Implantation of defined activities of phosphorus 32 with reduced target damage.

Materials doped with the unstable isotope phosphorus 32 are promising candidates for use in brachytherapeutic applications. One way to dope a material with P is by ion implantation. However, the bombardment of the target with ions other than P due to impurities of the ion beam leads to unnecessary damages of the target, which might reduce its potential for medical applications. Furthermore, implanting a pre-selected activity of an unstable isotope into a target requires the repeated determination of the target's activity, which requires removing the target from the implantation chamber. This prolongs the total implantation time and requires handling the radioactive target multiple times, which in turn increases the risk of accidental exposure. We have incorporated an online-detector system into the implantation chamber of a 60 kV ion implanter that allowed us to determine the activity of the target without removing the target from the implantation chamber. We then used this system to investigate the implantation of ions with = 38 u-instead of ions with = 32 u-to reduce the fraction of other ions than P implanted into the target to reduce the induced damages.