Absolute cross sections have been measured for the first time for the electron-impact single ionization of the fullerene ions C6o + > C6o 2+ , C6o 3+ , and Cio + as well as for double ionization of C6o + ions at electron energies ranging from threshold up to 1000 eV. It is found that the cross sections o\,2 for C6o + and C7o + ions coincide within error bars and, furthermore, that at energies greater than 60 eV the cross section <72, 3 for ionization of C6o 2+ ions is larger than o\ t i. In addition, cross sections for fragmentation C6o + -* Cs6 + and for fragmentation ionization C<>o + -* Cs6 2+ are presented.PACS numbers: 34.80. Gs, 36.40.+d, The discovery of the buckminsterfullerene C6o and other stable carbon clusters such as C70 by Kroto, Smalley, and co-workers [l] initiated research on this new form of carbon. After Kratschmer et al. [2] found a method to produce fullerene soot in macroscopic quantities, this research has been increasing at a phenomenal rate and several studies involving collisions between fullerenes and atoms, electrons, or photons have been reported [3][4][5].In this Letter we report the first investigations of electron-impact ionization and fragmentation of singly and multiply charged fullerene ions. Absolute cross sections for single ionization of the ions C6o 4 \ C6o 2+ , C6u 34 \ and C70 4 " as well as for double ionization of C6o + ions have been measured for electron energies ranging from below the ionization thresholds to 1000 eV. Furthermore, we have studied the fragmentation process e + Cw* -* C56 + + * * • and the fragmentation-ionization process e + Cto*-* C56 2+ + * * • in the same electron energy range.For the cross section measurements we employed our electron-ion crossed-beams technique described in detail earlier [6,7]. The fullerene ions were produced by evaporating carbon soot containing about 6% C60/C70 f rom an oven into the second stage of a 10 GHz electroncyclotron-resonance (ECR) ion source [8l. In order to limit fragmentation of fullerene ions in the ion source, the RF power was kept below 200 W. Relatively intense ion beams of several hundred pA of C 6 o + could be extracted from the source at an accelerating voltage of +7 kV. Figure 1 (a) shows an ion mass spectrum of the extracted fullerene ions. Masses are given in multiples of the 12 C atomic mass. The ions were momentum analyzed using a double-focusing 90° sector magnet. For enhancement of mass resolution, the analyzed beam was transported through a collimation system [6] which reduced the intensity by more than 2 orders of magnitude. The strongest peaks in the spectrum correspond to singly and doubly charged C60 ions. Also present are series of singly and doubly charged fragments of C60: C58 + ,C56 + , C 54 + , ...,C 44 ' f and C 5828), C 54 2+ (m/?=27), . . . ,C 44 2+ 0w/tf-22), respectively. Beyond these, the spectrum contains similar, but less intense series of singly and doubly charged C70 ions and their fragments. Note that only fragments with even numbers of carbon atoms are observed. The loss of even...

In order to understand the formation and stoichiometry of the x-ray storage phosphor BaFBr : Eu2+, the phase diagram of the quasi-binary BaF2-BaBr2 system has been investigated. The phase diagram was obtained by means of differential thermal analysis and temperature controlled x-ray diffraction experiments. The resulting phase diagram indicates that BaFBr forms a compound with no detectable solid solubility for neither BaF2 nor BaBr2. Experiments to obtain non-stoichiometric BaFBr via the synthesis route using BaF2 and NH4Br as proposed in the literature could not be verified. It will be shown that the type of colour centre created during x-ray irradiation is related to the non-stoichiometry of the starting compositions before sintering. A surplus of either barium fluoride or barium bromide during sintering allows the controlled formation of F(Br-)- and F(F-)-centres, respectively.

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An electron-cyclotron-resonance ion source (ECRIS) designed for use on a high voltage terminal that has limited power availability and space has been built. To reduce the power consumption of the ion source, the necessary magnetic fields were produced entirely by permanent magnets. Eighteen FeNdB magnets divided into three hexapolar arrangements yielded a min-B structure with an axial magnetic mirror ratio of 4:1. The microwave power at a frequency of 2.45 GHz with up to 300 W cw was supplied to the plasma by means of a slotted line radiator. This antenna, known as a Lisitano-Coil, allowed the use of a plasma vessel much smaller in diameter than is usually required by the wavelength of the utilized microwaves. The ion source produced stable beams of multiply charged ions at various intensities up to a total ion current of 8 mA for oxygen.