High precision X-ray spectroscopy in hydrogen-like fermionic and bosonic atomic systems

Some time after its formation an exotic atom may be considered a hydrogen-l ike system consisting of a nucleus and an exotic particle in a bound state. In this situation it is an ideal tool to study cascade properties, while f or the innermost orbits it can be used to probe the interaction with the nu cleus. From an extended series of experiments using high resolution X-ray s pectroscopy for both aspects typical examples are reported and preliminary results are given: 1. To determine the complex scattering length in (p) ove r bar H the 3D --> 2P hyperfine transitions have been measured. 2. To deter mine the pion mass the 5 --> 4 transitions in pi(14)N have been studied. In all cases a major contribution to the uncertainty originates from the cali bration. Therefore a new method is proposed that will establish a universal set of high precision calibration lines for pionic, muonic and electronic systems.