
300
350
400
0
0
50
100
150
200
×2
250
300
350
6
400
0
0
50
100
150
200
×1
250
300
350
400
0
0
50
100
150
200
250
× 0.25
300
350
400
Parameters Measured
PGNAA measurements
S
Ash
Moisture
Heating Value
Ash Constituents
SiO2
Al2O3
Fe3O4
CaO
TiO2
K2O
Na2O
Cl
7
Calibration is critical to good performance
 Thermo uses high purity chemicals to calibrate the analyzers in
the factory before they are shipped to the field.
• This is critical as it insures that there are no correlations between
elements in the calibration.
• This is not possible to do if calibration is done in the field with coals.
• The value of the factory calibration is that the analyzer will perform
properly with any mixture of coal seams.
 The calibration uses every element normally seen in coal.
• With out information on all the elemental data, the result would be
less accuracy.
8
How are the analysis calculated?
 PGNAA measures the weight (in kg) of the elements of interest in the
sample. (S, Si, Al, Fe, Ca, K & Ti)
 The elemental weight of the ash oxide elements are converted to the
weight of the oxides in the ash.
• Eg. Ca + ½ O2 → CaO therefore 1kg Ca = 1.39919kg CaO
 The kg are then each divided by the analyzed sample weight to get the
% weights.
 The percent as received ash is then calculated
• AR Ash = (sum of six oxides)/(1 - % other as a percentage of ash)
• Other is the sum of SO3 + MgO + Na2O + P2O5 + Undetermined
• In situations where the Na2O content is great enough (0.20% of coal), it is
used in the ash calculation above.
9
Calibration Ranges
Ultimate
Range
Ash Oxides
Range % Coal
S
0-6%
SiO2
0-21%
C
30-80%
Al2O3
0-16%
H
3-8.5%
Fe2O3
0-6.5%
N
0.4-1.7%
CaO
0-16%
Cl
0-0.5%
K2O
0-1.1%
Moisture*
0-35%
TiO2
0-1.0%
Ash**
3-38.5%
Na2O
0-1.0%
* Moisture is determined from Moisture Gauge
** Ash is determined from the sum of ash oxides
No correlations exist between components
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Moisture Measurement
 Thermo uses microwave moisture gauges to measure the free
moisture in the coal.
 Total moisture is the sum of the free moisture plus the bound
moisture for the coal being analyzed.
 Moisture measurements are needed to:
• Determine the dry analysis values (PGNAA measures as received)
• To calculate the heat content of the coal
• To calculate the emissions potential as a function of heat content
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CV and emission calculations
 %Moisture % AR Ash 
CV  MAF CV  1 


100
100


 CV is calculated based on the
moisture ash free CV (MAF CV)
of the coals being analyzed.
 Lbs SO2/million Btu (in USA)
lbs SO2
20,000 % AR Sulfur

m illion Btu
AR Btu
 Or any empirical formula the
customer uses to measure
performance.
12
Information on Coal input by the customer
 The following coal parameters need to be input by the customer.
• Other Ash oxides
• MAF CV
• Bound Moisture
 COBOS Thermo’s coal blending software package will weight
average these values to allow the correct constants to be applied
to the analysis results.
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Analysis differences between PGNAA and Dual-gamma
analysis technologies
Dual-gamma ash gauge
PGNAA elemental gauge
Measures Elements that make up the ash
Measures average Atomic Number
Detector
Cf Source
neutrons
gamma rays
Am & either Ba
or Cs Source
NaI
Detector
PGNAA much less affected by composition differences
within the cross-sectional profile of coal on the conveyor
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