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Abstract
This work describes the studies and research activities performed to examine
the ability of nuclear techniques based on using radio-isotopic neutron and
gamma sources for detection of landmines and illicit materials. The thesis gives a brief description to the work plan towards Ph.D in nuclear physics, through the performance of experimental studies to develop nuclear techniques to detect landmines and illicit materials hidden inside cargo containers. The research activities were concerned with the development and construction of combined systems based on nuclear techniques for detection of buried landmines and illicit materials. These activities have succeed to construct and develop a landmine
detection system called ESCALAD, Egyptian SCAnning LAndmine Detector,
which combines two nuclear sensors based on measuring thermal neutron
backscattered and gamma rays emitted from the interactions of fast and thermal neutrons with the nuclei of the hidden object. As a complementary part of the work presented in this thesis, combined systems based on using gamma rays and neutrons to scan cargo containers and identify the suspected hidden objects are designed, constructed, and tested.
The ESCALAD system is based on using neutrons emitted from point isotopic source/sources to detect buried landmines by measuring the variation in hydrogen density and elemental ratios by neutron backscattering NBS and
neutron elemental analysis techniques. The NBS device detect landmines by the
recognition of hydrogen density variation between explosive material, a
landmine and its surroundings, soil and other scattered objects. The device
operates by irradiating the soil with fast neutrons (MeV) emitted from Pu-α-Be
source/sources and to measure the backscattered thermal neutrons by an array of gas detectors. These gas detector or thermal neutron detector monitors the low energy neutron flux coming back from the soil. The facility was equipped with two dimensional position sensitive thermal neutron detectors, electronic modules for calculating the position of the neutrons hit along the tubes with
respect to the position on the ground. The facility includes as well neutron
source/sources fast neutron scatterers reflectors gamma ray detector data
acquisition and analysis and electrical driven trolley to carry radiation sources and measuring devices facilities.
ESCALAD system workability was checked to detect landmines of different amount of explosives that are buried at different depths in soil of different roughness. Measurements were carried out at different scan speed for
landmines buried at different depths and side distances. The results obtained by NBS device are given in the form of two dimensional images of the scanned areas. Using the two dimensional distributions of measured thermal neutrons. A position with more concentration of hydrogen is indicated by hot spots with more or less circular area with higher neutron radiation intensity as compared to the surroundings. The measured detector response for gamma-rays resulting
from fast and thermal neutron interrogation are given as gamma ray spectra i.e. number of gamma photons/s against photon energy in keV within an energy range varies from 1 to 11400 keV. The net gamma spectra were analyzed for gamma energy lines emitted from the elements of explosive as indicator for the presence of explosive material, i.e. a landmine.
The detection of illicit materials was performed using low cost combined
systems. The combined systems are composed of a scanner applying gammarays
emitted from 60Co source and material identifier based on using neutrons of
continuous energy to distinguish the suspected object through elemental analysis by fast and thermal neutron interrogations. These two devices which are installed to locate and distinguish the hidden illicit materials in cargo containers are described and discussed. The systems include as well especially mechanical system to move the inspected container between the radiation sources and detector. The mechanical system is equipped with an electrical controller unit to adjust the movement increment of the inspected container and time of
measurement. The obtained results are presented in the form of 2D image for the suspected object and in the form of displayed gamma spectrum for gamma-rays
emitted from the suspected objects by neutron interrogation analysis. The
constructed 2D images and gamma-ray spectra measured for different hidden
illicit materials clearly indicate that the system is of low scanning cost, very fast and efficient for detecting contraband screened by steel shield of 1cm thick. In addition, the system weight is very low compared with other scanners and therefore can be used as mobile or fixed system and can be easily installed at different locations.