Measurement of Ge detector by New cooling system @ KEK

Apr 25th K.Shirotori

Purpose Present Ge detectors are cooled by LN2. But with

this method, the large LN2 dewar makes Hyperball array geometry difficult to be flexible and filling LN2

every 12h is cumbersome and difficult to operate in the counter hall in J-PARC.

Automatic, Compact, Easy to operate, (+Maintenance free)New cooling system is needed.

Requirements of new cooling system The operating temperature should be the

same as LN2 cooling or better. → ～ 90[K] Ge detector which has sever radiation damage shows resolution

degradation for more than 90[K] (energy resolution >10keV).

It works stably for several months. Our beam time is 1~2 month long. During beam time, once Ge

detectors are warmed up, their resolution will deteriorate because of radiation damage. In such a case they need to be annealed!

　　 when achieved Make it as compact, cheap, and easy operation

as possible while low maintenance and so on. (Next development)

PopTop type detector

Present status of LN2 cooling and energy resolution of 60Co 1.3MeVγ-ray

Ge

Ge Easily removable

Relative efficiency @ 1MeV γ-ray →30% (compared with NaI 3Φ)

P-type semiconductor

Size 5cmΦ×5cm

Ge Coolingmachine

LN2Dewar

Temperature measurements @ LN2 Temperature aft

er LN2 filling. It is measured at

thermo couple. It takes 12 hours

to reach the final (equalibullium) temperature.

The operating temperature is 97[K].

Resistance

513446.5391315

174 143143.4

148

533

143.5 145.4145.3

142

0

100

200

300

400

500

600

0 10 20 30 40 50[hour][Ω

]

Resistance[Ω ]

Temperature

246218180

111 979797

9799

280

9796

290

050100150200250300350

0 10 20 30 40 50[hour]

[K]

Temperature[K]

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

Set up of measurement

1.72[keV](3μs is 1.80[keV])

New cooling system “Pulse tube”

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

What to check in KEK Can new cooling system reach the LN2

cooling temperature ～ 90[k] or under the threshold temperature where radiation damage appears, ～ 85[k] ?

Dose the oscillation of compressor for pulse tube cooler make energy resolution worse ?

Are there any problems when operating new cooling system ?

Set up @ KEK

Temperature @ Cooling machine The final (steady states)

temperature is 77[K]. The goal that temperature is

below 85[K] is achieved. But, after switching on the

preamp of Ge detector, the heat from amp makes temperature increased to 84[K]. The temperature of Ge is sensitive to the increase from external environment.

The connection and electrical insulation between Ge and the cooling machine are not optimized.

Resistance

0100200300400500600

0 10 20 30 40 50[hour]

[Ω]

Resistance[Ω ]

ResistanceKEK[Ω ]

Temperature

050100150200250300350

0 10 20 30 40 50[hour]

[K]

Temperature[K]

TemperatureKEK[K]

Energy resolution @ KEK Energy resolution is very bad because of a lot

of noise, such as motor of vacuum pump, power supply of the cooling machine and ….

The oscillation of cooling machine and noise from power supply are large factors which make energy resolution worse .

Present resolution is 12[keV]. When the cooling machine is switched off,

energy resolution is 6.5[keV] (still a lot of noise).

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

Ge detector and the cooling machine. → improvement on this connection.

The oscillation of cooling system. Noise.

But….. They were almost expected before this

measurement. We gained some information whether or not these problems can be solved.

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, the oscillation and noise.

The second is to cool and measure the resolution again and to test the long time stability.

Summary The new cooling system has comparable or

better performance than LN2 cooling. There are a lot of problems that we identified,

but these problems are expected and we think they are manageable.

The next point of development is clear.

一目瞭然