Aging investigation of straw drift tubes using nuclear reaction analysis

Recent results of aging investigations of straw drift tubes with different gas mixtures have shown that an oxidation process takes place underneath the gold coating of the anode wire. We demonstrate the efficiency of the Nuclear Reaction Analysis (NRA) in combination with Scanning Electron Microscopy/X-ray Emission Spectroscopy (SEM/XEM) analysis for such processes in aging investigations of straw drift tubes flushed with a 40% Ar+40% CO2+20% C2H2F4 gas mixture. The sensitivity of NRA to carbon, oxygen and nitrogen is better than 5×10−2. The precision of the quantitative evaluation of the element content depends on the accuracy to which the differential cross-sections for the following nuclear reactions are known: 16O(d,p)17O, 12C(d,p)13C, 14N(d,p)15N, 14N(d,α)12C, 19F(p,αγ) 16O (about 5%). A thorough study of the aging degradation of gold-cladded tungsten wire has been carried out. An aging test under sustained irradiation from an intense 90Sr β-source was carried out up to a total accumulated charge of 1.6C/cm. Subsequent SEM/XEM analysis demonstrated the destruction of the gold surface and showed that many spots along the wire, both in the irradiated zone and downstream along the direction of the gas flow, contained oxygen and tungsten. The wire diameter was found to increase in this region. Using the NRA, we established the distribution of oxygen and carbon along the wire, confirming the SEM/XEM data and matching the observed increase in the wire diameter. The concentration of oxygen and carbon as a function of depth within the wire has also been investigated by means of the NRA.