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Title: Studies in medical neutron physics
Author: Miola, Ueber Jose
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1982
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The first part of the thesis deals with new applications of neutron and nuclear physics to the detection and measurement of trace quantities of toxic elements, silicon and beryllium in human lungs. Reaction 28Si (n,n'gamma)28 Si has been used to measure small quantities of silicon in an anthropomorphic lung phantom. A satisfactory suppression of interferences from aluminium present in the experimental equipment from phosphorus present in the body and from hydrogen capture Compton continuum, was achieved with the use of pulsed neutron beams of energy in the range 5--10 MeV, The 2a detection limit, predicted on the basis of extrapolation of experimental results, is 150 mg of Si for a dose of 0.01 Sv, assuming the use of six Ge(Li) detectors, each having efficiency of 35%. The thesis gives also an account of experiments on build-up and decay of thermal neutron flux in small moderators exposed to bursts of fast neutrons, of energy 2.5 and 14 MeV. The technique of detection of beryllium in vivo utilized very low threshold of Be for photodisintegration. The photoneutrons, following a burst of bremsstrahlung with maximum energy not exceeding 2.220 MeV, are thermalized and either detected by a large array of BF3 detectors or captured by nuclei of hydrogen in the body and in the external moderator, so that the hydrogen capture radiation can be recorded. For a dose of 5 cGy this technique may lead to a detection sensitivity (2a) of 50--120 micrograms of Be. The second part of the thesis describes the technique of lyoluminescence dosimetry applied to the fast neutron beams. After analysis of factors affecting accuracy, precision and reproducibility of neutron dosimetry for gamma radiation fields, which have been tested in a series of international comparisons with other dosimetric techniques sponsored by IAEA, the results of in-house comparison with TLD are also included. Lyoluminescent phosphors, mannose and glutamine, have shown better reproducibility than individually calibrated TLD chips. Amino acids, isoleucine and valine are shown to be particularly good Lyo-luminescence phosphors for fast neutron beams, isoleucine having energy response very closely approximating that of ICRU muscle. The energy and dose responses of mannose, glutamine, valine and leucine were measured in the neutron energy range from about 1 MeV to 15 MeV. In addition, the thesis gives information on the use of lyoluminescent phosphors containing 6Li in the mapping of thermalized neutron radiation fields. It is suggested that lyoluminescent dosimeters can be used for mailed dosimeter intercomparisons between radiotherapy centres. One of the appendices to the thesis gives information on the properties and development of a neutron target based on 7LiD, intended for use on low energy cyclotrons accelerating deuteron beams.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available