K. Blazek

Multi-crystal YAP: Ce detector system for position sensitive measurements

Abstract Yttrium aluminum perovskite (YAP:Ce) scintillation crystal has a light efficiency of about 40% relative to NaI. Because of the yttrium atomic number ( Z = 39) and the relatively high density (5.37 g/cm 3 ) it has a good gamma-ray absorption. Furthermore it is not hygroscopic and is inert. Its peculiarity consists of material processing that provides us with crystal pillars down to 0.3 × 0.3 mm 2 aperture size and up to some centimeters in length. An array consisting of 11 × 22 YAP:Ce elements was made where each crystal has an aperture of 0.6 × 0.6 mm 2 and a length of 7 mm. Each scintillation crystal is optically separated by a reflective material resulting in a separation layer between elements of about 5 μm. The multicrystal detector was optically coupled to a Hamamatsu Position Sensitive Photomultiplier Tube (R2486). The intrinsic spatial resolution of the PSPMT is better than 0.3 mm but it is strongly dependent on the Point Spread Function (PSF) generated on the photocathode. The multicrystal detector very well matched the PSPMT characteristics resulting in a spatial resolution of about 0.7 mm at 140 keV ( 99m Tc) gamma irradiation.

First Results from a YAP:Ce Gamma Camera for Small Animal Studies

The YAP (yttrium aluminum perovskite) camera is a novel gamma camera with intrinsic submillimeter spatial resolution and detection efficiency comparable to a standard Anger camera. At the first stage, it is a miniature gamma camera with a field of view of 4/spl times/4 cm/sup 2/ and is currently utilized for radio tracer studies on small animals. The YAP camera consists of a multicrystal array coupled to a position sensitive photomultiplier tube (Hamamatsu R2486) with a parallel hole collimator. The preliminary results are presented and discussed, in particular the intrinsic characteristics of the scintillating array, which are measured, as well as the position linearity and the spatial resolution, with a parallel collimator. Images were obtained from /sup 99m/Tc line source and nude Balb C mice, which have been injected with /sup 99m/Tc MDP, a bone-seeking agent. The observed images show the importance of the small-field YAP camera in radiopharmaceutical research.

Toward a nuclear medicine with sub-millimiter spatial resolution

Abstract The HIRESPET Collaboration is developing a new concept of a gamma camera with sub-millimiter spatial resolution. The first prototype consists of a small field size gamma camera based on a Position Sensitive Photo-Multiplier Tube (PSPMT) coupled to a novel scintillation crystal. The intrinsic spatial resolution of the PSPMT is better than 0.3 mm. The scintillation crystal consists of yttrium aluminium perovskit (YAP:Ce). It has a light efficiency of about 40% relative to NaI, a good gamma radiation absorption ( Z = 39) and a high density (5.37 g/cm 3 ). It is inert and not hygroscopic. To match the PSPMT characteristics, a special crystal assembly has been made consisting of a bundle of YAP pillars, where a single crystal has the transversal dimension of 0.6 × 0.6 mm 2 and a thickness ranging between 1 mm and 28 mm. Each scintillation pillar is optically separated from the other by a reflective layer of 5 μm thick. The preliminary results obtained from the gamma camera prototype (YAP camera) show spatial resolution values ranging between 0.6 mm and 1 mm and an intrinsic detection efficiency comparable with a standard Anger camera.

YAP multi-crystal gamma camera prototype

The Anger camera principle has shown a practical limit of a few millimeters spatial resolution. To overcome this limit, a new gamma camera prototype has been developed, based on a position-sensitive photomultiplier tube (PSPMT) coupled with a new scintillation crystal. The Hamamatsu R2486 PSPMT is a 76-mm diameter photomultiplier tube in which the electrons produced in the conventional bi-alkali photocathode are multiplied by proximity mesh dynodes and form a charge cloud around the original coordinates of the light photon striking the photocathode. A crossed wire anode array collects the charge and detects the original position. The intrinsic spatial resolution of PSPMT is better than 0.3 mm. The scintillation crystal consists of yttrium aluminum perovskit (YAP:Ce or YAlO/sub 3/:Ce). This crystal has a light efficiency of about 38% relative to NaI, no hygroscopicity and a good gamma radiation absorption. To match the characteristics of the PSPMT, a special crystal assembly was produced by the Preciosa Company, consisting of a bundle of YAP:Ce pillars where single crystals have 0.6/spl times/0.6 mm/sup 2/ cross section and 3 mm to 18 mm length. Preliminary results from such gamma camera prototypes show spatial resolution values ranging between 0.7 mm and 1 mm with an intrinsic detection efficiency of 37/spl divide/65% for 140 keV gamma energy. >

Influence of Si-codoping on YAG:Ce scintillation characteristics

A set of undoped, Ce/sup 3+/-doped and Si/sup 4+/-codoped Y/sub 3/Al/sub 5/O/sub 12/ (YAG) single crystals were grown by the Czochralski method and submitted to /spl gamma/ irradiation in the dose range 1-236 Gy at RT. Their irradiation induced absorption coefficient was calculated and analyzed. Crystals also underwent light yield (LY) and scintillation decay measurements using the /sup 241/Am and /sup 22/Na radioactive sources, respectively, in 1 /spl mu/s time gate. The induced absorption at 550 nm (at the Ce/sup 3+/ luminescence peak) decreases with Ce concentration and further decrease is obtained in the Si/sup 4+/-codoped samples. LY values are independent on the Ce/sup 3+/ concentration within 0.12% - 0.3% and on the moderate Si/sup 4+/ codoping as well.

Scintillation Properties of

We summarize the latest R&D state-of-art of Ce³⁺ and Pr³⁺-doped mixed (Lu_xY_1-x)₃Al₅O₁₂ (LuYAG) garnet scintillator crystals and compare their properties with those of Lu₃Al₅O₁₂ (LuAG) and Y₃Al₅O₁₂ (YAG) single crystal analogues. Light yield, energy resolution and proportionality were studied under radioisotope excitation within 8-1300 keV energy range. The highest light yield of about 27000 ph/MeV is obtained in the newest prepared Ce³⁺ -doped LuAG crystals while up to 17000 ph/MeV was measured in the Pr³⁺-doped ones. On the contrary, the energy resolution and proportionality are noticeably better in the Pr³⁺ -doped crystals. Mixed Ce³⁺- or Pr³⁺-doped Lu_xY_1-xAG (x=0.9-1) crystals show comparable light yield and energy resolution compared to those doped pure LuAG, but the content of slow components in scintillation pulses lower.

{\rm Ce}^{3+}

Abstract Spectroscopy of Pr-doped YA1O 3 (YAP) has been investigated under synchrotron radiation and laser excitations. Fast UV fluorescence was shown to be due to allowed d–f transitions of Pr 3+ . Light yield of Pr-doped YAP has been measured in comparison with Ce-doped YAP. The relatively low scintillation efficiency of Pr: YAP is explained by the very different concentration of the dopant ions in both systems and by the presence in Pr: YAP of Ce trace impurities which can act as trap centers for the fast UV scintillation of Pr 3+ ions.

- and

Abstract Optical absorption, emission and excitation spectra and fluorescence decays of Ce3+-doped GdAlO3 single crystals are presented. Ce3+ and Gd3+ energy level schemes were determined and the influences of various transfer processes on Ce3+ fluorescence decays or fluorescence intensity are qualitatively discussed.

{\rm Pr}^{3+}

Abstract Various methods of crystal growth of Ce 3+ -doped Lu x (RE 3+ ) 1− x AlO 3 heavy and fast perovskite scintillators (Lu x (RE 3+ ) 1− x AP:Ce) are described and discussed (Czochralski, EFG and Bridgman–Stockbarger ones). Structural, spectroscopic and scintillation properties of these crystals are reviewed. Possible use and applications of these scintillators for hybrid photodetectors and γ-camera medical imaging are shortly discussed.

-Doped LuAG, YAG and Mixed

Thinking about the pumping and generated power of the longitudinally diode-pumped solid-state laser enhancement, the question of an active material cooling should be solved. One of the possible solutions is the active material cooling surface enlargement. Besides the cylindrical surface of the crystal, the laser rod front surfaces could be cooled through undoped ends. The temperature gradient effect in three various samples was investigated in a computer experiment, and the differences in generated output power were measured experimentally. The samples were three Nd:YAG rods - one conventional, one with one undoped end, and one with two undoped ends. The crystal samples were placed in sequence into a resonator 6 cm long and longitudinally diode-pumped. The dependencies of the generated power on the absorbed pump power have shown that with the two undoped ends the output power is more than twice as high as against the conventional Nd:YAG sample. The results were explained by a computer experiment based on the heat transfer equation solution where the changes of the temperature gradient were least for the Nd:YAG rod with two undoped ends.