Stopping powers of LiF thin films deposited onto self-supporting Al foils for swift protons

Abstract

The energy losses of ~(0.273-3.334) MeV protons in Lithium Fluoride thin films deposited by vacuum evaporation onto self-supporting Al foils have been measured using the transmission method. The thicknesses of selected and used Lithium Fluoride/Al target samples were accurately determined via systematic energy loss measurements for alpha particles from a very thin mixed 241Am/239Pu/233U radioactive source. The samples were investigated in detail for their stoichiometry and their impurity contents by backscattering Rutherford spectrometry and nuclear reaction analysis. Then, Lithium Fluoride stopping powers have been determined with overall relative uncertainty of less than 2.7% arising mainly from errors in the determination of target sample thicknesses. These S(E) data are reported and discussed in comparison to previous experimental data sets from the literature and to values calculated by the Sigmund-Schinner binary collision stopping theory both for molecular Lithium Fluoride and for the Lithium Fluoride compound assuming the Bragg's additivity rule. Our S(E) data show to be in excellent agreement with the latter theory for molecular Lithium Fluoride over the whole proton energy range explored, which supports the use of modified hydrogenic wave functions for evaluating atomic shell corrections in the case of low-Z2 target materials. In contrast, they exhibit a slightly increasing deviation from theoretical values derived for the Lithium Fluoride compound with assuming stopping force additivity as the proton energy decreases from ~400 Kev towards lower proton velocities.