Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 2006"

LUCIA, a microfocus soft XAS beamline

Abstract: The beamline “LUCIA” (line for ultimate characterization by imaging and absorption) is a “tender” (0.8–8 keV) X-ray microprobe with capabilities for chemical speciation by micro-X-ray absorption spectroscopy (μ-XAS) and for elemental mapping by X-ray micro-fluorescence (μ-XRF). It allows the possibility to study heterogeneous samples at a micrometer scale and to combine these two element-specific and non-destructive techniques. A monochromatic beam of a few micrometer in size is incident on a sample which is mounted on a scanning x–y–z stage. μ-XRF shows the location of the elements, their relative abundances, and their association with other elements. One can take advantage of the monochromatic beam which allows separating out different elements by their absorption edges. After mapping the fluorescence, spots of interest can be analysed by XAS to determine the speciation (local chemistry, quantitative determination of the local geometric structure around the absorbing atom) of the elements and how they depend on the different components. Installed at first at the SLS of the Paul Scherrer Institute (Switzerland), the LUCIA beamline will be transferred to SOLEIL by the beginning of 2008. The energy range offered by the beamline corresponds to the best performances of SLS and SOLEIL in terms of brightness. It allows XAS experiments at the K edge of elements ranging from Na to Fe, L edges from Ni to Gd, and M edges of rare earths and actinides.

Molecular dynamics simulations of threshold displacement energies in Fe

Abstract: We compare systematically the threshold displacement energy surface of 11 interatomic potentials in Fe. We discuss in detail different possible definitions of threshold displacement energies, and how they relate to different kinds of experimental threshold displacement energies. We compare the threshold results to experiments, and find that none of the 11 tested potentials agrees fully with experiments. However, all the potentials predict some qualitative features in the same way, most importantly that the threshold energy surface close to the 100 crystal direction is flat and that the largest threshold energies occur around very roughly the 123 crystal direction.

Molecular dynamics simulations of helium cluster formation in tungsten

Abstract: Molecular dynamics simulations of helium implantation into single-crystalline tungsten at 0 and 300 K have been performed. Non-damaging ion energies of 50, 100 and 200 eV were used. Clusters containing up to the order of 100 He atoms were formed. These clusters were nucleated athermally, via the creation of (111) crowdion interstitials and interstitial dislocation loop punching. Ruptures of He clusters were observed, but no associated ejection of W atoms.

Synthesis and characterisation of hydrogels based on poly(vinyl pyrrolidone)

Abstract: Poly(vinyl pyrrolidone) (PVP) hydrogels were crosslinked by using gamma irradiation technique. The effects of the PVP concentration and the absorbed dose on gel content were investigated. Equilibrium swelling study was performed to calculate molecular weight between crosslinks of swollen gel using Flory Rhenner theory. The oxygen effect was studied through the yield of crosslinking G x which was deducted from the gel–sol analysis performed with the GelSol95 program. Systematic analysis of the influence of the dose and the concentration showed that the gel fraction increased with increasing dose and PVP concentration. The highest degree of swelling of PVP hydrogels was obtained at doses near the gelation point. The polymer concentration of 7% seems to be the most adequate to obtain an appreciable gel content, even at low irradiation doses. The crosslinking process is affected by the presence of oxygen in the solution. The microbe penetration tests showed that this hydrogel constitutes a good barrier against bacteria.

A novel Al2O3 fluorescent nuclear track detector for heavy charged particles and neutrons

Abstract: A novel Al2O3 fluorescent nuclear track detector (FNTD), recently developed by Landauer, Inc., has demonstrated sensitivity and functionality superior to that of existing nuclear track detectors. The FNTD is based on single crystals of aluminum oxide doped with carbon and magnesium, and having aggregate oxygen vacancy defects (Al2O3:C,Mg). Radiation-induced color centers in the new material have an absorption band at 620 nm and produce fluorescence at 750 nm with a high quantum yield and a short, 75 ± 5 ns, fluorescence lifetime. Non-destructive readout of the detector is performed using a confocal fluorescence microscope. Scanning of the three-dimensional spatial distribution of fluorescence intensity along the track of a heavy charged particle (HCP) permits reconstruction of particle trajectories through the crystal and the LET can be determined as a function of distance along the trajectory based on the fluorescence intensity. Major advantages of Al2O3:C,Mg FNTD over conventionally processed CR-39 plastic nuclear track detector include superior spatial resolution, a wider range of LET sensitivity, no need for post-irradiation chemical processing of the detector and the capability to anneal and reuse the detector. Preliminary experiments have demonstrated that the material possesses a low-LET threshold of <1 keV/μm, does not saturate at LET in water as high as 1800 keV/μm, and is capable of irradiation to fluences in excess of 106 cm−2 without saturation (track overlap).

e-Induced secondary electron emission yield of insulators and charging effects

Abstract: Based on a more realistic description of the in-depth secondary electron generation than that of standard (constant loss) model, a new model for the e-induced secondary electron emission yield, δ = f(E0), is applied to account for the observed mean atomic number dependence of the reduced yield curves (RYC), δ / δ max = f ( E 0 / E max 0 ) of a wide variety of inorganic insulators. It is next used to extract and to discuss physical information on secondary electron escape probability and attenuation length of a number of oxides and alkali halides and to deduce their X-ray-induced secondary electron emission yield, δX = f(hν). Extrapolation of experimental data above the few keV energy range including the estimate of the nominal critical energy E 2 0 is also illustrated. Correlation between time dependence of charging and of secondary electron emission is next analyzed and various charging effects such as the observed negative charging when a positive charging was expected or the possible change of sign of the specimen current, are explained by the difference between E 2 0 and E 2 C (critical energy obtained under permanent irradiation). Strategies to identify charging effects via their influence on the distortion of the yield curve and to reduce them are finally suggested.

Polyethylene as a radiation shielding standard in simulated cosmic-ray environments

Abstract: Radiation risk management for human space missions depends on accurate modeling of high-energy heavy ion transport in matter. The process of nuclear fragmentation can play a key role in reducing both the physical dose and the biological effectiveness of the radiation encountered in deep space. Hydrogenous materials and light elements are expected to be more effective shields against the deleterious effects of Galactic Cosmic Rays (GCR) than aluminum, which is used in current spacecraft hulls. NASA has chosen polyethylene, CH2, as the reference material for accelerator-based radiation testing of multi-function composites that are currently being developed. A detailed discussion of the shielding properties of polyethylene under a variety of relevant experimental conditions is presented, along with Monte Carlo simulations of the experiments and other Monte Carlo calculations in which the entire GCR flux is simulated. The Monte Carlo results are compared to the accelerator data and we assess the usefulness of 1 GeV/amu 56Fe as a proxy for GCR heavy ions. We conclude that additional accelerator-based measurements with higher beam energies would be useful.

SHI induced modification of ZnO thin film: Optical and structural studies

Abstract: Thermally evaporated ZnO thin films have been irradiated with 100 MeV Au8+ ions at different fluence from 5 × 1011 ions/cm2 to 5 × 1013 ions/cm2. The optical and structural properties of the irradiated and pristine films were studied using Fourier transform infrared spectroscopy (FTIR), UV–visible absorption spectroscopy, photoluminescence (PL), atomic force microscopy (AFM) and XRD. FTIR results showed that for low fluence, the transmittance of the film decreased and increased again at higher fluence but Zn–O bond remains unaffected by irradiation. As revealed from the absorption spectra, absorption edge is not changed by the irradiation but the optical absorption is increased. The AFM study of the films implied that roughness decreased at low fluence values up to 5 × 1012 ions/cm2 and at higher fluences the roughness increased.

Effects of deposited nuclear and electronic energy on the hardness of R7T7-type containment glass

Abstract: The effects of elastic and inelastic interactions induced by cumulative alpha decay on the hardness of R7T7-type nuclear containment glass were investigated on actinide-doped glass specimens and by external irradiation of inactive glass by light and heavy ions. Vickers microindentation and nanoindentation hardness measurements showed that in the deposited energy range investigated (below 3 × 1022 keV/cm3) inelastic effects have no influence on the plastic response of the glass. Conversely, identical hardness variations versus the nuclear energy deposited in the material were observed on curium-doped glass and on glass irradiated by ion bombardment. The observed hardness variation stabilized after the deposited energy reached about 3 × 1020 keVnucl/cm3. These findings indicate that the change in the plastic response of the glass is a consequence of ballistic effects.

The biocompatibility of the tantalum and tantalum oxide films synthesized by pulse metal vacuum arc source deposition

Abstract: The surface modification technique is extensively employed to improve and control biocompatibility for blood and cell attachment. In this paper, tantalum thin films were synthesized by pulsed metal vacuum arc source deposition, the tantalum oxide films were fabricated by tantalum films heated at 700 °C for 1 h in air. The films were characterized using X-ray diffraction (XRD). In vitro investigations of cultured human umbilical vein endothelial cells (HUVEC) on Ta, tantalum oxide films, 316L stainless steel and CP-Ti revealed that the growth and proliferation behavior of endothelial cells on the sample surfaces varied significantly. The adherence, growth, shape and proliferation of endothelial cells on tantalum and tantalum oxide films were much better than 316L stainless steel and CP-Ti. The Ta and tantalum oxide films shown to fulfill the requirements necessary for the application as a blood-contacting device (such as stent) coating.

Ultraviolet visible absorption of gamma-irradiated transition metal ions doped in sodium metaphosphate glasses

Abstract: Spectrophotometric studies of sodium metaphosphate glasses doped with 3d transition metals (0.1% Ti → Cu) were carried out before and after successive gamma irradiation. In the undoped glass, strong charge-transfer ultraviolet absorption bands are observed and are related to trace iron impurities in the raw materials used for glass preparation. These charge-transfer bands are observed to interfere or mask the characteristic ultraviolet bands due to some of the transition metals which possess ultraviolet absorption. Gamma irradiation produces characteristic induced bands in the base undoped and TM doped phosphate glasses. The response of the glasses to gamma irradiation is related to the creation of numerous induced defect color centers, the approach of a saturation condition and the possible photochemical effect on the transition metal ions.

Modification of nanostructures by high-energy ion beams

Abstract: This paper highlights three recently reported examples in which nanostructures in silica have been modified by bombardment with high energy heavy ions. The first example concerns the transformation of spherical nanocolloids into ellipsoids with the aim to built a photonic crystal by irradiation with 4 MeV xenon ions. The second example refers to writing of micro-structures using an 18 MeV silicon micro-beam and the resulting limitations in structurability. The last example deals with the deformation of metallic cobalt nanoparticles in silica by 200 MeV iodine bombardment. Various deformation mechanisms are briefly examined. The experiments are in favor of melting of the clusters by ion impacts and flow of cobalt into the silica tracks.

Measurements of materials shielding properties with 1 GeV/nuc 56Fe

Abstract: The design of future spacecraft such as the Crew Exploration Vehicle must take into account the radiation shielding properties of both the structural components as well as dedicated shielding materials. Since modest depths of shielding stop the vast majority of Solar Energetic Particles (SEP), the greater challenge is posed by the need to shield the crew from the Galactic Cosmic Rays (GCR), which include highly-charged and highly-energetic particles. Here, we report on results from tests performed with beams of 1 GeV/nuc 56 Fe at the Brookhaven National Laboratory. A wide variety of targets, both elemental and composite, was placed in the particle beams, and the spectra of particles emerging from the targets were measured using a stack of silicon detectors. Results are presented primarily in terms of dose reduction per g cm −2 of target material, and support the conclusions of an earlier calculation by Wilson et al. showing that performance improves as the shield’s mass number decreases, with hydrogen being by far the most effective shielding material. The data also show that, as depth increases, the incremental benefit of adding shielding decreases.

Modification of surface properties of polyethylene by Ar plasma discharge

Abstract: Polyethylene (PE) surface was modified by Ar plasma discharge. The changes of surface morphology and surface wettability (characterized by contact angle) were followed using AFM microscopy and standard goniometry, respectively. The changes of chemical structure of PE polymeric chain were characterized by FTIR and XPS techniques. A nanoindenter was used to study mechanical properties (microhardness, elasticity module and microscratch test) of modified PE. After exposition to the plasma discharge a fast decline of the contact angle is observed. The decline depends on the discharge power and the time elapsed from the plasma exposition. FTIR and XPS measurements indicate an oxidation of degraded polymeric chains and creation of hydroxyl, carbonyl, ether, ester and carboxyl groups. Surface morphology of modified PE depends on the plasma discharge power and exposure time. Maximum microhardness and elastic module, observed on PE specimens exposed to plasma discharge for 240 s, may be connected with PE crosslinking initiated by plasma discharge.

Indentation method to measure the residual stress induced by ion implantation

Abstract: A depth-sensing indentation system was used to measure the residual stress in a stainless steel plate implanted by Fe2+ ions with an energy of 3 MeV at a dose of 3 × 1016 cm−2. Unlike other measurement methods, such as substrate curvature and X-ray diffraction techniques, depth-sensing indentation provides an accurate measurement of local residual surface stresses in the thin ion-implanted layer. Micromechanical analysis was carried out based on the premise that elastic unloading responses during indentation are fully independent of any pre-existing residual stresses at the indented surface. The correctness of this premise was verified by FEM simulation. It is found that the surface stress is proportional to the load shift induced by the surface stress. By using the energy method, a formula was derived for determining the surface stress by depth-sensing indentation studies. The residual surface stress induced by ion implantation was evaluated by using this formula.

Trace elemental correlation study in malignant and normal breast tissue by PIXE technique

Abstract: Particle induced X-ray emission technique was used to study the variations in trace elemental concentrations between normal and malignant human breast tissue specimens and to understand the effects of altered homeostasis of these elements in the etiology of breast cancer. A 3 MeV proton beam was used to excite the biological samples of normal and malignant breast tissues. The elements Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb and Sr were identified and their relative concentrations were estimated. Almost all the elements were found to be elevated (p < 0.05, Wilcoxon signed-ranks test) in the cancerous tissues when compared with normal tissues. The excess levels of trace elements observed in the cancerous breast tissues could either be a cause or a consequence of breast cancer. Regarding their role in the initiation or promotion of breast cancer, one possible interpretation is that the elevated levels of Cu, Fe and Cr could have led to the formation of free radicals or other reactive oxygen species (ROS) that adversely affect DNA thereby causing breast cancer, which is mainly attributed to genetic abnormalities. Moreover, since Cu and Fe are required for angiogenesis, elevated concentrations of these elements are likely to promote breast cancer by increasing the blood supply for tumor growth. On the other hand elevated concentrations of elements in breast cancer tissues might also be a consequence of the cancer. This can be understood in terms of the biochemical and histological differences between normal and cancerous breast tissues. Tumors, characterized by unregulated multiplication of cells, need an ever-increasing supply of essential nutrients including trace elements. This probably results in an increased vascularity of malignant tissues, which in turn leads to enhancement of elemental concentrations in tumors.

Electronic excitation effects in CeO2 under irradiations with high-energy ions of typical fission products

Abstract: In order to understand the formation mechanism of a crystallographic re-structuring in the periphery region of high-burnup nuclear fuel pellets, named as “rim structure”, information on the accumulation process of radiation damage and fission products (FPs), as well as high-density electronic excitation effects by FPs, are needed In order to separate each of these processes and understand the high-density electronic excitation effects, 70–210 MeV FP ion (Xe 10–14+ , I 7+ and Zr 9+ ) irradiation studies on CeO 2 , as a simulation of fluorite ceramics of UO 2 , have been done at a tandem accelerator of JAEA-Tokai and the microstructure changes were determined by transmission electron microscope (TEM) Measurements of the diameter of ion tracks, which are caused by high-density electronic excitation, have clarified that the effective area of electronic excitation by high-energy fission products is around 5–7 nm ϕ and the square of the track diameter tends to follow linear function of the electronic stopping power ( S e ) Prominent changes are hardly observed in the microstructure up to 400 °C After overlapping of ion tracks, the elliptical deformation of diffraction spots is observed, but the diffraction spots are maintained at higher fluence These results indicate that the structure of CeO 2 is still crystalline and not amorphous Under ion tracks overlapping heavily (>1 × 10 15 ions/cm 2 ), surface roughness, with characteristic size of the roughness around 1 μm, is observed and similar surface roughness has also been observed in light-water reactor (LWR) fuels

Status of ion beam data analysis and simulation software

Abstract: The status of ion beam data analysis codes dedicated to Rutherford backscattering, elastic recoil detection analysis and non-resonant nuclear reaction analysis, is reviewed. The most important methods and approaches employed are discussed. The stopping power and scattering cross-section databases used, the ion–target interaction physics, the experimental and detection system characteristics and the structure of samples all have a strong impact on the analytical results. The models and algorithms used by different codes are reviewed and discussed in detail. Limitations in existing codes and perspectives for further developments are presented. The importance of ascertaining the correctness and accuracy of different methods and codes used in ion beam data analysis is stressed.

The ion-catcher device for SHIPTRAP

Abstract: An ion-catcher device consisting of a buffer-gas stopping cell and a radio-frequency quadrupole (RFQ) has been built for the SHIPTRAP facility at GSI. Results of characterisation measurements with the buffer-gas cell and the extraction RFQ performed at GSI in Darmstadt and at the MLL (Maier-Leibnitz-Laboratory) in Garching are presented. The set-up was tested off-line using laser-produced ions and on-line using stable beams and fusion–evaporation products. During the on-line measurements the ions with total energies of around 200 keV/u were thermalised in helium buffer gas at 40–60 mbar. In the following they were guided by a combination of electric RF- and DC-fields until they were transported by the gas flow through the extraction nozzle. After being extracted by a supersonic gas jet the ions were separated from the buffer gas and guided by the extraction RFQ towards subsequent detection systems. Depending on the electric-field strength average extraction times of around 10 ms and an overall efficiency (including stopping and extraction) between 4% and 8% have been achieved.

Anisotropy in the momentum density of tantalum

Abstract: The [1 0 0], [1 1 0] and [1 1 1] directional Compton profiles of tantalum have been measured, at an intermediate resolution, with 66165 keV γ-radiation and a well-defined scattering vector We have also computed the Compton profiles within the framework of pseudopotential using CRYSTAL03 code of Torino group The measured anisotropy is found to be smaller to that predicted by our pseudopotential computations and also the available augmented plane wave (APW) calculations A comparison of the absolute theoretical and the experimental profiles shows clearly for the first time the importance of anisotropic electron–electron correction effect in the third series transition metals A quantitative comparison between the experimental and theoretical directional difference profiles reveals some accurate information about the Fermi surface topology of tantalum

Monte Carlo simulation of the transport of atoms in DC magnetron sputtering

Abstract: In this work, we present a Monte Carlo simulation for the transport of sputtered particles during DC magnetron sputter deposition through the gas phase. The nascent sputter flux has been simulated by SRIM and TRIM, while the collisions of the sputtered atoms with the sputter gas are simulated with a screened Coulomb potential, with the Moliere screening function and the Firsov screening length. The model calculates the flux of the atoms arriving at the substrate, their energy, direction and number of collisions they underwent. The model was verified by comparing the simulated thickness profiles with experimental profiles of deposited layers of Al, Cu and Zr/Y (85/15 wt%) on large substrates (ratio of the substrate diameter to the target diameter is 8). A good agreement between the experimental data and the simulations for sputter pressures (0.3–1 Pa) and target–substrate distances (7–16 cm) is obtained.

Photoluminescence and Raman studies of ZnS nanoparticles implanted with Cu+ ions

Abstract: In the present study ZnS nanoparticles were prepared through chemical route. The particle size was calculated from the XRD line broadening. Pressed pellets of nanostructured ZnS were implanted with Cu + ions at doses of 5 × 10 14 , 1 × 10 15 and 5 × 10 15 ions/cm 2 . The photoluminescence and Raman spectra of as prepared and Cu + ion implanted samples were recorded. PL emission peaks were observed around 412 and 518 nm in as prepared and in samples with Cu + ions implanted at higher doses of 1 × 10 15 and 5 × 10 15 ions/cm 2 . PL spectra of samples implanted at a low dose of 5 × 10 14 ions/cm 2 showed a peak around 490 nm instead of the peak at 518 nm. PL spectra of Cu + implanted samples showed a decrease in intensity and an increase in FWHM of the emission peaks with increase in the implantation dose. The Raman spectra of unimplanted and Cu + ion implanted samples of nanostructured ZnS showed LO mode and LOPC (L − ) mode. The peak position of LOPC mode decreased with increase in implantation dose due to the passivation of free electrons by Cu + ions.

Comparison between electron-beam and chemical crosslinking of silicone rubber

Abstract: Silicone rubber (SR) was irradiated by electron beam over a dose range of 50–300 kGy in the absence of chemical reagents. Molecular weight between crosslinks ( M c ) in the network of SB was determined by two methods of solvent swelling and modulus of elasticity. The network structure of the elastomer crosslinked by electron beam irradiation and chemical vulcanization was compared. Mechanical tests were performed to determine shore hardness, tensile elongation, strength and modulus of the samples. It was found that SR is effectively crosslinked by electron beam irradiation. The tensile strength, hardness, modulus and elongation of irradiated SR were higher than peroxide-crosslinked SR. The optimum dose for the neat rubber was 150 kGy which reduced to 50 kGy with addition of 10 wt.% fumed silica. The synergistic effect of fumed silica was verified by M c measurements which showed a dramatic decrease in presence of fumed silica in the rubber. The synergism in properties was also verified by comparing the modulus values calculated from the Guth–Smallwood equation and experimental data. Absence of chemical reagents in irradiated SR samples makes them a proper choice for medical applications.

Wettability and biocompatibility of nitrogen-doped hydrogenated amorphous carbon films: Effect of nitrogen

Abstract: Amorphous carbon films have been applied in biomedical fields as potential biocompatible materials with wettability that can be adjusted by doping with other elements, including F, Si, Ti, O and N. In this study, nitrogen-doped hydrogenated amorphous carbon (a-C:H:N) films were deposited by PIII-D using C 2 H 2 + N 2 gas mixtures. The biocompatibility and anti-thrombotic properties of the films were assessed in vitro. The surface morphology and surface wettability of the films were characterized using atomic force microscopy (AFM) and a contact angle method. The results show no cytotoxicity for all films, and films with appropriate nitrogen doping possess much better endothelial cell growth and anti-thrombotic properties.

Biomonitoring of Heavy Metals and Arsenic on the East Coast of the Middle Adriatic Sea Using Mytilus Galloprovincialis

Abstract: Results of two years monitoring of heavy metals and arsenic concentrations in soft tissue of Mediterranean blue mussel Mytilus galloprovincialis are presented. Samples were taken at six localities (five exposed to various pollution sources and one control site) on the east coast of the Middle Adriatic in October 2003 and 2004 and in April 2004 and 2005. All measurements were carried out with source excited Energy Dispersive X-ray Fluorescence Method (EDXRF). Measured concentrations were in the following ranges: Pb (2–7 mg/kg); As (4–30 mg/kg); Cr (1–2.9 mg/kg); Mn (2–13 mg/kg); Fe (53.4–719 mg/kg); Ni (0.8–5 mg/kg); Cu (3.7–11.1 mg/kg) and Zn (59.1–273 mg/kg). Maximum values of the most elements were measured in samples from the most polluted Vranjic region. Statistically significant difference among six localities (p = 0.05) was found for As, Fe and Zn while Mn, Fe and Cu showed significantly higher concentrations in spring period. None of the selected elements showed significant difference between the control and exposed regions.

Ion beam enhanced etching of LiNbO3

Abstract: Single crystals of z - and x -cut LiNbO 3 were irradiated at room temperature and 15 K using He + - and Ar + -ions with energies of 40 and 350 keV and ion fluences between 5 × 10 12 and 5 × 10 16 cm −2 . The damage formation investigated with Rutherford backscattering spectrometry (RBS) channeling analysis depends on the irradiation temperature as well as the ion species. For instance, He + -irradiation of z -cut material at 300 K provokes complete amorphization at 2.0 dpa (displacements per target atom). In contrast, 0.4 dpa is sufficient to amorphize the LiNbO 3 in the case of Ar + -irradiation. Irradiation at 15 K reduces the number of displacements per atom necessary for amorphization. To study the etching behavior, 400 nm thick amorphous layers were generated via multiple irradiation with He + - and Ar + -ions of different energies and fluences. Etching was performed in a 3.6% hydrofluoric (HF) solution at 40 °C. Although the etching rate of the perfect crystal is negligible, that of the amorphized regions amounts to 80 nm min −1 . The influence of the ion species, the fluence, the irradiation temperature and subsequent thermal treatment on damage and etching of LiNbO 3 are discussed.

Cosmogenic activation of germanium and its reduction for low background experiments

Abstract: Production of 60 Co and 68 Ge from stable isotopes of germanium by nuclear active component of cosmic rays is a principal background source for the new generation 76 Ge double beta decay experiments like GERDA and Majorana. The biggest contribution of cosmogenic activity is expected to be produced during transportation of either enriched material or already grown crystal. In this article the properties and feasibility of a movable iron shield are discussed. An activation reduction factor of about 10 is predicted by simulations with the SHIELD code for a simple cylindrical configuration. This is sufficient for the GERDA Phase II background requirements. The possibility of further increasing the reduction factor and physical limitations are considered. The importance of activation reduction during germanium purification and detector manufacturing is emphasized.

Anisotropic deformation of metallo-dielectric core–shell colloids under MeV ion irradiation

Abstract: We have studied the deformation of metallo-dielectric core–shell colloids under 4 MeV Xe, 6 and 16 MeV Au, 30 MeV Si and 30 MeV Cu ion irradiation. Colloids of silica surrounded by a gold shell, with a typical diameter of 400 nm, show anisotropic plastic deformation under MeV ion irradiation, with the metal flowing conform the anisotropically deforming silica core. The 20 nm thick metal shell imposes a mechanical constraint on the deforming silica core, reducing the net deformation strain rate compared to that of pure silica. In colloids consisting of a Au core and a silica shell, the silica expands perpendicular to the ion beam, while the metal core shows a large elongation along the ion beam direction, provided the silica shell is thick enough (>40 nm). A minimum electronic energy loss of 3.3 keV/nm is required for shape transformation of the metal core. Silver cores embedded in a silica shell show no elongation, but rather disintegrate. Also in planar SiO2 films, Au and Ag colloids show entirely different behavior under MeV irradiation. We conclude that the deformation model of core–shell colloids must include ion-induced particle disintegration in combination with thermodynamical effects, possibly in combination with mechanical effects driven by stresses around the ion tracks.

In-air PIXE analysis by means of glass capillary optics

Abstract: A novel technique to introduce high energy ion beams to atmospheric environment is presented, which enables in-air PIXE measurements. Slightly tapered glass capillary optics is applied to work as a differential pumping orifice as well as a focusing lens. The flux intensity is enhanced by at least one order of magnitude due to the focusing effect. Using capillaries of 10–20 μm outlet diameters, we obtain several hundreds pA of 4 MeV He2+ ion beam and apply it to PIXE analysis of the seabed sludge without any sample treatments. A comparison of spectra between wet and dry sludge samples suggests the usefulness of our new technique.

A compact 1 MV multi-element AMS system

Abstract: HVE has designed and built a compact 1 MV multi-element AMS system with a footprint of 3.8 m × 6.3 m. The system is primarily designed for the analysis of light elements like beryllium, carbon and aluminium, but it also supports the measurement of heavy ions like iodine and plutonium. The analysis of 14C is done using the charge state 1. For this, the accelerator terminal is designed for high stripper gas thickness to efficiently destroy the interfering molecules like 13CH and 12CH2. For the analysis of 10Be, suppression of the isobaric 10B is achieved using an absorber foil that can be inserted in front of the electrostatic analyser. The analysis of 26Al can be done using charge-state 1 or 3. The rare isotopes are identified in a dual-anode high-resolution detector and a two-dimensional data acquisition system.