uta gem prototype chamber characterization using cs137

UTA GEM Prototype Chamber Characterization using Cs137

Snowmass 2005, Aug. 15 – 27, 2005Jae Yu and ChangHee Hahn

University of Texas at ArlingtonChang Won National University, Korea

*On behalf of the HEP group at UTA.

• Introduction• UTA GEM Prototype Chamber• The Problem• The solution• Results• Conclusions and plans

8/23/2005 UTA GEM CharacterizationJ. Yu

1

Introduction• Fine cell sizes needed for calorimeter cluster

identifications and associations w/ tracks to minimize confusion in jet energy

• DHCAL: a solution for keeping the cost manageable for PFA

• GEM chamber characteristics good for a DHCAL for PFA

• A prototype chamber built w/ 10x10cm2 CERN foils– Cs137 and Sr90 sources used for characteristics, along with

cosmic ray


2

UTA GEM Prototype Chamber• Thinner plexiglass window

for easier source penetration• Single cell (1cmx1cm pad)

readout• Saw signal from cosmic-ray• Measured Landau

distribution using Cs137 source

• Measured double GEM intrinsic gain


3

UTA GEM Calorimeter Prototype Cosmic Event

Preamp Output

Trigger


4

Landau Distribution from Cs137 Source


5Signal Amplitude (mV)

GEM/MIP Signal Size Computation-Double GEM – applied 419V/foil -Total Ionization (C): ~93 i.p./cm

48 e- / MIP (5mm gap)-Double GEM Intrinsic Gain: G-Charge preamp sensitivity (GC) : 0.25 µV/e-

-Voltage amp. gain 10 (GV)-Output signal = C x G x GC x GV

-Observed ~370mV signal (mean of Landau) G = 3100 ± 20%


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Measured UTA GEM Gains

CERN GDD group measurements

UTA Prototype


7

The problem• When the chamber self-trigger was used, we saw

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2500

1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201

What is this peak due to?


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The decay characteristics of Cs137

Decay modes of Cs13755

1. β-decays to excited Ba13756

• End point energy 0.512 MeV2. γ emission of Ba decays to Ba

ground state: Monochromatic γw/ E=0.662MeV.

3. Direct β-decay to Ba ground state• End point energy: 1.174MeV

4. Monochromatic e from internal conversion electrons (624, 656 and 660keV)

5. Monochromatic 32 keV X-ray through Coulomb interactions

Decay modes of Cs13755

keV Error (keV) %

Gamma 661.645 0.004 85.0 monochromatic energy

X-ray 32.19(Ba-Kα1) 0.012 3.9031.82(Ba-Kα2) 0.007 2.1136.4(Ba-Kβ) 0.005 1.42

Characteristic X-ray-(monochromatic energy)

EmaxBeta 512 94.6

1174 5.4Continuous energy spectrum

Electron 624 8656 1660 0.6

Internal conversion electron or Auger electron(monochromatic energy)


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0500

100015002000

25003000

35004000

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Channel Number

Cou

nts

Charactaristic X-ray

Lead X-ray

BackscatteringComptonEdge

PhotopeakEγ=0.662MeV

E=0.032MeV

Cs137 Decay Spectrum


10


11

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1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 205 217 229

7.5

142.

527

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412.

554

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682.

581

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952.

510

87.5

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V19

00V

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00V

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00V

0.00.51.01.52.02.53.03.5

Perc

enta

ge o

f To

tal

Signal Voltage GEM Voltage

Sr-90 - 70:30

The small peak in Cs137 doesnot appear in Sr90 beta source!

Decay Mode of Sr90 Emax (keV) %E1 523 <1E2 546 100E3 2284 100

Sr90 Results

How do we separate Cs137 signals?1. Use Sr90 source and 1.65mm Cu plate

• Confirmed that all electrons from Sr90 are blocked by 1.65mm Cu and verified the stopping range expectation

2. Separate noise and cosmic ray, by removing the source3. Separate pulse heights from all electrons and X-ray, using 1mm

Cu plate• Provide pulse height distributions of 660keV γ-ray• These deposit energy through photoelectric and Compton effects

4. Use Cu of 0.65 mm to remove all betas but leave 660keV γ and X-rays

5. Use Cu of 0.1mm, 0.15mm and 0.2mm to determine whether the peak is due to internal conversion electrons or 32keV X-ray


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Electron Stopping Range (EST)In Copper In Copper : : ρρ= 8.960 [= 8.960 [g/cmg/cm³³]]

0.512 MeV 0.1883 mm0.624 MeV 0.2473 mm 1.0 MeV 0.4598 mm1.1 MeV 0.5185 mm1.174 MeV 0.56234 mm1.2 MeV 0.5778 mm2.284 MeV 1.2299 mm

Therefore,The 1.05mm copper plate can block all betas and IC electrons from Cs-137,Because Q-values of betas of Cs-137 are 0.512, 1.174 MeV,the kinetic energies of internal conversion electrons are 0.624, 0.656, 0.660 MeV,and the signals of 32 and 36 keV X-ray can be removed in the data.So, we can see only the signals of 662 keV gammas.

r=R/ρ

EST for End Point Energy of Cs-137 Beta

EST for End Point Energy of Sr-90 Beta

EST for Kinetic Energy of Internal Conversion

Electron

The 1.65mm Intercepting copper plate can intercept all betas of Sr-90.


13If we use 0.65mm intercepting Cu plate, we can see noise, gamma 663 keV and X-ray 32, 36 keV because most of betas and internal conversions are intercepted.

Mean Energy Loss of Electrons and Mean Ion Pairs Produced by Various Electrons in ArCO2(85:15)

Photoelectron by X-ray 32keV 1.226keV/mm 44.e /mm

Photoelectron 662keV Gamma662keV 0.261keV/mm 9.5e/mm

End point energy of Beta-1512keV 0.271keV/mm 9.9e/mm

End point energy of Beta-2 1174keV 0.253keV/mm 9.2e/mm


14

The SetupRadioactive source: Cs137/Sr90

2.1mm Cu collimator w/ a 5mm hole

Interceptor copper plate w/ 0, 0.1, 0.15, 0.2, 0.3, 0.6, 1.05, 1.65 and 2.0 mm

GEM Chamber


15

Reproduction of Cs137 Result

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NO

. of C

ount

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Pulse Height (mV)

ChangHee’sPeak


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660keV γ Spectrum(Corrected data w/ 1mm Cu plate)

• Noise and cosmic-ray subtracted• The 32 and 36 keV X-rays removed.• The internal conversion electrons and

betas are removed.

No ChangHee’s Peak!!

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NO

. of C

ount

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Pulse Height (mV)


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200400600800

NC

1 21 41 61 81 101 121 141 161 181 201 221

PH

32keV X-ray Spectrum(All – 660keV γ – all betas - noise)

ChangHee’sPeak

Separation of 32keV X-ray and Internal Conversion Electrons


19

200 400 600 800 1000 12000

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NO

. of C

ount

s

Pulse Height (mV)

0 mm Cu

•If ChangHee’s Peak were caused by internal electrons its position will shift to right as Cu plate thickness increases since the electron energy reduces.•If it’s X-ray, its amplitude will reduce.

Studies with various thicknesses of Cu plates show that the peak stays at the same location but its amplitude reduced.

The peak is due to 32keV X-ray not due to conversion electrons

200 400 600 800 1000 12000

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O. o

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Pulse Height (mV)

0.15mm Cu

Conclusions• UTA GEM Chamber characteristic study using CERN foils

made good progress– Thanks for the help of our visiting professor from Korea

• Chamber gains consistent w/ other measurements within the uncertainties

• Electrons MiP signals observed from Sr90 and verified• The origin of ChangHee’s peak in Cs137 source measurement

has been understood to be caused by photoelectrons from 32keV X-ray

• Electron MiP signals from Cs137 and 660keV γ isolated• This study will be written up for NIM• Will expand the study with 30x30cm2 3M foils


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uta gem prototype chamber characterization using cs137

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