X-ray spectroscopy of electronic quasimolecules

Angular dependences and differential production cross sections for characteristic K x-ray and noncharacteristic continuum x-ray radiation from Ni + Ni, Ni + Nb, Ge + Ge, and Nb + Nb collisions were measured. The measurements show that noncharacteristic high energy x-ray emissions associated with the decay of vacant inner orbitals of a transient molecular projectile--target system formed during the collision are produced. Production mechanisms for these quasimolecular emissions are studied and the possibility of using these x-rays to extract information on the energy level structure of the quasimolecule is investigated. Studies of the Ni + Ni system at five beam energies from 15 to 95 MeV, the Ni + Nb system at 70 MeV, the Ge + Ge system at 67 MeV, and the Nb + Nb system at 40, 60, and 85 MeV were carried out. At the highest photon energies, both the frequency and angular dependences of the noncharacteristic x-ray emissions produced by these various collision systems are found to be dominated by dynamic effects associated with the rapid rotation of the internuclear axis which accompanies collisions at small impact parameters. These dynamic effects tend to obscure the amount of spectroscopic information which may be extracted from measurements of the photon energydistribution of the continuum emissions but result in a characteristic angular dependence of the radiation which might allow spectroscopy of the united (projectile + target) quasiatom to be performed. The results provide hope that extension of these measurements towards the construction of transient superheavy quasiatoms in, for example, 1 GeV U + U collisions may be feasible and the extremely strong K shell binding energies of the Z = 184 quasiatomic system thereby constructed could allow completely new, fundamental tests of quantum electrodynamics to be made