A cylindrical silicon-on-insulator microdosimeter: charge collection characteristics

A novel silicon-on-insulator microdosimeter for estimating the radiobiolgical effectiveness (RBE) of a mixed radiation field is presented. An ion beam induced charge collection study has confirmed the microdosimeter possesses well defined micron sized 3D cylindrical sensitive volumes. An array of these SVs has the capabilitiy of studying the track structure of high energy heavy ions typical of a deep space environment

3D silicon microdosimetry and RBE study using C-12 ion of different energies

This paper presents a new version of the 3D mesa "bridge" microdosimeter comprised of an array of 4248 silicon cells fabricated on 10 µm thick silicon-on-insulator substrate. This microdosimeter has been designed to overcome limitations existing in previous generation silicon microdosimeters and it provides well-defined sensitive volumes and high spatial resolution. The charge collection characteristics of the new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe, utilizing 5.5 MeV He2+ ions. Measurement of microdosimetric quantities allowed for the determination of the Relative Biological Effectiveness of 290 MeV/u and 350 MeV/u 12C heavy ion therapy beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. The microdosimetric RBE obtained showed good agreement with the tissue-equivalent proportional counter. Utilizing the high spatial resolution of the SOI microdosimeter, the LET spectra for 70 MeV 12C+6 ions, like those present at the distal edge of 290 and 350 MeV/u beams, were obtained as the ions passed through thin layers of polyethylene film. This microdosimeter can provide useful information about the lineal energy transfer (LET) spectra downstream of the protective layers used for shielding of electronic devices for single event upset prediction

Thin Silicon Microdosimeter utilizing 3D MEMS Fabrication Technology: Charge Collection Study and its application in mixed radiation fields

New 10-μm-thick silicon microdosimeters utilizing 3-D technology have been developed and investigated in this paper. The TCAD simulations were carried out to understand the electrical properties of the microdosimeters\u27 design. A charge collection study of the devices was performed using 5.5-MeV He2+ ions which were raster scanned over the surface of the detectors and the charge collection median energy maps were obtained and the detection yield was also evaluated. The devices were tested in a 290 MeV/u carbon ion beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in Japan. Based on the microdosimetric measurements, the quality factor and dose equivalent out of field were obtained in a mixed radiation field mimicking the radiation environment for spacecraft in deep space

Silicon on insulator microdosimetry for radiation protection in mixed radiation fields for aviation and space dosimetry

Radiation protection is used for determining the doses received by persons from avariety of sources. The recommendations for external radiation protection were outlined in ICRP Publication 51 and ICRP Publication 60. There is a growing need to measure the doses received from extraterrestrial sources at high altitudes. In the European Union (EU), flight staff are already classified as radiation workers following the European Commission Council Directive 96/29/EURATOM of 13 May 1996 defining the need for the exposure of the airline crew to the elevated levels of radiation to be monitored. The radiation exposure from a mixed source can be measured using a regional microdosimetric approach. The advantage of this approach is that a priori knowledge of the type of radiation is not required. The microdosimetric approach studied in this thesis is a solid state approach to microdosimetry using a Silicon on Insulator (SOI) design. The SOI Microdosimeter is advantageous over conventional low pressure gas chamber microdosimetry in that it does not require a constant supply of tissue equivalent gas or high voltages to operate and is physically small in size. The mixed radiation fields tested in this dissertation are mixed neutron gamma sources (252Cf, PuBe), the CERN-EU High Energy Reference Facility (CERF) field and the quasi-monoenergetic neutron source at Uppsala University

Proton beam characterisation of a prototype thin-tile plastic scintillator detector with SiPM readout for use in fast-neutron tracker

We present details of the construction and characterisation of a prototype thin-tile plastic scintillation detector for use in a multi-layer Fast Neutron Tracker. Scintillation light is read out using solid-state silicon photomultiplier detectors (SiPMs). The Tracker consists of alternating scintillator and Timepix detector layers. The scintillator tile provides a hydrogen-rich target, in which impinging fast neutrons produce recoil protons. The energies lost by protons in the plastic scintillator are measured and recoil protons exiting the scintillator are tracked in the Timepix detector. The combination of signals from the scintillator and Timepix provides information to reconstruct the energy or direction of the impinging neutron, using calculations based on the kinematics of the elastic neutron scattering. Three prototype scintillation detectors were constructed, using either a pair of 3 × 3 mm sensitive area SPMMicro3035 SiPMs from SensL or a pair of MAPD-3n SiPMs from Zecotek. The detector performances were characterised using a mono-energetic proton beam. An absolute energy calibration was measured at 3, 4 and 5 MeV proton energies with good linearity. The best measured energy resolution was 29.8% at 5 MeV. Spatial uniformity was assessed by measuring the response across the detector face. Finally, the tile detector\u27s ability to provide a trigger for Timepix acquisition in the stack configuration was demonstrated for single and double neutron recoil events using a DT neutron source. The SiPM-based design was found to be well-suited for the application of the multi-layer fast neutron tracker

Characterization of prompt gamma rays for in-vivo range verification in hadron therapy: A Geant4 simulation study

Prompt gamma (PG) rays have been proposed for in-vivo beam range verification during treatment delivery. As a secondary by-product emitted almost instantaneously upon ion-nuclear interaction, PG rays offer real-time tracking of the Bragg peak (BP). However their detection is challenging since they have a broad energy spectrum with interference from neutrons and stray gamma rays. Numerous approaches have been proposed to utilise PG for in-vivo beam range verification. In this work, Geant4 Monte Carlo (MC) simulations have been used to study the spectral, spatial, temporal and angular distribution characteristics of PG emission and detection from hadron radiation fields of varying energy. Proton, 12 C and 4 He beams irradiated homogeneous water phantoms. These studies will provide valuable information for the development of clinically suitable and reliable PG detector systems

Characterization of prompt gamma ray emission for in vivo range verification in particle therapy: A simulation study

In this paper we investigate the emission and detection characteristics of prompt gamma (PG) rays for in vivo range verification during hadron therapy, using Geant4 simulations. Proton, 4 He and 12 C beams of varying energy are incident on water phantoms. The PG production yield, energy spectral characteristics and spatial correlation with the Bragg Peak (BP) have been quantified. Further, the angular distributions for PG detection with respect to a point-of-reference on the phantom surface have been explored. The temporal properties of PG emission and time-of-flight (TOF) of PG detection have also been investigated in correlation with the changing particle beam range. Our results show that the primary PG rays from nuclear interactions of the primary beam exhibit the closest correlation to the beam range but its signal is significantly masked by the concurrent secondary PG rays, particularly for heavier ions such as carbon ion beams. The PG TOF spectroscopy encodes the essential information of the beam range but requires high time resolution measurements to retrieve it. A hybrid PG detection system to utilize the energy, timing and spatial characteristics of PG rays is desirable for BP tracking in real-time

Silicon Microdosimetry in Heterogeneous Materials: Simulation and Experiment

Microdosimetry spectra obtained experimentally utilizing a Silicon-On-Insulator (SOI) microdosimeter within biological materials, was used to provide information on secondary radiation spectra at tissue boundaries. Comparative GEANT4 simulations of the experimental conditions were also conducted

Tissue equivalence correction in silicon microdosimetry for protons characteristic of the LEO Space Environment

The tissue equivalence of solid state silicon detectors in proton radiation fields was determined to improve the radiation protection applications of silicon detectors in aviation and space missions. The study was performed by means of Geant4 simulations. Results are presented showing that a simple geometrical scaling factor (~0.56) of linear dimensions is adequate to convert experimentally obtained microdosimetric energy deposition spectra in silicon to equivalent microdosimetric energy deposition spectra in water