Ph.d. degree
Università degli Studi di Napoli Federico II - Italy, 2019

Pierluigi Casolaro

Supervisor: Luigi Campajola

Innovative detection methods for radiation hardness

Keywords:

• Dosimetry concepts and apparatus
• Radiation monitoring
• Radiation damage monitoring systems
• Neutron detectors (cold, thermal, fast neutrons)

Abstract:

This PhD thesis focuses on the development of new techniques of radiation detection in Radiation Hardness Assurance tests. The effects of radiation on a material or electronic component are reproduced with many types of radiation such as X-ray, gamma-ray, charged particle and neutron. Each test is specific and demands for dedicated instrumentation for the correct delivery of the dose on the device under test. Radiochromic films are suited for these applications being non-invasive dosimeters sensitive in a wide dose range from 10^-3 to 10^5 Gy. The response of radiochromic films to the dose was investigated and found to be independent of the type, energy and dose rate. The physical law that describe the phenomenon of the film darkening was determined for the first time and used as the absolute calibration function for all radiochromic film types. The use of radiochromic films in the practice is constrained by the impossibility of performing real-time dosimetry with standard methods. In order to overcome this important limitation, a new real-time dosimeter based on radiochromic films and opto-electronic instrumentation with optical fibres has been developed and results reported in this thesis. The new dosimeter allows for precise and accurate dosimetry through the real-time analysis of the spectral response of the films. It also allows the extension of the dynamic range of commercial radiochromic films by more than one order of magnitude. Owing to the numerous advantages compared to commercial technologies, this invention was patented in 2019. Neutron irradiations of materials and electronics are of crucial importance for specific tests of radiation hardness. Methods for the production of well-characterized fast neutron beams (both quasi-mono-energetic and continuous spectrum) with charged particle accelerators are discussed. A beam line for fast neutrons, in particular, was implemented, for the first time, at the medical cyclotron of University of Bern. Furthermore, this thesis reports on the characterization of a new detector prototype for fast neutrons based on silicone rubbers. The innovative techniques of radiation detection proposed in this thesis can exploited also in domains other than the radiation hardness. As an example, the new real-time dosimeter based on radiochromic films and optical fibres can be used as a dosimeter for quality assurance in radiotherapy applications; also, the miniaturization of the present prototype can pave the way to challenging applications such as in-vivo dosimetry.