PWO crystal study

1
PWO crystal study

• Alexander Toropin
• New York University

2
WLS (Wave Length Shifter) studies

• 4 All measurements were made with Blue LED with
  Peak emission
• wavelength of 430 nm which is compatible
  with light emission
• spectrum from PbWO4 crystal peaking at
  about 440 nm with
• 140 nm FWHM.
• 4 The studies were made by measuring DC voltage
  as shown below
• 4 Crystal was wrapped by Tyvek and opaque black
  paper.
• 4 APD was glued to crystal by special optical
  grease.

3
WLS studies

• On the previous meeting was shown picture
  with differences in light outputs from the
  crystal and from the crystal with WLS

4
WLS studies

• For further study of light yield from matrix
  of
• APDs more careful investigation of light
  source
• uniformity was made. As the light source Blue
  
• LED placed in the middle of rectangular tube
• (3x3 cm2) connected to the crystal was used.
• Distance between edge of crystal and LED was
• 10 cm. The voltages measured by Voltmeter
• KEITHLEY 197 for HV 300 V applied to APD
• 0002 are shown in the picture.
• New light source was made from 2 Plexiglas
• plates 3x3x2.5 cm3. LED was inserted into the
• tight hole in the middle of one plate.
  Surfaces
• was developed by abrasive paper to make
• diffused light . In the figure are shown
  the
• voltages in the case of this source.

5
WLS studies

• WLS 10 mm. Back connection of APDs.
• WLS 10 mm. No grease. Back connection.
• WLS 10 mm. Grease between crystal and WLS.

6
Crystal with APD Matrix

• Three APDs 0001, 0002 and 0004 were used.
  For each APD
• were measured 7 points around working point
  (gain 50) .
• Total current from all APDs at working point
  was calculated
• by taking into account real values of
  resistors and voltages.
• Matrix - UP
• Back connection.
• Total current 26.0 mA.
• Matrix - DOWN
• Back connection.
• Total current 26.1 mA.

7
WLS with APD Matrix

• Matrix - UP
• WLS 10 mm. Back connection.
• Total current 22.8 mA.
• Matrix - DOWN
• WLS 10 mm. Back connection.
• Total current 22.7 mA.
• WLS 10 mm. Edge connection.
• Total current 26.3 mA.

8
Measurements of Preamplifier noise

• h Preamplifier developed at BNL for ATLAS (CERN)
  with scale
• 324 mV / fC was used.
• h Pulse Generator HP 8013A as a signal source
  was used .
• h To differentiate pulse from generator were
  used simple circuits
• with capacitor 3 (10) pF or resistor 10
  000 W.
• Circuit with capacitor

9
Circuit with capacitor

• 1. Input capacitor 3 pF, input pulse 3 mV, 1
  ms. The shape
• of output signal from preamplifier is
  shown below
• Input charge for preamplifier could be
  calculated as
• Q C x V 3 x 10-12 x 3 x 10-3 9 fC

10
Circuit with capacitor

• Distributions of output signals and
• pedestal level (no input signal) are
• shown on the right side of this slide
• Noise of preamplifier as the number
• of electrons could be estimated as
• DNe Q x s / Mean x 6.24 x 1018,
• Mean Mean MeanNoSignal ,
• s (s2 s2NoSignal)1/2 where Mean
• and s are numbers from histogram
• In this case DNe 2.56 x 103 e

11
Circuit with resistor

• Input circuit with resistor
• For the signal from pulse
• generator 5 mV and 20 ns
• the output signal from
• preamplifier is shown here
• In this case input charge is
• Q V / R x Dt 10 fC

12
Circuit with resistor

• In this case thermal noise of resistor
• have to be taken into account
• QT VT / R x Dt, where
• VT (4kT x R x Df)1/2,
• k 1.38 x 10-23 J / K, T 300 K,
• 1 / Df Dt 70 ns (connected to
• preamplifier)
• QT (4kT x Dt / R)1/2 0.34 fC
• DNeT 2.12 e
• If DNe ( (DNePA)2 (DNeT)2 )1/2,
• DNePA 2.52 x 103 e

13
Measurements of Preamplifier noise

• APD connected to preamplifier could be
  simulated as additional
• parallel capacitor with C 80 pF connected
  to the simple circuits
• mentioned above. To estimate a level of noise
  could be produced
• by APD two curves were measured for the noise
  as a function of
• the additional parallel
• capacitor for circuits
• with the serial capacitor
• 10 pF and the resistor
• 10 000 W. In the case of
• resistor the thermal
• noise was subtracted .

14
Measurements with pulsed light

• These measurements were made with APD 0002.
  Pulse generator was used to feed Blue LED with
  V 3.4 V and Dt 20 ns.

15
Measurements with cosmic rays

• For these measurements three scintillation
  counters 3x11x1 cm3 were prepared. Signal from
  one of the counters if two other
• counters were used to make trigger signal is
  shown below.
• Preparation of set-up to measure the signals
  from crystal produced
• by cosmic rays is in progress.

16
Plans for the nearest future

• 4 To finish preparation of set-up to study
  signals from crystals
• produced by cosmic rays
• h Crystal (1 4) APDs
• h Crystal Photomultiplier
• 4 Repeat some measurements of WLS response with
  new
• Hamamatsu APDs
• 4 To study WLS effects with real light produced
  by particles
• from cosmic rays
• 4 Prepare matrix of 3x3 crystal counters for
  further study of
• calorimeter performance