Ametek ORTEC MOBIUS-B, User Manual, Page: 19 / 28

805709F / 1115 ORTEC
® MÖBIUS™ HPGe Detector Cooling System
13
13) At this point, the MÖBIUS is a closed system that is designed to contain all nitrogen vapor. You are now ready
to connect the detector cable to the detector and multichannel buffer.
NOTE: Mobius is designed to operate without liquid nitrogen refilling for up to two years under normal,
continuous operating conditions (e.g. no power loss). The display will blink when the LN2 levels drops below
85%. This value was established to alert the user that the LN2 level in the Mobius is not sufficient to provide
cooling for a full seven days upon an extended power outage.
3.3. SAFETY AND EQUIPMENT WARNINGS
3.3.1. Liquid Nitrogen Safety
Before filling the MÖBIUS, be sure to read the following LN2 advisories as well as the information in Section 3.3.2.
DANGER
●
The large expansion ratio of LN2 from liquid to gas (1 to 692) can generate high pressures if the dewar does
not have adequate venting or pressure relief provisions.
●
When filling the MÖBIUS, you may be tempted to use dry nitrogen gas to pressurize the supply dewar. ORTEC
STRONGLY RECOMMENDS AGAINST THIS PRACTICE . Instead, only the self-generated pressure of the supply
dewar should be used. Compressed gases (even purportedly dry “house” nitrogen) may contain moisture, oil,
and oxygen.
Any oxygen will liquefy at LN2 temperatures (77 K), creating an explosion hazard. In addition,
the moisture and oil can freeze, making the safety valves inoperable. Use a pressure relief of 22 psi
(152 kPa) on the supply dewar to avoid over-pressurization in the event of ice blockage. A blockage can
rupture the dewar and/or expel the detector/cryostat with explosive force.

If the MÖBIUS dewar becomes contaminated with oil, the unit must be returned to ORTEC for service.
Do not use a degreaser or attempt any other remediation unless authorized to do so by our ORTEC
Global Service Center.

If water accumulates in the dewar, remove the LN2; obtain a cylinder of high-purity, oil-free, dry
nitrogen gas (not “house” nitrogen); and stream the gas at very low pressure through the dewar until all
water has evaporated.
●
Piping or transfer lines should always be constructed so as to avoid trapping LN2 in the line. Evaporation can
result in pressure buildup and eventual explosion of the line. If all lines cannot be emptied, install safety relief
valves and rupture discs. Also keep in mind that some materials become brittle and fracture when exposed to
LN2 temperatures. For advice on selecting materials for use in storing and transferring LN2, contact ORTEC or
your LN2 supplier. Other sources of information include the
CRC Handbook of Laboratory Safety and the
American Society of Mechanical Engineers’ Boiler and Pressure Vessel Code, Section VIII .
●
Nitrogen gas can pose an asphyxiation hazard by displacing air. Transfer LN2 only in a well-ventilated area .
Vent storage containers to a well-ventilated area or to the outside to avoid buildup of nitrogen gas in the
work area.
WARNING
●
On contact with skin, LN2 causes burns similar to thermal burns or frostbite. Eyes are especially vulnerable to
this type of exposure. Avoid wearing anything capable of trapping or holding spilled liquid nitrogen close to
your skin (for instance, mesh-top running shoes). An impervious apron or coat, cuffless trousers, and high-
topped shoes are recommended. Wear safety glasses or, better yet, full-face protection. Remove all watches,
rings, bracelets, or other jewelry. When gloves are used to handle containers or cold metal parts, they should
be impervious and sufficiently large to be easily tossed off the hand in case of a spill.
●
Before removing a detector/cryostat assembly from a MÖBIUS, always vent the system by opening both the
fill and vent valves (Figure 2). Failure to do so may result in the entire contents of the dewar spewing