The goal of this project is to enhance the recently demonstrated concept of electron-tracking based Compton imaging of gamma radiation. This concept promises to increase the detection, localization, and characterization capabilities for nuclear security but also in other areas such as biomedical imaging or astrophysics. Our approach is based on high-resolution Si-based charge-coupled device (CCD) sensors which provides sufficient resolution to determine the initial direction of the electron that was scattered by means of the Compton scattering process. This enables the reconstruction of incident gamma rays on event-by-event basis without using a sensitivity-limiting collimator. The combination of Si and a pixel size of 10 um enables both sufficient position resolution to determine the incident direction and efficiency to induce the Compton scattering process. This project specifically aims at systematically evaluate and enhance the current implementation in terms of hardware and software. Preliminary algorithms to track the electron and to perform image reconstruction have been developed which can be improved by taking into account more details of the features that can be observed and by correlating the electron and gamma-ray information. The slow frame rate of the CCD approach is currently limiting the event-to-event reconstruction. We will implement the strip readout of the CCD to enable the event-to-event reconstruction of the electron track and the associated gamma ray and demonstrate electron-tracking-based Compton imaging in real time.
The goal of this project is the demonstration of a new concept in radiation detection that enables potentially significant increased capabilities in the detection, localization, and characterization of nuclear materials. Recent and ongoing developments of very-high-resolution Si sensors can be used to measure details of interaction processes that can be used to gain more information to reconstruct gamma radiation. Applications can be envisioned in homeland security, nuclear non-proliferation and international safeguards, biomedical imaging as well as astrophysics and nuclear physics. The project will provide the excellent training of young scientists.
Compton-scatter based gamma-ray imaging was recently demonstrated to be a highly sensitive tool in the detection of small amounts of nuclear materials. It provides the ability to detect, identify, and localize weakly emitting sources in the midst of natural and man-made backgrounds and background fluctuations. Semi-conductor based Compton imaging provides excellent energy and image resolution with superior capabilities e.g. for standoff detection and in complex radiation fields as compared with other imaging or non-imaging instruments. However, current implementations fail to track the Compton-scattered electron within the detector introducing an uncertainty in the direction of the incident photon, which ultimately limits signal-to-background contrast in the final reconstructed images. In comparison, the ability to measure the electron-track within the detector allows the direction of the incident gamma ray to be determined on an event-by-event basis, and thereby maximizes the achievable signal-to-background ratio. Thie work perfomed in this project aims at the continuation and expansion of our program to develop and demonstrate electron-tracking based Compton imaging for Homeland-Security specific applications. Recently, we demonstrated – for the first time - the feasibility of this concept employing a high-resolution Charge-Coupled Device (CCD). Over the one-year funding cycle by NSF, we have refined experiments, data analysis schemes, and simulations to evaluate and enhance the currentyl achieved performance. Specifically, we have evaluated instrumentation- as well as physics limitations in the measurement and reconstruction of electron tracks, we have improved the readout of the current system, and we have developed new gamma-ray reconstruction schemes that enable the full reconstruction of the energy and location of the gamma-ray source by just measuring the Compton-scattering induced electron track. The latter provides new opportuniities in a variety of different implementations of gamma-ray imaging systems, such as gas-based systems. In terms of the broader impact, advanced gamma-ray detection and imaging concepts as developed within this grant will not only significantly improve the ability to detect and identify weak radioactive materials for Homeland Security but will also enhance capabilities in other national nuclear security related fields such as nuclear non-proliferation and abroad, e.g. for defense related nuclear detection. In addition, applications in basic research such as astrophysics or nuclear physics will benefit from the improved imaging capabilities. In fundamental physics, the ability to distinguish different particle types by their characteristic energy loss can potentially provide a sensitive tool to discriminate a signal from background. In biomedical imaging, whether small-animal imaging for drug development or nuclear medicine to improve early cancer detection and cancer treatment will benefit from the proposed research.
