Speaker
Raffaele DE LEO
(PHYSICS Department Bari University)
Description
In the framework of the feasibility studies of the 3D Axial HPD-PET, consisting of
axially oriented arrays of long (Lc from 100 to 150 mm) scintillation crystals of
small cross section (3.2 x 3.2 mm2) read-out on both sides by a Hybrid Photon
Detector (HPD), various investigations are being performed on the features of the
crystals to be employed. In fact, the axial spatial, energy, and time resolutions
of such a device are influenced by No and Leff, the key parameters of the HPD-PET
concept. No is the number of photoelectrons produced by a 511 KeV gamma-ray in a
crystal of short length (Lc→ 0). Its value depends both on the physical and optical
properties of the chosen scintillator (including its surface finishing and
coating/wrapping) and on the characteristics of the photodetector. Leff is the
effective light attenuation length of optical photons on their way inside the
crystal from the scintillation point to the photodetectors. While an increase of No
improves all the resolutions, an increase of Leff, although improving energy and
time resolutions, worsens the axial one. We will present the experimental study
carried out to optimize the effective light attenuation length, Leff, for a set of
polished YAP:Ce scintillators of dimensions 3.2×3.2×100 mm3 produced by Preciosa
Crytur Co at Turnov, Czech Republic, and of polished LYSO:Ce of equal size,
produced by Photonic Materials, Bellshill, Scotland. We will discuss the
resolutions that have been measured for the various Leff values obtained in
polished and wrapped crystals at 511 keV gamma-rays by means of standard
photomultipliers with borosilicate windows and bialkali photocathodes. Even if the
choice of the scintillator-wrapping to be used in the final project has not yet
been made, these values, extrapolated for the HPD photodetectors, that will be
equipped with a thin sapphire entrance window, give hints on the capabilities of
the novel 3D Axial HPD-PET concept. The possible perspectives will also be
discussed.
Author
Raffaele DE LEO
(PHYSICS Department Bari University)
