Preparation of radiotherapy glass by phosphorus ion implantation at 100 keV

A chemically durable glass containing a large amount of phosphorus is useful for in situ irradiation of cancers. It can be activated to be a β emitter (half-life of 14.3 days) by neutron bombardment. Microspheres of the activated glass injected into the tumors can irradiate the tumors directly with β rays without irradiating neighboring normal tissues. In the present study a P⁺ ion was implanted into a pure silica glass in a plate form at 100 keV in order to find the fundamental conditions for obtaining such a glass. Little phosphorus was present in the surface region, at least to a depth of 2.4 nm for doses of 5 x 10¹⁶ and 1 x 10¹⁷ cm^-2, whereas an appreciable amount of it was distributed on the glass surface and a part of it was oxidized for doses above 5 x 10¹⁷ cm^-2. The glasses implanted with doses of 5 x 10¹⁶ and 1 x 10¹⁷ cm^-2 hardly released the P and Si into water at 95 °C, even after 7 days, whereas the glasses implanted with doses above 5 x 10¹⁷ cm^-2 released appreciable amounts of these elements. Implantation energies of 20 and 50 keV (even at doses of 5 x 10¹⁶ and 1 x 10¹⁷ cm^-2, respectively), formed oxidized phosphorus on the glass surfaces and gave appreciable releases of the P and Si into the hot water. This indicates that a chemically durable glass containing a larger amount of phosphorus could be obtained if a P⁺ ion is implanted at higher energies to localize in a deeper region of the glass surface.