N4B1  Scintillator Development

Thursday, Nov. 5  10:30-12:10  Town and Country

Session Chair:  Rainer Novotny, University Giessen, Germany; Gregory Bizarri, LBNL, United States

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(10:30) N4B1-1, Light Yield Maximization of Triclinic La-GPS Scintillator by Optimizing La and Ce Concentration

Y. Tsubota1, T. Waki2, J. H. Kaneko2, M. Higuchi2, H. Ishibashi3

1Japan Atomic Energy Agency, Tokai-mura, Japan
2Hokkaido University, Sapporo, Japan
3Hitachi Chemical co. ltd, Hitachinaka-shi, Japan
Inorganic scintillators with high light yield, high detection efficiency and fast decay time have been desired in the fields of nuclear medical diagnostics, oil and/or gas well-logging and non-distractive inspections. The authors have been developing Gd2Si2O7:Ce (GPS) as novel rare-earth oxide scintillator with large light yield and without hygroscopicity. Especially, the orthorhombic GPS grown by a TSSG method showed the light yield c.a. 1.4 times larger than the commercially available NaI:Tl (4B4, Ohyo Koken Kogyo). The orthorhombic GPS showed the light yield 74% at 573K compared to the one at RT. Therefore, it is expectable to contribute for well logging. In addition, thin sintered GPS scintillator plate have large light yield and good energy resolution of approx. >11% for alpha particles, development of alpha particle survey meter using GPS plate and position detection photo multiplier tube is undergoing. The triclinic La-GPS, which substituted Gd site for La, also have LY close to NaI:Tl. Although several trials on growth of La-GPS were reported, systematic research on LY were not sufficiently carried out. In this report, the optimization of La and Ce concentration of La-GPS was conducted to maximize LY. (LaxGd1-x-yCey)2Si2O7 (x= 0.1, y= 0 - 0.16) and (x= 0 - 0.15, y= 0.025) were sintered. All La-GPS except for (Ce, La= 2.5%, 0%) have the triclinic structure. Sintered compacts were fixed on glass plates and mechanically polished to be approx. 100 micro-meter thick. For the evaluation of scintillation LY, alpha-particle response function measurement using 241Am was performed. For the Ce= 2.5% samples, La-GPS with 5 - 6.7% of La concentration showed the highest LY; then LY was decreased as the La concentration increased. For the La=10% samples, LY increased as Ce concentration increased in the range of Ce=0.5-2.5%. Decrease of LY due to concentration quenching was observed in the range of Ce>4%.

(10:50) N4B1-2, Eu2+ Activated K(Ca1-xSrx)I3: High-Light-Yield and High-Energy-Resolution Mixed Halide Scintillators

Y. Wu, A. C. Lindsey, M. Zhuravleva, C. L. Melcher

Scintillation Materials Research Center, University of Tennessee, Knoxville, TN, USA
Mixed crystal strategy was recently proposed to be an effective way to improve the performances of inorganic scintillators. This work focused on the development of a mixed halide scintillators based on potassium calcium strontium iodide activated with divalent europium. A systematic study from screening and optimization of matrix composition to further scale-up of single crystal size was conducted in this work. A full concentration range of K(Ca1-xSrx)I3:Eu2+ (x=0, 0.2, 0.4, 0.6, 0.8, 1) crystals with 6 mm diameter grown by Bridgman method. The relationship between composition and scintillation properties in the range of solid solution was established. It was found that the scintillation light yield increased in the range of 0

(11:10) N4B1-3, Isovalent Co-Doping of CsI(Tl)

J. Glodo, R. Hawrami, K. S. Shah

RMD, Watertown, MA, USA
Since its introduction in 1951 CsI(Tl) has become one of the most prevalent scintillator for gamma-ray detection. In recent years, there has been an effort to improve properties of this material through co-doping with different divalent ions. The main goal of that research was to reduce the afterglow that the material exhibits, which was driven by the needs of x-ray imaging (reduction of ghosting). Recently, we have investigated effects of isovalent co-doping of this materials. The co-dopants included Na and Rb ions. We selected these ions under the assumption that they will act as the shallow donor states in the vicinity of the conduction band. This is based on the higher first ionization potentials of Na/Rb in comparison to Cs ions. We tested basic scintillation properties such as emission spectra, energy spectra and non-proportionality, as well as some of the temperature dependencies including thermoluminescence and changes in the total emission intensity.

(11:30) N4B1-4, Tl2LiLaBr6:Ce and Tl2LiYCl6:Ce : New Elpasolite Scintillators

R. Hawrami, E. Ariesanti, L. Soundara Pandian, J. Glodo, K. Shah

Radiation Detection & Imaging, Radiation Monitoring Devices, Inc., Watertown, MA, USA
During the last decade, the search for new dual mode gamma/ neutron elpasolite crystals has been extensive and number of scintillation materials such as Ce-doped Cs2LiYCl6 (CLYC), Cs2LiLaCl6 (CLLC), and Cs2LiLaBr6 (CLLB), and have developed and explored as radiation detectors. In addition, some of these materials have been scaled-up to 2 inch size and beyond. Recently, we discovered Tl2LiLaBr6:1:Ce (TLLB:Ce), a new gamma/neutron dual mode lithium-based cerium doped elpasolite scintillator crystal. (TLLB:Ce) compositions belong to a group of the elpasolite crystal family. TLLB:Ce has a higher effective atomic number (Zeff = 64) than Cs2LiLaBr6:Ce (CLLBC, Zeff = 47). The theoretical density (?= 6 g.cm-3) is also higher than that of CLLBC (?= 4.2 g.cm-3), thus ensuring a better gamma-ray absorption. Sixteen mm diameter crystals were grown using the melt based vertical Bridgman method. (TLLB:Ce) shows 5.7% gamma ray energy resolution, light yield of 53,000 Ph/MeV, decay time of 28 ns, which are all promising parameters for medical imaging as well as homeland defense, nuclear non-proliferation and particle physics.

(11:50) N4B1-5, Novel Alpha-Gamma Discrimination Method for LaBr3:Ce Scintillator

R. Ogawara1, M. Ishikawa2

1Department of Medical Physics and Engineering, Hokkaido University graduate school of Medicine, Sapporo, Hokkaido, Japan
2Department of Biomedical Science and Engineering, Hokkaido University graduate school of Heal Science, Sapporo, Hokkaido, Japan
Objective
LaBr3:Ce scintillator performed an excellent energy resolution is useful for ?-ray spectroscopy. However it has a serious defect to be a-decay self-activity caused by decay of Ac-series nuclei contained in LaBr3:Ce crystal. We have developed a novel analysis method named Vp/Q discrimination method, which is based on a ratio of peak voltage Vp to integrated charge Q of the waveform, aiming at a background (BG) rejection for a-decay self-activity. Moreover the difference of scintillation decay time between a and ? event is estimated by GEANT4 Monte Carlo code, and we evaluated the decay time resolution of the present method.
Materials and Methods
The rejection accuracy of alpha events was assessed quantitatively by comparing the energy spectrum between Vp/Q discrimination method and conventional method (background subtraction) using Ga-68 1.883 MeV ?-ray, where the energy was overlapped with a-decay self-activity. To improve the tracking of scintillation fluorescence, the PMT response and the geometry with a few optical properties are defined in detail.
Results and Discussions
The difference in measured peak counts of both method was 0.716 % with improvement of statistical error of 44.7 %. Thus the higher-accuracy measurement could be achieved using the Vp/Q discrimination method. In the simulation results, the difference in experimental Vp/Q between a and ? event is well reproduced with different scintillation decay time of 1.14ns. And it is found that the Vp/Q has excellent decay time resolution of 551 ps in FWHM.
Conclusion
The excellent performance of BG rejection for the a-decay in LaBr3:Ce scintillator is demonstrated using the Vp/Q (decay time equivalent) discrimination method, and it is useful for measurement of high energy environmental ?-ray. Moreover the present method is available as depth of interaction detector, since it can be separated different decay time with high accuracy in common readout of single PMT.