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Title: Back scatter imaging with megavoltage radiation
Author: Ulmer, Bernd
ISNI:       0000 0001 3540 8709
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1998
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This thesis presents a novel radiographic technique for imaging radiographically dense materials using photon-induced positron annihilation radiation (PIPAR). Back-scattering experiments with X-ray tubes have been carried out to show the principal limitations of the Compton back-scatter imaging. The results are compared with simulations with the EGS4 Monte-Carlo code and generally good agreement is obtained. Simulations of higher incident energies (up to 10 MeV) show a rapid increase of the single to total scatter ratio (S/T) by extracting the 511 keV annihilation line. This new PIPAR technique extends significantly the inspection depth of materials which may be investigated with gamma rays in the reflection geometry. EGS4 simulations of the PIPAR principle have been carried out to optimize the relevant parameters for the use of a PIPAR scanner. A possible radiation source and detector system are discussed and a scanner for use in the field is proposed. The maximum inspection depths for a cavity in sand, water and concrete are estimated. Preliminary experimental results showing the feasibility of PIPAR imaging are presented in this work. These were obtained with megavoltage radiation from a linear accelerator exciting positrons in elemental samples through the pair production effect. The 511 keV annihilation line was extracted from the back-scattered radiation using a plastic scintillator detector and a difference filter technique. The experimental arrangement is described and potential applications are briefly discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nuclear physics & particle accelerators