Initial evaluation of the scintillator LFS for positron emission tomograph applications

A new scintillator (LFS) has been developed by Zecotek Innovations and made available to our laboratory for evaluation for applications in positron emission tomography. Our initial tests compared several different formulations of the crystal that produced a variety of light outputs, maximum emission values, and densities. Some of the formulations are emission shifted to be more efficient with APDs while others are more efficient with Bialkali PMTs. From the initial tests, two formulations were selected for further development for use with PMTs-LFS-5 and LFS-6. Our initial measurements were done with 4times4times30 mm crystal samples coupled to a Hamamatsu R1548 dual cathode PMT. For each measurement, the crystal was centered over one of the photocathodes (one crystal per PMT). LFS produced a light output that was 11 percent greater than LYSO and 21 percent greater than LSO. The energy resolution was 12% and the density was 7.34 g/cc. The decay time was 35 nsec and we have obtained a timing resolution of <1 nsec between two LFS crystals. Samples from several different locations in a boule were measured and the light output variation (one standard deviation) was 4.7%. Relative stopping power (photopeak efficiency) compared to LYSO was 1.04. The scintillator is undergoing further development with the goal to further improve light output and timing characteristics. Because of refinements in the growth process the cost per cc is expected to be $20 (US) or less for cut and polished crystals