Ph.D. degree thesis
UniversitÓ degli Studi di Milano and INFN, Milan, Italy, in 2010
Supervisor: Grazia Gambarini
Development of Detectors for Dosimetry and Spectrometry in BNCT Epithermal Neutron Fields
Neutron detectors (cold, thermal, fast neutrons)
Micropattern gaseous detectors (MSGC, GEM, THGEM, RETHGEM, MICROMEGAS, InGrid, etc)
Solid state detectors
The work described in this thesis has been devoted to several physical topics concerning BNCT, an experimental radiotherapy method that makes use of neutron beams. Studies regarding the neutron transport, the interaction with water equivalent materials and
the spectral variations of a neutron beam with energies until few tens of MeV have
been carried out. Dosimetric methods that enable to perform reliable measurements in BNCT fields are still under development.
This thesis concerns the development of radiation detectors for dosimetry and spectrometry in BNCT neutron fields. The first part is devoted to the development of radiochromic gel dosimeters, that are based on Fricke solutions and are manufactured in the laboratory in form of layers. FGLDs (Fricke Gel Layer Dosimeters) can provide bidimensional images of the different dose components absorbed in a water equivalent material. A procedure
was studied for measuring 2D spatial distributions of all secondary radiation doses
in neutron fields by means of gel dosimeters of suitable isotopic composition. FGLDs were used for the characterization of the neutron source a BNCT facility. Detailed Monte Carlo (MC) calculations, simulating in-phantom neutron transport and dose absorption, were performed by means of the MCNP5 code.
In BNCT, reliable measurements of neutron spectrum and spatial resolution would be therefore very important for accurate treatment planning. To this purpose, the second part of the research activity described in this thesis concerns the development of a novel neutron spectrometer with imaging capability, consisting of a neutron moderator, a neutron-to-charged particles converter and a gaseous detector based on Thick Gas Electron Multiplier
(THGEM) electrodes. The gaseous detector was characterized and optimized at the Weizmann Institute of Physics.
The spectrometer prototype was designed and built, assembling together a gas detector, a neutron converter and a set of moderators. The detector response functions and imaging performance were evaluated by means of MC simulations and irradiating the detector in reference neutron fields at PTB in Braunschweig.