Mikhail Korzhik

New inorganic scintillation materials development for medical imaging

In this paper the results of one year of effort to develop the production technology of LuAP crystals will be presented. As already advertised since several years Lu based compounds doped with trivalent Ce which show fast and bright scintillation seem to be the most promising scintillators for a new generation of PET scanners. Two crystals. namely LSO:Ce and LuAP:Ce are already in the phase of mass production technology development but there is still an interest to search for materials with better combination of price/performance. As already mentioned in our contribution to the IEEE2000 conference in Lyon, the Crystal Clear Collaboration strategy is to look for a host where Lutetium is associated to another heavy cation to reduce the cost of the material. In our present study we paid attention to the compounds containing rare earth and Ba, Zr, Hf, which being doped with Ce show a very bright and fast luminescence in the blue-green region. Materials have been synthetized with a the same time an increase of the effective charge of the host matrix and a decrease or even a complete suppression of the Lu fraction. In our report we discuss spectroscopic and scintillation properties of several new heavy compounds such as Lu/sub 2/Hf/sub 2/O/sub 7/, La/sub 2/Hf/sub 2/O/sub 7/ and Ba/sub 3/Lu/sub 4/O/sub 9/ doped with Ce and the possibilities of their industrial production.

Large volume Ca_Mo_O-4 scintillation crystals

Several scintillation CaMoO4 crystals with size up to 28times28times220 mm3 were grown by the Czochralski method. Their scintillation properties have been evaluated. Light yield of full size crystals measured with a XP2020 PMT is about 4% relative to a small reference CsI(Tl) crystal. Radio luminescence spectrum under gamma-excitation contains single emission peak with maximum at 520 nm. Optical transmission spectra contain a weak absorption band around 420 nm, which has almost no influence on scintillation light. This allows to produce even larger scintillation elements without deteriorating the light yield. Scintillation kinetics was measured under gamma- and alpha-particle excitation both in fast (2000 ns) and slow (200 mus) time scales. Fast components - 12 ns, (0.1%); 200 ns (0.5%) were detected along with slow - 3.8 mus (3.4%); 20 mus (96%) - components. Difference in fast component contribution under gamma and alpha excitation allows to implement pulse-shape discrimination of alpha-radioactive background coming from impurities in the crystals.

Radiation hardness of mass produced PWO crystals

Studies of the distribution of the induced absorption in the spectral region of scintillation for mass produced PWO crystals and kinetics recovery have been made at the Bogoroditsk Techno-Chemical Plant using a specially developed rapid analysis method and at CERN with tests at various facilities, which are easy to compare with electron beam damage and easy to access in a close vicinity. A probability for crystals with poor radiation hardness to be installed into a calorimeter and a probability for crystals with good radiation hardness to be rejected during certification are estimated. It is shown that instead of measurements of the loss of light yield transmitted through PWO crystals under electron beam irradiation, it is possible to use a sampling based measurement method of radiation induced adsorption of crystals, i.e. to control the PWO crystal distribution by their radiation hardness.

Mass production of PWO crystals for electromagnetic calorimetry: peculiarities and prospects

This paper is devoted to mass production of the most popular now scintillation material in high energy physics. Among recently developed scintillation materials lead tungstate (PbWO/sub 4/, PWO) has already found applications in electromagnetic calorimetry in the CMS and ALICE collaborations at the LHC. The status of the crystal production, peculiarities of crystal machining and property certification, the distribution of scintillation parameters as well as long term stability of crystal scintillation properties will be discussed.

Lead tungstate scintillator for the future particle physics detectors

Here we describe scintillation properties of Pb(W0.95-Mo0.05)O4:La,Y material. It is fast, dense and radiation hard scintillation material with scintillation band maximum 512 nm. Scintillator allows effective discrimination of scintillation and Cherenkov light from the crystal. It can be applied at the upgrade of CMS and ALICE detectors to meet SLHC requirements and further experiments at CLIC.

(Lu/sub x/Y/sub 1-x/)AP:Ce scintillation crystals

REAlO/sub 3/:Ce/sup 3+/ (RE=Y, Lu) scintillation crystals have impressive prospects for wide application in many branches of industry and are now being actively investigated. Here we report the scintillation mechanism in these crystals and possible ways of their scintillation properties improvement. The scintillation properties of (Lu/sub 0.5/-Y/sub 0.5/)AlO/sub 3/:Ce and (Lu/sub 0.7/-Y/sub 0.3/)AlO/sub 3/:Ce scintillation crystals grown under the mass production conditions also have been discussed.