M. Dietrich

On-line yields obtained with the ISOLDE RILIS

The ISOLDE resonance ionization laser ion source (RILIS) allows to ionize efficiently and selectively many metallic elements. In recent yield surveys and on-line experiments with the ISOLDE RILIS we observed 23–34 Mg, 26–34 Al, 98–132 Cd, 149 Tb, 155–177 Yb, 179–200 Tl, 183–215 Pb and 188–218 Bi. The obtained yields are presented together with measured release parameters which allow to extrapolate the release efficiency towards more exotic (short-lived) nuclides of the same elements. 2002 Elsevier Science B.V. All rights reserved.

Charge state dependence of the diffusivity of interstitial Fe in silicon detected by Mössbauer spectroscopy

Interstitial 57mFe atoms excited in the 14.4 keV Mossbauer state have been created in silicon at 400–800 K as a result of the recoil imparted on these daughter atoms in the β− decay of ion-implanted, substitutional 57Mn. Diffusional jumps of the interstitial 57mFe cause a line broadening in their Mossbauer spectra, which is directly proportional to their diffusivity. Thus, the charge-state-dependent diffusivity has been determined in differently doped material.

Oxide fiber targets at ISOLDE

Abstract Many elements are rapidly released from oxide matrices. Some oxide powder targets show a fast sintering, thus losing their favorable release characteristics. Loosely packed oxide fiber targets are less critical since they may maintain their open structure even when starting to fuse together at some contact points. The experience with various oxide fiber targets (titania, zirconia, ceria and thoria) used in the last years at ISOLDE is reviewed. For short-lived isotopes of Cu, Ga and Xe the zirconia and ceria targets respectively provided significantly higher yields than any other target (metal foils, oxide powders, etc.) tested before. Titania fibers, which were not commercially available, were produced in a relic process by impregnation of a rayon felt in a titanium chloride solution and subsequent calcination by heating the dried felt in air. Thoria fibers were obtained either by the same process or by burning commercial gas lantern mantle cloth. In the future a beryllia fiber target could be used to produce very intense 6He beams (order of 1013 ions per second) via the 9Be(n,α) reaction using spallation neutrons.

Creation and annealing of defect structures in silicon-based semiconductors during and after implantations at 77–500 K

Defect structures created in implantations of radioactive 57Mn+ ions into silicon-based semiconductors held at temperatures of 77–500 K have been studied by Mossbauer spectroscopy on the 14 keV γ-radiation emitted in the decay of the 57Fe daughter atoms. For implantations at <300 K, the majority of Fe atoms is located in a specific defect structure, likely within an “amorphous pocket”, which anneals partially at 100–200 K and completely at 300–450 K. The latter is proven to occur within minutes by isothermal time delayed measurements and results in a substitutional incorporation of the 57Mn probe atoms. The atomic structure of the annealing defect is compared to that of Fe in amorphous silicon upon 57Mn implantation.

Implantation sites of Ce and Gd in diamond

Abstract The implantation sites of rare earth (RE) probes 141 Ce (t1/2=32 d) and 149 Gd (t1/2=9.28 d) in diamond have been investigated using the emission channeling (EC) technique. Parent isotopes 141 Cs and 149 Dy were implanted into type IIa diamond samples at an energy of 60 keV at the online isotope separator ISOLDE at CERN. 141 Cs decays through the chain 141 Cs– 141 Ba– 141 La– 141 Ce– 141 Pr. EC measurements were made on the 102 keV conversion electrons emitted in the decay of 141 Pr to its ground state. The decay of 149 Dy follows the chain 149 Dy– 149 Tb– 149 Gd– 149 Eu–149Sm. EC measurements were made on the 101 keV electrons emitted in the decay of 149 Eu. Two-dimensional channeling patterns of the conversion electrons were obtained along 〈1 1 0〉 and 〈1 1 1〉 axial directions by raster scans with a Si surface barrier detector. Comparison of the observed patterns with simulated spectra show that in diamond 45–50% of the RE atoms are located near substitutional sites, unlike the case in Si.

Mössbauer study of 57 Fe in CVD diamond following 57 Mn implantation

57Fe Mossbauer spectroscopy, following the implantation of radioactive parent 57Mn+ ions, has been performed on two chemical vapour deposited diamond samples, one synthesized in 2003 (CVD03) and the other in 2005 (CVD05). The spectra of sample CVD05 were as observed previously in natural IIa diamonds: single lines corresponding to substitutional and interstitial Fe were superimposed on a broad quadrupole split doublet. The site fraction of Fei reached 30% at 90 K. The spectra of the CVD03 sample showed, in addition to the above features, a strong contribution (>30%) from a quadrupole doublet attributable to the presence of intrinsic amorphous inclusions in the crystallites. This observation has been confirmed by X-ray diffraction.