Measurement of Ge detector by New cooling system 2 @ KEK

May 30th K.Shirotori

Problems of previous experiment The heat leak around the connection

between Ge detector and the cooling machine.

→ improvement on this connection.

The oscillation of cooling system. Noise from environments.

We can’t test it.

Energy Resolution @ KEK Side room.HV +2500 (P-type semi-con)60Co 1.33MeV6μs shaping time @ 671 AmpDAQ Amptek MCA8000A (maru-chan)

Set up of measurement

60Co 1.72[keV]Test pulse 0.79[keV](3.2ch for ADC)Consistent with the measurement

in Tohoku Univ.

Eγ[keV]

Counts

Set up - LN2 @ KEK

Ge detectorLN2 Dewar

60Co source

Set up – Refrigerator @ KEK

Vacuum pumpPower supply

Ge detector

Cooling machine

Thermo couple

日本語で

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大き

さ

Noise from environmentsLarge noises are …. Power supply of cooling machine→Prepare two types of power supply(Previous one and “clean” one) Vacuum pump, Thermo couple→Separable

We checked themby Test Pulsar.

Noise and resolution by test pulsarResolution

[keV]Power supply

Vacuum pump

Thermo couple ※

19.0 ○ ○ ○

13.6 ○ ○ ×

4.79 ○ × ×

0.79 × × ×

Contribution

[keV]4.7 13 13

σ2energy resolution=(σ2

crystal+)σ2elec+σ2

power+σ2pump+σ2

thermo

Noise from thermo couple by Ge detector coverOpen

↓Noisy

・ Unstable ground connection・ Electric wave from environment

Noise of Previous power supply Too bad …

↓We didn’t measure this condition.(Same as previous measurement)

・ 20kHzchopping noise form power supply

Output from PreAmp

Noise of Clean power supplyIt looks good, but energy resolution is bad.→～ 4[keV]

Output from PreAmp

Noise check of power supply

Power supply : OFFVacuum pump : ON→13[keV]

Power supply : ONVacuum pump : ON→19[keV] by test pulse

Power supply : ONVacuum pump : OFF→5[keV]

50[mV]

10[μs]

671 AmpOutput

Noise check of power supply

Bad Power supply : ONVacuum pump : OFF→Impossible…

Power supply : OFFVacuum pump : OFF→0.8[keV] same as LN2Ideal condition

Everything connected with Ge detector contribute its noise.→No solution without insulation.

671 AmpOutput

Energy resolution of 60Co 1.33MeVγ-rayWe only checked the important part, the contribution of noise from Power supply.

[ch]

WithPowersupply

WithoutPowersupply

Test pulse[keV]

Ge

ResolutionWith Power Supply

60Co 1.7 5.0

Test

Pulse0.85 4.7

We can know each contribution.

Contribution for Energy resolutionEnergy resolutionσ2

energy resolution=σ2crystal+σ2

elec+σ2power+σ2

vibration Test pulseσ2

test=σ2elec+σ2

power

σcrystal = 1.5[keV] σelec = 0.85[keV] σpower = 4.6[keV] σvibration = 0.82[keV]

The effect of vibration is small.

→Microphonics is small.

σ2resolution =σ2

crystal+σ2elec+σ2

vibration

→1.9[keV]

Temperature @ Cooling machine 2 The final (steady states)

temperature is 97[K]. The contact between Ge

and the cold head is worse than previous measurement.

The heat conducting grease is not enough.

Resistance

0100200300400500600

0 5 10 15 20[hour]

[Ω]

Resistance[Ω ]

ResistanceKEK[Ω ] 4/ 20

ResistanceKEK[Ω ] 5/ 22

Temperature

0

100

200

300

400

0 5 10 15 20[hour]

[K]

Temperature[K]TemperatureKEK[K] 4/ 20

TemperatureKEK[K] 5/ 22

Problems and things to do The heat leak around the connection betwee

n Ge detector and the cooling machine. → Improvement on this connection. The oscillation of cooling system.→Relatively small. Noise (electric).→We need electric insulation between Ge and

cooling machine. Next test.

Next step The first thing is to construct new connection

parts between Ge detector and the cooling machine. This improvement will reduce the heat leak and noise.

The second is to test the long time stability.

Summary It is clear which contribution of noises makes

energy resolution worse. It is most important to insulate Ge detector from cooling machine.

Cooling Mechanism The cooling mechanism

is simply a heat cycle. 1

2

3

4

1→2 : Isothermal absorption (等温吸熱 )2→3 :Adiabatic compression (断熱圧縮 )3→4 :Isothermal heat rejection (等温放熱 )4→1 :Adiabatic expansion (断熱膨張 )

TCTH TH

TH

TC

The harmonic wave for heat cycle The heat cycle is made by “LC circuit of fluidity”.

Commpressors move symmetrically.→To reduce vibrationElectricity ⇔ Fluid