A depth-encoding Anger detector using scintillating fibers

Abstract

Parallax error during coincidence imaging with dual-head cameras causes infidelity in tomographic images, worsening as one increases crystal thickness to combat poor detection efficiency. We are integrating wavelength-shifting (WLS) scintillating fibers onto a thick NaI(Tl) crystal to create an Anger detector capable of measuring depth-of-interaction (DOI). Our studies target eventual implementation on the large-area detectors of commercial multihead coincidence imaging systems. The prototype detector uses a 127 127 25.4 mm 3 NaI(Tl) crystal. The crystal is sealed in a two-windowed aluminum enclosure-both faces of the crystal are coupled optically to glass windows. A ribbon of 125 square 1-mm WLS fibers is coupled lengthwise to the entrance window; enhanced-green-response photomultiplier tubes (PMTs) detect the light from the fibers. The number of fibers exhibiting signals above a threshold value determines the DOI. For interactions near the ribbon, light localizes in only a few fibers; light from distant interactions illuminates many fibers. Four PMTs, for position centroid calculation and energy windowing, are coupled through a light-guide to the exit window of the detector. This paper summarizes the concept of the depth-encoding Anger detector, describes the design of the detector prototype, and details on-going feasibility testing and optimization of the detector.Index Terms-Coincidence imaging, depth of interaction (DOI), parallax error, wavelength-shifting scintillating fibers.

The use of energy windowing to discriminate SNM from NORM in radiation portal monitors

“…Moreover, the total energy deposited in PVT is not necessarily directly proportional to the original gamma-ray energy, but is spread over a broad energy range (Compton continuum). This is opposed to detector materials for which photo-absorption is significant, such as thallium-doped sodium iodide [NaI(Tl)] crystals, where all of the energy of the incident gamma ray is often deposited as an easily discernable full-energy peak [11,12]. It is this full-energy peak that is directly proportional to the incident energy and, along with the information in the full spectrum, can be used for spectroscopy.…”

“…At the relevant count rates, individual incident photon events can be resolved. 2 Note that the application of EW in plastic scintillators is not the same as when used with spectroscopic-capable detector materials like thalliumdoped sodium iodide NaI(Tl), for example, in the medical field [11]. The spectra in these applications contain full-energy photopeaks, and partitioning the full spectra into smaller regions in which characteristic photopeaks are located enables rapid determination of the presence of specific radiation sources.…”

Depth of interaction detection with enhanced position-sensitive proportional resistor network

“…[3][4][5], the g-ray's DOI is strongly correlated to the width of the scintillation light distribution and thus its standard deviation s. To understand this behavior, we developed a theoretical model of the scintillation light density as a function of the detection position.…”

The CASTER Black Hole Finder Probe

“…A second approach, also adapted from medical imaging applications, is analogous to the design of solid state strip detectors [11]. In this case, one layer of wavelength-shifting fibers is laid in the x-direction across the top of a scintillator and a second layer of fibers is laid in the y-direction across the bottom.…”