R Mann

Selective electron capture into highly stripped Ne and N target atoms after heavy-ion impact

Auger electron and X-ray spectra from Ne and N gas targets excited with 1.4 MeV amu-1 Ar12+, Kr15+, Xe24+, and Pb36+ ions are measured, varying the target pressure and mixing other gases into the target volume. A dramatic change of line intensities from outer-shell configurations having a KL two-electron core and a third electron in the n=4, 5, 6 shell is observed, depending on the target pressure and systematically on the target ionisation potential. This effect is explained by highly selective electron capture from neutral target atoms or molecules into outer-shell orbitals of slowly (Er<10 eV) recoiling and highly stripped target atoms with metastable core states. It turns out that selective electron capture is a dominant mechanism for the population of H-, He- and Li-like states of low atomic number (Zt<or=10) target atoms after bombardment with heavy-ion projectiles. The capture process is discussed in the framework of a simple classical model and a capture cross section in the order of 10-14 cm 2 is estimated from the experiment.

Auger emission for highly ionised neon produced in 200 MeV Xe31++Ne collisions

Neon K Auger electrons were measured with high resolution at different observation angles using 200 MeV Xe31+ incident on Ne. The spectra consist of a few distinct lines which originate primarily from Li-like Ne. Significant anisotropy is observed for the Auger electron emission indicating that the target atom is aligned in the collision.

Auger electron emission from target ions under heavy-ion impact after molecular dissociation

The line shape of the (1s2s2p)4P (metastable) to (1s2)1S+e- Auger electron transition from heavy-ion impact is measured for targets containing carbon, nitrogen, oxygen and neon. The angular distribution of this transition is also measured for molecular gas targets containing carbon. Ar, Kr, Xe and U projectiles from the UNILAC were used with energy 1.4 MeV amu-1. It is found that the line shape depends strongly on the initial molecular target. Kinematic effects such as projectile-induced target recoil do not account well for these changes. A simple model is proposed that assumes the creation of a highly ionised molecule. The line shape is due to Doppler broadening from the velocity acquired by the dissociation of the molecule. Reasonable agreement between this Coulomb explosion model and the experimental results is found, allowing dissociation velocities to be calculated from the experimental line shapes.

X-ray and Auger transitions in highly ionised argon recoil ions

Argon recoil ions were produced by heavy-ion collisions and the argon K X-rays and Auger electrons emitted were measured with a crystal spectrometer and an electrostatic electron-energy analyser. Ions of Kr, Xr, Pb and U of 2.5-9.0 MeV amu-1 specific energy were used to bombard argon gas. This is the first systematic study of resolved K X-ray radiation and for K-Auger electrons of argon where the nuclear charge of the projectiles is larger than the nuclear charge of the target atoms (Z1>Z2). In these collision systems one-, two-, and three-electron spectra are observed which have been analysed in detail. From the kinematic broadening of Auger electron lines of Ar15+ the authors deduce a mean recoil energy of ER=21+or-3 eV. A drastic charge state effect as well as the systematics in the K alpha satellites for primary charges 26<or=q1<or=66 lead to a universal scaling of the L-hole probability pL as a function of projectile charge and velocity.

High-charge-low-velocity electron capture studied by X-ray line quenching

High-charge-low-velocity neon recoil ions have been produced by impact of 3.6 MeV amu-1 krypton ions. Electron capture from surrounding neutral parent gas atoms in subsequent collisions has been studied by observing the quenching of K alpha X-ray lines from the metastable states in Ne VIII and Ne IX. In the case of charge exchange between Ne8+ and Ne the photon quenching rate of the 1s2p 3P1 state yields a capture rate coefficient of kc=(2.8+or-0.8)*10-9 cm3 s-1.

Electron capture by slow Ne8+ recoil ions

High-charge low-velocity neon recoil ions have been produced by impact of 1.4 MeV amu-1 uranium ions. Electron capture from surrounding neutral background atoms in subsequent collisions has been studied by observing the quenching of K alpha X-ray lines from metastable states. Capture rate coefficients have been determined for the systems Ne8+ on He, Ne, Ar, CH4 and Xe.