PNNL X-coolerII-GEM120P4

From New IAC Wiki
Jump to navigation Jump to search

PNNL's HpGe X-cooler poptop detector

Model: GEM120P4

The above model number indicates that the detector has an relative efficiency of 120% with respect to a 3" x 3" NaI crystal, a resolution of 1.3 keV for 122 keV photons, resolution of 2.1 keV for 1.33 MeV photons, a peak to compton ratio of 86:1, and end cap diameter of 0.108 mm.

serial #: 44-TP41387A

GEM model => p-type => Usually a positive HV bias

GMX model => n-type => Usually a negative HV bias



HV shutdown signal

Condition 1: With the HV and HV Shutdown connected and the preamp disconnected the detector will be in shutdown mode as there will be no current signal from the preamplifier to the HV power supply.

Condition 2: With the HV , HV Shutdown and Preamp connected when the detector is warm, there will be a positive voltage signal to the HV power supply which will activate shutdown.

Condition 3: With the HV , HV Shutdown and Preamp connected when the detector is cold there will be a negative voltage signal from the preamp to the HV power supply which will allow the application of HV.

Condition 4: With the HV and Preamp connected and the HV Shutdown disconnected when the detector is cold the detector will be in shutdown mode.



The compressor is a refrigeration unit that should remain horizontal. You have a time window from 5 minutes after the 120 Volts is interrupted until 10 min afterward to restore power. It is recommended that you allow it to settle for 6 hours if power is restored after 10 minutes as well as thermally cycle the system (i.e. let it sit for a minimum of 6 hours ideally 24 hours and then turn it back on). The compressor must not exceed an inclination angle of 10 degrees.

Vance Harmon from Ortec beliefs that a cart can be used to move the compressor if floor obstacles, like transitions to the Hall, are rolled over gently.


The detector may be positioned at any angle and height just do not exceed the bending limits ( 6" bend radius) of the cooling lines. (information confirmed by Vance Harmon at Ortec



Face of detector was cold to the touch and the HV shutdown would not allow voltage to be applied.

We decided to pump out the detector chamber. A pen mark at the pump out port was observed indicating that on 12/15 the vacuum was [math]1.6 x 10^{-6}[/math] Torr. There was every indication that the vacuum was in the milli-Torr range and at best 2 x 10^{-5} Torr (The milli-Torr gauge registered a pressure at the moment the valve was opened on the detector to pump out the detector chamber). After a few minutes the pressure was at 6 x 10^{-6} Torr. After about 10 minutes it was at 3 x 10^{-6} Torr. We pumped it out for 3 hours and achieved a pressure of 1 x 10^{-6} Torr. We stopped pumping it for 2 hours to see if the vacuum would spoil. The vacuum may have change from 1.6 to 2.0 x 10^{-6} Torr after 2 hours.