On the comparison of three methods of assessing beam quality for broad beam in vitro cell irradiation

The interaction of charged particles with living matter has recently attracted increasing interest in the field of biomedical applications such as hadron therapy, radioprotection and space radiation biology. Particle accelerators are particularly useful in this area.In vitro radiobiological studies with a broad beam configuration require beam homogeneity. The goal is to produce a dose distribution given to a cell population that is as close to uniform as possible.In this paper, we compare the results of three devices used to assess the beam quality for broad beam irradiation: a passivated implanted planar silicon (PIPS) particle detector, a position-sensitive solid state detector, which is camera-like, and a solid state nuclear track detector (CR39).The first device is a PIPS detector of 300 μm nominal depletion depth and an entrance window with a thickness of about 500 Å. It is collimated with a 0.5 mm aperture and mounted in air on an XY moving table as close as possible to the exit window of the beam line.The second device is a CMOS position-sensitive detector (technological process 0.6 μm AMS CUA), 112 × 112 pixels, with 153 × 153 μm² pixel size. It allows the user to rapidly obtain dose uniformity over a surface of 1 × 1 cm². During uniformity and dose rate assessment it is placed in air at the PIPS location.For both detectors, beam profile was obtained for various proton fluxes (from ∼5 × 10⁴ to 10⁶ particles cm⁻² s⁻¹). Preliminary tests were made with CR39 using 4 MeV He⁺⁺ ions.Results are analysed using Poisson distribution and cell hit probability.     

An external sub-milliprobe optimized for PIXE analysis of archaeological samples

A simple and compact electrostatic quadrupole triplet lens has been designed and fabricated as part of the dedicated beam line for analysis of archaeological samples. A Fortran based ion optics program has been developed to simulate the beam line and lens parameters to achieve a focused sub-millimeter beam spot. The results of simulations are utilized to design and fabricate beam-line elements. The beam spot was measured by wire scanning method to be 0.3 mm for the object-slit width of 1 mm at a distance of 15 mm from the exit window. The improved Ion Beam Analysis setup allows accelerated PIXE analysis of samples whose details are comparable with the beam probe in size. The PIXE spectrum obtained by external analysis of a historical enameled ceramic sample with a sub-millimeter beam is compared with that obtained by in-vacuum standard PIXE analysis.     

Structural characterization of buried nitride layers formed by nitrogen ion implantation in silicon

The synthesis of buried silicon nitride insulating layers was carried out by SIMNI (separation by implanted nitrogen) process using implantation of 140 keV nitrogen (¹⁴N⁺) ions at fluence of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² into 〈1 1 1〉 single crystal silicon substrates held at elevated temperature (410 °C). The structures of ion-beam synthesized buried silicon nitride layers were studied by X-ray diffraction (XRD) technique. The XRD studies reveal the formation of hexagonal silicon nitride (Si₃N₄) structure at all fluences. The concentration of the silicon nitride phase was found to be dependent on the ion fluence. The intensity and full width at half maximum (FWHM) of XRD peak were found to increase with increase in ion fluence. The Raman spectra for samples implanted with different ion fluences show crystalline silicon (c-Si) substrate peak at wavenumber 520 cm⁻¹. The intensity of the silicon peak was found to decrease with increase in ion fluence.     

Depth profiling of hydrogen under an atmospheric pressure

Nuclear reaction analysis of hydrogen with a use of the ¹H(¹⁵N,αγ)¹²C reaction was performed under a atmospheric condition. A 100 nm-thick silicon nitride membrane coated with gold of 10 nm was used for the extraction of the ¹⁵N beam into the sample chamber filled with gas molecules. Hydrogen contained in a Y film with a thickness of 80 nm was detected in N₂ of 10⁵ Pa. This nuclear reaction analysis (NRA) setup was also applied to H₂ gas, and the yield curve revealed a plateau feature. The plateau level was, furthermore, found to be constant independent of the H₂ pressure. We show that this plateau intensity can be used to obtain the detection efficiency of a NRA setup.     

The Columbia University proton-induced soft x-ray microbeam

A soft X-ray microbeam using proton-induced X-ray emission (PIXE) of characteristic titanium (K_α 4.5 keV) as the X-ray source has been developed at the Radiological Research Accelerator Facility (RARAF) at Columbia University. The proton beam is focused to a 120 μm × 50 μm spot on the titanium target using an electrostatic quadrupole quadruplet previously used for the charged particle microbeam studies at RARAF. The proton induced X-rays from this spot project a 50 μm round X-ray generation spot into the vertical direction. The X-rays are focused to a spot size of 5 μm in diameter using a Fresnel zone plate. The X-rays have an attenuation length of (1/e length of ∼145 μm) allowing more consistent dose delivery across the depth of a single cell layer and penetration into tissue samples than previous ultrasoft X-ray systems. The irradiation end station is based on our previous design to allow quick comparison to charged particle experiments and for mixed irradiation experiments.     

Measurements with compound refractive lenses at the “BAMline”

A set of compound refractive lenses (CRLs), mounted on a silicon wafer, was obtained from the Institut für Mikrostrukturtechnik Karlsruhe. The CRLs were characterized at the BAMline at the synchrotron BESSYII in Berlin. It could be demonstrated that beam diameters below 1 μm can be obtained. The beam size accepted by the lenses is (140 × 140) μm², thus the intensity gain in the micrometer spot, including absorption, is about 15,000. It is possible to switch between different beam energies within a few minutes. First results of scans and the application of the lenses for MicroXANES (X-ray absorption near-edge structure) measurements are presented in this paper. Also, the possibility of MicroEXAFS (extended X-ray absorption fine structure) measurements is discussed.     

Synchrotron X-ray induced damage in polymer (PS) thin films

Thin polystyrene (PS) films (M_w = 234,000) are spin coated on silicon substrates with a Chromium (Cr) layer as a sandwiched metallic layer that produces photoelectrons (by synchrotron X-rays). Earlier studies on synchrotron radiation damage in PS films, without metallic layer, have shown a decrease in interfacial roughness and a slight increase in thickness, at temperatures below T_g [A.G. Richter, R. Guico, K. Shull, J. Wang, Macromolecules 39 (2006) 1545]. Similar trend is observed in the presence of a thin layer of Cr film (∼2.5 nm). For the sample with a thick Cr layer the opposite effect was observed for X-ray radiation damage. For the 50 nm thick Cr film system thickness of the polystyrene film decreased by ≈4.4% which amount to a loss of about 0.021 nm³ per incident photon in the fluence range studied (6.8 × 10⁹ photons mm⁻² to 1 × 10¹⁴ photons mm⁻²). Interfacial roughness also increased from about 1.0 nm to 2.1 nm in the process. These effects are explained by invoking the presence of more number of X-ray induced photoelectrons and secondary electrons for 50 nm thick Cr film case compared to 2.5 nm thin film case.     

Comparison of detector systems for the separation of 36Cl and 36S with a 3-MV tandem

The possibility of detecting ³⁶Cl for geological exposure dating has been explored for several years at VERA (the Vienna Environmental Research Accelerator). First results on real samples were obtained with an ionization chamber (developed at the ETH/PSI, Zürich, Switzerland) with two anodes. To improve the suppression of ³⁶S, we equipped the ionization chamber with an exit window and added a Time-of-Flight (TOF) system with a double-sided silicon strip detector (50 × 50 mm²) as stop detector. We optimized the TOF setup by using silicon nitride foils to reduce scattering tails in the energy spectra.At 3 MV terminal voltage, corresponding to a particle energy of 24 MeV of ³⁶Cl⁷⁺, we achieved a ³⁶S⁷⁺-suppression of 21,500 (50% ³⁶Cl-detector-efficiency).     

Use of silicon drift detectors for the detection of medium-light elements in PIXE

In order to fully exploit in PIXE the superior performance of silicon drift detectors especially for the detection of low- and medium-energy X-rays, avoiding in particular the negative effects of backscattered particles, we developed a custom spectrometer based on a 10 mm² chip with a thermoelectric Peltier cooler and home-designed front-end electronics, coupled to a weakly focusing polycapillary lens.This paper briefly describes the detector + lens assembly and reports the results of first tests carried out at an external beam line of the LABEC laboratory in Florence. Excellent energy resolution is achieved under real operating conditions in a PIXE run (measured FWHM at 1 keV is 81 eV with a count-rate of 480 cps) and also the lineshapes are very good (FW1/10M over FWHM ratio is 2.1). As a whole, our preliminary tests gave encouraging results and also helped to point out some aspects which it is worthwhile to investigate further (e.g. how X-ray peak intensity ratios may be affected by inaccurate lens alignment), in order to profit fully from such a good performance of the spectrometer.     

Fabrication of microfluidic devices using MeV ion beam Programmable Proximity Aperture Lithography (PPAL)

MeV ion beam lithography is a direct writing technique capable of producing microfluidic patterns and lab-on-chip devices with straight walls in thick resist films. In this technique a small beam spot of MeV ions is scanned over the resist surface to generate a latent image of the pattern. The microstructures in resist polymer can be then revealed using a chemical developer that removes exposed resist, while leaving unexposed resist unaffected. In our system the size of the rectangular beam spot is programmably defined by two L-shaped tantalum blades with well-polished edges. This allows rapid exposure of entire rectangular pattern elements up to 500 × 500 μm in one step. By combining different dimensions of the defining aperture with the sample movements relative to the beam spot, entire fluidic patterns with large reservoirs and narrow flow channels can be written over large areas in short time. Fluidic patterns were written in PMMA using 56 MeV ¹⁴N³⁺ and a 3 MeV ⁴He²⁺ beams from K130 cyclotron and a 1.7 MV Pelletron accelerators, respectively, at the University of Jyväskylä Accelerator Laboratory. The patterns were characterized using SEM, and the factors affecting patterns quality are discussed.     

Development of micro-beam NRA for hydrogen mapping: Observation of fatigue-fractured surface of glassy alloys

A micro-beam NRA system by means of a resonant nuclear reaction of ¹H(¹⁵N, αγ)¹²C has been developed at the beam line in MALT, University of Tokyo. The beam optics was analyzed in terms of the phase diagram. By carefully suppressing the spherical aberration of the final quadrupole magnetic lens, the ¹⁵N beam at the energy of 6.4 MeV was focused on targets with a size of 17 μm × 30 μm. For the precise positioning of the sample and beam spot, a combination of the mirror and optical microscope was adopted, so that the hydrogen concentration can be measured at a desirable position of the sample. With this new system, the hydrogen concentrations of fatigue-fractured surfaces of glassy alloys were determined from the viewpoint of the hydrogen embrittlement: Zr₅₀Cu₃₇Al₁₀Pd₃ and Zr₅₀Cu₄₀Al₁₀. Depth-resolved two-dimensional (2D) mapping of hydrogen concentration was performed in the area of 3 mm × 3 mm with an in-plane resolution of 150 μm. The maps taken at three different depths revealed that the hydrogen concentration is higher in the fatigue-fractured regions in both samples.     

A deceleration system at the Heidelberg EBIT providing very slow highly charged ions for surface nanostructuring

Recently, it has been demonstrated that each single-impact of a slow (typically 1-2 keV/u) highly charged ion (HCI) creates truly topographic and non-erasable nanostructures on CaF₂ surfaces. To further explore the possibility of nanostructuring various surfaces, using mainly the potential energy stored in such HCIs, projectiles with kinetic energies as low as possible are required. For this purpose a new apparatus, capable of focusing and decelerating an incoming ion beam onto a solid or gaseous target, has been installed at the Heidelberg electron beam ion trap (EBIT). An X-ray detector and a position-sensitive particle detector are utilized to analyze the beam and collision products. First experiments have already succeeded in lowering the kinetic energy of HCIs from 10 keV/q, down to ∼30 eV/q, and in focusing the decelerated beam to spot sizes of less than 1 mm², while maintaining the kinetic energy spread below ∼20 eV/q.     

A systematic study on analysis-induced radiation damage in silicon during channeling Rutherford backscattering spectrometry analysis

Channeling Rutherford backscattering spectrometry (RBS) is an essential analysis technique in materials science. However, the accuracy of RBS can be significantly affected by disorders in materials induced by the analyzing ion beam even under channeling mode. We have studied RBS analysis-induced radiation damage in silicon. A 140-keV H⁺ ion beam was incident along 〈1 0 0〉 Si axis at room temperature to a fluence ranging from 1.6 × 10¹⁶ cm⁻² to 7.0 × 10¹⁶ cm⁻². The evolution of the aligned yields versus fluences has been examined and found to agree well with a model proposed by us.     

Temperature effect study of silicon-on-insulator structures prepared by high dose implantation of nitrogen

The temperature effect on the microstructure of the N⁺-ion implantation-induced Si₃N₄ buried layer was investigated. The underlying silicon nitride layers were formed in a Si (1 1 1) wafer after implantation of 50 keV nitrogen ions (fluence: 1 × 10¹⁷, 2 × 10¹⁷ and 5 × 10¹⁷ ions/cm²). It was observed that a continuous amorphous layer of about 200 nm thickness was formed in all implanted samples due to the irradiation damage. After 30 min annealing at 900 °C, poly-crystalline Si₃N₄ products were found by TEM examination in the specimen implanted with 5 × 10¹⁷ ions/cm² dose. In the case of annealing at 1200 °C a continuous single-crystalline α-Si₃N₄ buried layer was formed indicating that the amorphous layer in the implanted samples could be transformed into three successive layers, which are amorphous SiO₂, single-crystal α-Si₃N₄ and retained defects from surface to inner substrate, respectively.     

Design of the thermal neutron beam for neutron radiography at the Syrian MNSR

Neutron beam design was studied at the Syrian reactor (MNSR, 30 kW) with a view to generating thermal neutron beam in the vertical irradiation sites for neutron radiography. The design of the neutron collimator was performed using MCNP4C and the ENDF/B-V cross-section library. Thermal, epithermal and fast neutron energy ranges were selected as <0.4 eV, 0.4 eV–10 keV, >10 keV, respectively. To produce a good neutron beam quality, bismuth was used as photon filter. In this design, the L/D ratio of this facility had the value of 125. The thermal neutron flux at the beam exit was about 2.548 × 10⁵ n/cm² s. If such neutron beam were built into the Syrian MNSR many scientific applications would be available using the neutron radiography.     

Ion induced segregation in gold nanostructured thin films on silicon

We report a direct observation of segregation of gold atoms to the near surface regime due to 1.5 MeV Au²⁺ ion impact on isolated gold nanostructures deposited on silicon. Irradiation at fluences of 6 × 10¹³, 1 × 10¹⁴ and 5 × 10¹⁴ ions cm⁻² at a high beam flux of 6.3 × 10¹² ions cm⁻² s⁻¹ show a maximum transported distance of gold atoms into the silicon substrate to be 60, 45 and 23 nm, respectively. At a lower fluence (6 × 10¹³ ions cm⁻²) transport has been found to be associated with the formation of gold silicide (Au₅Si₂). At a high fluence value of 5 × 10¹⁴ ions cm⁻², disassociation of gold silicide and out-diffusion lead to the segregation of gold to defect - rich surface and interface regions.     

FTIR and RBS study of ion-beam synthesized buried silicon oxide layers

Single crystal silicon samples were implanted at 140 keV by oxygen (¹⁶O⁺) ion beam to fluence levels of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² to synthesize buried silicon oxide insulating layers by SIMOX (separation by implanted oxygen) process at room temperature and at high temperature (325 °C). The structure and composition of the ion-beam synthesized buried silicon oxide layers were investigated by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques. The FTIR spectra of implanted samples reveal absorption in the wavenumber range 1250-750 cm⁻¹ corresponding to the stretching vibration of Si-O bonds indicating the formation of silicon oxide. The integrated absorption band intensity is found to increase with increase in the ion fluence. The absorption peak was rather board for 325 °C implanted sample. The FTIR studies show that the structures of ion-beam synthesized buried oxide layers are strongly dependent on total ion fluence. The RBS measurements show that the thickness of the buried oxide layer increases with increase in the oxygen fluence. However, the thickness of the top silicon layer was found to decrease with increase in the ion fluence. The total oxygen fluence estimated from the RBS data is found to be in good agreement with the implanted oxygen fluence. The high temperature implantation leads to increase in the concentration of the oxide formation compared to room temperature implantation.     

Dense plasma focus ion-based titanium nitride coating on titanium

We report the synthesis of titanium nitride coating on a titanium substrate by utilizing energetic nitrogen ions emitted from a 2.3 kJ dense plasma focus device for 30 focus shots. The number of nitrogen ions transferred to the sample by a single ion pulse of about 140 ns duration in the energy interval (40-600 keV) is about 1.09 × 10¹² with a mean energy per ion of 58 keV. The corresponding energy flux delivered to the titanium surface is estimated to be 6.17 × 10¹⁴ keV cm⁻³ ns⁻¹ leading to a transient temperature rise of the top layer of about 5400 K which helps layer growth. The coating is investigated on the basis of its morphological, compositional and hardness properties. X-ray diffraction analysis of the sample reveals the formation of a nanocrystalline titanium nitride coating having (1 1 1) and (2 0 0) plane reflections with an average crystallite size of 40 nm. The compressive residual stresses in the nitride coating have been evaluated to be 2.80 GPa and 6.81 GPa corresponding to (1 1 1) and (2 0 0) plane orientations. A complete restructuring of the manually polished titanium substrate has been observed with appearance of nano-sized multidimensional granular surface morphologies. The thickness of the nitride coating is about 1 μm, whereas the coating has a nitrogen content of 35.35 at.% and 13.78 ± 3.57 wt.% and a surface hardness of 8.19 GPa.     

Early experiences with the Mount Allison University four-detector X-ray fluorescence bone lead measurement system

A four-detector (4 × 500 mm²) low energy Germanium detector array has recently been acquired for use in a ¹⁰⁹Cd source K-shell X-ray fluorescence bone lead measurement system. In this paper, system calibration results are presented, along with preliminary measurement results using lead-doped bone phantoms. Measurement uncertainty and reproducibility values are noted. System comparisons are made with our conventional (1 × 2000 mm²) detector system, and future directions outlined.