Studies of radiation aging of the straw proportional tubes with Xe-CO2-CF4 gas mixture

We have investigated the radiation aging caused by 20keV X-rays of the straw proportional tubes, which are supposed to be used in a transition radiation and tracking detector (TRT) in the ATLAS experiment at the LHC.The main result of these investigations is that no observable drop in gas gain has been found up to the doses 5C/cm. Still it has been found that at certain experimental conditions the gas gain of a straw transient, and the value of gas gain returns slowly to its initial value after the X-ray irradiation is switched off. The value of the gas gain decrease depends strongly on the dose rate and on the gas flow rate. The results show that the observed transient aging of the straw proportional tubes will be quite negligible at the experimental conditions expected for TRT at the LHC. (orig.)