Radiation damage enhanced trapping of low-energy He+ions in rhenium

A polycrystalline rhenium target was bombarded in UHV at room temperature with low-energy A+ and He+ ions. The ions retained in the solid were desorbed into a closed volume by raising the target temperature linearly, with respect to time. The differential signal in a mass spectrometer provided desorption spectra and trapping coefficients were estimated. The behaviour was found to be similar to that observed in other metals. In the case of He+ ion bombardment, the damage state of the target prior to injection was varied by pre-bombarding with A+ ions. It was found that this damage considerably increased the amount of helium trapped: the trapping was predominantly at defects caused by the pre-bombardment. Helium was released at temperatures characteristic of the release of the argon, which caused the damage. The helium thus traced the damage present in the target prior to bombardment.