1. INSTITUTE OF NUCLEAR SCIENCE AND TECHNOLOGY
MASTERS THESIS DEFENCE Development of a Prompt Gamma Neutron Activation Analysis (PGNAA) system at the Institute of Nuclear Science and Technology (INST)
TOLLAH STEPHEN
S56/74427/12
Supervisors: 1. Mr. David Maina
2. Prof. David Chettle
3. Prof. Michael M. Gatari
INSTITUTE OF NUCLEAR SCIENCE AND TECHNOLOGY
UNIVERSITY OF NAIROBI
February, 2017

2. Multi-elemental analytical technique
PGNAA
Multi-elemental analytical technique 1 2
Non-destructive 3
Its sensitive to the entire periodic table 4
Possible for in-situ performance
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3. Principle neutron Radioactive decay Compound nucleus Target
Neutron capture
Radioactive decay
Compound nucleus
Target
Prompt gamma radiation(PGNAA)
Decay gamma radiation (NAA)
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4. Schematic setup for a PGNAA system based on INSPb S Ca Hg
Excited level Pb S C Hg O Mg Pb C C S O Mg Ca
Ground level Ca S Hg S O
HPGe detector
Data processing system
for prompt γ-ray
Neutron Source
Sample {(n, γ) reaction} 4
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5. Elements which decay too rapidly to be measured by DGNAA;
Elements with extremely high neutron capture cross-sections (H, B, C, Si, P, S and Cl) – applied to oil exploration
Applications
Elements which decay too rapidly to be measured by DGNAA;
Elements that produce only stable isotopes; or elements with weak decay gamma-ray intensities.
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6. Problem statement
Analysis of light and rare earth elements is a special challenge to the XRF techniques.
XRF techniques also require sample preparation which may cause contamination to sample.
NAA is insensitive to some important elements such as H, B, C, O, N, Si, P, S and Pb
Isotopic neutron source at INST has not been adequately utilized.
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7. Justifications The technique is non- destructive .
PGNAA provide a unique tool for the analysis of low-Z and rare earth elements 1
Aid in analysis of hydrogen content in Kenyan petroleum byproducts.
Complement NAA 2 3
The technique is non- destructive .
It does not require special sample preparation 4 5
New research filed in M. Physics at INST - analysis of boron content in biological samples & BNCT. 6
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8. Objectives General objective:
conduct a computational investigation into developing a PGNAA analysis tool for elemental analysis using the Am-Be neutron source at INST. The design tool used in this work is the MCNP5
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9. Specific Objectives To obtain the sensitivity and detection limits
To investigate the neutron energy distribution and flux emitted from the INST Am-Be neutron source
To model the response of the detection system.
To obtain the sensitivity and detection limits
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10. MCNP5 modelling and simulation of the PGNAA system

11. MCNP Code
MCNP is a general purpose Monte Carlo n-particle transport code used for neutron, photon and electron transport and interaction with matter as well as radiation protection and dosimetry
MCNP simulates the path of each particle from source to their death and tally specific aspects as specified by the user
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12. MCNP Setup TITLE CARD CELL CARDS SURFACE CARDS DATA CARDS
MCNP5 AmBe input deck, flux profiling
c the irradiation channel modelled in the center of the paraffin block.
c =========define cells================
$source
#1 #6 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19
$moderator material .
$tally at 24cm
c =============define surfaces================
rcc $ ambe source
rcc $port inner surface
rcc $tally13 
mode n
c ==========define materials==================
m $AmO2Be
imp:n r r $ 1, 19
c ===========source definition====================
sc1 Am-Be SPECTRUM (ISO 8529)
f4:n $tally neutrons
e4 5e
nps
MCNP Setup
TITLE CARD
CELL CARDS
SURFACE CARDS
DATA CARDS
Geometry specification
Geometry specification
Materials selection and properties
The location and characteristics of the neutron, photon, or electron source
Output desired (tallies )
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13. MCNP Setup CELL CARDS SURFACE CARDS
c =========define cells================
$source
#1 #6 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19
$moderator material .
$tally at 24cm
c =============define surfaces================
rcc $ ambe source
rcc $port inner surface
rcc $tally13 
MCNP Setup
Geometry specification
CELL CARDS
SURFACE CARDS
Geometry specification
cross sectional view of the Am-Be neutron source facility as modelled in MCNP5
vertical and
horizontal
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14. RESULTS AND DISCUSSIONS Neutron energy and flux distributions
MCNP5 geometry for Irradiation site1
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15. Neutron energy and flux distributions
MCNP5 geometry for Irradiation site2
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16. Neutron energy and flux distributions
Am-Be Neutron source
MCNP5 geometry for Irradiation site3
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17. Average neutron flux Irrad. sites Flux % flux %flux Site 1(0cm) 31.3
Flux
% flux
%flux
Site 1(0cm)
31.3
17.5
51.1
Site2 (5cm)
55.3
18.3
26.4
Site3(10cm)
69.3
14.5
16.2
Site4 (15cm)
71.3
13.7
14.9
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18. Neutron ratios Irrad. sites Site 1(0cm) 1.8 1.0 Site2 (5cm) 3.0 2.8
4.8
5.2
Site4 (15cm)
5.7
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19. Mncp5 PGNAA configurations
configuration A
configuration B
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20. -the boron showed a better response
Nuclide
Configuration A
Configuration B
Hydrogen
2.223
7.9912
17.762
Boron
0.478
3.1429
7.887
Carbon
1.261
0.0002
0.0006
Nitrogen
1.885
0.1086
0.1281
Silicon
3.539
0.0005
0.0003
Phosphorus
0.638
0.0029
0.0034
Elements
Detection limit (mg)
Configuration A
Configuration B
Hydrogen
10.71
5.48
Boron
21.96
10.0
Carbon
50,691
10,911
Nitrogen
142.2
215.5
Silicon
19,518.99
26,107
Phosphorus
8,243.7
9,077
-the boron showed a better response
Generally, the results obtained for sensitivity in this work are very low due to the low thermal flux at the sample position
- Detection limit were better in A for the first 3 elements
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21. Conclusions
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22. Conclusions…
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23. Wednesday, April 11, 2018