The attachment behaviour of xenon and krypton following (n, γ) events on sintered thoria powders of particle size 105–125 μm, 63–75 μm, 37–45 μm and less than 10 μm has been studied at different gas pressure ranging from 9.33 × 102to 6.67 × 104Pa. The attachment efficiency of Xe-125 is maximum compared to other isotopes of xenon. It has been observed that for powders of particle size less than 10 μm, the attachment efficiency is independent of gas pressure, but for larger particle size it decreases at higher pressures (> 4 × 104Pa).