Pre-liquid helium filling.

  1. Pump the warm detector guard vacuum space with a turbo station to <1 x 10-4 Torr, as read at the pump.
  2. Fill the outer liquid N2 reservoir with liquid nitrogen, then fill the inner liquid He reservoir also with liquid nitrogen. Inspect the liquid He fill portís Teflon gasket. Attach the cap/relief fitting to the liquid N2 reservoir fill port.
  3. After proper cooling with liquid N2, empty the liquid He reservoir of all liquid N2.

Liquid helium filling procedures:

  1. Purge the transfer line with He gas. Vent the liquid He storage dewar through the vent valve, then connect a purged gas line from a regulated He cylinder set at ~ 2 psi to the vent fitting.
  2. Open the liquid He storage dewar top valve, close both the vent valve and the low-pressure relief valve, then gradually insert the purged transfer line until it reaches the bottom of the storage dewar. Tighten the compression fitting. Avoid jamming the transfer line into the bottom.
  3. Open the vent valve (connection to the He gas cylinder) as necessary to pressurize the storage dewar and induce flow through the transfer line.
  4. When the transfer line interior is cold, insert the delivery end into the detector liquid He fill port so that it reaches to near the bottom of the detector's liquid He reservoir. Turn on the detector pre-amplifier power.
  5. When the detector liquid He reservoir is full (increase in dense white plume, cascading across top of detector), stop the transfer by deisconnecting the He gas line and vent the storage dewar through the vent valve.
  6. Loosen the compression fitting and remove the transfer line. Then close the storage dewar top valve and vent valve, and open the low-pressure relief valve.
  7. Without delay, attach the detector's safety fixture to the detector liquid He fill port. The safety fixture must be connected to either a relief valve or draped hose.

Operation and Re-filling:

  1. Maintain a reasonably full liquid N2 reservoir. A fill every 8 hours is usually adequate.
  2. To re-fill liquid He (if needed), start at step 4. The detector's liquid He safety fixture should be removed just prior to step 8.


  1. Turn off the input switch, bias switch, and preamplifier power. Check that the liquid He safety fixture and liquid N2 cap/relief valve are properly attached. The detector is then allowed to warm up on it's own.