Neutron dosimetry and spectrometry in complex radiation fields using CR-39 track detectors

The CR-39 track detector, also known as Solid State Nuclear Track Detector (SSNTD) or even PADC (poly(allyl diglycol carbonate)) is extensively used for radiation dosimetry. Its tissue equivalent polymer, with chemical composition of C12H18O7, makes it an excellent dosimeter for assessing the dose equivalent, expressed in Sieverts (Sv), from stray fast neutrons in complex radiation fields. In this scope, a novel technique for neutron dosimetry has been developed based on LET spectrometry for measuring absorbed dose and dose equivalent from fast neutrons using CR-39 detectors. Indeed the Politrack automated reader can be successfully used to measure the particle's lineal energy by measuring the track image parameters to obtain the LETnc, which is intrinsic to the energy deposited along the track length of the particle inside the first 10-15 µm of the CR-39 track detector. The LETnc can be used as a first order approximation of the unrestricted LET of the particle within a given range of particle energy, charge and mass. This range of particle LET within which the LETnc technique is valid has been demonstrated in this thesis focusing on the characterisation of CR-39 in energetic carbon beams. In addition, the thesis focuses the application of the LETnc technique for fast neutron dosimetry. For practical applications, the LETnc can be used to derive a good approximation of the ambient dose equivalent and the personal dose equivalent. The dosimeter is realised by coupling the CR-39 SSNTD, primarily made of polyallyl diglycol carbonate (PADC) to a 10 mm PMMA (composition C5O2H8) radiator. The thickness of 10 mm is used so as to have a first order approximation of the Hp(10) dose equivalent defined by the ICRP 60 recommendations. Furthermore, due to the sub-micron spatial resolution of the CR-39 for particle tracking, an imaging technique has been developed based on the Politrack system in order to reconstruct and measure neutron beam profiles.