Nanosecond pulsed proton microbeam

We show the preparation of a pulsed 20 MeV proton beam at the Munich tandem accelerator which offers a fluence of more than 1 × 10⁹ protons/cm² being deposited in a beam spot smaller than 100 μm in diameter and within a time span of 0.9 ns fwhm. Such a beam is produced by an ECR type proton source using charge exchange in cesium vapor to obtain a beam of negative hydrogen of high brightness that is bunched, chopped, accelerated and then focused by the superconducting multipole lens of the microprobe SNAKE. Single beam pulses are generated in order to irradiate cell samples or tissue and to measure their biological effect in comparison to continuous proton or X-ray irradiation.     

Micro-ERDA,micro-RBS and micro-PIXE techniques in the investigation of fish otoliths

Elemental distribution in the otolith of the fresh water fish burbot (Lota lota L.) collected in Hungary was measured with Elastic Recoil Detection Analysis (ERDA), Rutherford Backscattering Spectrometry (RBS) and as a complementary technique, Particle-Induced X-ray Emission (PIXE) with a focussed ion beam of 1.5 × 1.5 μm² spot size. The organic- and inorganic-rich regions of the otolith are distinguished and they are presented as hydrogen and calcium maps at depth regions of 0–70, 70–140 and 140–210 nm. The textured surface of the sample and its porosity were characterized from the effect on the RBS spectra. The oxygen and carbon PIXE elemental maps can also be used to identify the organic- and inorganic-rich regions of the otolith. The calcium map was found to be more homogeneous because the otolith structure is averaged in a larger depth. The trace elements Fe, Zn and Sr were detected only in very low concentration by micro-PIXE.     

Ion implantation into aluminum and copper by a beam of carbon nanoparticles from regenerative sooting discharges

We present a new technique to generate light carbon nanoparticles from regenerative sooting discharges and its use for ion implantation on aluminum and copper surfaces at an energy of 40 keV. Films formed at fluences up to 3 × 10¹⁵ C⁺/cm² for aluminum and 10¹⁶ C⁺/cm² for copper are studied using Raman spectroscopy, X-ray diffraction and atomic force microscopy. Raman spectroscopy reveals the existence of graphite and diamond like structures in all samples. Precipitates of Al₄C₃ of rhombohedral and hexagonal types were found in the nanometer ranges from the X-ray diffraction pattern for aluminum samples and the probable formation of body-centered cubic diamond and hexagonal carbon in copper samples. The average grain sizes of Al₄C₃ were calculated ～40 nm for Al and ～35 nm for Cu. Mass spectra from a graphite hollow cathode duoplasmatron ion source are also presented. Atomic force microscopy images of a Cu sample also support the existence of 46 nm structures. Light carbon nanoparticles are readily available from the ion source in which a special carbonaceous environment creates regenerative soot. Support gas Ar produces more C₃ than Ne.     

Controlling the microstructure of ZnO nanoparticles embedded in Sapphire by Zn ion implantation and subsequent annealing

(0 0 0 1) α-Al₂O₃ single crystals (sapphire) were implanted with Zn ions of 60 keV at a fluence of 1 × 10¹⁷ ions/cm². Transmission electron microscopy and optical absorption spectroscopy studies show the formation of ZnO nanoparticles in the sapphire substrate after the implanted sample was annealed at 700 °C in oxygen ambient. The photoluminescence spectrum of the annealed sample indicates the formation of ZnO nanoparticles with perfect lattice structure. The selected-area electron diffraction pattern proves that the ZnO nanoparticles have the (0 0 0 2) orientation which follows the orientation of Al₂O₃ substrate. The result shows that the crystallographic orientation of nanoparticles obtained through ion implantation is defined by the substrate.     

Ion beam shaping of Au nanoparticles prepared by micellar technique

Irradiation-induced burrowing and ion-induced shaping effects of Au nanoparticles are investigated. Hexagonally arranged Au nanoparticles prepared by micellar technique with diameter ～10 nm and inter-particle distance of about 80 nm were sequentially irradiated with 200 keV Ar⁺ ions to fluences of 5×10¹⁵ ions/cm². Irradiation with Argon ions causes sinking of the Au nanoparticles into the subjacent SiO₂ layer due to capillary driving forces related to specific wetting conditions while the spherical shape is conserved. Subsequent irradiation with 54 MeV Ag⁸⁺ swift heavy ions of these spherical Au nanoparticles confined within a silica matrix shapes them into prolate nanorods and nanowires whose principal axes are aligned along the beam direction. Above a threshold fluence two deformation regimes have been observed. For relatively low fluences Au nanoparticles elongate into nanorods depending on their volume. For high fluences, the formation of nanowires is observed provided that the inter-particle distance is short enough to allow for an efficient mass transport through the silica matrix.     

Porous iron pellets for AMS 14C analysis of small samples down to ultra-microscale size (10–25 μgC)

We developed the use of a porous iron pellet as a catalyst for AMS ¹⁴C analysis of small samples down to ultra-microscale size (10–25 μgC). It resulted in increased and more stable beam currents through our HVEE 4130 ¹⁴C AMS system, which depend smoothly on the sample size. We find that both the expected decrease of oxalic acid standards and increase of backgrounds with decreasing sample size, due to increasing influence of contamination, are reproducible. Using a mass-dependent background correction for dead (1.0 ± 0.4 μgC) and modern (0.25 ± 0.10 μgC) contamination, we obtain reliable results for small samples down to 10 μgC and possibly smaller. Due to our low graphitization yield for ultra-small samples (increases from 40% to 80% on average with sample size), we measured graphite standards as small as 3 μgC. The standard deviation of the corrected activity is about 5% for a 10-μgC HOxII standard.Here we report the iron pellet technique, which is new to the best of our knowledge. It is generally applicable for AMS ¹⁴C laboratories that want to measure small samples down to ultra-microscale size. As an illustrative test-case, we analyze ¹⁴C data for IAEA-C5, C7 and C8 samples with masses ranging from 15 to 300 μgC.     

Swift heavy ion induced modifications of optical and microstructural properties of silver–fullerene C60 nanocomposite

In this paper, we study the optical and microstructural properties of silver–fullerene C₆₀ nanocomposite and their modifications induced by swift heavy ion irradiation. Silver nanoparticles embedded in fullerene C₆₀ matrix were synthesized by co-deposition of silver and fullerene C₆₀ by thermal evaporation. The nanocomposite thin films were irradiated by 120 MeV Ag ions at different fluences ranging from 1 × 10¹² to 3 × 10¹³ ions/cm². Optical absorption studies revealed that the surface plasmon resonance of Ag nanoparticles showed a blue shift of ～49 nm with increasing ion fluence up to 3 × 10¹³ ions/cm². Transmission electron microscopy and Rutherford backscattering spectroscopy were used to quantify particle size and metal atomic fraction in the nanocomposite film. Growth of Ag nanoparticles was observed with increasing ion fluence. Raman spectroscopy was used to understand the effect of heavy ion irradiation on fullerene matrix. The blue shift in plasmonic wavelength is explained by the transformation of fullerene C₆₀ matrix into amorphous carbon.     

Thermal and irradiation induced interdiffusion in Fe3O4/MgO(0 0 1) thin film

The interface reactions in an epitaxial 10 nm-thick Fe₃O₄/MgO(0 0 1) film were investigated by using Rutherford Backscattering spectrometry (RBS), channeling (RBS-C) and X-ray reflectometry (XRR). The as-grown film had a good crystallinity indicated by the minimum yield and the half-angle value for Fe, respectively, χ_min(Fe) = 22% and ψ_1/2(Fe) = 0.62°. Annealing the films under partial argon pressure up to 600 °C led to a large enhancement of Mg out-diffusion into the film forming a wustite-type phase, but the total layer thickness did not change much. Ion irradiation of the film by 1 MeV Ar ion beam caused a strong Fe ion mixing resulting in a large interfacial zone with a thickness of 23 nm.     

Detection of beryllium treatment of natural sapphires by NRA

Since the 1990’s, artificial treatment of natural sapphires (Al₂O₃ crystals coloured by impurities) by diffusion of beryllium at high temperature has become a growing practice. This process permits to enhance the colour of these gemstones, and thus to increase their value. Detection of such a treatment – diffusion of tens of μg/g of beryllium in Al₂O₃ crystals – is usually achieved using high sensitivity techniques like laser-ablation inductively coupled plasma mass spectrometry (LA-ICP/MS) or laser-induced breakdown spectrometry (LIBS) which are unfortunately micro-destructive (leaving 50–100-μm diameter craters on the gems). The simple and non-destructive alternative method proposed in this work is based on the nuclear reaction ⁹Be(α, nγ)¹²C with an external helium ion beam impinging on the gem directly placed in air. The 4439 keV prompt γ-ray tagging Be atoms are detected with a high efficiency bismuth germanate scintillator. Beam dose is monitored using the 2235 keV prompt γ-ray produced during irradiation by the aluminium of the sapphire matrix through the ²⁷Al(α, pγ)³⁰Si nuclear reaction. The method is tested on a series of Be-treated sapphires previously analyzed by LA-ICP/MS to determine the optimal conditions to obtain a peak to background appropriate to reach the required μg/g sensitivity. Using a 2.8-MeV external He beam and a beam dose of 200 μC, beryllium concentrations from 5 to 16 μg/g have been measured in the samples, with a detection limit of 1 μg/g.     

Determination of the local gold contact morphology on a photoactive polymer film using nanobeam GISAXS

Grazing incidence small-angle X-ray scattering is performed with a nanometer sized X-ray beam (nGISAXS) to probe the local gold contact morphology on a photoactive polymer film. By evaporation a 50 nm thick gold contact is installed on a diblock copolymer film, which consists of a non-conducting poly(styrene) (PS) and a semi-conducting poly(paraphenylene) (PPP) block. The region around the edge of the gold contact of 200 μm is probed with nGISAXS by scanning the sample position in steps of 1 μm with respect to the X-ray beam. The diblock copolymer film has a densely packed micellar structure with a characteristic distance between adjacent micelles of 19 nm which is unaffected by the gold deposition. The gold contact exhibits a tail region which extends its lateral dimension. For the full extended surface area of the gold contact with its tails an interdiffusion of gold into the diblock copolymer film is observed. For comparison imaging ellipsometry, atomic force microscopy and optical microscopy measurements are performed.     

Rearranging a nanoprobe: Line foci,grid shadow patterns and performance tests

After a major modification of the target chamber at the Leipzig high energy ion nanoprobe the probe forming lens system, consisting of two separated quadrupole doublets, had been carefully realigned. This was done by adjusting the line foci position of each individual quadrupole on the centre position defined by the unfocused beam. Using a high magnification microscope the alignment process is very effective and precise. The lens system could be precisely realigned except an intrinsic rotational misalignment which is essentially reduced by a correction lens.Grid shadow patterns have been taken and analysed in order to assess the characteristics of the system. The dominant aberrations are spherical with an additional parasitic octupole.The grid shadow method is also very useful to determine the best position of the aperture diaphragms which minimizes the influence of the aberrations onto the beam spot size.The rearrangement allowed larger aperture diaphragms for higher beam currents at a moderate increase in beam spot sizes. Performance tests yielded proton microbeam currents and half-widths of 4.5 nA at 1.5 μm, 8.3 nA at 1.5 μm and 17.2 nA at 2 μm. For high resolution work the expected beam spots around 0.3 μm at 100 pA were not achieved. The reason is very likely interference on the beam scanner, correlated in x- and y-direction, which results from the insufficiently rectified power supply voltage of the transconductance amplifier.     

Biological studies using mammalian cell lines and the current status of the microbeam irradiation system,SPICE

The development of SPICE (single-particle irradiation system to cell), a microbeam irradiation system, has been completed at the National Institute of Radiological Sciences (NIRS). The beam size has been improved to approximately 5 μm in diameter, and the cell targeting system can irradiate up to 400–500 cells per minute. Two cell dishes have been specially designed: one a Si₃N₄ plate (2.5 mm × 2.5 mm area with 1 μm thickness) supported by a 7.5 mm × 7.5 mm frame of 200 μm thickness, and the other a Mylar film stretched by pressing with a metal ring. Both dish types may be placed on a voice coil stage equipped on the cell targeting system, which includes a fluorescent microscope and a CCD camera for capturing cell images. This microscope system captures images of dyed cell nuclei, computes the location coordinates of individual cells, and synchronizes this with the voice coil motor stage and single-particle irradiation system consisting of a scintillation counter and a beam deflector. Irradiation of selected cells with a programmable number of protons is now automatable. We employed the simultaneous detection method for visualizing the position of mammalian cells and proton traversal through CR-39 to determine whether the targeted cells are actually irradiated. An immuno-assay was also performed against γ-H2AX, to confirm the induction of DNA double-strand breaks in the target cells.     

An advance process of aluminum rich coating as tritium permeation barrier on 321 steel workpiece

We have proposed an advance three-step process, Al-electroplating in ionic liquid followed by heat treating and selectively oxidation, preparing aluminum rich coating as tritium permeation barrier (TPB). In present work, the advance process was applied to 321 steel workpieces. In the Al-electroplating, pieces were coated by galvanostatic electrodeposition at 20 mA/cm² in aluminum chloride (AlCl₃)–1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid. The Al coating on those pieces all displayed attractive brightness and well adhered to surface of pieces. Within the aluminizing time from 1 to 30 h, a series of experiments were carried out to aluminize 321 steel pieces with Al 20 μm coating at 700 °C. After heat treated for 8 h, a 30 μm thick aluminized coating on piece appeared homogeneous, free of porosity, and mainly consisted of (Fe, Cr, Ni)Al₂, and then was selectively oxidized in argon gas at 700 °C for 50 h to form Al₂O₃ scale. The finally fabricated aluminum rich coating, without any visible defects, had a double-layered structure consisting of an outer γ-Al₂O₃ layer with thickness of 0.2 μm and inner (Fe, Cr, Ni)Al/(Fe, Cr, Ni)₃Al layer of 50 μm thickness. The deuterium permeation reduction factor, PRF, of piece (Φ 80 × 2, L 150 mm) with such coating increased by 2 orders of magnitude at 600–727 °C. The reproducibility of the process was also showed.     

Detection efficiency and spatial resolution of the SIRAD ion electron emission microscope

An axial ion electron emission microscope (IEEM) has been built at the SIRAD irradiation facility at the 15 MV Tandem accelerator of INFN Legnaro National Laboratory (Padova, Italy) to obtain a micrometric sensitivity map to single event effects (SEE) of electronic devices. In this contribution we report on two experiments performed with the IEEM. Si₃N₄ ultra-thin membranes with a gold deposition were placed on the device under test (DUT) to ensure a uniform and abundant secondary electron emission In the first experiment we measured an IEEM ion detection efficiency of 83% with a ⁵⁸Ni (220 MeV) beam, in good agreement with the expected value. The second experiment allowed us to estimate the lateral resolution of the IEEM. The positions of ion induced single event upsets (SEU) in a synchronous dynamic random access memory (SDRAM), used as a reference target, were compared with the corresponding ion impact points reconstructed by the IEEM. The result (FWHM ～4.4 μm with a ⁷⁹Br beam of 214 MeV) is encouraging because of the residual presence of distortions of the image and mechanical vibrations.     

Carbon film growth and hydrogenic retention of tungsten exposed to carbon-seeded high density deuterium plasmas

Tungsten (W) targets have been exposed to high density (n_e ? 4 × 10¹⁹ m^?3), low temperature (T_e ? 3 eV) CH₄-seeded deuterium (D) plasma in Pilot-PSI. The surface temperature of the target was ～1220 K at the center and decreased radially to ～650 K at the edges. Carbon film growth was found to only occur in regions where there was a clear CII emission line, corresponding to regions in the plasma with T_e ? 2 eV. The maximum film thickness was ～2.1 μm after a plasma exposure time of 120 s. ³He nuclear reaction (NRA) analysis and thermal desorption spectroscopy (TDS) determine that the presence of a thin carbon film dominates the hydrogenic retention properties of the W substrate. Thermal desorption spectroscopy analysis shows retention increasing roughly linearly with incident plasma fluence. NRA measures a C/D ratio of ～0.002 in these films deposited at high surface temperatures.     

Challenges and opportunities in high-precision Be-10 measurements at CAMS

We determined the overall efficiency for ¹⁰Be of the high-intensity LLNL modified Middleton cesium sputter source in combination with the CAMS FN mass spectrometer. BeO^? ionization efficiency is >3%. Charge exchange efficiency including transmission through the tandem for 7.5 MeV Be⁺³ is ～34%, resulting in a total system efficiency of just over 1%. At this efficiency and with very low backgrounds, we estimate our detection limit to be ～1000 ¹⁰Be atoms. Cathodes prepared with only ～80 μg of ⁹Be show only an ～33% reduction in ⁹Be beam current compared to a sample with ～200 μg. These same samples, prepared from 07KNSTD1032 standard material, contained 1 × 10⁷ and 5 × 10^{6 10}Be atoms and exhibited similar ionization and total system efficiency. These results demonstrate the feasibility of pursuing applications that require precise measurement of samples with low ¹⁰Be concentrations and/or small sample size.     

Micro and nano patterning by focused ion beam enhanced adhesion

We report a new method of generating nano and micro patterns using focused ion beam (FIB) induced adhesion. The method utilizes selective irradiation of thin metallic films grown on substrates by focused ion beam followed by peel off. After peel off of the irradiated thin film it is observed that the ion beam scanned portions are retained on the substrate, creating nano and micro patterns. The method is suitable for materials of which the adhesion to the substrate can be improved by ion bombardment. The phenomenon has been demonstrated by creating gold nano patterns of different shapes and sizes ranging from 500 nm to 5 μm on SiO₂–Si substrate using 10–30 keV Ga FIB at beam currents up to 10 pA. The mechanism involved in the process has been discussed. The technique could be utilized to prepare micro and nano patterns of thin films deposited on an appropriate substrate for optical, plasmonic and sensor related applications.     

Inactive and mutagenic effects induced by carbon beams of different LET values in a red yeast strain

To evaluate biological action of microorganism exposed to charged particles during the long distance space exploration, induction of inactivation and mutation in a red yeast strain Rhodotorula glutinis AY 91015 by carbon beams of different LET values (14.9–120.0 keV μm^?1) was investigated. It was found that survival curves were exponential, and mutation curves were linear for all LET values. The dependence of inactivation cross section on LET approached saturation near 120.0 keV μm^?1. The mutation cross section saturated when LET was higher than 58.2 keV μm^?1. Meanwhile, the highest RBE_i for inactivation located at 120.0 keV μm^?1 and the highest RBE_m for mutation was at 58.2 keV μm^?1. The experiments imply that the most efficient mutagenic part of the depth dose profile of carbon ion is at the plateau region with intermediate LET value in which energy deposited is high enough to induce mutagenic lesions but too low to induce over kill effect in the yeast cells.     

Developments in micro-sample 14C AMS at the ANTARES AMS facility

We continue development of micro-sample radiocarbon sample preparation and AMS measurement at the ANTARES AMS facility. We routinely prepare samples containing 10–200 μg of carbon using an iron catalyst with an excess of hydrogen in ～2.5 mL graphitisation reactors. These use a tube furnace to heat the catalyst to 600 °C and a Peltier-cooled water trap. Samples containing just a few micrograms of carbon can be prepared. We describe progress with a 0.5 mL laser-heated ‘microfurnace’ we are developing for the rapid and efficient graphitisation of ～5 μg samples. Following operating experience with a prototype unit, work has commenced on the development of a second-generation device with the goal of fully automated operation with minimal introduction of extraneous carbon.Key to development of micro-sample ¹⁴C AMS is the ability to reliably handle the graphite/iron sample and to mount it in the ion source target holder. We have developed a target holder that permits the sample to be loaded in a 1 mm diameter recess and rear pressed, ensuring a high quality surface finish, at a reproducible depth. Additionally we have developed a method for systematically aligning the sample stage with the cesium beam following ion source servicing.     

129I AMS at 0.5 MV tandem accelerator

The ¹²⁹I measurement program has been established at the 0.5 MV ‘Tandy’ accelerator of the PSI/ETH Zürich AMS facility. This development was made possible by using a SiN window instead of Mylar one in a gas ionization detector. The setting up of the ¹²⁹I measurement at Tandy is simple, the acquired performance is stable and reliable, and the quality of results is equal to or better than at our larger EN-tandem. With this setup, high sample throughput, which is required in many ¹²⁹I studies, can be easily achieved. The measurements are performed in the +3 charge state. At this charge state the major difficulty in the ¹²⁹I⁺³ identification is caused by a highly abundant 43⁺¹ (m = 43, q = +1) molecule interference. This is a positive molecular ion, because its intensity reduces exponentially with an increase in gas stripper pressure. We conclude that this molecule is ²⁷Al¹⁶O⁺ (m/q = 43/1 = 129/3) and comes from the break-up of (Al₂O₃ + Al)^? (m = 129) precursor at the terminal: (Al₂O₃ + Al)^? → ²⁷Al¹⁶O⁺. The expected isobaric interferences ⁴³Ca⁺¹ and ⁸⁶Sr⁺², which also originate from the break-up of molecules in the stripper, were found to be low and do not disturb the ¹²⁹I⁺³ measurements. The best repeatable performance with our standard sample material was achieved at 0.14 μg/cm² Ar gas stripper pressure with machine blanks showing ～6 × 10^?14 normalized ¹²⁹I/I ratio and 9% transmission through the accelerator. However, high ²⁷Al¹⁶O⁺ molecular rates were observed from the user samples, and in order to destroy these molecules we had to increase the stripper pressure to ～0.22 μg/cm². This increase in the stripper pressure degraded the machine blank values to ～9 × 10^?14 and reduced transmission to 8%. Nevertheless, the achieved measurement conditions are sufficient for measurement of nearly all ¹²⁹I samples that have been submitted to PSI/ETH over the last few years.