H. Voit

Desorption of organic compounds from solid surfaces by bombardment with heavy ions from a tandem accelerator

Abstract It is shown that heavy ion beams from a 5 MV tandem accelerator are capable to induce desorption of organic compounds from solid surfaces. The observed mass spectra of the desorbed secondary ions are comparable with those obtained from the bombardment with fission fragments. The unique features of the accelerator beam, such as known mass and well defined energy, have been used in order to study the desorption mechanism. Relative yields and energy distributions of H + , Na + , [valine + H] + , and [valine -COOH] + desorbed from a valine sample have been measured as a function of the incident energy of the primary ions. For increasing energy loss in the sample surface the secondary ion yield increases, whereas the yield ratios of different ions desorbed from the same surface remain unchanged. Evidence has been found that only a certain portion of the energy loss contributes to the desorption process.

Heavy ion induced desorption of organic compounds

Abstract The desorption of organic compounds has been studied using 16 O and 32 S ions as primary ion beam in the energy range from 8 to 40 MeV. The observed mass spectra are comparable to those obtained by bombardment with heavier ions at higher energies ( 252 Cf-fission products). Using the amino acid valine as sample the energy distributions and the yield of desorbed ions like H + , Na + , [valine+H] + and [valine-COOH] + were measured as a function of the stopping power in the sample, which is also called linear energy transfer (LET). For increasing LET the secondary ion yield increases too, but the ratio of the yields of different ions desorbed from the same surface remains unchanged. There are indications that only a certain portion of the LET contributes to the desorption process. The ratio of that portion to the total LET (as calculated by the Bragg rule) seems to be an universal function of ζ = ν ν 0 Z , where ν is the velocity of the primary ion and ν 0 Z is the Bohr velocity of a K-electron of the primary ion.

Secondary ion emission from dielectric films as a function of primary ion velocity

Abstract Secondary ion emission from (CsCl + RbBr) and Valine films irradiated by 16O and 32S ions has been studied as a function of the primary ion velocity. By means of a two fold time-of-flight technique mass spectra of secondary ions were measured simultaneously for primary ion velocities between 0.05 and 1.2 cm/ns. The yield functions show two branches, one below 0.2 cm/ns and one above, which are probably related to the nuclear and electronic energy loss, respectively, of the primary ions. A general agreement with available desorption models is not apparent.

Dependence of the desorption yield for valine on the charge state of the primary ions

Abstract The yield for molecular ions desorbed from a valine sample has been measured as a function of the charge state of the incident fast heavy ions. The data can be interpreted in the following way: (i) the yield depends on the square of the primary ion charge, and (ii) desorption takes place not only at the sample surface but also within a layer underneath. The depth of this layer is smaller than the depth needed to achieve charge state equilibrium for the primary ions.

Einfluß der Bestrahlung mit hochenergetischen Sauerstoffionen auf die kritische Stromdichte supraleitender Nb3Sn-Schichten

Nb3Sn diffusion layers were irradiated with 24 MeV oxygen ions at fluences from 3.2×1013 up to 1.6×1015 cm−2. The enhancement of the superconducting critical current density Δjc has been measured as a function of fluence and of the external magnetic fieldHa(jc⊥Ha). The thermal annealing treatment of the defects concerning thejc and induced by irradiation, has been investigated in the temperature region from 200 to 800 °C. The results are compared with the measurements of irradiation of Nb3Sn with protons and deuterons. The measured data are discussed in connection with size of defects, cluster distance, fluxline distance and pinning-force.

Fast heavy ion induced desorption: Dependence of the yield on the angle of incidence of the primary ions

Abstract The yield for secondary ions desorbed from organic samples (amino acids) by 9 MeV oxygen ions has been investigated for different angles of incidence θ of the primary ions. Primary ions with definite charge states and an equilibrium charge state distribution have been used. The yield increases rapidly with θ and deviates strongly from a (cos θ) 1 distribution at large angles.

Energy dependence of fast heavy ion induced desorption of secondary ions

Abstract Yields for positive and negative secondary ions desorbed by 12C, 160 and 32S ions with velocities ν≳109cm s 1 and equilibrium charge state distributions have been measured. The data show that the yields depend on the charge and the velocity of the primary ions and the secondary ion species. They are independent of the primary ion mass.

Experimental investigations of fast heavy ion induced desorption

Abstract Yields of secondary ions desorbed by energetic (1 MeV/amu) heavy ions from different solid samples have been measured as a function of the primary ion energy. The results are compared with predictions of models for the desorption mechanism.

Fast heavy ion induced desorption: Dependence of the yield on the primary ion energy

Abstract The dependence of the secondary ion yield on the energy of the fast primary ions has been investigated for several organic samples. We find different dependences for positive secondary ions desorbed from polar and ionic compounds as well as for positive and negative secondary ions desorbed from the same sample (polar compounds).

Search for quasimolecules in heavy-ion reactions in the region of the coulomb barrier

Abstract We have been looking for resonant structures of the well-known 12C-12C type in the excitation functions of some selected heavy-ion reactions. The reactions investigated are 12C(13C, α)21Ne, 12C(13C, p)24Na; 12C(14N, α)22Na, 12C(14N, p) 25Mg; 10B(14N, α) 20Ne and 10B(14N,12C)12C. The excitation functions have been measured using thin targets of 10–15 μg cm 2 in small energy intervals of 50–100 keV in the region of the Coulomb barrier. The excitation functions show no evidence for correlated structure as measured in the 12C-12C system.