Determination of free radicals concentration in γ-irradiated polymethylmethacrylate using positron annihilation lifetime spectroscopy

Abstract EN

Low dose γ-irradiation effects on Polymethylmethacrylate (PMMA) polymer are studied by means of positron annihilation lifetime spectroscopy.

An empirical formula is suggested to relate the ortho-positronium (o-Ps) lifetim,τ3 with the molecular weight of the polymer, Mn, and the concentration of the free radicals, [X], generated in PMMA polymer due to irradiation in air.

It is shown that free radicals concentration increase with the absorbed dose, and it is measurable from the results of τ3.

The results showed that the positron lifetime parameters illustrate a significant behavior as the dose increase.

In addition, a unique behaviors of the free positron.

τ2 is found to increase as the dose annihilation and I2, are reported parameters τ 2 and I2 the formation of (free radicals-positron) compound is thought to explain this result.

The value of value at a threshold dose, which is shown to support the lifetime results I2 is found reach a nearly constant (saturated) value at a threshold dose, which is shown to support the lifetime results.