Measurement of lubricant thickness on needles using proton scattering

Hypodermic needles are coated with lubricants to reduce the shear force necessary to penetrate the skin. Shear force is minimized for an intermediate lubricant thickness and thus it is desirable to assure that needles are coated with the optimum thickness. Two ion beam analysis techniques (Feldman and Mayer, 1986) were used to measure polymeric coating thickness in the approximate range of 100-5000 nm on needles. An elastic backscattering (EBS) technique was used to measure the carbon content within a scanned volume. The carbon content is determined by analysis of the spectrum obtained by scattering protons whose energy overlaps the strong elastic scattering resonance of 12C at 1.686 MeV. A second technique, which infers lubricant thickness by the shift of the spectral edge in the Rutherford backscattered spectrum (RBS) due to energy loss within the lubricant, was also investigated. The RBS method can be applied for lubricants with low 12C content or for proton energies below the carbon resonance.