The Centre for Medical Radiation Physics introduced the concept of Silicon On Insulator (SOI) microdosimeters with 3-Dimensional (3D) cylindrical sensitive volumes (SVs) mimicking the dimensions of cells in an array. Several designs of high-definition 3D SVs fabricated using 3D MEMS technology were implemented. 3D SVs were fabricated in different sizes and configurations with diameters between 18 and 30 µm, thicknesses of 2–50 µm and at a pitch of 50 µm in matrices with volumes of 20 × 20 and 50 × 50. SVs were segmented into sub-arrays to reduce capacitance and avoid pile up in high-dose rate pencil beam scanning applications. Detailed TCAD simulations and charge collection studies in individual SVs have been performed. The microdosimetry probe (MicroPlus) is composed of the silicon microdosimeter and low-noise front–end readout electronics housed in a PMMA waterproof sheath that allows measurements of lineal energies as low as 0.4 keV/µm in water or PMMA. Microdosimetric quantities measured with SOI microdosimeters and the MicroPlus probe were used to evaluate the relative biological effectiveness (RBE) of heavy ions and protons delivered by pencil-beam scanning and passive scattering systems in different particle therapy centres. The 3D detectors and MicroPlus probe developed for microdosimetry have the potential to provide confidence in the delivery of RBE optimized particle therapy when introduced into routine clinical practice.

Despite the low contribution of heavy ions to the total fluence in the space radiation environment, their radiobiological effect on the human body is extremely high. In this article, we investigated the radiation field which resulted from the interaction of galactic cosmic rays (GCRs), specifically some heavy ions and energies, typically encountered in space with a realistic multilayer sample of the International Space Station (ISS) Columbus module's shielding wall. The quality factor, Q, and the normalized dose equivalent, H, derived from microdosimetric measurements for C, Ne, and Si ions behind different spacecraft wall configurations and materials are presented in this article. Particularly, carbon fiber, polyoxymethylene, and perspex with same areal density compared to currently used aluminum were investigated.

The responses of two silicon on insulator (SOI) 3D microdosimeters developed by the Centre for Medical Radiation Physics (CMRP) were investigated with a range of different low energy ions, with high linear energy transfer (LET). The two microdosimeters n-SOI and p-SOI were able to measure the LET of different ions including 7Li, 12C, 16O and 48Ti with ranges below 350 μm in silicon. No plasma effects were seen in the SOI microdosimeters when irradiated with the high LET ions. A Monte Carlo simulation using Geant4 was compared to the experimental measurements, whereby some discrepancies were observed for heavier ions at lower energies. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and overlayers of the devices. The microdosimetric measurements of low energy 16O ions were obtained and compared to a therapeutic 16O ion beam. The radiation hardness of the two devices was studied using the Ion Beam Induced Charge Collection technique (IBIC). Both types of microdosimeters when biased had no essential changes in charge collection efficiency (CCE) in the SV after irradiation with low energy ions.

This article presents a study of the response of the silicon on insulator (SOI) microdosimeter with 3-D sensitive volumes (SVs) to 400 MeV/u ¹⁶ O and 500 MeV/u ⁵⁶ Fe ions mimicking galactic cosmic rays outside and inside the International Space Station (ISS). An average quality factor (Q̅) and the dose equivalent (H) of the radiation field were obtained experimentally, and the results were compared with GEANT4 simulations.

We performed a systematic study involving simulation and experimental techniques to develop induced-junction silicon photodetectors passivated with thermally grown SiO₂ and plasma-enhanced chemical vapor deposited (PECVD) SiN_x thin films that show a record high quantum efficiency. We investigated PECVD SiN_x passivation and optimized the film deposition conditions to minimize the recombination losses at the silicon–dielectric interface as well as optical losses. Depositions with varied process parameters were carried out on test samples, followed by measurements of minority carrier lifetime, fixed charge density, and optical absorbance and reflectance. Subsequently, the surface recombination velocity, which is the limiting factor for internal quantum deficiency (IQD), was obtained for different film depositions via 2D simulations where the measured effective lifetime, fixed charge density, and substrate parameters were used as input. The quantum deficiency of induced-junction photodiodes that would be fabricated with a surface passivation of given characteristics was then estimated using improved 3D simulation models. A batch of induced-junction photodiodes was fabricated based on the passivation optimizations performed on test samples and predictions of simulations. Photodiodes passivated with PECVD SiN_x film as well as with a stack of thermally grown SiO₂ and PECVD SiN_x films were fabricated. The photodiodes were assembled as light-trap detector with 7-reflections and their efficiency was tested with respect to a reference Predictable Quantum Efficient Detector (PQED) of known external quantum deficiency. The preliminary measurement results show that PQEDs based on our improved photodiodes passivated with stack of SiO₂/SiN_x have negligible quantum deficiencies with IQDs down to 1 ppm within 30 ppm measurement uncertainty.

The response of a 5 lm thin silicon on insulator (SOI) 3D microdosimeter was investigated for single event upset applications by measuring the LET of different high LET ions. The charge collection characteristics of the device was performed using the Ion Beam Induced Charge collection (IBIC) technique with 3 and 5.5 MeV He2+ ions incident on the microdosimeter. The microdosimeter was irradiated with 16O, 56Fe and 124Xe ions and was able to determine the LET within 5% for most configurations apart from 124Xe. It was observed that on average, measured LET was 12% lower for 30 MeV/u 124Xe ion traversing through different thickness Kapton absorbers in comparison to Geant4 simulations. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and thickness of the SOI layer of the devices. The effects of overlayer thickness variation is not easy observed for ions with much lower LET as O and Fe. Based on that it is difficult to make conclusion that plasma effect is observed for 30 MeV/u 124Xe ions and further research to be carried out for ion with LET higher than 12 MeV/µm.