the use of this technique for hydrogen depth profiling. Some of the prominent features of ERDA with high energy heavy ions are: Large recoil cross section with heavy ions provides good sensitivity. Moreover, all chemical elements, including hydrogen, can be detected simultaneously with similar sensitivity and depth resolution. Concentrations of 0.1 atomic percent can be easily detected. The sampling depth depends on the sample material and is of the order of 1.5-2.5 µm. For the surface region, a depth resolution of 10 nm can be achieved. The resolution deteriorates, with increasing depth due to several physical processes mainly the energy straggling and multi-scattering of the ions in the sample. Same recoil cross section for a wide mass range of target atoms The unique characteristic of this technique is that element depth profiling of a wide range of elements from hydrogen to rare earth elements. ERDA can overcome some of the limitations of Rutherford backscattering (RBS). ERDA has enabled depth profiling of elements from lightest elements like hydrogen up to heavy elements with high resolution in the light mass region as discussed above. Also, this technique has been highly sensitive because of the use of large area position sensitive telescope detectors This detector is used especially when the elements in the sample have similar masses. Telescope detectors are one way to distinguish such elements in the sample as it becomes extremely difficult to separate the elements using a normal detector. Principles of ERDA The calculations that model this process are relatively simple, assuming projectile energy is in the range corresponding to Rutherford scattering. Projectile energy range for light incident ions is in 0.5-3.0 MeV range. For heavier projectile ions such as 127I the energy range is usually between 60-120 MeV; and for medium heavy ion beams,36Cl is a common ion beam used with an energy of approximately 30 MeV. For the instrumentation section, the focus will be on heavy ion bombardment. The E2 transferred by projectile ions of mass m1 and energy E1 to sample atoms of mass m2 recoiling at an angle ϕ, with respect to the incidence direction is given by the following equation. (1) Equation 1 models the energy transfer from the incident ions striking the sample atoms and the recoiling effect of the target atoms with an angle of ϕ. For heavier ions in elastic recoil detection analysis, if m2/m1 <<1, all recoiling ions have similar velocities.