Ionic liquids as solvents for Čerenkov counting and the effect of a wavelength shifter

Highlights: • Wavelength shifter effect with a highly fluorescent ionic liquid on the Čerenkov radiation was studied. • Activities of high energy β emitters can be quantified by TDCR–Čerenkov technique using fluorescent ILs mixture. • A significant increment in a TDCR detection efficiency was achieved using a fluorescent ionic liquid mixture. • The addition of a wavelength-shifter breaks the anisotropy of the Čerenkov radiation. - Abstract: We study the wavelength shift of the Čerenkov light – generated in the ionic liquid (BMIMCl) – caused by the addition of the highly fluorescent ionic liquid (BMIMHPTS). ¹⁸F and ³²P efficiencies increases up to 124% and 14%, respectively, compared with the values obtained with pure BMIMCl. With this improvement, ionic liquid mixtures become a good alternative – when using the TDCR-Cherenkov technique – to standardize radionuclides having electron emissions energies close to the threshold energy in water (∼ 260 keV). As an advantage compared with other solvents, the Ionic liquid mixture can be reused, in the case of short-lived radionuclides, by simply removing all water content in a vacuum oven.