Calorimetry Techniques for Absolute Dosimetry of Laser-Driven Ion Beams

The use of ultra-short, intense laser pulses for the purposes of particle acceleration has been proposed for compact generation and delivery of energetic particle beams, and opened up interest in their applications in a biomedical context. Over the last number of years, such potential applications have triggered many large-scale research initiatives, with some focusing on the advancement of laser-driven ion acceleration as a possible form of cancer therapy. Particle therapy for the treatment of cancers has become a fairly well-established form of treatment within certain countries outside of the UK, but there is currently a strong interest involving the integration of this treatment protocol within cancer therapies in the UK. As a result, several centres are being developed both by the NHS and private investors in England. However, the large cost and size of these installations have led to a growth in interest for alternative approaches (including the aforementioned laser-driven technique). Laser accelerated ion beams display a number of distinct features including broad energy and angular distributions, and extremely high dose-rate per pulse.

Measurement of the absolute dose under such extreme conditions requires novel measuring techniques that are capable of doing so with high accuracy. Subsequently, calorimetry techniques which measure temperature rise resulting from particle irradiation in an absorber, have emerged as an ideal choice for the performance of dose characterisation in these circumstances. Calorimetric dosimeters are capable of providing measurements of the energy deposition by radiation directly, even when the process takes a few nanoseconds, unlike other detectors such as ionization chambers and Faraday cups. They also have the fundamental advantage of directly measuring the heat to which the absorbed dose degrades, without dependence on any coefficient of conversion, such as to ionization or to chemical yield. Calorimeters are already well-established primary standard level instruments within dosimetry, but their application to laser-driven beams is not trivial given the apparent time dependent and instantaneously inhomogeneous dose deposition patterns.

The aim of this project is to investigate the potential of calorimeters for dosimetry of laser-driven beams, extend the use of graphite calorimeters as a primary standard level instrument, and provide traceability for an emerging radiation modality aiming to revolutionize hadron-therapy and clinical practice. A calorimeter capable of providing meaningful, dose-rate independent measurements of ultra-short bursts of particles would be a development with significant hadron-therapy market potential. Doing so will involve taking part in experimental campaigns at both national and international facilities, contributing to develop simulations for modelling, and working in close contact with medial physicists. This project will involve not only carrying out research at the host university (QUB), but also at the partner organisation (NPL), with whom QUB has well established connections, particularly in relation to investigations of dosimetry and radiobiology applied to the context of laser-driven sources.