Kinematic tuning: A proposed new method for measuring electron momentum density

Abstract

Radiative electron capture (REC) in fast ion-atom collisions has the unrealized potential to sensitively probe the momentum distribution of bound electrons. A kinematic tuning technique appears to promise a momentum resolution of 0.001 au, an order of magnitude improvement over existing techniques. By varying the projectile energy is small steps, the REC X-ray peak is tuned across a sharp absorption edge thereby producing an integral spectrum. Numerical differentiation of that spectrum unfolds the REC lineshape, an accurate copy of the momentum distribution. The electron involved in REC goes into a bound state of the projectile, so post-collision interactions that cause shifts and asymmetries found in certain inelastic electron and photon scattering cross sections should be altered in REC. Kinematic tuning will be sensitive to these effects signifying the breakdown of the impulse approximation.