CsI Veto Detector Performance Study

1
CsI Veto Detector Performance Study

• He Dao
• DMRC. Tsinghua University
• For KIMS Collaboration

2
ULE WIMP Experiment

• WIMP search
• Ultra-Low Energy wimp experiment
• HPGe detector
• Expected threshold 100 eV
• Correspond WIMP mass limit 1GeV

3
System Structure
4
CsI detector structure

• Three parts of crystal
• Cylinder top with a slope
• Tube side
• Cylinder bottom
• Optical gel connection
• Cooler hole
• Low background PMT
• Al Shell only for safety

5
HV Selection

• Daq CAMAC Source Cs-137 Output signal
  amplitude

• -1300V selected
• A reference if HV changed

6
Incidence position dependency

• Influence factors
• Big dimension causes serious photon absorption
• Conjunction section reflection
• Cooler hole
• Only one PMT used

• Daq MAC
• Source Cs-137
• Test consideration height and angular dependency

7
Source position dependency
Height (cm) 1.5, 7, 13, 22, 28 Angle
(degree) 180
Height (cm) 5 (near the hole) Angle
(degree) 0, 90, 150, 180
8
Height dependency

• Peak position
• The nearer incident position from PMT, the larger
  amplitude of output signal
• About 70 response while source near the bottom
  relating to the top position
• Peak resolution
• Round 16, best situation when source in middle
  height, top and bottom worse.
• Main reason Big size causes photon absorption
  pieces section reflection

9
Angular dependency

• Peak position
• No obvious difference
• Resolution
• The cable hole causes serious resolution
  difference, 90 degrees response is best. That
  maybe because the cooler hole is void while I did
  this test. Fortunately, as a veto detector, the
  resolution is not very important.

10
Oscilloscope Calibration (Crystal top)for
internal background measurement
HV -1200V Source information
Calibration Result

• E(keV) ( channel - p0 ) / p1

11
Internal background

• Only CsI crystal top
• 15cmPb, 5cm Cu
• Daq Oscilloscope
• 10 days

Possible source Decay chain, internal source,
and Radon. More accurate measurement by HPGe
detector running in Y2L.
12
Photon collection efficiency comparison
According to HV selection result, if high voltage
is set at 1300V the signal amplitude should be
about 705/463 to that of 1200V, considering the
scale change, the photon collection efficiency of
CsI crystal top is 705/463 100/50 5942/5884
3 times to that of whole detector!
13
Summary

• Working Voltage
• Wide range , -1300V selected
• Incidence position dependency
• Obvious height dependency, weakest situation 70
  signal amplitude compared to strongest
• Not serious angular dependency
• Internal background
• Decay chain, internal source, and Radon.
• More accurate measurement running now by HPGe
  detector in Y2L
• Photon collection comparison
• Only top 3 times better than whole detector

14
Plan

• Pulse Shape Discrimination
• More accurate internal background content and
  activity
• MC simulation

Thank you!