A compact micro-beam system using a tapered glass capillary for proton-induced X-ray radiography

A compact micro-beam system, containing a tapered glass capillary tube with a tip diameter on the order of 10 μm, was constructed to examine the applicability of capillary-generated micro-beams to high-contrast radiography based on proton-induced quasi-monochromatic X-rays. The transport efficiency of swift protons (2-3 MeV) through the capillary was examined as a function of the capillary tilt angle and the capillary tip diameter. We obtained transport efficiencies of approximately three times larger than would be expected from the geometrical shape of the capillary. This enhancement indicates that a focusing effect occurred in the capillary. A metallic thin foil was irradiated with the micro-beam and quasi-monochromatic X-rays were produced. By calculating the X-ray yields induced by proton bombardment in the foil and comparing them with the X-ray counts observed at the detector, the throughput efficiency of the X-ray imaging system was evaluated. We demonstrated magnification radiography of a small object to show that a spatial resolution on the order of 10 μm was achievable in our system.     

A beam optics study of the biomedical beam line at a proton therapy facility

A biomedical beam line has been designed for the experimental area of a proton therapy facility to deliver mm to sub-mm size beams in the energy range of 20-50 MeV using the TRANSPORT/TURTLE beam optics codes and a newly-written program. The proton therapy facility is equipped with a 230 MeV fixed-energy cyclotron and an energy selection system based on a degrader and slits, so that beam currents available for therapy decrease at lower energies in the therapeutic beam energy range of 70-230 MeV. The new beam line system is composed of an energy-degrader, two slits, and three quadrupole magnets. The minimum beam sizes achievable at the focal point are estimated for the two energies of 50 and 20 MeV. The focused FWHM beam size is approximately 0.3 mm with an expected beam current of 20 pA when the beam energy is reduced to 50 MeV from 100 MeV, and roughly 0.8 mm with a current of 10 pA for a 20 MeV beam.     

Preliminary results of proton beam characterization for a facility of broad beam in vitro cell irradiation

The interaction of charged particles with living matter needs to be well understood for medical applications. Particularly, it is useful to study how ion beams interact with tissues in terms of damage, dose released and dose rate.One way to evaluate the biological effects induced by an ion beam is by the irradiation of cultured cells at a particle accelerator, where cells can be exposed to different ions at different energies and flux.In this paper, we report the first results concerning the characterization of a broad proton beam obtained with our 2 MV tandem accelerator. For broad beam in vitro cell irradiation, the beam has to be stable over time, uniform over a ∼0.5 cm² surface, and a dose rate ranging from 0.1 to 10 Gy/min must be achievable. Results concerning the level of achievement of these requirements are presented in this paper for a 1 MeV proton beam.     

A sextupole ion beam guide to improve the efficiency and beam quality at IGISOL

The laser ion source project at the IGISOL facility, Jyväskylä, has motivated the development and construction of an rf sextupole ion beam guide (SPIG) to replace the original skimmer electrode. The SPIG has been tested both off-line and on-line in proton-induced fission, light-ion and heavy-ion induced fusion-evaporation reactions and, in each case, has been directly compared to the skimmer system. For both fission and light-ion induced fusion, the SPIG has improved the mass-separated ion yields by a factor of typically 4-8. Correspondingly, the transmission efficiency of both systems has been studied in simulations with and without space charge effects. The transport capacity of the SPIG has been experimentally determined to be ∼10¹² ions s⁻¹ before space charge effects start to take effect. A direct comparison with the simulation has been made using data obtained via light-ion fusion evaporation. Both experiment and simulation show an encouraging agreement as a function of current extracted from the ion guide.     

Second-order theory of helical hexapole lens of infinite length

Expressions which can be used to calculate the focusing coefficients applicable to the interior regions (no fringe fields) of magnetic helical hexapole lenses of infinite length have been derived through second-order. It is shown that the helical hexapole has better focusing properties than the non-helical case. Expressions for the aberration coefficients are derived and, for appropriate value of the twisted angle, the helical hexapole reduces aberrations compared to the non-helical case. The numerical examples of a magnetic helical hexapoles in the case of a 25 MeV proton and 250 GeV electron beams are performed.     

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.     

Study of Al measurement on the Shanghai Mini-cyclotron based AMS

We present a modification to the ¹⁴C-dedicated SMCAMS (Shanghai mini-cyclotron based AMS) system to allow the measurement of ²⁶Al for biomedical applications with the existing devices. This is accomplished by determining the turn number, harmonic number and RF frequency theoretically and then making the appropriate orbit programming and beam optics calculation and experimental adjustments. The tests were conducted using pencil graphite (for the carbon pilot beam), Al₂O₃ powder and metal aluminum to accelerate ions with mass number of 24, 25, 26 and 27. The frequency response curves for those ions are shown. Finally, the Al₂O₃ standard sample with a known isotope ratio of 1.0 × 10⁻¹⁰ is measured. The ²⁶Al⁻ ions are detected and its frequency response curve shows the peak of ²⁶Al⁻ though very weak is well separated from the most neighboring interfering molecular ions ²⁵MgH⁻.     

First observation of coherent Smith-Purcell radiation in the highly relativistic regime

Coherent Smith-Purcell (SP) radiation has already been applied as a technique to measure the longitudinal bunch profile of charged particle beams in the low to intermediate energy range. However, with the advent of the International Linear Collider and the need to develop a non-invasive method of measuring the bunch profile, it has become necessary to carry out experiments at the highest possible energies. The paper summarizes some recent work at intermediate (45 MeV) energy and presents the first observations of SP radiation from a 28.5 GeV beam at SLAC. The experimental challenges and future possibilities of coherent Smith-Purcell radiation as a longitudinal bunch profile diagnostic tool are also discussed.     

Stability and delayed fragmentation of highly charged C60 trapped in a conic-electrode electrostatic ion resonator (ConeTrap)

We employed a conic-electrode electrostatic ion resonator (ConeTrap) to store the recoil ions resulting from collision between 56 keV Ar⁸⁺ ions and C₆₀ in order to study their stability over a long time range (several milliseconds). The originality of our method, based on the trapping of a single ion to preserve the detection in coincidence of all the products of the collision, is presented in detail. Our results show that C₆₀ ions produced in such collisions are stable in the considered observation time. By employing the ConeTrap as a secondary mass spectrometer in order to let the ions oscillate only for a single period, we have been able to observe delayed evaporation of cold ions 20 μs after the collision. We interpret quantitatively the relative yields of daughter ions with a cascade model in which the transition rates are estimated via the commonly used Arrhenius law, taking into account the contribution of the radiative decay.     

Response of l-alanine and 2-methylalanine minidosimeters for K-Band (24 GHz) EPR dosimetry

Minidosimeters of l-alanine and 2-methylalanine (2MA) were prepared and tested as potential candidates for small radiation field dosimetry. To quantify the free radicals created by radiation a K-Band (24 GHz) EPR spectrometer was used. X-rays provided by a 6 MV clinical linear accelerator were used to irradiate the minidosimeters in the dose range of 0.5-30 Gy. The dose-response curves for both radiation sensitive materials displayed a good linear behavior in the dose range indicated with 2MA being more radiation sensitive than l-alanine. Moreover, 2MA showed a smaller LLD (lower limit detection) value. The proposed system minidosimeter/K-Band spectrometer was able to detect 10 Gy EPR spectra with good signal-to-noise ratio (S/N). The overall uncertainty indicates that this system shows a good performance for the detection of dose values of 20 Gy and above, which are dose values typically used in radiosurgery treatments.     

High precision Hf ion implantation using a high-current ion implanter

The development of accurate mass spectrometry, enabling the identification of all the ions extracted from the ion source and further precise ¹⁸⁰Hf isotope implantation, in a high current implanter is described. The spectrometry system uses two signals (x-y graphic), one proportional to the magnetic field (x-axes), taken from the high-voltage potential with an optic fiber system, and the other proportional to the beam current intensity (y-axes), taken from a beam-stop. The ion beam mass register in a mass spectrum of all the elements magnetically analyzed with the same radius and defined by a pair of analyzing slits as a function of their beam intensity is presented. Hence, it is possible to implant ¹⁸⁰Hf⁺, with less than 1% contamination from neighboring isotopes, in order to conduct material characterization studies by Perturbed Angular Correlations. The precision of the low fluence ion implantation has been done by neutron activation analysis.     

Radiation damage in ZnO ion implanted at 15 K

Commercial O-face (0 0 0 1) ZnO single crystals were implanted with 200 keV Ar ions. The ion fluences applied cover a wide range from 5 × 10¹¹ to 7 × 10¹⁶ cm⁻². The implantation and the subsequent damage analysis by Rutherford backscattering spectrometry (RBS) in channelling geometry were performed in a special target chamber at 15 K without changing the target temperature of the sample. To analyse the measured channelling spectra the computer code DICADA was used to calculate the relative concentration of displaced lattice atoms.Four stages of the damage evolution can be identified. At low ion fluences up to about 2 × 10¹³ cm⁻² the defect concentration increases nearly linearly with rising fluence (stage I). There are strong indications that only point defects are produced, the absolute concentration of which is reasonably given by SRIM calculations using displacement energies of E_d(Zn) = 65 eV and E_d(O) = 50 eV. In a second stage the defect concentration remains almost constant at a value of about 0.02, which can be interpreted by a balance between production and recombination of point defects. For ion fluences around 5 × 10¹⁵ cm⁻² a second significant increase of the defect concentration is observed (stage III). Within stage IV at fluences above 10¹⁶ cm⁻² the defect concentration tends again to saturate at a level of about 0.5 which is well below amorphisation. Within stages III and IV the damage formation is strongly governed by the implanted ions and it is appropriate to conclude that the damage consists of a mixture of point defects and dislocation loops.     

Micro-crystalline inclusions analysis by PIXE and RBS

A characteristic feature of the nuclear microprobe using a 3 MeV proton beam is the long range of particles (around 70 μm in light matrices). The PIXE method, with EDS analysis and using the multilayer approach for treating the X-ray spectrum allows the chemistry of an intra-crystalline inclusion to be measured, provided the inclusion roof and thickness at the impact point of the beam (Z and e, respectively) are known (the depth of the inclusion floor is Z + e). The parameter Z of an inclusion in a mineral can be measured with a precision of around 1 μm using a motorized microscope. However, this value may significantly depart from Z if the analyzed inclusion has a complex shape. The parameter e can hardly be measured optically. By using combined RBS and PIXE measurements, it is possible to obtain the geometrical information needed for quantitative elemental analysis. This paper will present measurements on synthetic samples to investigate the advantages of the technique, and also on natural solid and fluid inclusions in quartz. The influence of the geometrical parameters will be discussed with regard to the concentration determination by PIXE. In particular, accuracy of monazite micro-inclusion dating by coupled PIXE-RBS will be presented.     

Influences of surfactants on the preparation of copper nanoparticles by electron beam irradiation

Electron beam radiation was applied to prepare nano-size copper in water system using polyvinyl alcohol, sodium dodecyl benzene sulfonate, gluten and polyethylene glycol as the surfactants, respectively. The irradiated products were characterized by XRD, TEM and LSPSDA. The XRD and TEM showed that relative pure copper products with an average size of 20 nm, 40 nm and 20 nm can be obtained by using gluten, PEG and SDBS as surfactant, respectively. An admixture of copper and cuprous oxide was obtained in PVA system. The LSPSDA showed that the size of the Cu nanoparticles decreased with increasing the glutin concentration.     

Middle-frequency magnetron sputtering for GaN growth

A middle-frequency magnetron sputtering system was designed and constructed for GaN growth, in which a pair of back cooled pool-shaped twin magnetrons were used for Ga metal targets. GaN films were prepared using this system under various gas pressure (0.5-3.0 Pa) in a mixture of N₂ and Ar with N₂/Ar ratio of 6:1. X-ray diffraction showed that the GaN films had a strong (0 0 0 2) orientation, and the film deposited at 1.5 Pa had two more weak peaks attributed to and . The full width at half maximum (FWHM) of the (0 0 0 2) peak for the GaN film deposited at 1.5 Pa and 0.5 Pa is ∼721 and ∼986 arcsec, respectively. The deposition rate was in the range of 43.5-87.8 nm/min and was mainly influenced by the deposition pressure. The films deposited at higher pressures are columnar in structure. A root-mean-square roughness of 4.4 nm was obtained from the atomic force microscopy (AFM) surface morphology of the film deposited at 0.5 Pa.     

Evaluation of radiation dose and positioning accuracy on X-ray volume imaging system for image-guided radiotherapy

Linear accelerators equipped with X-ray volumetric cone-beam Imaging (XVI) system enable verification of location of patients and displacement of tumors for image-guided radiotherapy (IGRT). The objective of this study is to evaluate the positioning accuracy using the XVI system for image-guided patient setup and to establish a lower-dose imaging protocol without sacrificing positioning accuracy for routine treatment courses. Several low-dose imaging protocols are proposed by modifying tube voltage from 120 to 100 kV and lowering tube current from 40 to 10 mA. The positioning accuracy of both bone and gray value registration methods provided by XVI system were also evaluated. Phantom study revealed that the gray value algorithm was more accurate than the bone algorithm in position and registration. However, both translational and rotational accuracies were less than 0.15 mm and 0.8^° at all dimensions, which were considered negligible in clinical applications. In addition, the lower-dose protocol (100 kV, 10 mA) produced relative much less radiation dose compared to the default CBCT protocol in the XVI system. In conclusion, our proposed lower-dose protocol results in significant radiation dose reduction without compromising positioning accuracy and may have the potential to be adopted for clinical usage in the future.     

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.     

Conduction mechanism in un-irradiated and γ-irradiated PVA-H3PO4 polymer electrolytes

The a.c. conductivity and the dielectric properties of both un-irradiated and γ-irradiated PVA-H₃PO₄ complexed electrolytes are investigated as a function of frequency and temperature. The dielectric constant and dielectric loss have been studied in the frequency range of 10 kHz-1 MHz and in the temperature domain of 303-383 K. The a.c. conductivity is found to obey the “Universal power law”. The variation of frequency exponent with temperature obtained from experimental results has been used to explain the mechanism of ion transport. It has been shown that correlated barrier hopping is the suitable model to study the electrical conduction mechanism of the complexed system. According to this model the maximum barrier height was calculated to be 0.31 eV for un-irradiated sample while for γ-irradiated, it was 0.28 eV. Moreover, the frequency exponent, which is a function of temperature, decreases slowly in the lower temperature range and at a faster rate in higher temperature range. The electrical activation energy at various frequencies was estimated in the range of 0.44-0.80 eV in two distinct temperature ranges.     

RBS study of Ti/ZnO interface

We have studied the interface stability of the Ti(overlayer)/ZnO(substrate) system. Ti thin film was grown on the Zn face of single crystal ZnO(0 0 0 1) substrate by the vacuum deposition technique. The Ti film thickness was typically 16 nm. Then the samples were annealed in air at 300 and 400 °C for 15 min, respectively. The deposition and annealing effects on the interface structure were investigated with Rutherford backscattering and channeling spectroscopy using 2 MeV He⁺ ion beam. After Ti deposition the minimum yield from the ZnO substrate increased from 2% to 7%. This suggests severe damage caused by deposition, i.e. the interface reaction between Ti and ZnO (even at room temperature). A significant amount of Zn (approximately 6.4 × 10¹⁶ atoms/cm²) moved onto the surface after post-annealing at 400 °C. Since Ti has a stronger tendency to react with O than Zn, it is expected that Ti reacts with substrate oxygen leaving behind free Zn atoms, which can easily migrate onto the surface. We discuss how the Ti/ZnO interface reaction in detail, and seek to find another good metallic contact for ZnO devices, which are attracting much attention recently for practical applications as well as scientific aspects.