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

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 Wednesday, April 11, 2018

Principle neutron Radioactive decay Compound nucleus Target Neutron capture Radioactive decay Compound nucleus   Target     Prompt gamma radiation(PGNAA)     Decay gamma radiation (NAA) Wednesday, April 11, 2018

Schematic setup for a PGNAA system based on INS Pb 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 Wednesday, April 11, 2018

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. Wednesday, April 11, 2018

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. Wednesday, April 11, 2018

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 Wednesday, April 11, 2018

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 Wednesday, April 11, 2018

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 Wednesday, April 11, 2018

MCNP5 modelling and simulation of the PGNAA system  

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 Wednesday, April 11, 2018

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================ 1 0 -1 $source 2 5 -0.001205 -2 #1 #6 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19 3 3 -0.93 -3 6 $moderator material . 19 5 -0.001205 -18 $tally at 24cm c =============define surfaces================ 1 rcc 0 0 -2.5 0 0 5 1.5 $ ambe source 2 rcc 0 0 -2.52 0 0 30 1.6 $port inner surface 18 rcc 0 0 26.51 0 0 0.3 1.5 $tally13  mode n c ==========define materials================== m1 95241. 0.08 8016. 0.001 4009. 0.909 $AmO2Be imp:n 1 3r 0 1 13r $ 1, 19 c ===========source definition==================== sc1 Am-Be SPECTRUM (ISO 8529) f4:n 6 8 9 10 11 12 13 14 15 16 17 18 19 $tally neutrons e4 5e-7 .5 12 nps 5000000 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 ) Wednesday, April 11, 2018

MCNP Setup CELL CARDS SURFACE CARDS c =========define cells================ 1 0 -1 $source 2 5 -0.001205 -2 #1 #6 #8 #9 #10 #11 #12 #13 #14 #15 #16 #17 #18 #19 3 3 -0.93 -3 6 $moderator material . 19 5 -0.001205 -18 $tally at 24cm c =============define surfaces================ 1 rcc 0 0 -2.5 0 0 5 1.5 $ ambe source 2 rcc 0 0 -2.52 0 0 30 1.6 $port inner surface 18 rcc 0 0 26.51 0 0 0.3 1.5 $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 Wednesday, April 11, 2018

RESULTS AND DISCUSSIONS Neutron energy and flux distributions MCNP5 geometry for Irradiation site1 Wednesday, April 11, 2018

Neutron energy and flux distributions MCNP5 geometry for Irradiation site2 Wednesday, April 11, 2018

Neutron energy and flux distributions Am-Be Neutron source MCNP5 geometry for Irradiation site3 Wednesday, April 11, 2018

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 Wednesday, April 11, 2018

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 Wednesday, April 11, 2018

Mncp5 PGNAA configurations configuration A configuration B Wednesday, April 11, 2018

-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 Wednesday, April 11, 2018

Conclusions   Wednesday, April 11, 2018

Conclusions…   Wednesday, April 11, 2018

Wednesday, April 11, 2018