Efficiency of plasma-based ion implantation of radioisotopes (32P)

Radioactive phosphorus (32P) can be implanted in biomedical devices using plasma-based ion implantation (PBII). A pulsed ECR (2.45 GHz) coaxial argon plasma reactor has been developed in which the radioisotopes are implanted into a negatively biased target. A 1 ms microwave pulse creates the plasma, which sputters material from a sputter target. A fraction of the radioisotopes is then ionized and the ions are implanted into a negatively biased cylindrical titanium implant. The theory underlying plasma-based radioisotope ion implantation is described in this article and the calculations are compared to experimental results for different plasma conditions and sputtering target positions. This study confirms the importance of radioactive source positioning and the impact of high plasma densities when using a PBII reactor. Implantation efficiency rates of about 1% are measured, which is about 100 times higher than conventional beam-line ion implantation.