Ion measurements in gas detectors in the spotlight
"An article published by the LIP Gaseous Detectors Group in Coimbra has been highlighted in the newsletter of the company Hidden Analytical, specialized in the manufacture and sale of mass spectrometers."
From high-energy physics to medical physics, gas detectors are widely used in several areas, usually with a noble gas (namely xenon) as detection medium. The use of molecular additives such as trimethylamine with the noble gas (TMA - (CH3)3N) to improve some characteristics has been suggested. There is, however, little data on either the possible additives or the mixtures obtained (e.g. Xe-TMA).
In the study now published, a residual gas analysis mass spectrometer was used to determine the ionisation thresholds and relative abundances of the ions produced by the impact of electrons with energies between 7.5 and 70 eV. The work described makes use of a mass spectrometer manufactured by Hiden - Residual Gas Analyser (RGA) of the quadrupole type, model HAL 200 RC.
Noteworthy is the ingenious experimental method, which allows the study to be carried out entirely with the RGA alone. This makes it much simpler and more practical than the methods generally used in this type of study — in which the mass spectrometer is used for the detection of the ions but the production of the electrons is performed by monoenergetic sources — which guarantee a better energy resolution but require much more complex systems.
In order to validate the method, methane (CH4), a gas whose ionisation properties are well established, was previously studied. The ionisation energy of TMA measured using this method was 7.9 ± 0.2 eV. This is the formation threshold for the ion C3H9N+, the most abundant species for electron energies below18 eV, being replaced by the ion C3H8N+ ion above this energy.
Links:
Highlight: https://www.hidenanalytical.com/research/determination-of-ionizing-threshold-of-trimethylamine-ions/
Paper DOI: https://iopscience.iop.org/article/10.1088/1748-0221/17/02/P02031