Yoshiyuki Usuki

Development of Pr:LuAG Scintillator Array and Assembly for Positron Emission Mammography

Abstract-In order to detect the breast cancer at the early stage with high efficiency, we intend to develop positron emission mammography (PEM), using Pr:LuAG single crystal as a scintillator of this scanner. PEM has the same mechanism of PET, where two 511 keV annihilation gamma-rays are detected by two gamma cameras at opposite side, and reconstruction of the data shows the position of the cancer with malignancy grades. After cutting and polishing processes for each crystal to a physical dimensions of 2.1 × 2.1 × 15 mm3, Pr:LuAG array covered with BaSO4 reflector was used as a sensor head. The one camera unit consisted of 20 × 64 pixels optically coupled with three H8500-03 multi anode PMTs. Our PEM required four cameras at each side. Finally, eight cameras were installed in both sides of the prototype instrument and the spatial resolution was evaluated using the 18F in the breast phantom.

Scintillation characteristics of PbWO4 single crystals at room temperature

Abstract Single crystals of PbWO 4 at room temperature show a narrow excitation peak around 325 nm with the FWHM as small as 10 nm and a broad emission peak around 420–440 nm. The light output is about 4.4% of that in BGO. The luminescence is fast with the decay constant less than 10 ns for 84% and as fast as 40 ns for the rest. Degradation in optical transmittance due to γ-ray irradiation is not large up to at least 10 7 rad in the present crystals which are slightly coloured yellow. Spontaneous recovery of the radiation damage occurs to some extent with a time constant much shorter than 18 days. The above result indicates a possibility that this material may be resistive enough against radiation if colourless crystals could be grown.

Scintillation Properties of Praseodymium Activated

Scintillation properties of LuAG:Pr grown by Furukawa Co. Ltd., Japan, have been studied. The best crystals display light outputs up to 19000 ph/MeV and an energy resolution of 4.6% at 662 keV. The scintillation yield is found to be a function of size and temperature of the sample; it can be enhanced by 40% upon heating to 450 K. Radioluminescence spectra show both d- f and f-f transitions of Pr3+ ions; the contribution of the latter increases with temperature. The scintillation decays are complex, with a fast decay constant of 20 ns. The presence of 176Lu induces high background activity.

{\rm Lu}_{3}{\rm Al}_{5}{\rm O} _{12}

There are two types of crystals with respect to luminescence. In dc measurement, type A gives a primary emission at 410–430 nm (blue) with a second one at around 500 nm. Type B gives only dominant emission at 480–500 nm (green). This apparent difference can be interpreted as follows; the characteristic scintillation of PbWO4 is dominantly blue and subdominantly green. Intense phosphorescence with a decay constant of about 15 ms exists only in Type B at about 500 nm with one to two orders of magnitude larger intensity than scintillation, hiding the blue scintillation in its tail. The cause of the phosphorescence may be Mo.

Single Crystals

(a) ENEA-INN/TEC, Via Anguillarese 301, S.Maria di Galeria, 00060 Roma, Italy (b) Institute of Physics, Cukrovarnicka 10, 16200 Prague, Czech Republic (c) INFN, Dept. of Physics, University of Roma 1, P. le A. Moro 2, Roma, Italy (d) SIT, Shonan Institute of Technology, Fujisawa 251, Japan (e) CRYTUR Preciosa a.s., Palackeho 175, 51119 Turnov, Czech Republic (f) KEK, National Laboratory for High Energy Physics, Tsukuba 305, Japan (g) INFM and Dept. of Physics, University of Milano, Via Celoria 16, 20133 Milano, Italy (h) Furukawa Co., Yoshima, Iwaki 970-11, Japan

Scintillation and phosphorescence of PbWO4 crystals

Scintillation properties of praseodymium doped LuAG have been investigated. The crystal is a dense (6.7 g/cm3) scintillator with a short decay time around 20 ns and wavelength emission spectrum peaked at 310 nm. The tested sample was 10 mm times 10 mm times 5 mm cuboid, polished on all surfaces. The dopant concentration amounts to 0.23 mo1%. A light yield of 16000plusmn1600 ph/MeV was measured using high sensitivity (13.7 muA/1mF) Photonis photomultiplier (PMT) XP5500B. High quantum efficiency of this PMT (35%) allowed us to register 5600plusmn400 phe/MeV using 12 mus shaping time in the spectroscopy amplifier. The measured energy resolution was equal to 5.0plusmn0.1%. Response of LuAG:Pr to gamma-rays was found to be proportional over wide energy range. Deviation from proportionality does not exceed 10% at 16.6 keV. This results in good intrinsic energy resolution of LuAG:Pr amounting to 3.0plusmn0.3%, measured with 662 keV gamma-rays from 137Cs.

Influence of La3+-Doping on Radiation Hardness and Thermoluminescence Characteristics of PbWO4

Abstract In this paper we report the crystal growth of lead tungstate crystals by the vertical Bridgman method with a flat-bottom crucible. The crystals were grown with different melt compositions. Other parameters such as effect of crucible thickness and growth orientation were also studied. Measurement of lattice parameters and phase analysis was carried out by X-ray diffraction method at different stages of crystallization and the region of congruent composition is investigated. Electron probe micro analyzer was used to image the eutectic flux mixture at the end of crystallization. It is concluded that the stoichiometric composition of PbWO 4 is congruent.

Light Yield Non-Proportionality and Energy Resolution of Praseodymium Doped LuAG Scintillator

In this work we tried to grow 2-inch-diameter and high quality Pr:LuAG single crystals by the Czochralski (Cz) method. To grow the large diameter Pr:LuAG single crystal, we have optimized growth conditions and the furnace design. As a result, we have succeeded in the growth of 2-inch-diameter Pr:LuAG single crystal with a length of 110 mm. To determine light yield and energy resolution the energy spectra were collected under 662 keV gamma-ray excitation (137Cs source) and detection by a photomultiplier (Hamamatsu H7826). The light yield was around three times higher than that of BGO and almost homogeneous with increasing solidification fraction up to 0.32. The energy resolution was around 8%. Furthermore, scintillation decay time was around 23 ns and almost homogeneous all over the crystal.

Crystal growth of PbWO4 by the vertical Bridgman method : Effect of crucible thickness and melt composition

Properties of praseodymium and cerium doped Lutetium Aluminum Garnet (LuAG) were compared with cerium doped Lutetium Oxyorthosilicate (LSO) and Lanthanum Bromide (LaBr3). Light yield, its non-proportionality relative to 662 keV γ-rays and the dependence of the energy resolution on energy of the detected γ-rays were measured. LuAG:Pr turned out to have good proportionality, with deviation from unity around 10% at 16.6 keV and 3% at 59.5 keV. This, together with relatively high light yield of 5600 phe/MeV results in a very good energy resolution of LuAG:Pr of 5.1% measured with 662 keV γ-rays. Coincidence time resolution was measured to be 308 ps, significantly larger than that of LSO:Ce - 166 ps. This can be explained by smaller light yield of LuAG:Pr and the fact that only around 25% of its scintillation is emitted in short decay time modes of 17.6 ns and 52 ns, while the rest is decaying with long time modes of 1.4 μs and 9 μs.

Crystal Growth and Scintillation Properties of 2-Inch-Diameter

Experimental results are presented on the neutron scintillating properties of a custom-designed Pr3+ (praseodymium)-doped lithium (Li) glass. Luminescence was observed at 278 nm wavelength, originating from the 5d-4f transition. Time-resolved measurements yielded about 20 ns decay times for ultraviolet and x-ray excitation while much faster decay times of about 6 ns were observed for alpha particle and neutron excitation. Actual time-of-flight data in laser fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University reveal that it can clearly discriminate fusion neutrons from the much stronger x-rays signals. This material can promise improved accuracy in future scattered neutron diagnostics.