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Calibration of uniformity between LYSO crystals

Zhigang WangInstitute of High Energy Physics, CAS

2016.01.20

The Third International Workshop on the High Energy cosmic-Radiation Detection

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Outline

1, LYSO performance test from a 137Cs source2, Calibration results from pions beam3, Exploited LYSO intrinsic background for calibration purposes

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1, LYSO performance test from a 137Cs source

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Intrinsic background of LYSO crystal

LYSO= Lu2(SiO4)YO:CeLutetium based scintillator175Lu Stable: 97.4%176Lu Radioactive: 2.6%

LYSO crystal contains a fraction of the naturally occurring isotope 176Lu, which undergoes β-decay followed by the emission of 88,202and 307 keV gamma rays causing signals which can cause phosphorescene.

Decay chain of 176Lu Spectrum of LYSO intrinsic background

597 keV

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Test setup in laboratory

In the measurement, one face of the LYSO crystal was coupled to PMT(XP2020) with an air gap, while all other faces were wrapped with ESR reflector.

Data acquired by DT5751.The DT5751 is a 2-4 Channel 10 bit 2/1 GS/s Desktop Waveform Digitizer with self trigger. 

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LYSO irradiation with 137Cs source

1: Background(Red) 2:Background + 137Cs(blue)

137Cs Spectrum: [1]-[2]

Limited by the transfer rate of the DT5751, only the high energy events are selected by set a proper energy threshold.

Light output and resolution results used to selected crystals.

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Relative light output of 250 LYSO cubes

250 LYSO crystals were selected from 260 pieces.The difference of light output of 250 LYSO is ~25%, as shown in figure.The difference of six sides of one LYSO crystal cube is little than 4%.

Crystal number

Light output

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Energy resolution of 250 LYSO cubes

The energy resolution of the 250 LYSO crystals we selected is <5%.

Crystal number

σ/E

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2, Calibration results from pions beam

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During the beam test at CERN, we carried out Pion(50GeV/c) calibration four times. The forth calibration data is significantly larger than other three.

Pion calibration resultsPion calibration-1Pion calibraton-2Pion calibration-3Pion calibraton-4

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Variation of the calibration

Select second set of data as standard, compare calibration data which from the same crystal.

For the same piece of crystal, the calibration result shows up an increasing trend.

Very preliminary result

Pion calibration-1Pion calibraton-2Pion calibration-3Pion calibraton-4

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3, Exploited LYSO intrinsic background for calibration purposes

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ICCD readout system of HERD

The image intensifier has two roles in the readout system: electronic shutter andsignal amplifier.

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LYSO intrinsic background image

The energy deposited by MIP in HERD LYSO crystal is about 30 MeV, the highest peak of intrinsic background from LYSO is about 600 keV. In the normal data taking mode, the image intensifier worked with proper gain: the ICCD can detect MIP, while the intrinsic background will have no influence on it.If adjust the image intensifier with higher gain , the intrinsic background will produce signal in ICCD.

Fiber distribution Intrinsic background image in ICCD

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LYSO intrinsic background signal

The intrinsic background signal with different image intensifier gain.

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Compared with Pion calibration

The intrinsic background and pion calibration results.

Pion calibration-1Pion calibraton-2Pion calibration-3Pion calibraton-4LYSO background

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 To a certain degree, the intrinsic background of LYSO can be used as a complementary calibration method. The accuracy of LYSO intrinsic background calibration need to improved.

Compared with Pion calibration

Pion calibration-1Pion calibraton-2Pion calibration-3Pion calibraton-4LYSO background

Very preliminary result

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Radiation damage of LSO and YSO under 24 GeV protons

E. Auffray , A. Borisevitch, A. Gektin , et al.

E. Auffary, A.Barysevich, A. Fedorov, et al. “Heavy charged particles, such as protons, hadrons, or nuclear fragments, lose much more energy and generate a shower of displaced ions in the crystal.A set of radioisotopes is created in the crystal.”

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Radiation damage of LYSOLYSO background during beam test

LYSO background before beam test

This may be one of the reasons why the calibration and resolution results are not good as expected. We need to work even

harder!

We can expect that after LYSO crystals interacting with heavy charged particles, will also create a set of radioisotopes.One of the main consequences of radiation damage in LYSO crystals is the induced phosphorescence.

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Thanks!

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Peak position at 12030 ADCMIP energy ~ 375 p.e.