SPI ACS EM Scientific Measurements

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SPI - ACS EM Scientific Measurements

• August 19 - September 4, 1998
• at DSS (Friedrichshafen)
• A. v. Kienlin, R. Georgii, C. Wunderer

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Overview

• ACS EM configuration for scientific measurements
• Results
• Linearity and Calibration of Energy and Event
  Thresholds
• Single Photoelectron Spectrum
• Gamma-ray Line Spectra
• Processing Times and Jitter
• Overrange Signals, overall ACS rate monitor
  (burst mode)
• Problems encountered
• SPI Documents SPI-MPE-PL-12-22
  (Plan) SPI-MPE-RP-12-26 (Report, in
  preparation)

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ACS EM
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ACS EM Configuration for scientific measurements
(I)

• 1 BGO detector module
• 2 PMTs
• 1 BGO crystal, consisting of 2 crystal blocks
  glued together, total dimensions 1.6 ? 5 ? 8 cm3
• 1 LED dummy
• 2 PMTs
• 3 LEDs for generation of single photoelectrons
  (SPE), lower energy and overrange events
• 1 RC circuit (charge box) for precise charge
  injection to CSA input of FEE

C
R
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LED-Dummy
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BGO Crystal Detector Module
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ACS EM Configuration for scientific measurements
(II)

• 1 FEE with CSA output connector (reference
  FEE)(not officially part of ACS EM)
• FEE Unit Tester (FEE-UT)
• 2 FEEs
• EMC representative ACS EM with VCU
• VCU Unit Tester (VCU-UT)
• all 3 FEEs design status MARCH 1998

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FEE-Unit Tester with FEE and LED-Dummy
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VCU - Unit Tester
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Linearity of Event-Trigger Thresholds
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Linearity of Energy Thresholds
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Generation of Differential Spectra

• Measure number of counts per 5 sec for each
  energy or event-trigger threshold setting
• This Stepping Method yields integral energy
  spectra (counts above threshold)
• Differentiate to obtain energy spectra (counts
  per channel)

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Single Photoelectron (SPE) Spectrumusing LED
Dummy
PMT HV nominal (1129 V)
HV low (1088 V)
HV high (1170 V)
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Single Photoelectron Measurements

• Using
• FEE event-trigger threshold calibration
  (knowledge of charge at CSA input corresponding
  to an event-trigger level)
• knowledge of PMT gains at different HVs
• observed peaks correspond to 1.7 x 10-19 (? 0.3 x
  10-19) Cb generated at photocathode
• SPE spectrum from LED with a different FEE
  corresponds to 2.0x10-19 (? 0.3 x10-19) Cb
• results consistent with expected values (single
  photoelectrons!)!! So far SPEs measured only
  using LED Dummy !!

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Ab hier Reservefolien
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Detail ACS EMLED-Dummy and Crystal Dummy
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LED - SPE Spectrum measured automatically using
VCU-UT program