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Why SrI 2 : Eu?

Enhanced Resolution in Large Volume SrI 2 : Eu Detectors Jamie Brown Nuclear Security Detection Workshop 16 th April 2019 University of Surrey. Why SrI 2 : Eu?. Why SrI 2 :Eu?. ~120,000 photons/MeV, (c.f. 63,000 photons/MeV for LaBr 3 :Ce) <2.7% FWHM reported for small crystals (<1cm 3 )

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Why SrI 2 : Eu?

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  1. Enhanced Resolution in Large Volume SrI2:Eu DetectorsJamie BrownNuclear Security Detection Workshop16th April 2019University of Surrey

  2. Why SrI2:Eu?

  3. Why SrI2:Eu? • ~120,000 photons/MeV, (c.f. 63,000 photons/MeV for LaBr3:Ce) • <2.7% FWHM reported for small crystals (<1cm3) • high Zeff • low internal radioactivity • suitability to grow large crystals • excellent proportionality • 435 nm peak emission

  4. SrI2:Eu resolutions

  5. Self-absorption- re-emission What’s the problem?

  6. GEANT4 Simulations of SrI2:Eu • Geant4 optical simulation • WLS (wavelength shifting) method • Absorption and emission spectra taken from literature • Varied intrinsic decay time and absorption length (scaled absorption spectrum) to match peak emission and effective decay time, as function of thickness • This yields a fit to 5% Eu doped SrI2, as used in Alekhin2011 M. S. Alekhin, et al. (2011). IEEE Transactions on Nuclear Science, 58(5), 2519–2527. • Can match properties reported by other authors simply by changing the absorption scaling (as a proxy for different Euconcentrations)

  7. GEANT4 Simulations of SrI2:Eu Light collection changes as function of interaction depth Leads to degradation of energy resolution in larger crystals

  8. GEANT4 Simulations of SrI2:Eu Light collection changes as function of interaction depth Leads to degradation of energy resolution in larger crystals Methods of position determination: Ratio of light arriving at two sides of crystal Decay time changes as function of interaction depth

  9. Regulated N2 environment Low H2O content (<0.5 ppm) Low O2 content (<0.5 ppm) Light collection vs. interaction depth • Experimental setup 6x6x26mm3 SrI2:Eu crystal (RMD) Single 6x6mm2SensL C-series SiPM PTFE wrapping Glove box! 137Cs source 1mm slit collimator (copper) Scan crystal across slit Caen V1730B digitizer

  10. Light collection vs. interaction depth Peak shifts of ~5.5% are observed Other authors have reported shifts of ~1% Need to stabilise/compensate for temperature shifts

  11. Methods to determine interaction depth Two-sided readout • Same 6x6x26mm3 crystal • One SiPM at each end of crystal • PTFE wrapped • Flood illumination data and collimated scan

  12. Further Work Larger Crystals • 2 larger crystals from CapeSym 13x13x26mm3 26x26x26mm3 • Expect some variation in light collection with x, y, and z Can we extend to 3d?

  13. Thank you for listening Thank you to Victor Monier for taking data. Thank you to NuSec for funding.

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