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Neutron damage of DSSDs

Neutron damage of DSSDs. Neutron irradiation. 5. Nakayama-san expects ~ 100 MeV neutrons However, the rate is still 10 11 /cm 2 /year! ~10 12 /cm 2 during Belle II lifetime! near the type inversion (but needs proper scaling...). Neutron background. Neutron energy is around 5MeV. 3.

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Neutron damage of DSSDs

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  1. Neutron damage of DSSDs Manfred Valentan (HEPHY Vienna)

  2. Neutron irradiation 5 • Nakayama-san expects ~100 MeV neutrons • However, the rate is still 1011/cm2/year! • ~1012/cm2 during Belle II lifetime! • near the type inversion (but needs proper scaling...) Manfred Valentan (HEPHY Vienna)

  3. Neutron background Neutron energy is around 5MeV. 3 Manfred Valentan (HEPHY Vienna) • Neutron from radiative Bhabha • Gammas from radiative Bhabha event will propagate along beam axis and hit the beam pipe/magnet iron at ~10m downstream, then coming back to Belle. Main source of KLM neutron BG. Scales with luminosity (KEKBx40), we should increase the shields in tunnel. • Neutrons generated in Touschek loss shower • Touschek particles hit the beam pipe at s=~1m (inside detector) • More dangerous, because generated very close to detector and almost impossible to shield . • Showers generated by 4GeV e+ hitting beam pipe consists of high energy neutrons(~100MeV) • Beam tests so far is done at ~370keV. • Any sub-detector using Si or readout FPGA might be affected.

  4. Assuming no stopping power by detector materials, 0.9GHz e+  at 1m away, ~104/cm2/sec neutrons  at 1m away, ~1011/cm2/year neutrons (PID group assumption: 1011/year/cm2) (Radiation test at Yayoi, 370keV: 1012/cm2) 0.9GHz e+ LER e+ At 1m away, ~1011/cm2/year of ~100MeV neutrons 2m Neutron energy is around 5MeV. 3m • Thanks to the additional collimators, the neutron flux are now comparable to the PID estimation (1011/cm2/year), but the neutron energy is much higher (~100MeV, not 370keV). • Detailed neutron spectrum will be given by GEANT4 full simulation soon. 4 Manfred Valentan (HEPHY Vienna)

  5. Neutron damage • Even the corrected background simulation results predict considerable neutron damage • Neutron dose seems to be too high • near type inversion „feels“ unplausible • Please ask Nakayama-san if neutron rate is really 1011/cm2/year! • If so, we must still be very careful and think about a neutron irradiation test! Manfred Valentan (HEPHY Vienna)

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