1

Cosmic Ray Test Stand with Scintillating Cells for Digital Hadron Calorimeter

06/23/2003

Kurt Francis - Northern Illinois University

2

Introduction

• At NICADD we studying technology for the design of a Digital Hadron Calorimeter using scintillating cells

• As a first step we built a cosmic ray test stand with 2 layers of 7 hexagonal scintillating cells (9.4 cm2 x 5mm thick BC408 with sigma groove, painted white)

• Light from the 14 cells is fed through optical fibers into a 16 channel PMT

• The analog electrical output of the PMT is digitized with a VME bus QDC and then read into a PC

3

Multi-ChannelPMT

Cosmic Ray Test Stand• 14 Hexagonal Cells and Optical Fibers connected to 16

channel Hamamatsu H6568 Multichannel-PMT

Multi-ChannelPMT

Top view

Side view

4

COSMIC RAY TEST STAND

TRIGGER COUNTER #1-set of 7 cells ganged to one

single channel PMT

TRIGGER COUNTER #2

TRIGGER COUNTER #3

14 cells connected to 16 channel PMT to collect comic ray data under

investigation

BLOCK OF PASSIVE ABSORBER MATERIAL (STEEL, BRASS, LEAD)NUCLEAR INTERACTION LENGTH

~ 1.5

LIGHT PROOF BOX

5

Software

• Used National Instruments LabView to create software to collect data from 32 channel VME QDC

• Data is dumped into a flat data file

• Wrote my own software to view and analyze data – used Microsoft Visual Basic

– displays histograms or scatter plots

– plots can be arranged by cell or by PMT channel

• Also used Excel, Origin, JAS, and PAW

6

7

First Layer of Cells Second Layer of Cells

SCATTER PLOTS

8

First Peak: Crosstalk?

Initial Observations: Data collected has two curves to right of pedestal. What is first peak?

9

Channel 4 Not Isolated

First step isolate a channel

Channel 4 isolated from other channels by black paper between cells and by

covering all but ch4 photocathode withblack paper

10

Crosstalk

• Isolating a single channel from others reduces the first peak - indicates the first peak is caused by crosstalk from the other cells / channels

• Crosstalk can be:– Optical crosstalk between cells

– Optical crosstalk at PMT due to photocathode cover

– Electrical crosstalk at PMT

11

3

62

4

87

5

14%

10%

11%

11%

11%

15%

5%

10%

5%

13%8%

6%8%

7%

Standard Configuration with no black paper

Cells 5,8,6 covered by black paper and layers separated by paper

Crosstalk at cells evaluated by covering some of cells with black paper.

Note: this apparently weak cell (#5) was later found to be due

to the ADC channel

Cell numbering scheme

Number on cell is percent of total events in first peak

-->Suggests Optical crosstalk at cells can be reduced by isolating cells with black paper

12

Scatter plot of all PMT channels with Channel 4 stimulated by several fibers driven by LED-Other channels are not connected-Cells are not connected

-->Suggests crosstalk at PMT

Crosstalk at PMT evaluated by covering all but one channel.

13

Another way to view crosstalk at PMT

15

91316 15 14 13

0%

20%

40%

60%

80%

100%

Crosstalk in other channels due to channel 4 as a percentage of channel 4

In this case only channel 4 is connected to a cell collecting cosmic ray data - all other channels have crosstalk from channel 4

14

Summary of crosstalk issues

• Part of crosstalk is optical crosstalk between cells– Initially used cells painted in white paint to reflect light back into

scintillator

– We can reduce optical crosstalk by covering cells with black paper

– Another option would be to paint cells with black paint

• A greater part of crosstalk occurs at the PMT– Probably due to optical diffusion in the photo-cathode cover

– This crosstalk is significant only on adjacent channels

15

Finding the single photo-electron peak for a single channel

• Use 2,3,4,5 layers of neutral density gelatin filter material– (Kodak No.96 N.D. 0.20 = 63% transmission)

• Stimulate with an LED channeled through optical fiber

• Start with 2 layers of filter -> get peak far from pedestal

• Increase filter layers -> pedestal appears and grows,

• Position of peak moves closer to pedestal, shrinks and merges with pedestal

• When the position of the peak stops changing as filter layers are added then moving closer top pedestal then we have found the single photo-electron peak

16

Example using channel 4/20

17

Light Attenuation versus Number of Filter Layers(Channel 4)

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6 7 8

Number of filter layers (63% transmission)

Po

siti

on

of

Pe

ak

in A

DC

C

ou

nts

--> plots with 4 - 8 filter layers is approximately flat and linear - expected for the single photo electron peak

18

Distance from Pedestal in ADC Counts32 29 25 2730 24 26 2533 17 27 2531 29 23 28

--> Indication of ‘gain’ for that particular channel

Single Photo-Electron Map

Single Photo-electron peak

19

Light Yield by Channel (P.E.)--- 12.8 10.2 11.1

14.6 16.2 --- 10.711.1 16.6 8.3 8.411.8 14.4 12.8 11.0

Light Yield Map

The light yield for the cell/channel combination is equal to the ADC Counts from the pedestal of the MIP peak (determined from cosmic ray data sets) divided by the ADC Counts from pedestal of the S.P.E peak (determined from the LED with filter layer tests as described on the previous slides)

20

Distribution of Light Yield

0

1

2

3

4

5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Light Yield in P.E. (rounded)

Nu

mb

er

of

Ch

an

ne

ls

Range of a factor of 2

21

Summary

• NICADD has developed a cosmic ray test stand using scintillating cells to prepare for DHC

• The test stand reveals crosstalk

– Optical crosstalk between cells - can be reduced by isolating cells with black paper or paint = 30 to 40% of total crosstalk

– Crosstalk at PMT (probably optical) = 60 to 70 % of total

• Can use LED driven by pulse generator and layers of filter material to find Single photo-electron peak (S.P.E.)

• S.P.E. and M.I.P. average can be used to determine light yield cells

• The light yield has a range of 8 to 17 P.E.