An elastic recoil detection technique has been developed to depth profile light isotopes (A≲35) in low‐atomic‐mass solids (A≲16). It utilizes the maximum‐scattering‐angle property rather than an absorber to reduce background, with resultant depth precision of about ±2 &mgr;g/cm2(100 A˚). The sensitivity is ?5×1016atoms/cm2for isotopes lighter than the substrate and ?1015atoms/cm2for heavier ones.