Atomic Parameters of Some Commonly Used Liquid Crystals

Abstract

In the present work, different methodologies have been used to find the gamma energy dependence of two atomic parameters of three commonly used liquid crystals, 4-Cyano-4’pentylbiphenyl (5CB), 4-heptyl-4’-cyanobiphenyl (7CB) and 4-n-nonyl-4'-cyanobiphenyl (9CB).The atomic parameters calculated as a function of gamma energy were the effective atomic number (Zeff) and effective electron density (Neff). This work helps to identify the crystal which is most sensitive to gamma energies compared to the other crystals, and compares the different methods used to calculate the atomic parameters. Three different methods have been used to find the dependence of effective atomic number of the crystals on gamma energy, namely: Direct, Direct-Zeff and Auto- Zeff Methods. But only two of the methods, Direct and Direct-Zeff, were used in this work to find the gamma energy dependence of effective electron density of the selected crystals because the Auto Zeff method is not designed for calculating Neff. The results of Direct and Direct-Zeff methods are in good agreement with each other. The Zeff as evaluated by Auto-Zeff was lower than the Direct and Direct-Zeff predictions in the higher gamma energy region (>10MeV). In the gamma energy region, approximately between 100keV and 10MeV, all the three methods predict that the Zeff of the crystals are independent of the gamma energy. Finally, Zeff decreases as we go from 5CB through 7CB to 9CB crystals. This means that liquid crystal 5CB is more affected by the radiation compared to 9CB. Therefore, the device furnished with 5CB crystal will have shorter life time inside reactor centers, accelerators or at any gamma radiation areas.

Keywords: Attenuation coefficients, Effective atomic number Zeff, Effective electron density Neff, 5CB, 7CB, 9CB liquid crystals