Interference effect of electron-capture X-rays from an 125I-labeled protein monolayer in an aqueous solution

We have measured the vertical distribution of a radioactively labeled protein in an aqueous solution by using the interference effect of electron-capture X-rays from radioisotopes. This interference is between the direct monochromatic emission from radioactive atoms and the emission totally reflected by the substrate surface. Structural information about radioactive atoms can be obtained by analyzing the measured interference fringes, since the period of these fringes depends on the position of the radioactive atoms relative to the substrate surface. In this work we used bovine serum albumin radioiodinated with carrier free 125 I by using Chloramine T. The protein molecules were electrostatically adsorbed in a monolayer form by the positively charged Langmuir layer at the air-water interface.