Science-Driven Candidate Search for New Scintillator Materials FY 2014 Annual Report
Total Page：16
File Type：pdf, Size：1020Kb
PNNL-23752 PNNL-23752 Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830 Science-Driven Candidate Search for New Scintillator Materials FY 2014 Annual Report SN Kerisit LW Campbell F Gao D Wu YL Xie MP Prange October 2014 PNNL-23752 Science-Driven Candidate Search for New Scintillator Materials FY 2014 Annual Report SN Kerisit LW Campbell F Gao D Wu YL Xie MP Prange October 2014 Prepared for the U.S. Department of Energy under Contract DE-AC05-76RL01830 Pacific Northwest National Laboratory Richland, Washington 99352 Abstract This annual reports presents work carried out during Fiscal Year (FY) 2014 at Pacific Northwest National Laboratory (PNNL) under the project entitled “Science-Driven Candidate Search for New Scintillator Materials” (Project number: PL13-SciDriScintMat-PD05) and led by Drs. Fei Gao and Sebastien N. Kerisit. This project is divided into three tasks: 1) Ab initio calculations of electronic properties, electronic response functions and secondary particle spectra; 2) Intrinsic response properties, theoretical light yield, and microscopic description of ionization tracks; and 3) Kinetics and efficiency of scintillation: nonproportionality, intrinsic energy resolution, and pulse shape discrimination. Detailed information on the results obtained in each of the three tasks is provided in this Annual Report. Furthermore, peer-reviewed articles published this FY or currently under review and presentations given this FY are included in Appendix. This work was supported by the National Nuclear Security Administration, Office of Nuclear Nonproliferation Research and Development (DNN R&D/NA-22), of the U.S. Department of Energy (DOE). 1.3 Acronyms and Abbreviations ABINIT Electronic structure computer package CBM Conduction Band Minimum DOE Department of Energy DOS Density of States ERSP Electronic ReSPonse FY Fiscal Year GGA Generalized Gradient Approximation GGA+U GGA with Hubbard correction KMC Kinetic Monte Carlo LCPM Local Principal Curve Method LDA Local-Density Approximation LLNL Lawrence Livermore National Laboratory LO Longitudinal Optical NWEGRIM NorthWest Electron and Gamma-Ray Interaction with Matter PNNL Pacific Northwest National Laboratory STE Self-Trapped Exciton STEL Self-Trapped Electron STH Self-Trapped Hole VBM Valence Band Maximum WFU Wake Forest University YAG Yttrium Aluminum Garnet (Y3Al5O12) YAP Yttrium Aluminum Perovskite (YAlO3) 1.4 Contents Abstract ............................................................................................................................................ 1.3 Acronyms and Abbreviations .......................................................................................................... 1.4 1.0 Objective, Strategy and Findings Summary ............................................................................ 1.9 1.1 Objective ......................................................................................................................... 1.9 1.2 Computational strategy ................................................................................................... 1.9 1.3 Summary of findings ..................................................................................................... 1.10 2.0 Task 1: Ab initio calculations of electronic properties, electronic response functions and secondary particle spectra ...................................................................................................... 2.11 2.1 Summary of progress .................................................................................................... 2.11 2.2 Publications/Presentations ............................................................................................. 2.11 2.3 Progress during FY14.................................................................................................... 2.11 2.3.1 New theoretical approaches for more realistic thermalization models ............... 2.11 2.3.2 First-principles calculations of doped LaI3......................................................... 2.14 2.3.3 Electronic response to heavy particles ............................................................... 2.15 3.0 Task 2: Intrinsic response properties, theoretical light yield, and microscopic description of ionization tracks ..................................................................................................................... 3.16 3.1 Summary of progress .................................................................................................... 3.16 3.2 Publications/Presentations ............................................................................................. 3.16 3.3 Progress during FY14.................................................................................................... 3.16 3.3.1 Lanthanum halide series ..................................................................................... 3.17 3.3.2 Elpasolite series .................................................................................................. 3.18 3.3.3 Local principal curve analysis of ionization tracks ............................................ 3.19 4.0 Task 3: Kinetics and efficiency of scintillation: nonproportionality, intrinsic energy resolution, and pulse shape discrimination ............................................................................ 4.20 4.1 Summary of progress .................................................................................................... 4.20 4.2 Publications/Presentations ............................................................................................. 4.20 4.3 Progress during FY14.................................................................................................... 4.20 4.3.1 Scintillation model of SrI2 .................................................................................. 4.20 4.3.2 Electron and hole thermalization in alkali halides ............................................. 4.23 1.5 Figures Fig. 1. Flow chart of computational modeling process (with names of the codes developed in this project shown in the upper left-hand corners of each box). ..................................................... 1.9 Fig. 2. Computed phonon band structure of CsI. ........................................................................... 2.12 Fig. 3. Ab initio calculations of the rate of energy transferred to the CsI lattice by emission and absorption of phonons at 0 K and at room temperature. Also shown is the room temperature phenomenological model used in previous work. .................................................................. 2.12 Fig. 4. Computed band structure and density of states in CsI compared to the effective mass approximation. ....................................................................................................................... 2.13 Fig. 5. Average of the magnitude of the group velocity calculated from the band structure using Equation 2. Also shown are the velocities computed from the effective mass approximation and a model applicable to the KMC program. ....................................................................... 2.13 Fig. 6. Density of states of pure LaI3 crystal from GGA, GGA+U, and GW calculations. ........... 2.15 3+ 3+ Fig. 7. Density of states of LaI3 pure and doped with Ce and Bi in the ground state, as calculated with GGA+U. ....................................................................................................... 2.15 Fig. 8. Variation of the mean energy per electron-hole as a function of incident photon energy. 3.17 Fig. 9. Theoretical maximum light yields of a range of scintillators together with experimental values reported in the literature. ............................................................................................. 3.17 Fig. 10. Calculated spatial distributions of electron-hole pairs for a 10-keV photon event in CLLB and CLLC. Holes are shown in yellow and electrons generated via interband transition, plasmon, ionization event, and relaxation are shown in green, red, blue, and purple, respectively. ........................................................................................................................... 3.18 Fig. 11. Simulated spatial distributions of electron-hole pairs with local principal curves for two ionization tracks produced by 10-keV photon events in CsI. ................................................ 3.19 Fig. 12. Comparison of calculated and experimental percentages of the impurity emission in Eu- doped SrI2. Also shown is the impurity concentration required to optimize agreement with experimental data. .................................................................................................................. 4.22 Fig. 13. Temperature dependence of the total light yield, light yield from (Eu2+)* emission, and light yield from defect emission, from experiment and KMC simulations. ........................... 4.22 Fig. 14. Experimental and simulated scintillation decay curves of a 6-mm thick SrI2:2%Eu crystals at 295, 450 and 600 K. .............................................................................................. 4.23 2+ Fig. 15. Experimental and simulated decay curves of 2-mm, 6-mm, and 15-mm thick SrI2:2%Eu crystals at 295 K. ................................................................................................................... 4.23 Fig. 16. Thermalization time distributions of electrons with kinetic energies of 0.1 or 3.0 V as obtained with the