Kuniaki Amemiya

Estimation of the latent track size of CR-39 using atomic force microscope

Abstract As a frame work of the study for the latent track size measurement using atomic force microscope, we have measured the minute etch pits and the extremely small amount of bulk etch of CR-39 at the beginning of chemical etching, and obtained its growth curves in nanometer dimensions. The pieces of CR-39 were exposed to 6 MeV / n C and Fe ions with normal incidence angle and were etched in 70°C 7 N NaOH solution for 0.5,1,2,3,5 min . The diameters of latent track were estimated to be ∼17 nm for Fe ions and ∼8 nm for C ions, respectively. These values are comparable to the experimental data on the average ‘track core diameters’ that have been obtained by various experimental techniques.

Track sensitivity and the surface roughness measurements of CR-39 with atomic force microscope

Atomic Force Microscope (AFM) has been applied to evaluate the surface roughness and the track sensitivity of CR-39 track detector. We experimentally confirmed the inverse correlation between the track sensitivity and the roughness of the detector surface after etching. The surface of CR-39 (CR-39 doped with antioxidant (HARZLAS (TD-1)) and copolymer of CR-39/NIPAAm (TNF-1)) with high sensitivity becomes rough by the etching, while the pure CR-39 (BARYOTRAK) with low sensitivity keeps its original surface clarity even for the long etching.

Soft X-ray imaging using CR-39 plastics with AFM readout

Abstract Soft X-ray microscopy using CR-39 plastic track detectors was demonstrated with an atomic force microscope (AFM) readout for the first time. A transmission X-ray image of the biological cells was recorded on the CR-39 surface, and revealed as relief after etching process. The resolution of the X-ray imaging is expected to be 100 nm or less, therefore imaging of biological cells is possible at an intracellular structure level. Using this technique, the high resolution image of both biological cells and charged particle tracks can be obtained simultaneously on a CR-39 with the AFM. In boron neutron capture therapy, this new technique provides the information on the distribution of boron compounds and radiation dose by charged particles mapping inside a cell.

Ultra-high resolution radiography using CR-39 solid state track detectors and atomic force microscopy

Abstract We have developed an ultra-high resolution charged particle radiography technique using CR-39 solid state track detectors and an atomic force microscope (AFM). Very small etch pits about 80 nm in diameter were measured with the AFM. We planned to apply this technique to high resolution autoradiography. Such practical applications often require accurate positioning between the sample mounted on a CR-39 detector and particle tracks recorded in the CR-39 in order to determine the radiation dose distribution inside the sample. As a fiducial marker for the positioning, aluminum patterns were deposited on the CR-39 surface using a photolithography technique. The aluminum patterns were dissolved through a typical etching process for CR-39 detectors and pattern-shaped steps were left on the surface. Using these patterns should ensure accurate positioning between the sample and the etch pits in autoradiography. This method provides a new technique for radiation imaging of biological samples at a subcellular scale.

Spatial Distribution Measurement of Ions Surrounding an Alpha Source using a New Micro-ionization Chamber

Recently, a new alpha radioactivity measurement technique was proposed, which directly measures ions surrounding alpha radioactivity. In order to implement this technique, a better understanding of ions behavior is required. We have developed a micro-ionization chamber with multi-channel charge-integrating ASICs (Application Specific Integrated Circuit). In this study, we will introduce the design of the micro-ionization chamber and show first results from ion measurements using an 241 Am alpha source. When we increase the electric field, the spatial distribution of ions exhibited two different components. Simulation calculations were also performed to account for these components.

Improvements in the AIST Cryogenic Radiometer With Superconducting Thermometer

We are developing a cryogenic radiometer (CR) with a superconducting thermometer for the optical laser power calibration. This device consists of a niobium transition edge sensor and an electrical substitution heater on a silicon substrate. The device temperature is locked at the niobium transition temperature with a superconducting quantum interference device amplifier and a proportional-integral-derivative controller. The device successfully determines the absolute optical power in the range from 20 nW to 600 muW, with a fast response of 3 s. The equivalence measurement shows that the response difference between the substitution power and the simulated optical power is less than 0.0034%. These properties are very attractive for next generation of a high-accuracy CR

Determination of BSH (Na2B12H11SH) Absorbed in Tumor Tissue

Since 1968 we have tried BNCT using the combination of BSH (Na2B12H11SH) and thermal neutron beam. However, it is still controversial that BSH is selectively absorbed in the tumor cells especially in the cell nucleus. In this study, in order to investigate the accumulation of absorbed BSH in the tumor cells, we intended to demonstrate them using alpha autoradiography, immunohistochemical study and atomic force microscope in experimental brain tumor model in rats.

Simultaneous visualization of contact microscopic image and energetic charged particle tracks and its application to medicine

Contact microscopy, enables us to visualize the detailed internal structure of biological cells. Exposure of biological specimen mounted on X-ray or UV sensitive materials to soft X-ray or UV introduces chemical damage to the materials, and the damage distribution due to the absorption of the X-rays or the UV by the specimen reveals as relief on the surface of the material after development process. The relief can be visualized with an AFM at high resolution of ~100 nm. We have applied the contact microscopy technique to high-resolution neutron-induced alpha-autoradiography for boron imaging in boron neutron capture therapy (BNCT). In BNCT, energetic alpha/lithium particles (range ~ single cell) from boron-neutron reactions introduce lethal damage to tumor cells selectively through thermal neutron irradiation with tumor-accumulating boron compounds. To understand the mechanism of drug delivery of those boron compounds is significant to evaluate the efficacy of BNCT. In the new technique, we can visualize those alpha/lithium particle tracks as etch pits and contact X-ray/UV microscopic image of tumor cells as relief on the surface of CR-39 plastic track detectors after etching process. Achievable resolution was ~100 nm with AFM readout, so that we can perform the boron imaging at subcellular scale.

Very low-noise large-area calorimeter based on bimetallic micromechanical transduction: toward sub-nanowatt resolution in air at room temperature

We demonstrated a very low-noise, large-area calorimeter based on a micromechanical heat-flow sensor. The input heat flow is transduced to the bimetallic deformation of the sensor, which is observed using a high-resolution fiber optic interferometer. The characteristics of 5-mm-square Si–Al bimetallic micromechanical sensors fabricated using silicon-on-insulator micromachining processes were investigated. We experimentally achieved a heat-detection noise of 12 nW, which is comparable to the best performance of thermopiles. The developed sensor is free of Johnson noise, which constrains the signal-to-noise ratio. In principle, this technique can provide a sub-nanowatt resolution even in air at room temperature.

High-Resolution Alpha-Autoradiography with Contact Microscopy Technique

We have been developing a novel method for high-resolution neutron-induced alpha-autoradiography (NIAR) using CR-39 plastic track detectors and an atomic force microscope (AFM) with contact microscopy technique. In this technique,sliced samples such as tissues including boron compounds are mounted on CR-39 plates, and then irradiated by thermal neutrons. The irradiated samples are exposed to soft X-rays, and then etched in NaOH solution for short time.Etch pits for alpha/lithium particle tracks and relief for transmission X-ray image of the specimen can be observed on the CR-39 surface with an AFM at about 100 nm resolution. In the NIAR, discrimination of proton background is required for quantification of boron concentration, and incident angle measurement is significant for accurate positioning of the alpha/lithium tracks on the specimen image. These properties were tested for the measurement of small etch pits observed with an AFM. It was confirmed that alpha/lithium particles and protons could be distinguished by etch pit size, and that incident angle of those charged particles could be measured at the accuracy of several degrees. These informations approve the reliability of the NIAR, especially for the subcellular measurement of boron compound distribution inside a cell in boron neutron capture therapy (BNCT).