NGX Specifications

System description

NGX is a static vacuum multi-collector mass spectrometer designed to measure isotope ratios of the noble gases at high precision and accuracy. It uses a 90 degree, 27 cm radius electromagnet with asymmetric geometry. This shortens the image dispersion length which reduces the instrument volume increasing relative sensitivity.

Initial pumping is provided by 80 L/s turbo molecular pump backed by an oil free diaphragm pump. Sample pumping is provided by a 40 L/s ion pump. During sample inlet, the pumping line is isolated from the analyser volume by means of an automated valve. A GP50 non-evaporable getter combined with a vacuum envelope manufactured using the latest in UHV techniques and fully bakeable to 350^oC provides the ultimate static vacuum of 10^-10mbar.

Multi-collector

The multi-collector can be configured in a variety of formats depending on the expected instrument workload. This can range from a single detector (Faraday or multiplier) providing extremely low volume for use with peak jumping, up to a maximum of 9 Faradays configured to collect Xe isotopes. A wide variety of Faraday/multiplier combinations are possible subject to consultation during the ordering process.

Provisional Specifications

Mass range
1 – 200 Daltons at 8kV accelerating voltage

Background
5 x 10^-14 cc STP at m/z 36

Sensitivity
Argon : > 1×10^-3 amps/Torr at 200μA trap current
Helium : > 2 x 10^-4 amps/Torr at 800μA trap current

Abundance Sensitivity
1ppm at 10^-7 Torr (defined as the relative contribution of ⁴⁰Ar at m/z 39)

Static Volume
~800cc (6 Faradays/Multipliers configured for Ar)

Rate of rise
< 1 x 10^-12 cc STP/min for ⁴⁰Ar

Resolution
Faraday : >600
Multiplier : >600

Peak side stability
<25ppm in mass over 30 min

Amplifier response
1×10¹¹ Ω Signal decay of <5ppm of 8 volts in 2 seconds
1×10¹² Ω Signal decay of <5ppm of 5 volts in 4 seconds