Köln 2004 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 12: Poster Session: Instrumentation and Applications
HK 12.38: Poster
Tuesday, March 9, 2004, 13:30–15:30, Foyer
Background in the ALICE TRD and in the TPC electronics based on FLUKA calculations. — •Georgios Tsiledakis1, A. Fassò1,2, P. Foka1,2, A. Morsch2, and A. Sandoval1,2 — 1GSI, Darmstadt — 2CERN, Geneve
The main focus of the ALICE experiment at LHC is the study of Pb–Pb collisions at nucleon-nucleon center-of-mass energy of 5.5 TeV. Due to the high luminosity (1027 cm−2s−1) and the high particle multiplicities anticipated in these collisions, a high background of thermal neutrons is expected to build up as the particles shower and get stopped in the material of the detectors, magnets, support structures, and in particular in the concrete walls of the experimental cavern. The Transition Radiation Detector (TRD) contains a gas mixture of 85% Xe, 15% CO2 with a total volume of 27.2 m3. Especially 131Xe (abundance 21.18%) has a very high neutron capture cross-section. This leads to multi-gamma de-excitation cascades which can then produce low energy electrons through photo-effect, Compton scattering, and pair production, thus resulting in an uncorrelated background. We estimate the level of this random background during the 3 µs gating time of the TRD chambers. In addition, neutron fluences, doses, and the induced Xe radioactivity in the gas of the TRD are calculated. We also estimate the radiation level in the region where the electronics of the Time Projection Chamber (TPC) is located, and we quantify the slow proton background that would originate from a small admixture of CH4 to the 90% Ne, 10% CO2 TPC gas.