Current Research Projects
Orion Digital 3-Dimensional Position Sensitive CdZnTe Detectors (DOD, DTRA)
Digital ASIC system is the newest generation of readout system to acquire the signals from CdZnTe detectors. It reads waveforms from 121 anode plus 1 cathode onboard preamplifiers. This lossless data acquisition provides much more information than just the peak amplitude and time provided by the older analog ASIC. This ASIC can achieve energy resolution of 0.41 % FWHM for single-pixel events and 0.58 % FWHM for all events combined at 662 keV with 3-MeV dynamic range. Furthermore waveform tracking allows sub-pixel position resolution; we can achieve position resolution of 300 um or better at 662 keV. Waveforms also allow limited event identification, such as differentiating charge sharing and Compton scattering. We have also just scratched the surface in terms of this ASICs potential.
Researchers: Yuefeng Zhu, Michael Streicher and Jiawei Xia
Gamma-Ray Imaging (DOE NNSA NA-22)
The pixelated CZT detectors developed by our group provide 3-D positions and energy depositions of gamma-ray interactions within their volume. This detailed information allows us to determine the incident direction of gamma rays, based on the physics of their interactions with the CZT. We use both Compton and coded aperture imaging techniques to determine the spatial distribution of gamma-ray emitting materials around our detectors.
The focus of the imaging group is to develop new imaging techniques and algorithms for real-world applications. Past research includes real-time tracking of moving objects, 3-D mapping of gamma-ray emissions inside a room, source detection algorithms, and imaging high energy (>3 MeV) gamma-rays. Recent collaboration includes work with NASA for imaging gamma rays from neutron-activated materials as well as measurements with researchers interested in imaging gamma-rays emitted from tissue during proton cancer therapy. Knowledge of the uncertainty and physics of interactions in our detectors also enables us to develop more advanced, iterative reconstruction techniques and to solve inverse problems to characterize gamma-ray emitting materials such as SNM. Recent work on neutron detection via cadmium capture in our detectors has also expanded our capability to location of neutron-emitting sources.
Another project has the goal to achieve robust, direction-dependent isotope detection using large volume CdZnTe gamma-ray detectors. In this work, data from both Compton and coded aperture imaging are combined in a probability-based algorithm to solve for gamma-ray spectra as a function of direction. In collaboration with Sandia National Laboratories, the well-established GADRAS (Gamma Detector Response and Analysis Software) will utilize this data to autonomously detect isotopes of interests and point to their direction. Of interest is the ability of directional information to improve the discrimination of background from isotopes of interest. Although this technology is designed with homeland security in mind, a range of other applications can be imagined: from space to medical imaging and radiation protection.
Researchers: Steven Brown, Jiyang Chu and David Goodman
Development of Black Box Isotope Identification Spectrometer (DOE NNSA NA-22)
A new CZT spectrometer is being developed to identify radioactive source shape, composition and activity in a black box. Although similar to existing Polaris units, this new system has two independently-positionable CZT planes, allowing for great positioning flexibility. Hardware research will focus on performance characterization of the system when configured for maximum detector surface area for coded aperture imaging, maximum stopping power for Compton imaging, or when it is in an arbitrary geometry.
Additionally, our group will develop new imaging algorithms to take advantage of the binocular disparity introduced with two separate imaging planes. Instead of mapping images to the surface of an imaginary sphere surrounding a traditional imaging detector, we will develop algorithms to generate true 3D source distributions.
Researchers: Steven Brown and Bennett Williams
Development of TlBr gamma-ray spectrometers (DNDO, RMD, and LLNL)
TlBr is an attractive material for room-temperature gamma-ray spectroscopy because of its high stopping power, wide badgap, and low melting point. Spectrometers have achieved < 1% FWHM at 662 keV but these results are limited to stable operation at -20 °C. Degradation over time (referred to as polarization) occurs in TlBr devices after hours to months of room-temperature operation. Our group’s goal is to characterize the polarization phenomena to help manufactures improve the lifetime of TlBr detectors.
In addition to room-temperature characterization, our group also tests detectors at -20 °C where they can operate indefinitely. We write new software algorithms to deal with material specific characteristics like the relatively high hole mobility and are currently developing a portable two stage cooling system. Our goal is to move to the digital ASIC readout system currently used on CZT.
Researchers: Will Koehler, and Sean O’Neal
Thermal Neutron Imaging (DOE NNSA NA-22)
Thermal neutron imaging is a new-developed capability for CdZnTe that allows us to locate and discern the shape of low-Z material near neutron-emitters such as plutonium. By detecting the interaction locations of cascade gammas following neutron capture on 113Cd, it has been shown that a directional “pointer” can be used to estimate the direction to a thermal neutron source. A special moving coded aperture mask technique is also under development, allowing us to obtain high resolution images of stationary extended sources.
Researchers: Steven Brown
CZT System Applications in the Nuclear Power Industry
The position-sensitive CdZnTe gamma-ray imaging spectrometer technology developed in the group is widely used throughout the US nuclear power industry. The commercially available version of these instruments is primarily used to locate radioactive source term throughout nuclear power plant facilities, but the imaging algorithms and energy resolution (cited as
These research efforts focus on measuring activity and dose in complex radiation fields generated inside these facilities using the advanced capabilities of the imaging technology. Applications of industrial health physics often require these quantitative measurements for individual plant components (e.g. for radiation level assessment and control), and the contribution from surrounding components adds layers of uncertainty to other contemporary measurement methods. The goal is to apply CdZnTe imaging spectrometers in order to minimize this uncertainty in the nuclear power field.
Researchers: Bennett Williams
Consortium for Verification Technology (CVT)
The Orion group is an active member of the CVT managed at U of M. Research thrusts include measuring special nuclear material (SNM) spatial distributions and enrichment. Recent research campaigns include trips to the Device Assembly Facility (DAF) in Nevada and DC Cook Nuclear Power Plant.
Orion and Polaris systems measuring a sphere of 93% HEU at DAF
Reconstructed images of an extended HEU sphere next to a point Am-Be driver
Orion spectrum of weapons grade plutonium where Pu-240 content was successfully measured to within 2σ uncertainty.
Researchers: David Goodman
Exploratory Research Projects
In addition to the funded projects listed above, the Orion group is also working on several exploratory projects. These are intended as seeds for future projects with high risk and high impact to diverse problems throughout the radiation detection and measurements field.
Proton cancer therapy is an exciting new field of radiation therapy that utilizes the exquisite precision of the proton Bragg peak to target and destroy cancerous tissue. However, there is a strong need for in vivo dose verification with millimeter accuracy to ensure that the proton dose is delivered to the correct location within the patient. This is especially true for high-risk treatments near critical organs. It has been shown that prompt gamma rays offer fine position resolution information since the secondary gamma emission distribution follows the proton dose distribution very closely. In collaboration with assistant professor Jerimy Polf’s group at the University of Maryland School of Medicine’s department of radiation oncology, we have taken preliminary measurements of prompt gamma-rays from proton beams using several CdZnTe arrays. Work on this topic continues as initial results indicate there is a promising future for this technology.
Long-term stability of CdZnTe detectors is studied in a low background cave designed to hold the first Polaris system. Continuously collected data are used to determine the performance of the system over time, these data can also be used to study the potential application of CdZnTe to measurements of low activity sources or other applications that require extremely low backgrounds.
Past Research Projects
Polaris 3-D Position-Sensitive CdZnTe Gamma-Ray Imaging spectrometers (DOD DTRA, DOE NA-22)
Develop room-temperature CZT semiconductor gamma-ray spectrometers, with energy resolution of better than 1% at 662keV.
Researchers: Feng Zhang, Andy Boucher, Josh Mann, and Jim Berry
Digital 3-D semiconductor gamma-ray spectrometers (DOD DTRA, DOE NA-22)
Develop digital acquisition system for room temperature CZT and alternative semiconductor gamma-ray spectrometers.
Researchers: Feng Zhang, Yuefeng Zhu, Hao Yang, and Michael Streicher
Exploration of alternative room-temperature semiconductor gamma-ray detectors (Radiation Monitoring Devices and DNDO of DHS)
Develop alternative wide band-gap semiconductor radiation detectors from materials such as HgS, HgO, TlBrI and InBrI.
Researcher: Crystal Thrall, and Will Koehler
Feasibility study on neutrino-less double-beta decay
Fundamental science/basic physics investigation.
Researcher: Feng Zhang, and Andy Boucher
Study on high count-rate gamma-ray spectroscopy using 3-D CdZnTe detectors (DOE NA-22)
Simulate and measure pulse waveforms under high flux applications where the variation of space charge and the signal induction from charge drift cannot be decoupled.
Researcher: Meisher Rodrigues
Feasibility study on measuring elemental compositions of planetary bodies using 3D CdZnTe gamma-ray imaging spectrometer (NASA Goddard Space Flight Center)
Determine the feasibility of identifying elemental composition of Mars and the Moon using spectra obtained from 3D CdZnTe gamma-ray imaging spectrometry.
Researcher: Andy Boucher, and Steven Brown