Studies on tetrafluoropropene-CO2 based gas mixtures for the Resistive Plate Chambers of the ALICE Muon IDentifier

• Main Author: Ferretti, Alessandro
• Format: Journal Article
• Language: English
• Published: 16-12-2021
• Subjects: Physics - High Energy Physics - Experiment; Physics - Instrumentation and Detectors
• DOI: 10.48550/arxiv.2112.08899

Due to their simplicity and comparatively low cost Resistive Plate Chambers
are gaseous detectors widely used in high-energy and cosmic rays physics when
large detection areas are needed. However, the best gaseous mixtures are
currently based on tetrafluoroethane, which has the undesirable characteristic
of a large Global Warming Potential (GWP) of about 1400 and because of this, it
is currently being phased out from industrial use. As a possible replacement,
tetrafluoropropene (which has a GWP close to 1) has been taken into account.
Since tetrafluoropropene is more electronegative than tetrafluoroethane, it has
to be diluted with gases with a lower attachment coefficient in order to
maintain the operating voltage close to 10 kV. One of the main candidates for
this role is carbon dioxide. In order to ascertain the feasibility and the
performance of tetrafluoropropene-CO2 based mixtures, an R&D program is being
carried out in the ALICE collaboration, which employs an array of 72 Bakelite
RPCs (Muon Identifier, MID) to identify muons. Different proportions of
tetrafluoropropene and CO2, with the addition of small quantities of isobutane
and sulphur hexafluoride, have been tested with 50x50 cm2 RPC prototypes with 2
mm wide gas gap and 2 mm thick Bakelite electrodes. In the presentation,
results from tests with cosmic rays will be presented, together with data
concerning the current drawn by a RPC exposed to the gamma-ray flux of the
Gamma Irradiation Facility (GIF) at CERN.