Poly (methyl methacrylate) (PMMA) is widely used in scientific and industrial applications. Because of its favorable properties, it is used in various fields such as optical, medical, and nuclear applications. Effects of ionization radiations on physical properties of PMMA have greatly studied in recent years. However, to the best of our knowledge, there have been no reports on the effects of ionizing radiations, especially the gamma radiation, on the nonlinear optical properties of PMMA. In this paper, for the first time, detection of large and measurable nonlinear refractive index of PMMA after interaction with the gamma radiation is reported. The optical Z-scan technique is used for measuring the nonlinear optical properties of the gamma-irradiated PMMA samples in the 5-300 kGy dose range. It is shown that variation of the induced nonlinear refractive index in this dose range is more or less linear with deposited dose. A new dosimetry method is proposed, which is based on using the Z-scan technique for measuring the nonlinear refractive index of PMMA and obtaining the amount of absorbed dose using this linear response. The name Z-scan dosimetry is coined for this new dosimetry method.

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