Use of Microbeam at Jaea Takasaki

The TIARA facilities of JAEA in Takasaki is equipped with a several-MeV light-ion and a several-dozen-MeV heavy-ion microbeam formation systems of focusing type, and a several-hundred-MeV heavy-ion microbeam formation system of collimating type. The microbeams with a spot size of 1 μm or less in diameter are extensively utilized for the research in materials science and biotechnology. An in-air micro-PIXE analysis system using a 2 MeV proton microbeam is quite useful for medical science and dentistry to visualize twodimensional distribution of very small quantities of elements in a microscopic area like cells with very high sensitivity. A single-ion hit system using a severalhundred-MeV heavy-ion microbeam is available for medical and biological applications such as elucidations of cellular radiation response. Highly stable ion beams with energy spread less than 0.02 % are required for the microbeam production. Improvements of accelerator performance are indispensable to realize the ion beams of high quality. A flattop acceleration system and a magnetic field stabilization system have been developed for the JAEA AVF cyclotron. These accelerator technologies are also required for very precise spectroscopic studies in nuclear physics. Ultrahigh energy resolution of 0.005 % has been achieved at the RCNP cyclotron facility of Osaka University. INTRODUCTION The ion beam irradiation research facility, TIARA (Takasaki Ion accelerators for Advanced Radiation Applications), was completed in 1993 at the Takasaki Radiation Chemistry Research Establishment of Japan Atomic Energy Research Institute(JAERI), the predecessor of the present Takasaki Advanced Radiation Research Institute of Japan Atomic Energy Agency (JAEA) [1]. Ion beam applications to the research and development in materials science and biotechnology have been fairly progressing after the full-scale operation of the ion accelerator complex facility. The bird view of the TIARA facility is shown in Fig. 1. A variety of ion beams are provided by a K110 AVF cyclotron, a 3 MV tandem accelerator, a 3 MV single-ended accelerator and a 400 kV ion implanter. The wide energy range from 20 keV through 1 GeV is covered by the accelerator complex. Three kinds of lightand heavy-ion microbeams with a beam spot size of 1 μm or less in diameter are available at the TIARA facility. Use of the ion microbeam has greatly enhanced spatial and targeting resolutions of the ion irradiation in a finite area. . The helium ion microbeam with a spot size of 0.25μm has been produced using the high quality ion beam. The in-air micro-PIXE technique, first developed at TIARA, enables elemental analysis in cells without drastic change of the living cell condition by placing the frozen cell sample in atmosphere. The tandem accelerator is equipped with a severaldozen-MeV heavy-ion microbeam formation system. The heavy-ion microbeam is useful for material processing and elucidation of radiation effects such as single-event upset of semiconductor devices used in space, caused by high LET(Linear Energy Transfer) irradiation. As the integration level of the semiconductor devices increases, higher spatialand targeting-resolutions are required for the investigation of the radiation effects. The LET range from 10 to 1000 keV/μm in water equivalent is covered by several-hundred-MeV heavy ions accelerated by the AVF cyclotron. The deposit energy is transferred in a localized area along the ion track. In case of the cell irradiation, the heavy ion causes high dose localization within the cell. A heavy-ion microbeam formation system of collimating type has been installed in a vertical beam line of the AVF cyclotron for Figure 1: Bird view of the TIARA facility, equipped with four accelerators and three microbeam formation systems. The micro-PIXE analysis has become widespread in various fields. Proton or helium ion beam with energies from 2 to 3 MeV is produced by the single-ended accelerator with acceleration voltage stability of the order of 10 # [email protected] THZH102 APAC 2007, Raja Ramanna Centre for Advanced Technology(RRCAT), Indore, India 588 08 Applications of Accelerators, Technology Transfer and Industrial Relations U02 Materials Analysis and Modification the elucidation of cellular radiation response. Targeting precision of 5 through 10 μm has been achieved, which is sufficient to hit the cell nucleus or cytoplasm. The quality of the ion beam provided by the accelerators directly influences the microbeam production. The microbeam spot size is determined by a gap of slits and the chromatic aberration of the beam focussing lens. The chromatic aberration originates in the energy spread of the accelerated ion beam. In case of the electrostatic accelerator, the energy spread depends mainly on the stability of the acceleration voltage. In the case of the cyclotron beam, the energy spread can be minimized by a flattop acceleration technique. The flattop acceleration for the high quality beam production is also applied to the high energy resolution experiment in nuclear physics. PRODUCTION OF THE MICROBEAM A microaperture with a hole of 5 to 10 μm in diameter or a precisely manufactured slit is used in the microbeam formation system of collimating type. The minimum beam spot size was limited by the size of the microaperture or the slit gap. Contamination of particles scattered at the edge of the microaperture or the slit might bring deterioration of the microbeam spot size, in some case. A beam focusing using a multiplet of quadrupole lenses is a sophisticated technique to reduce the beam size less than 5 μm [2]. A schematic image of the focusing system for microbeam production is shown in Fig. 2. The object of the primary beam is determined by the first slits. Divergence of the beam is defined by a series of the second slits. An image of these slits can be projected at a focal plane by the focusing lenses. The microbeam spot size is determined by the demagnification factor of the lens system. Spherical and chromatic aberrations in the lens system are also taken into account to minimize the beam size. In order to measure the microbeam spot size, the microbeam is scanned on a silicon relief pattern, and the secondary electrons emitted from the silicon relief pattern are detected. The position of the microbeam can be known from the voltage supplied to an electrostatic beam scanner. We can estimate the beam spot size from the peak width of the secondary electron distribution obtained at the edge of the relief pattern. The beam spot size of 250 nm in diameter has been achieved for 2 MeV proton and helium ion beams. APPLICATIONS OF THE MICROBEAMS Several-Dozen-MeV Heavy Ion Microbeam A heavy ion microbeam, such as a 15 MeV nickel ion accelerated by the 3 MV tandem accelerator, is utilized to investigate SEU(single event upset) of semiconductor devices used for space [3]. A single ion hit system, consisting of single-ion detectors and a fast beam switcher has been developed for observation of the SEU phenomena at a specific position of the micro device. Several-MeV Light Ion Microbeam The micro-PIXE analysis using the 2 MeV proton microbeam has an overwhelming advantage in analyzing very small quantities of elements in a microscopic aria with very high sensitivity. Two-dimensional distribution of elements included in cells can be visualized by the inair micro-PIXE technique [4]. A schematic drawing of the in-air micro-PIXE system is shown in Fig. 3. A 4 μm thick Mylar film is used as a sample backing and a vacuum partition. The microbeam is focused on an experimental sample mounted on annular sample holder in the atmosphere. The X-rays emitted from the sample elements are measured by a Ge or Si(Li) detector placed upstream. The microbeam is scanned horizontally and vertically by the electrostatic beam scanner. The element species is identified by the X-ray energy. The in-air micro-PIXE system enables multi-elemental mapping of samples in atmospheric environment without drying the biological samples. The micro-PIXE analysis technique is widely applied to various research fields such as biomedical research, dentistry, environmental science, and geology. Several-Hundred-MeV Heavy Ion Microbeam The high energy heavy-ion microbeam formation system, installed in a vertical beamline of the JAEA AVF cyclotron, is used for living biological cell irradiation. The single ion hit technique was also applied to the microbeam formation system to irradiate the specific part of individual cells [5]. Heavy ions are delivered to atmosphere through the microaperture with an inner Figure 2: Image of the microbeam production. Object slit Divergencedefining slit Multiplet of quadrupole lenses Figure 3: Schematic drawing of the in-air micro-PIXE system. In vacuum In air Sample Microbeam X-ray detector for