Characterization of a polyphenyl ether oil irradiated at high doses in a TRIGA Mark II nuclear reactor

Samples of a commercially available polyphenyl ether (PPE) oil are irradiated in the mixed neutron and gamma
radiation field of the Pavia TRIGA Mark II reactor, at irradiation doses ranging from 0.78 MGy to 7.8 MGy.
The oil is a nuclear grade product, whose radiation resistance reported in the product specification is based
on cobalt-60 gamma irradiation data. The collection of additional data in a nuclear reactor radiation field
performed in the present work, is motivated by the need to use this oil in neutron-rich environments such as
targets and accelerators.
The post-irradiation characterization of the oil samples here reported includes viscosity measurements, total
acid number (TAN), Fourier transform infrared spectroscopy (FT-IR), gas chromatography (GC), gel permeation
chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy.
The presented results evidence a remarkable increase of kinetic viscosity with the absorbed dose.
Differences in the radiation-induced viscosity increase are observed comparing the data collected in mixed
neutron and gamma radiation with the previous ones collected in cobalt-60 gamma radiation. This result
emphasizes the need of further studies on the dependence of the radiation damage on different radiation
environments. A negligible increase of TAN is reported. The FT-IR, GC, GPC and NMR show progressive
polymerization with increasing dose. The increasing molecular size is in line with the viscosity data presented.