LSO - from Discovery to Commercial Development

1. LSO - from Discovery to Commercial Development C. L. Melcher CTI, Inc. Knoxville, TN, USA

2. Acknowledgments • Schlumberger-Doll Research, Ridgefield • J. S. Schweitzer, R. A. Manente, C. A. Peterson • California Institute of Technology, Pasadena • T. A. Tombrello, H. Suzuki • LETI, Grenoble • J. J. Aubert, Ch. Wyon • CTI, Inc., Knoxville • R. Nutt, M. Andreaco • St. Petersburg State Technical University, St. Petersburg • P. A. Rodnyi and co-workers • Institute of Single Crystals, Kharkov • B. Minkov, M. V. Korzhik, and co-workers • Ural State Technical University, Ekaterinburg • B. V. Shulgin and co-workers Calor 2002

3. Properties of the ideal scintillator • High light output • Fast decay time • High density • High atomic number • Good energy resolution • Suitable emission wavelength • Good mechanical strength • Non-hygroscopic • Practical crystal growth • Low cost Calor 2002

4. Strengths/weaknesses of various scintillators Calor 2002

5. Search strategy for new scintillators • Identify suitable luminescent center • Suitable emission wavelength • High transition probability • Compatible with host material • Identify candidates for host material • High density • High atomic number • Transparent • Non-hygroscopic • Practical crystal growth • Synthesize candidates • Solid state synthesis by sintering powders • Characterize scintillation properties • Single crystal growth Calor 2002

6. Powder synthesis of candidate materials Calor 2002

7. Ce3+ activators • 4f – 5d transition • Allowed dipole transition • Typically high quantum efficiency • Typically 20-60 ns decay time • Emission wavelength usually 350 –450 nm depending on crystal field of host; e.g. GSO:Ce, BaF2:Ce, CeF3 Calor 2002

8. Ln2SiO5 host materials “Growth of lanthanide oxyorthosilicate single crystals and their structural and optical characteristics,” G. V. Anan’eva, A. M. Korovkin, T. I. Merkulyaeva, A. M. Morozova, M. V. Petrov, I. R. Savinova, V. R. Startsev, and P. P. Feofilov, Akademii Nauk SSSR, Izvestiya, Seriya Neorganicheskie Materialy, V 17, N 6, p. 754-8, June 1981. • Czochralski crystal growth of Ln2SiO5, Ln = Y, Gd-Lu • Crystal structure • Physical characteristics • Melting point • Density • Refractive Index • Doping with Nd3+, Ho3+, Er3+, Tm3+, Yb3+ Calor 2002

9. Early papers • Melcher, U.S. Patent No. 4,958,080 (1990) • Melcher and Schweitzer, IEEE Conf. Rec. (1991) • Rodnyi (1992) • Minkov, Functional Materials (1994) • Shulgin et al. (1990) • Melcher and Schweitzer, IEEE Trans. Nucl. Sci. (1992) • Melcher and Schweitzer, Nucl. Instr. Meth. (1992) Calor 2002

10. Crystal structure vs. RE radius Calor 2002

11. Crystal structure: Lu2SiO5 (LSO) Monoclinic C Space group C2/c Lattice constants a = 14.254 Å b = 6.641 Å c = 10.241 Å b = 122.2º Calor 2002

12. Crystal growth – practical requirements • Congruent melting (solid and liquid have same composition in equilibrium) • Reasonable melting point (compatible with crucible and furnace materials) • Mechanically strong material • Reasonable distribution coefficient for dopant Calor 2002

13. Dopant concentration vs fraction of melt pulled Calor 2002

14. Czochralski growth of single crystals Pull ~ 1 mm/hr Rotation ~5 rpm Seed crystal Iridium crucible Crystal melt Induction heater Insulation Calor 2002

15. Czochralski growth of single crystal LSO 2070oC Calor 2002

16. Transmission of pure and Ce-doped LSO Calor 2002

17. Low temperature (11K) excitation spectra Calor 2002

18. Low temperature (11K) emission spectra Calor 2002

19. Ce1 + Ce2 = gamma ray emission Calor 2002

20. Pulse height spectrum of 137Cs Calor 2002

21. Coincidence resolving time (511 keV) Calor 2002

22. Intrinsic background radiation • 2.6% of naturally occurring Lu is Lu-176 • Beta decay with primary gamma rays of 88, 202, 307 keV • Count-rate from Lu-176 • 0 – 1000 keV: 40 counts/sec/g Calor 2002

23. Scintillation efficiency* h = bSQ * Lempicki et al., Nucl. Instr. Meth. A333, 304-311 (1994) Calor 2002

24. Scintillator properties Calor 2002

25. Photon interaction cross sections Calor 2002

26. Emission spectra at room temperature Calor 2002

27. Scintillation decay times Calor 2002

28. Coincidence resolving time Calor 2002

29. Commercialization issues • Raw materials • Availability of large quantities • Low cost • Recycling of scrap • Factory • Low cost growth stations • Reliable electrical power • Cooling water system • Growth control system • Detector processing Calor 2002

30. Abundance of Lu Element Abundance (ppmw) Lu 0.8 I 0.45 Tl 0.85 Cd 0.15 W 1.25 Bi 0.009 Ge 1.5 Hg 0.085 Calor 2002

31. Raw materials Lu2O3 Calor 2002

32. LSO factory Calor 2002

33. Electrical power Battery backup Dual electrical service (3 MW) Calor 2002

34. Cooling water system 1000 gpm Calor 2002

35. Cooling towers Calor 2002

36. Nitrogen supply Calor 2002

37. Crystal boules Calor 2002

38. LSO production boules Picture of 50 boules Calor 2002

39. Light output of all LSO crystals - 2002 Calor 2002

40. Energy resolution of all LSO crystals - 2002 Calor 2002

41. LSO decay time Calor 2002

42. Light output uniformity within a boule Calor 2002

43. Energy resolution uniformity within a boule Calor 2002

44. Decay time uniformity within a boule Calor 2002

45. Detector processing Calor 2002

46. Detector processing – robotic assembly of pixels Calor 2002

47. Detector processing – Ultraviolet light cures adhesive Calor 2002

48. Detector with PMTs Calor 2002

49. LBNL PET detector modules • PD Array Identifies Crystal of Interaction • PMT Provides Timing Pulse and Energy Discrimination • PD+PMT Measures Energy Deposit • PD / (PD+PMT) Measures Depth of Interaction 1” square PMT PD array 64 element LSO array Custom IC Calor 2002 Courtesy of W. W. Moses, LBNL - CFI

50. UCLA Calor 2002 Courtesy of UCLA Crump Institute