N. Yasuda

ATOMIC FORCE MICROSCOPIC ANALYSES OF HEAVY ION TRACKS IN CR-39

Abstract The track evolution for high energy C and Si ions in CR-39 was studied using an atomic force microscope (AFM). The image processing method of AFM observations and the 3-D images of C and Si tracks are reported. The track diameter increased linearly with the amount of bulk etch of CR-39, but the retardation of growth of the track length was observed at the early stage of the etching. As a result, considerable discrepancies between the track sensitivities calculated by using the track diameter and the length appeared especially in the early stage of the etching. The results reported here show that AFM observations are very useful in practical application to the quantitative analysis for minute etch pits in a track detector.

Properties of TNF-1 track etch detector

Abstract We have developed a new plastic track etch detector labeled TNF-1, which is the copolymer of CR-39 monomer with N-isopropylacrylamide (NIPAAm). It was found that copoly(CR-39/NIPAAm/ antioxidant) composed in weight ratio of 99/1/0.01 is highly sensitive to low linear energy transfer (LET) particles in the region below 10 keV/μm of LET200 eV. TNF-1 is the most sensitive plastic track etch detector reported so far and is able to record normally incident protons up to the energy of 27 MeV. This paper gives results of our studies on the track responses of TNF-1 as well as the brief results obtained by the performance tests of TNF-1 in various dosimetric experiments such as space radiation dosimetry, dosimetry for heavy ion cancer therapy and neutron dosimetry. These results are compared with the results obtained for CR-39 track detectors.

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.

CR-39 sensitivity analysis on heavy ion beam with atomic force microscope

Abstract Preliminary results of feasibility study to apply atomic force microscope (AFM) to the quantitative analysis for minute etch pits on CR-39 are reported comparing with the optical microscope observation. The growth curves of the Si track diameter and length obtained by both technqiues were discussed in relation to the track sensitivity and the etch induction time.

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.

A program for the precise observations of ultra heavy nuclei in galactic cosmic rays

The origin of galactic cosmic rays (GCRs) nuclei is still unknown. Precise observation of ultra heavy GCRs would be an important step in resolving their origin including the remaining problems in cosmic ray astrophysics. A program to observe UH nuclei in GCRs is proposed which involves the use of a high performance solid-state track detector on board a long-duration balloon. The program focuses measuring the elemental and isotopic compositions of UH nuclei up to the actinides. The observation of nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis in cosmic ray sources, chemical evolution of galactic material, the characteristic time of cosmic rays, and heating and acceleration mechanisms of cosmic ray particles.

The measurement of the fragment emission angles in the reactions of < 135 MeV/u 12C and 16O in tissue equivalent targets

Abstract Different stacks of tissue equivalent targets interleaved with CR-39 nuclear track detectors were irradiated with 135 MeV/u 12 C and 16 O ions. After track etching and measurement by an automatic image analysis system, a method of trajectory tracing was applied. The trajectories of particles were reconstructed using a pattern-matching method based on a comparison of relative track coordinates. Fragmentation products have a lower charge and can be clearly distinguished by their smaller track sizes. The track positions within the individual trajectory are additionally fitted to a straight line, from which we can determine the direction of the traversing ion within a path of a few mm. We performed an angular distribution study of the fragments, which we compared to simulation results obtained by a simple particle emission model. For the fitted parameters the model showed agreement within the margins of error but failed to describe the energy dependence and thus should be further improved and upgraded.

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.

Fragmentation of 370 MeV/n 20Ne and 470 MeV/n 24Mg in light targets

Total charge-changing cross sections and cross sections for the production of projectile-like fragments were determined for fragmentation reactions induced by 370 MeV/n Ne-20 ions in water and lucite, and 490 MeV/n Mg-24 ions in polyethylene, carbon and aluminum targets sandwiched with CR-39 plastic nuclear track detectors. An automated microscope system and a track-to-track matching algorithm were used to count and recognize the primary and secondary particles. The measured cross sections were then compared with published cross sections and predictions of different models. Two models and the three-dimensional Monte Carlo Particle Heavy Ion Transport Code System (PHITS) were used to calculate total charge-changing cross sections. Both models agreed within a few percent for the system Mg-24 + CH2, however a deviation up to 20% was observed for the systems Ne-20 + H2O and C5H8O2, when using one of the models. For all the studied systems, PHITS systematically underestimated the total charge-changing cross section. It was also found that the partial fragmentation cross sections for Mg-24 + CH2 measured in present and earlier works deviated up to 20% for Z = 6-11. Measured cross sections for the production of fragments (Z = 4-9) for Ne-20 + H2O and C5H8O2 were compared with predictions of three different semi-empirical models and JQMD which is used in the PHITS code. The calculated cross sections differed from the measured data by 10-90% depending on which fragment and charge was studied, and which model was used

High resolution imaging for charged particles using CR-39 and atomic force microscopy

Abstract Recently Atomic Force Microscopy (AFM) has been used for a readout of Solid State Nuclear Track Detectors (SSNTD). In this technique, the SSNTD is etched for very short time and scanned by an AFM to observe track etch pits. Etch pits of several hundred nm in diameter can be observed. We applied this technique to charged particle imaging using CR-39. CR-39 plates were etched for about 5xa0min in 27% NaOH solution at 70°C. Then very small etch pits were measured. A typical diameter of etch pits was below 1xa0μm and a typical etch pit depth was about several hundred nm. The obtained image has demonstrated a position resolution of less than 100xa0nm. Ion microbeam profiles were also measured by the system.