Time delay effects on K x-ray production probability in deep inelastic U + U and U + Pb nuclear reactions.

If an atomic collision is accompanied by a deep inelastic nuclear reaction with a time delay \ensuremath{\Delta}T, a phase change which affects the ionization probability ${P}_{K}$ of the target- and projectile-like products is introduced between the incident and outgoing ionization amplitudes. In a deep inelastic nuclear reaction, the nuclear reaction time \ensuremath{\Delta}T is monotonically related to the total kinetic energy loss (-Q) of the reaction products. Therefore a measurement of ${P}_{K}$ as a function of Q then yields \ensuremath{\Delta}T. The K-shell ionization probability ${P}_{K}$ has been measured in the deep inelastic reactions U + U and U + Pb at a beam energy of 1785 MeV as a function of the total kinetic energy loss -Q. ${P}_{K}$ was determined for Q values down to -190 MeV. After subtraction of the ionization induced by the internal conversion of \ensuremath{\gamma} rays, a strongly Q-dependent ${P}_{K}$ is found, in qualitative agreement with theoretical predictions. From the data we infer a nuclear reaction time of approximately 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ s at Q=-100 MeV. The observed reaction times agree fairly well with the predictions of the classical nuclear reaction models used to describe deep inelastic scattering processes.