δ-Ray Spectroscopy of Quasi-Atoms

Abstract

The subject of our studies is the spectroscopy of high energy δ-rays, emitted in collisions of very heavy ions. In this experimental talk I would like to discuss collision systems with combined charge (Z_u = Z_p+Z_t) of the projectile (Z_p) and the target (Z_t) atoms about equal or larger than the reciprocal of the fine structure constant: Z_u • α ≳ 1. Furthermore, we concentrate on δ-electrons with very high energies — above 100 keV up to 2000 keV. It is easy to be understood qualitatively that a large energy and momentum transfer to a bound electron is possible only if the initial momentum of the electron is also very high — i.e. high energy δ-rays originate mostly from the sharper localized, strongly bound innermost shells. For very heavy quasi-atoms one expects a rapid increase of the high-momentum components as a consequence of the enormous relativistic “shrinking” of the electronic wave functions^1,2,3. Hence, the high energy tail of the δ-ray spectrum can be attributed to the high energy component of the momentum distribution of strongly bound quasiatomic electrons and, thus, provide information about their wave function and and energy.