In an effort to fill data, knowledge and tool gaps that could reduce the expansion of X-ray for sterilization purpose, a comparative work has been realized on radio-induced free radicals in plastics after X-rays and gamma-rays from 60Co treatment. Radicals generated in polymers are the seeds for short and long-term modifications. Identifying and quantifying them can help evaluating interaction similarities between the two irradiation modalities.

The study presented hereafter has evaluated ~50 grades of polymers from most classical families found in medical and biopharmaceutical applications.  The polymer grades have been selected from Sartorius typical components.

Irradiations have been conducted at Aerial feerix® 7 MV X-rays irradiation plant (Illkirch-France) and at Ionisos Dagneux-France facility with 60Co gamma-rays. A unique dose of 50 kGy +/- 10% has been applied for both irradiation modalities.

Measurements have been conducted over one year period of aging with the following occurrence: Day 1, Week 1 and 2, Month 1, 2, 3 and 6 and Year 1. Between measurements, sample were aged in the dark in a controlled environment (22°C +/- 2°C and 45% +/- 15% RH).

In a qualitative point of view, each material exhibits similar EPR spectra when irradiated with X-rays or gamma-rays. This suggests that same radicals are measured and thus, occurring radiation induced mechanisms are very comparable.

In a quantitative point of view, large majority of the ~50 materials did not show a significant radical concentration difference produced when irradiated with gamma-rays or X-rays. The general trends which could be established on radical generation between X-rays and gamma-rays will be further discussed.