X-ray diffraction imaging (XDi) refers to the volumetric analysis of extended, inhomogenous objects by
spatially-resolved x-ray diffraction. Following a brief description of some of the areas in which x-ray diffraction
(XRD) is currently impacting on the detection of materials of interest in the security environment, the principles of
energy-dispersive x-ray diffraction tomographic systems of the 1st, 2nd and 3rd generation are described. The Multiple
Inverse Fan Beam (MIFB) topology for 3rd Generation XDi, in which the XRD properties of a 2-D spatial array of
volume elements are investigated in parallel without mechanical scanning, is described. 3rd Generation XDi is being
driven among other things by technological developments taking place in the field of Multi-Focus X-ray Sources
(MFXS) from which representative results are presented. MFXS source requirements for Next-Generation MIFB
XDi are summarized and the potential of 3rd Generation XDi for rapid, accurate and affordable screening in the
Checkpoint and Hold Baggage environments is summarized.
Proc. SPIE. 7306, Optics and Photonics in Global Homeland Security V and Biometric Technology for Human Identification VI
KEYWORDS: Imaging systems, Sensors, Calibration, Crystals, Field programmable gate arrays, Personal digital assistants, Gamma radiation, Data communications, Signal detection, Global Positioning System
The GE Intelligent Personal Radiation Locator (IPRL) system consists of multiple hand held radiation detectors and a
base station. Each mobile unit has a CZT Compton camera radiation detector and can identify isotopes and determine the
direction from which the radiation is detected. Using GPS and internal orientation sensors, the system continuously
transforms all directional data into real-world coordinates. Detected radiation is wirelessly transmitted to the base station
for system-wide analysis and situational awareness. Data can also be exchanged wirelessly between peers to enhance the
overall detection efficiency of the system. The key design features and performance characteristics of the GE IPRL
system are described.
X-ray diffraction imaging (XDI) is a novel modality in which the local x-ray diffraction (XRD) properties of
inhomogenous objects are measured. Following a brief description of some of the areas in which x-ray diffraction is
currently impacting on the detection of materials of interest in the security environment, the principles of
energy-dispersive x-ray diffraction tomography employed in XDI are described. The Multi-Inverse Fan Beam (MIFB)
topology for 3rd Generation XDI, in which the XRD properties of a spatial array of 2-D volume elements are
investigated in parallel without mechanical scanning, is described. 3rd Generation XDI is being driven among other
things by rapid technological developments taking place in the field of spectroscopic, room-temperature, semiconductor
x-ray detectors. Detector requirements for Next-Generation MIFB XDI are summarized and the potential of 3rd
Generation XDI for rapid, accurate and affordable screening in the Checkpoint and Hold Baggage environments is
Proc. SPIE. 7182, Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues VII
KEYWORDS: Signal to noise ratio, Photodetectors, Photon counting, Photomultipliers, Electrons, Manufacturing, Interference (communication), Avalanche photodiodes, Signal detection, Temperature metrology
Photomultiplier tubes (PMTs) are often used in scanning imaging systems requiring high sensitivity, due to their low
noise and high gain. Solid-state photomultipliers (SSPMs), an array of independent Geiger-mode avalanche photodiodes,
each with an integrated quenching resistor, have shown potential to outperform PMTs in terms of signal to noise ratio
(SNR) because of higher achievable photon detection efficiency and lower excessive noise factor. Here, the factors
affecting SNR of commercially available PMTs and SSPMs will be compared under different wavelengths (simulating
dye emissions: 500-700 nm) in order to quantify the potential performance gain when PMTs are replaced by SSPMs.
A 4π direction-sensitive gamma imager is presented, using a 1 cm3 3D CZT detector from Yinnel
Tech and the RENA-3 readout ASIC from NOVA R&D. The measured readout system electronic noise is
around 4-5 keV FWHM for all anode channels. The measured timing resolution between two channels
within a single ASIC is around 10 ns and the resolution is 30 ns between two separate ASIC chips. After
3D material non-uniformity and charge trapping corrections, the measured single-pixel-event energy
resolution is around 1% for Cs-137 at 662 keV using a 1 cm3 CZT detector from Yinnel Tech with an 8 x 8
anode pixel array at 1.15 mm pitch. The energy resolution for two pixel events is 2.9%. A 10 uCi Cs-137
point source was moved around the detector to test the image reconstruction algorithms and demonstrate
the source direction detection capability. Accurate source locations were reconstructed with around 200
two-pixel events within a total energy window ±10 keV around the 662 keV full energy peak. The angular
resolution FWHM at four of the five positions tested was between 0.05-0.07 steradians.
Thick segmented scintillating converters coupled to optical imaging detectors offer the advantage of large area, high stopping power sensors for high energy x-ray digital imaging. The recent advent of high resolution and solid state optical sensors such as amorphous silicon arrays and CCD optical imaging detectors makes it feasible to build large, cost effective imaging arrays. This technology, however, shifts the sensor cost burden to the segmented scintillators needed for imaging. The required labor intensive fabrication of high resolution, large area hard x- ray converters results in high cost and questionable manufacturability on a large scale. We report on recent research of a new segmented x-ray imaging converter. This converter is fabricated using vacuum injection and crystal growth methods to induce defect free, high density scintillating fibers into a collimator matrix. This method has the potential to fabricate large area, thick segmented scintillators. Spatial resolution calculations of these scintillator injected collimators show that the optical light spreading is significantly reduced compared to single crystalline scintillators and sub-millimeter resolution x- ray images acquired with the segmented converter coupled to a cooled CCD camera provided the resolution to characterize the converter efficiency and noise. The proposed concept overcomes the above mentioned limitations by producing a cost-effective technique of fabricating large area x-ray scintillator converters with high stopping power and high spatial resolution. This technology will readily benefit diverse fields such as particle physics, astronomy, medicine, as well as industrial nuclear and non-destructive testing.
Arrays of high speed, high gain avalanche photodiodes (APDs) have been developed for use as high sensitivity optical photon detectors. The 1 mm2 area APD pixels yield a maximum avalanche gain of 40,000 and a high signal-to-noise ratio with only moderate cooling (-22 degrees to -43 degrees C). These devices demonstrate 70% detection efficiency for 6 photon optical pulses and 35% detection efficiency for 3 photon optical pulses. The rise time is less than 2 nsec, and the fall time less than 7 nsec. Pixellating the PAD into a monolithic array will significantly reduce the cost per pixel compared to discrete devices. These devices will have great utility in various applications, ranging from high energy physics to biological instrumentation. The measured performance of these APD arrays as optical detectors will be discussed.
We are developing a large area structured CsI(Tl) imaging sensor for macro-molecular x-ray crystallography for use with both intense synchrotron sources and rotating-anode laboratory x- ray sources. The CsI(Tl) scintillator is grown on a specially designed optical substrate. Our work has produced x-ray sensors with up to 70% more light output, orders of magnitude faster decay time response, and greater spatial resolution (15% MTF at 20 lp/mm) than Gd2O2S screens currently used in CCD-based detectors for biological structure determination. These advances in performance will address some of the limitations of existing area detector technology. Performance measurements for a prototype CsI(Tl) scintillator are presented. With these new sensors the development of larger area x-ray crystallography detectors with millisecond data acquisition capabilities and high spatial resolution, suitable for synchrotron applications will be possible.
Avalanche photodiodes (APDs) are solid state devices having an internal signal gain which gives them a better signal-to-noise ratio than standard photodiodes. Although they have been studied for years, recent advances in the fabrication techniques have allowed the construction of multielement arrays (up to 10 X 10) with high performance capability. This progress has resulted in increased potential for exploiting the advantages of APDs in a variety of important applications including measurements requiring fast response such as nuclear and high energy physics research, industrial nondestructive testing, medical instrumentation, and biomedical research using low energy particles. Recent experimental data characterizing APDs and APD arrays used as x-ray, particle, and low level light detectors are presented.
Recent advances in photomultiplier tube technology have led to the availability of position sensitive photomultiplier tubes (PSPMTs). These tubes make it possible to build a new generation of imaging instruments for gamma rays and other types of ionizing radiation. We have investigated the use of these tubes for the construction of several prototype instruments. The first application investigated measures the quantity and distribution of radioactive compounds on filter papers used in microbiology research. The intent of this instrument is to replace film autoradiography with an electronic imaging system which can analyze samples 75 to 110 times faster than film. The second application involved the development of an intraoperative imaging probe to help surgeons identify cancerous tissue and ensure its complete removal. This instrument will replace a non-imaging probe now in use at many hospitals. A third prototype instrument under evaluation is an imaging nuclear survey system which obtains both a video and gamma ray image for the purpose of locating and quantifying radioactive materials. This system would be used at nuclear power plants and radioactive materials preparation facilities. A modification of this system could be built into robots used for inspecting and repairing power plants.