Properties of Silica Glass Implanted with Phosphorus Ion at 50keV for Radiotherapy

Abstract

A chemically durable glass containing a large amount of phosphorus is useful for in situ irradiation of can cers. It can be activated to emitter with 14.3d half-life by neutron bombardment. Microspheres of the acti vated glass injected to the tumors can irradiate ray directly to the tumors without giving radiation to neighboring normal tissues. In order to examine possibility for obtaining such a glass by ion implantation, P+ ion was implanted into a pure silica glass in a plate form under 50keV to different doses. This implanta tion energy is estimated to give the maximum concentration of P+ ion at 48.6nm in depth from the surface. Structural damage was produced near the surface of the glass by the ion implantation for all the doses in the range from 51016 to 1101cm-2.The phosphorus was localized only in the regions deeper than 1.2nm from the surface, taking a form of phosphorus colloids, for a dose of 51016cm2, whereas it was distribut ed up to the glass surface and a part of it near the surface was oxidized for doses above 11017cm2. The former glass little released both P and Si into water at 95 even after 7d, whereas the latter glasses released appreciable amounts of these elements. At implantation energy of 20keV, even a dose of 51016 cm-2 formed an oxidized phosphorus at the glass surface and gave appreciable releases of P and Si from the glass into water. This indicates that a chemically durable glass containing a larger amount of phosphorus could be obtained if P+ ion is implanted at higher energies and localized in a deeper region, even if the sur face structure of the glass is damaged by the ion implantation.

Phosphorus‐Implanted Glass for Radiotherapy: Effect of Implantation Energy

“…9. [14][15][16][17][18] The SIMS spectrum indicates that the phosphorus ions are widely distributed in a layer that is centered at a depth of 200-250 nm. This spectrum suggests that the implanted phosphorus ions diffused inward and outward during the ion implantation, because the phosphorus concentration at the maxi- Fig.…”

“…Figure 1 showed that an increasing amount of phosphorus ions can be implanted into the silica glass as the dose of the incident ion increases at least up to 1 × 10 18 cm −2 under an energy of 200 keV; at 20 keV, saturation occurred at 5 × 10 16 cm −2 , and, for 50 and 100 keV, saturation occurred at 5 × 10 17 cm −2 , as shown in the previous work. [14][15][16][17][18] These results indicate that the maximum amount of phosphorus ions that can be implanted into the glass increases as the implantation energy increases. This observation is explained by assuming that the maximum phosphorus concentration exists at a larger depth from the surface of the silica glass at 200 keV than at 20, 50, and 100 keV; i.e., the maximum concentrations of the phosphorus that has been implanted at 20, 50, 100, and 200 keV are theoretically estimated to be located at depths of 19.9, 48.6, 100.2, and 207.3 nm, respectively.…”

“…This result is contrary to the cases of 20, 50, and 100 keV; in these cases, the silica glass that was implanted with doses as low as 5 × 10 16 , 1 × 10 17 , and 5 × 10 17 cm −2 , respectively, released appreciable amounts of phosphorus and silicon into the water. [14][15][16][17][18] This observation is attributed to the presence of phosphorus oxide, which is known to be hygroscopic, 20 at the glass surface, as indicated in the XPS spectra in Fig. 9.…”

“…9. [14][15][16][17][18] When the phosphorus oxide dissolves into the water, the silicon oxide that is bonded to the phosphorus oxide also dissolves. Over a long period, even the chemically durable surface layer of the glass that has been implanted with the P + ions at 200 keV might be dissolved into water, and the phosphorus colloids that are localized in deeper regions might come into contact with the water.…”

“…The authors have previously proposed that P + ion implantation into a silica (SiO 2 ) glass can be a promising technique for obtaining a chemically durable glass with high phosphorus content. [14][15][16][17][18] The silica glass is chemically durable and is not activated by the neutron bombardment; its microspheres, in various sizes, are easily available commercially. However, the glasses that were implanted at 20 keV with a dose of 5 × 10 16 cm −2 , at 50 keV with doses >1 × 10 17 cm −2 , and at 100 keV with doses >5 × 10 17 cm −2 released appreciable amounts of phosphorus and silicon into hot water.…”