Illicit nuclear materials represent a threat for the safety of the American citizens, and the detection and interdiction of a
nuclear weapon is a national problem that has not been yet solved. Alleviating this threat represents an enormous
challenge to current detection methods that have to be substantially improved to identify and discriminate threatening
from benign incidents. Rugged, low-power and less-expensive radiation detectors and imagers are needed for large-scale
Detecting the gamma rays emitted by nuclear and fissionable materials, particularly special nuclear materials (SNM), is
the most convenient way to identify and locate them. While there are detectors that have the necessary sensitivity, none
are suitable to meet the present need, primarily because of the high occurrence of false alarms.
The exploitation of neutron signatures represents a promising solution to detecting illicit nuclear materials. This work
presents the development of several detector configurations such as a mobile active interrogation system based on a
compact RF-Plasma neutron generator developed at LBNL and a fast neutron telescope that uses plastic scintillating-fibers
developed at the University of New Hampshire. A human-portable improved Solid-State Neutron Detector
(SSND) intended to replace pressurized 3He-tubes will be also presented. The SSND uses an ultra-compact CMOS-SSPM
(Solid-State Photomultiplier) detector, developed at Radiation Monitoring devices Inc., coupled to a neutron
sensitive scintillator. The detector is very fast and can provide time and spectroscopy information over a wide energy
range including fast neutrons.
We report on developments of an intraoperative probe, capable of functioning in real time with high spatial resolution
and high sensitivity. This probe combines two novel technologies and is based on an electron multiplying charge
coupled device (EMCCD) bonded to a high spatial resolution microcolumnar CsI(Tl) scintillator via a flexible fiberoptic
cable. Our data demonstrates that the probe can be used with such beta-emitting radiolabels as 18F, 131I, and 32P. The
basic design of the probe and its evaluation using standard clinical phantoms is presented. In addition, the operational
data obtained on swine models is included to demonstrate the probe's efficacy in practical procedures.
We are developing a probe for image-guided surgery of cancer to be used in conjunction with traditional beta emitting radiopharmaceuticals such as I131 and F18-FDG. This device is based on a combination of two novel technologies, a microcolumnar film scintillator, CsI(Tl) and low-noise high sensitivity Electron-Multiplying CCD (EMCCD). The former allows high spatial resolution nuclear imaging and the latter facilitates detection of signal with significantly higher SNR than conventional CCDs by the virtue of internal signal gain built into its readout register. CsI(Tl) is bonded to the EMCCD via a flexible coherent fiberopic cable for easy handling. Due to its high sensitivity the probe is capable of functioning in real time providing high spatial resolution nuclear images for precise detection, delineation and excision of tumors. The evaluation of the probe using standard clinical phantoms as well as the operational data obtained on swine models and in clinical surgery will be presented.
We examined the spatial resolution of a columnar CsI(Tl), single-photon imaging system using an approach that
estimates the interaction position to better than the spread of the light distribution. A columnar scintillator was directly
coupled to a 512×512 electron multiplying CCD (EMCCD) camera (16 μm pixels) binned at 2×2 to sample at 32 μm
pixels. Optical photons from gamma-ray/scintillator interactions are sampled over multiple pixels. Resultant images
show clusters of signal at the original interaction site, clusters from Cs and I K x-rays up to several hundred microns
away, and clusters from collimator K x-rays. Also evident are depth-of-interaction effects which result in a broadening
of the light distribution. These effects result in a degradation of spatial and energy resolution. Cluster pixel data was
processed to better estimate the interaction position within the initial interaction cluster. Anger (centroid) estimation of
individual gamma-ray events yielded spatial resolutions better than 100 μm; a result previously achievable only with
pixellated semiconductor detector arrays. After proper calibration, depth-of-interaction (DOI) effects are corrected by
performing maximum-likelihood 3D position and energy estimation of individual gamma-ray interactions.
Columnar CsI(Tl) screens are now routinely used in indirect digital x ray imaging detectors. The CsI(Tl) scintillator provides high density, high atomic number, and high scintillation efficiency. These properties, coupled with the fact that CsI(Tl) can be grown in columnar form, provide excellent spatial resolution, high x-ray absorption, and low noise resulting in detectors with high overall detective quantum efficiency (DQE(f)). While such screens are now commercially available, developments leading to further improvements in scintillator performance are ongoing at RMD. Here we report on the recent progress in developing very thin (10 μm) to very thick (~3 mm) columnar screens and discuss their application potential in digital radiology and nuclear medicine.
We report on recent advances in the development of powdered Lu2O3:Eu scintillator screens. The Lu2O3:Eu scintillator has excellent intrinsic material properties including high density (9.5 g/cm3), high average atomic number (63), and a peak emission of 610 nm. We have characterized the performance of screens fabricated from this material in comparison with commercial Gd2O2S:Tb screens. This paper presents resolution in terms of MTF(f), noise properties in terms of NPS(f), and overall NEQ(f), obtained by coupling the screens to a CCD detector. We have included sample radiographic images that demonstrate the ability to produce high quality images. These screens are currently under development, and further improvements in performance are expected with optimization of the scintillator and fabrication methods.
We report on a new x-ray converter screen based on the powdered Lu2O3:Eu scintillator. Lu2O3:Eu offers high density (9.4 g/cm3), high average atomic number (63), and a peak emission of 610 nm. The high density of the material and a high packing fraction of the coating provide higher x-ray absorption efficiency, even with thin screens. As a result Lu2O3:Eu screens are expected to provide superior spatial resolution and x-ray stopping power compared to commercial powdered screens. This newly developed screen has excellent imaging performance and offers several practical advantages such as ease of fabrication, low cost, and durability. This paper will discuss preliminary results of the imaging performance of this novel screen.