Development and Flight Results from the C3D2 Imager Payload on AlSat Nano

An experimental CubeSat camera system using 3 separate CMOS imagers was flown in 2014 on UKube-1. In response to an announcement opportunity in December 2014, we proposed an upgrade to our C3D imager payload, which was accepted to fly on AlSat Nano. Launched in September 2016 the system has been operational for over 1 year and has returned both images and housekeeping data, including detailed temperature and radiation dosimetry measurements. Through these in-orbit demonstrations on CubeSans, the image sensors and payload have attained TRL9, and these are now being used in other flight opportunities. In this paper we describe the C3D imager payload, which comprises 3 independent CMOS image sensors used in different camera systems; two wide field cameras are specifically optimised with one to observe the Earth from the 650 km orbit, and the other with its focus set to 40 cm to observe a deployable boom from the CubeSat. The experiment controller also contained thermometry and two RADFET dosimeters, one located on the payload, with the other deployed at a different point on the spacecraft. In this paper we will describe the experiment design and operational performance, and review the in-orbit data obtained during the operations covering over 17 months in-orbit, in addition to discussing lessons learned from the flight experience. We also discuss further developments of the payload concept which we are currently working on toward future flight opportunities

Development and characterization of sensitive, energy-independent solid-state photon dosemeters with high spatial and temporal resolution. Applications in clinical radiology and radiation protection.

AbstractModern medicine and health care rely on a variety of diagnostic and therapeutic equipment and methods that involve ionizing radiation. To guarantee quality and the safety of patients and staff, advanced radiation detectors and dosemeters are needed that have low energy and operate with directional independence for X-ray and γ-ray photons. Similar instruments are also of great importance for measurements used in radiation protection and safety outside of hospitals and the health care sector and for nuclear and radiological emergencies. In this thesis, new sensors, detectors, and dosemeters based on silicon were designed, manufactured, characterized, and tested. The aim was to develop dosemeters with signals that are as independent as possible of the energy and direction of the incoming X-ray and γ-ray photons. Starting with a 350 µm silicon wafer, a sensor was constructed with electrical contacts on one side only. A flex card was adapted with anisotropic conductive adhesive (ACA) and mounted to the sensor. Since all components have low X-ray attenuation, the disturbance of the radiation field by the detector is minimal from all directions. Another important component is the metal filter encapsulating the silicon detector. Made of stainless steel, this encompassing filter compensates for the energy and directional variation of sensitivity of the silicon detector. The filter was designed using a series of Monte Carlo calculations. The hole pattern was selected so that the signal (proportional to the absorbed dose) was independent of the X-ray source position (in 4π). Due to the small structures, additive manufacturing (AM) in the form of metal 3D printing was needed to fabricate the filter. The functionality of the 4π dosemeter was verified by simulation to meet the quality criterion that the energy dependence is less than 5% for the IEC beam qualities RQR and RQT in the range 65–145 kV. The best way to microfabricate the sensor, sensor holder, flex card, and energy filter was evaluated and a method to control its mounting accuracy is proposed. The application of silicon detectors in radiology (CT, CBCT, and planar radiography) was tested, and a specific dosemeter construction also was tested for eye lens dosimetry and for emergency situations. To broaden the use of silicon detectors in future medical imaging and dosimetry applications, an overview of silicon photomultipliers (SiPM) for this area is included and a learning and training program targeted to graduate students is described

The Highly Miniaturised Radiation Monitor

We present the design and preliminary calibration results of a novel highly miniaturised particle radiation monitor (HMRM) for spacecraft use. The HMRM device comprises a telescopic configuration of active pixel sensors enclosed in a titanium shield, with an estimated total mass of 52 g and volume of 15 cm$^3$. The monitor is intended to provide real-time dosimetry and identification of energetic charged particles in fluxes of up to 10$^8$ cm$^{-2}$ s$^{-1}$ (omnidirectional). Achieving this capability with such a small instrument could open new prospects for radiation detection in space.Comment: 17 pages, 15 figure

Proton-counting radiography for proton therapy: a proof of principle using CMOS APS technology

Despite the early recognition of the potential of proton imaging to assist proton therapy (Cormack 1963 J. Appl. Phys. 34 2722), the modality is still removed from clinical practice, with various approaches in development. For proton-counting radiography applications such as computed tomography (CT), the water-equivalent-path-length that each proton has travelled through an imaged object must be inferred. Typically, scintillator-based technology has been used in various energy/range telescope designs. Here we propose a very different alternative of using radiation-hard CMOS active pixel sensor technology. The ability of such a sensor to resolve the passage of individual protons in a therapy beam has not been previously shown. Here, such capability is demonstrated using a 36 MeV cyclotron beam (University of Birmingham Cyclotron, Birmingham, UK) and a 200 MeV clinical radiotherapy beam (iThemba LABS, Cape Town, SA). The feasibility of tracking individual protons through multiple CMOS layers is also demonstrated using a two-layer stack of sensors. The chief advantages of this solution are the spatial discrimination of events intrinsic to pixelated sensors, combined with the potential provision of information on both the range and residual energy of a proton. The challenges in developing a practical system are discussed

Radiation-induced Nanoparticle Formation as Novel Means of in Vivo / in Vitro Dosimetry

abstract: Rapid development of new technology has significantly disrupted the way radiotherapy is planned and delivered. These processes involve delivering high radiation doses to the target tumor while minimizing dose to the surrounding healthy tissue. However, with rapid implementation of these new technologies, there is a need for the detection of prescribed ionizing radiation for radioprotection of the patient and quality assurance of the technique employed. Most available clinical sensors are subjected to various limitations including requirement of extensive training, loss of readout with sequential measurements, sensitivity to light and post-irradiation wait time prior to analysis. Considering these disadvantages, there is still a need for a sensor that can be fabricated with ease and still operate effectively in predicting the delivered radiation dose. The dissertation discusses the development of a sensor that changes color upon exposure to therapeutic levels of ionizing radiation used during routine radiotherapy. The underlying principle behind the sensor is based on the formation of gold nanoparticles from its colorless precursor salt solution upon exposure to ionizing radiation. Exposure to ionizing radiation generates free radicals which reduce ionic gold to its zerovalent gold form which further nucleate and mature into nanoparticles. The generation of these nanoparticles render a change in color from colorless to a maroon/pink depending on the intensity of incident ionizing radiation. The shade and the intensity of the color developed is used to quantitatively and qualitatively predict the prescribed radiation dose. The dissertation further describes the applicability of sensor to detect a wide range of ionizing radiation including high energy photons, protons, electrons and emissions from radioactive isotopes while remaining insensitive to non-ionizing radiation. The sensor was further augmented with a capability to differentiate regions that are irradiated and non-irradiated in two dimensions. The dissertation further describes the ability of the sensor to predict dose deposition in all three dimensions. The efficacy of the sensor to predict the prescribed dose delivered to canine patients undergoing radiotherapy was also demonstrated. All these taken together demonstrate the potential of this technology to be translatable to the clinic to ensure patient safety during routine radiotherapy.Dissertation/ThesisDoctoral Dissertation Chemical Engineering 201