Accuracy of beam positioning in TIARA

A beam scanning and target profiling technique that provides precise and easy beam positioning on samples has been established for the light ion and heavy ion microbeam systems in TIARA of JAERI. The beam positioning accuracy in these systems was measured using nuclear track detectors, CR-39's. The beam positioning accuracy and indirect beam positioning technique in the heavy ion microbeam system enabled extremely low current microbeam to hit targeted virgin points in micro-structure semiconductor test samples for study of single event upset (SEU) transient current properties. This paper gives details of the beam scanning and target profiling system, and describes and discusses the experiments by using this system.     

复旦大学单粒子微束研制进展

建设了一基于复旦大学2×3 MV串列加速器的单粒子微束装置。离子束经分析磁铁30°水平偏转传输后再经90°偏转磁铁竖直上行至辐照终端,以内径1.5 μm的毛细玻璃管微准直器获取离子微束。采用薄膜闪烁体结合光电倍增管的探测结构对微束离子进行精确探测和计数,并以高压静电偏转开关快速关断束流以实现对离子数目的精确控制。目前实验已获得在质子能量为3 MeV时,能散（能量分布曲线中半高宽FWHM）<60 keV、束分辨<2.2 μm、定量照射精度>95%的质子微束。本文对复旦大学单粒子微束的束流管道设计、微束获取、束开关及单粒子探测等核心环节的研制进展进行介绍。     

Application of heavy-ion microbeam system at Kyoto University: Energy response for imaging plate by single ion irradiation

A heavy-ion microbeam system for cell irradiation has been developed using an accelerator at Kyoto University. We have successfully developed proton-, carbon-, fluorine- and silicon-beams in order to irradiate a micro-meter sized area with ion counting, especially single ion irradiation. In the heavy-ion microbeam system, an imaging plate (IP) was utilized for beam diagnostics on the irradiation. The IP is widely used for radiography studies in biology. However, there are a few studies on the low linear energy transfer (LET) by single ions, i.e., low-intensity exposure. Thus we have investigated the energy response for the IP, which can be utilized for microbeam diagnostics.     

On the interpretation of micro-PIXE measurements on a prototype microstructured reference material

In order to determine the beam spot size and scanning properties of ion microbeam systems, a novel reference material has been developed, consisting of permalloy (81% Ni, 19% Fe) strip patterns on silicon substrate. Due to the choice of substrate and pattern materials, these samples exhibit a high elemental contrast suitable for analysis with X-ray detection and ion scattering techniques. The microlithographic production scheme is briefly described. A prototype chip of this material was investigated with PIXE and RBS analysis in a scanning nuclear microprobe. It proved to be extremely useful in the routine to focus the ion microbeam and to determine its spot size. Due to the microscopic structure of these samples, a geometric dependence of matrix effects in the production of Si X-rays from the substrate material could be shown. Even dead-time effects in the counting electronics, showing up as an apparent thickness gradient, could be observed. Besides its primary role in microbeam diagnostics, this reference material can serve an educational role in developing the analyst's ability to correctly identify and interpret such artefacts.     

Microbeam complex at TIARA: Technologies to meet a wide range of applications

Since 1990 R&Ds of microbeam technology has been progressed at the TIARA facility of JAEA Takasaki. In order to meet a wide variety of ion beam applications, analysis, radiation effect studies, or fabrication in regions of micro- or nano-structures, three different types of ion microbeam systems were developed. In these systems, high-spatial resolutions have been achieved and techniques of micro-PIXE, single ion hit and particle beam writing (PBW) were also developed for these applications. Microbeams, on the other hand, require the highest quality of beams from the accelerators, the cyclotron in particular, which was an important part of the microbeam technology of TIARA. In this paper, the latest progress of the ion microbeam technology and applications are summarized and a future prospect of them is discussed.     

Heavy ion microbeam vacuum requirements

Transport of heavy ions through an ion microbeam focusing system can be affected by insufficient vacuum within the beam transport tube. Due to interactions of heavy ions with atoms of residual gas in the vacuum tube of a microbeam facility, the angular, lateral and energy spreading of an ion beam increases prior to focusing, creating a beam halo. This beam halo can produce undesirable effects in some applications of ion microbeam techniques. In order to model this effect, the ion beam angular spread in residual gas has been approximated by Sigmund’s theoretical predictions for small-angle ion multiple scattering (MS), while ion energy loss straggling distributions have been applied for studying the energy spread. The extent of the beam halo has been estimated by combining the results of these calculations with ion optics calculations. Recommendations concerning microbeam focusing due to the vacuum conditions are given for different heavy ions in the MeV energy range.     

Layout of a nuclear microprobe beamline using a liquid metal ion source

The Bochum solenoid lens microprobe will be installed in a new configuration which can be fed both by the 4 MV Dynamitron tandem accelerator and by a new 500 kV accelerator of extremely low energy-spread (ΔE/E 10⁻⁵). Apart from a conventional duoplasmatron ion source, a commercial gallium liquid metal ion source (LMIS) will be implemented in this accelerator. Microprobe optics will benefit from the high brightness of the LMIS ( 10⁵ Am⁻²sr⁻¹eV⁻¹), thus enabling an increased lateral resolution. Ion optical ray tracing, simulating the accelerator tube and the solenoid lens, has allowed one to specify the beam parameters required at the accelerator entrance to yield a micrometer focus at the target position. Using this information and further simulations, the accelerator injection optics can be particularly optimized for the new microbeam line.     

WDX-PIXE analysis of low energy X-rays using a microbeam

A high-energy resolution PIXE system developed at a heavy ion microbeam line was used to analyze low energy X-rays below 1 keV. The system is equipped with a plane crystal spectrometer with a gas flow position sensitive proportional counter (PSPC), which enables high-energy resolution PIXE analysis using a microbeam. In order to improve the detection efficiency for the low energy X-rays, the X-ray entrance window of the PSPC was replaced with a thin polymer film supported by a metal grid. As the result, the detectable energy range was extended to carbon K X-rays and chemical effect in Fe and Cu L X-rays could be detected. A preliminary result of high-energy resolution PIXE mapping of Cu mesh (#500) showed that it is possible to obtain the Cu L mapping image using a 2 MeV proton microbeam with the size of 20 × 20 μm.     

Study of basic mechanisms of semiconductor devices using ion beam induced charge (IBIC) collection

A change of wave form of current transients induced by a single heavy ion was investigated around a pn junction with 8 μm width and 10 μm length as a function of the ion incident position. Three pn junctions were made on a 3 μm thick Si epilayer (1 × 10¹⁶/cm³) grown on Si substrate and were in a line along an aluminum electrode with 10 μm spacing between the adjacent junctions. The elements of a pn junction array were irradiated with a 1 μm diameter 15 MeV C⁺ heavy ion microbeam spacing steps by 3 μm. At a bias voltage of − 10 V, 148, 91, and 54 fC were collected at the pn junction center, and at 3 μm and 4 μm from the edge of the electrode, respectively. Internal device structure was examined by IBIC (ion beam induced current) method by using a 2 MeV He⁺ ion microbeam. From the IBIC spectrum and the IBIC image, the charge collected from the open space by the diffusion process was observed in addition to the charge collected from the depletion layer of the pn junction.     

The PTB single ion microbeam for irradiation of living cells

At the PTB's ion accelerators, a new microbeam facility is now in operation that is capable of delivering single ions, for example, to the nuclei of individual living cells. The wide range of proton and ⁴He²⁺ ion energies affords LET-values between 3 and 200 keV/μm. A beam diameter of less than 2 μm outside the vacuum system has been measured and a targeting accuracy of better than 2 μm has been determined. In contrast to other microbeam facilities operated for radiobiological research using mechanical collimators in front of the target to define the beam, the PTB facility utilises beam focusing by quadrupole magnets. The microbeam has a unique ion optical design that incorporates a 90° bending magnet in the beam transport system. This design has the advantage of providing a microbeam basically without scattered particles. Every ion reaching the target is detected by a thin scintillating foil and a photomultiplier tube with efficiency close to 100%. Presently up to 1500 single cells per hour can be automatically irradiated with a chosen number of particles. Procedures and results of first cell irradiations are described as an example.     

The Progress of a Microbeam Facility in the Institute of Plasma Physics

The progress of a microbeam facility in the institute of Plasma Physics was discussed in this paper.This kind of equipment can supply single-particle beam which may be implanted into cells in micrometer-radius and measured by a new outstanding detector among global microbeam systems.Measurements by some plain targets showed that the highest current after the accelerator tube can be larger than 20μA ,the H2^ current before the second bending magnet is near 0.9μA ,the current after the second bending magnet is near 0.8μA,and the current of the beam line(after a 2-mm diameter aperture)is near 0.25nA which is enough for the single-particle microbeam experiment.It took scientists 3 months to do their microbeam experiment after setting up the qccelerator beam line and get the microbeam from this equipment.Two pre0collimators were installed between the 2-mm diameter aperture and the collimator to survey the beam.Tracks on the CR39 film ectched in the solution of NaOH showed that the beam can go through the collimator including a 10μm diameter aperture and the 3.5μm thick vacuum sealing film(Mylar).A new method,which is called optimization of the beam quality,was put forward in this paper,in order to get smaller diameter of beam-spot in microbeam system.     

Quick change of ion species of heavy-ion microbeam by cocktail beam acceleration technique with the JAEA AVF cyclotron

A heavy-ion microbeam with hundreds of MeV energy is utilized for research in biotechnology and materials science at the JAEA AVF cyclotron facility. Beam users need microbeams providing a wide range of the LET. We have to change ion species and/or energy in order to vary the LET widely. However, it takes much time to develop a new microbeam of different ion species step by step using a flat-top acceleration system. A cocktail beam acceleration technique is frequently used to change the ion species and energy quickly. The cocktail beam acceleration has been first applied to the microbeam formation for quick change of the ion species. As a result, we have succeeded to reduce considerably microbeam changing time to within 30 min between a 520 MeV ⁴⁰Ar¹⁴⁺ and a 260 MeV ²⁰Ne⁷⁺. No deterioration of the microbeam spot size has been confirmed using a SE image of a copper grid.     

Slit scattering in a microbeam set-up

Slit scattering of beam particles in a microbeam set-up becomes significant for low current applications and thus limits its lateral resolution and application potential. In this work, the angular and energy distributions of beam particles interacting with cylindrically shaped slit-jaws of different radii, surface roughnesses, and materials are calculated numerically, employing the computer code SRIM. To quantitatively investigate their effect on the beam spot quality of a microbeam set-up, a quality factor is proposed as an index to evaluate the effect of slit-scattered particles on the beam spot. The results of the investigation reveal a high sensitivity of slit scattering in relation to the slit-jaw surface roughness.     

Proton beam micromachined resolution standards for nuclear microprobes

The quest for smaller spot sizes has long been the goal of many nuclear microprobe groups worldwide, and consequently there is a need for good quality resolution standards. Such standards have to be consistent with the accurate measurement of state-of-the-art nuclear microbeam spot sizes, i.e. 400 nm for high current applications such as Rutherford backscattering spectrometry and proton-induced X-ray emission, and 100 nm for low current applications such as scanning transmission ion microscopy or ion beam-induced charge. The criteria for constructing a good quality nuclear microprobe resolution standard is therefore demanding: the standard has to be three dimensional with a smooth surface, have an edge definition better than the state-of-the-art beam spot resolutions, and exhibit vertical side walls. Proton beam micromachining (PBM) is a new technique of high potential for the manufacture of precise 3D microstructures. Recent developments have shown that metallic microstructures (nickel and copper) can be formed from these microshapes. Prototype nickel PBM resolution standards have been manufactured at the Research Centre for Nuclear Microscopy, NUS and these new standards are far superior to the 2000 mesh gold grids currently in use by many groups in terms of surface smoothness, vertical walls and edge definition. Results of beam resolution tests using the new PBM standards with the OM2000 microprobe end station/HVEE Singletron system have yielded spot sizes of 290 nm×450 nm for a 50 pA beam of 2 MeV protons.     

单细胞单粒子微束的发展及放射生物学应用现状

综述了单细胞单粒子微束的发展及其在放射生物学方面的应用现状。通过准直或聚焦方式,可以将加速器粒子束流在空气中的束斑限定到微米或亚微米大小,而聚焦微束因其更高的空间分辨率和更快的电磁扫描照射速度成为发展主流;借助于先进的荧光显微镜及微速成像技术,当前的粒子微束能够对活细胞辐射诱导DNA损伤的早期响应进行在线可视化观测。微...     

Depth resolution calculations for heavy-ion microbeam RBS analysis

A detailed study has been made on the use of MeV heavy ions (Z₁ = 6–8) for microbeam Rutherford backscattering (RBS) analysis, to improve the depth resolution of this technique. The algorithm for determination of the depth resolution was created and applied to the Zagreb microbeam facility. Theoretical estimates of depth resolution for C and O ion RBS analysis of thin oxide films and semiconductors, using annular silicon surface barrier detector (SSBD), are compared to those for proton backscattering analysis. Depth resolution in certain cases may be improved by increasing the heavy-ion energy. Therefore, by the proper choice of the heavy ion and the heavy-ion energy, the depth resolution may be improved, maintaining the efficiency of the RBS method.     

微束背散射分析元素微区分布的研究

微束背散射分析元素微区分布的分析方法使上海原子核研究所的质子微探针能在微区内综合使用质子激发Ｘ射线荧光和背散射等多种核效应，为样品由轻元素到重元素的全面无损、双微（微区、微量）分析提供了依据。应用该方法还测量了Ｓｉ３Ｎ４／ＳｉＣ复合陶瓷材料，证明了该分析方法的可靠性。     

Analysis and Optimization of Stability of CAS-LIBB Single Ion Microbeam

Single ion microbeam is the most advanced technology which can emit a single ion for precise localization. A single-ion microbeam facility has been constructed at the Key Laboratory of Ion Beam Bioengineering （LIBB）, Chinese Academy of Sciences （CAS）, with a spatial resolutions of about 5 μm. Based on CAS-LIBB microbeam, three key elements affecting the quality of the system are assessed： the size of beam spot, the energy range and the counting accuracy of implanting ions. Various contributions to the ion beam stability, including the ion source, the terminal voltage of electrostatic accelerator and the components in beam pipeline, are discussed. Analysis shows that the improvement of terminal voltage stability is the most important issue for future optimization of CAS-LIBB facility. Some preliminary investigations and project aimed at optimization and development are proposed as well.     

A method for very low fluence implantations using Rutherford scattering

A simple method for extremely low fluence ion implantation is described. It is based on implanting ions which are Rutherford backscattered (RBS) from a thin gold layer into the desired target. This method enables ion implantations to be carried out, as are needed to realize quantum centers on the atomic scale to serve as qubits and other nano sized devices. The required implantation fluences are orders of magnitude below the commonly-used current integration capabilities; hence control on the implanted fluence is usually complicated. The described method enables control on the implanted fluence even when extremely low. The dependence of the energy and fluence of scattered ions on the angle and scattering target thickness is analyzed by using SRIM simulations. These are verified for the case of N scattering implantation by direct counting in a surface barrier detector and for the case of Xe by counting the tracks that scattered and implanted Xe ions leaved in HOPG as viewed by scanning probe microscopy.     

High energy resolution PIXE with high efficiency using the heavy ion microbeam

An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam (E < 6 MeV) with reasonable detection efficiency. The design of the spectrometer, such as detection geometry, detectable energy range and energy resolution, are described. This system was applied to high energy resolution PIXE analysis of Ti, SUS and Si with 2 MeV proton and 5 MeV Si³⁺ focused or collimated beams. The best energy resolution was 2 eV for the Si K line.