Imaging performance of lanthanum bromide scintillators with wavelength shifting fiber readout

B. Budden, IEEE
G. L. Case, IEEE
M. L. Cherry, IEEE
J. Isbert, IEEE
M. Stewart, Louisiana State University


Astrophysical x-ray/gamma-ray telescopes and standoff detectors for national security applications may require detector areas on the order of a meter squared or more. A finegrained meter squared scale scintillator with mm-scale resolution may require ∼10° pixels and electronics channels. In many applications, this can be prohibitive. Since LaBr3:Ce produces significantly more scintillation light (63 photons/keV) than other materials, it offers the possibility of a crossed optical fiber readout approach needing only a few thousand channels. A layer of 2 mm square, double clad waveshifting fibers can be laid in the x-directlon across the top of a LaBrs detection plane (separated from the LaBr3 by a thin glass seal that provides a moisture barrier), with a second layer of fibers in the y-direction laid across the bottom. With an absorption peak matched to the emission of LaBr3, the fibers will absorb the scintillation light and reemit it isotropically, a portion of which will be trapped in the fiber and propagated down the fiber axis, where the fiber ends are viewed by 64-channel MAPMTs. The crossed fiber layers are intended to measure x- and y-position only. Since only a small fraction of the light is trapped in the fibers, the energy is measured in nine large "energy measuring" PMTs viewing the scintillator through the bottom fiber layer. A lab-scale crossed-fiber LaBr3:Ce imager has been constructed as a protype for this concept. Results of measurements of energy, position, and angular resolution are given. The use of pre-processed Detector Pixel Source Image (DPSI) files, which provide a significant speed-up in the computationally intensive reconstruction process, is explained in detail. ©2007 IEEE.