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Radiation Damage Studies for Si Diode Sensors Subject to MRaD Doses

Radiation Damage Studies for Si Diode Sensors Subject to MRaD Doses. Bruce Schum UC Santa Cruz June 26 2013. The Issue: ILC BeamCal Radiation Exposure. ILC BeamCal: Covers between 5 and 40 miliradians Radiation doses up to 100 MRad per year

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Radiation Damage Studies for Si Diode Sensors Subject to MRaD Doses

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  1. Radiation Damage Studies for Si Diode Sensors Subject to MRaD Doses Bruce Schum UC Santa Cruz June 26 2013

  2. The Issue: ILC BeamCal Radiation Exposure ILC BeamCal: Covers between 5 and 40 miliradians Radiation doses up to 100 MRad per year Radiation initiated by electromagnetic particles (most extant studies for hadron –induced) EM particles do little damage; might damage be come from small hadronic component of shower? 2

  3. G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993) NIELe- Energy 2x10-2 0.5 MeV 5x10-2 2 MeV 1x10-1 10 MeV 2x10-1 200 MeV Damage coefficients less for p-type for Ee- < ~1GeV (two groups); note critical energy in W is ~10 MeV But: Are electrons the entire picture? 3

  4. Hadronic Processes in EM Showers • There seem to be three main processes for generating hadrons in EM showers (all induced by photons): • Nuclear (“giant dipole”) resonances • Resonance at 10-20 MeV (~Ecritical) • Photoproduction • Threshold seems to be about 200 MeV • Nuclear Compton scattering • Threshold at about 10 MeV;  resonance at 340 MeV •  These are largely isotropic; must have most of hadronic component develop near sample 4

  5. N.B.: Tungsten very expensive; use lead for target instead Post-radiator and sample Pre-radiator

  6. Proposed split radiator configuration 5mm Tungsten “pre” 13mm Tungsten “post” Separated by 1m Fluence (particles per cm2) 1.0 2.0 3.0 6 Radius (cm)

  7. Rastering • Need uniform illumination over 0.25x0.75 cmregion (active area of SCIPP’s charge collection measurement apparatus). • Raster in 0.05cm steps over 1x1 cm, assuming fluence profile on prior slide (see next slide for result) Exposure rate: e.g. 1 MRad at 0.1 nA of 4 GeV e-  ~ 1.5 Hrs

  8. Charge Collection Apparatus Sensors DAQ FPGA with Ethernet Sensor + FE ASIC • Recently upgraded for multiple samples • P-type and N-type sensors • Float-zone and Magnetic Czochralski bulk • Will maintain -10o C during and after irradiation • At least 3 samples of each of four types in hand 8

  9. RUN ACTIVITY We 6/19 Begin installation (open access) Th 6/20 Complete installation; search and secure 3-5pm Fr 6/21 Alignment with beam. Activation study with dummy sample. Accumulate 2 MRad of first 5 MRad run. Sa 6/22 Complete three of four 5 MRad runs. Accumulate 15 MRad of first 20 MRad run. Su 6/23 Complete first 20 MRad run and last 5 MRad run. Mo 6/24 Study first 5 MRad sample at UCSC. Tu 6/25 Complete 2nd 20 MRad run. We 6/26 Down: peltier cooler controller failure; up soon; start third 20 MRad run Th 6/27 Complete 3rd and 4th 20 MRad run; do short additional calibration run

  10. First results: 5 MRad Radiation Damage Study BULK: P-type Process: Float Zone

  11. Issues Doses measured with radiochroic film are x3 less than EGS-based estimate  Perform independent calibration with capillary dosimeter (tomorrow) Lost ~1/2 shift due to equipment failure (might be radiation related; not clear)

  12. Backup

  13. 5.5 GeV Shower Profile e+e- (x10) All  “Post” “Pre” Remember: nuclear component is from photons in 10-500 MeV range. Fluence (particles per cm2) E > 100 MeV (x20) E > 10 MeV (x2) 13 Radius (cm)

  14. Shower Max Results Photons with E > 100 MeV per electron, x 100 Photons with E > 10 MeV per electron, x10 Photons per electron Electrons, per GeV incident energy 1.0 2.0 3.0 14  Photon production ~independent of incident energy!

  15. Fluence (e- and e+ per cm2) per incident 5.5 GeV electron (5cm pre-radiator 13 cm post-radiator with 1m separation) Center of irradiated area ¼ of area to be measured ¼ of rastoring area (0.5mm steps)

  16. NIEL (Non-Ionizing Energy Loss) • Conventional wisdom: Damage proportional to Non- Ionizing Energy Loss (NIEL) of traversing particle • NIEL can be calculated (e.g. G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 [1993]) • At EcTungsten ~ 10 MeV, NIEL is 80 times worse for protons than electrons and • NIEL scaling may break down (even less damage from electrons/positrons) • NIEL rises quickly with decreasing (proton) energy, and fragments would likely be low energy •  Might small hadronic fractions dominate damage? 16

  17. Rates (Current) and Energy • Basic Idea: • Direct electron beam of moderate energy on Tungsten radiator; insert silicon sensor at shower max • For Si, 1 GRad is about 3 x 1016/cm2, or about 5 mili-Coulomb/cm2 • Reasonably intense moderate-energy electron or photon beam necessary What energy…? 17

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