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desorption ionization-mass spectrometry (MALDI-MS) have been applied to analyze etch products of CR-39 plastic (one of the most frequently used solid states nuclear track detector) for the understanding of track formation and etching mechanisms by heavy ion irradiation. The etch products of irradiated CR-39 dissolved in sodium hydroxide solution (NaOH) contain radiation-induced fragments. For the GC-MS analysis, we found peaks of diethylene glycol (DEG) and a small but a definitive peak of ethylene glycol (EG) in the etch products from CR-39 irradiated by 60 MeV N ion beams. The etch products of unirradiated CR-39 showed a clear peak of DEG, but no other significant peaks were found. DEG is known to be released from the CR-39 molecule as a fragment by alkaline hydrolysis reaction of the polymer. We postulate that EG was formed as a result of the breaking of the ether bond (C-O-C) of the DEG part of the CR-39 polymer by the irradiation. The mass distribution of polyallylalcohol was obtained from the etch products from irradiated and unirradiated CR-39 samples by MALDI-MS analysis. Polyallylalcohol, with the repeating mass interval of m/z = 58 Da (dalton) between m/z = 800 and 3500, was expected to be produced from CR-39 by alkaline hydrolysis. We used IAA as a matrix to assist the ionization of organic analyte in MALDI-MS analysis and found that peaks from IAA covered mass spectrum in the lower m/z region making difficult to identify CR-39 fragment peaks which were also be seen in the same region. The mass spectrometry analysis using GC-MS and MALDI-MS will be powerful tools to investigate the radiation-induced polymeric fragments and helping to understand the track formation mechanism in CR-39 by heavy ions.

The charge resolution (dZ) for heavy ions (nuclear charge: Z < 40) of 0.1–1 GeV/n energy in CR-39 plastic nuclear track detector (PNTD) and its dependence on etching time, and on projectile Z and energy were investigated and optimized as part of an effort to make precise measurements of projectile charge-changing cross sections. Two types of CR-39 PNTD, HARZLAS TD-1 and BARYOTRAK, were exposed to heavy ion beams with seven values of Z behind thick targets to produce projectile fragments. Following chemical etching (7 N NaOH at 70 degreeC) for varying etch times, dZ of the projectiles was determined for each detector type. A strong dependence of dZ on the amount of bulk etch (B) was seen. It was also observed that dZ can be remarkably improved with longer etching time as a function of B^-{1/2}, in accordance with the trend seen in other types of track detector such as glass nuclear track detector. However, for B > 60 lm(30 h etching), saturation occurs and there is no further improvement in dZ. Analysis of the correlations between projectile Z, energy, detector response, and fluctuation of the response make it possible to develop a model to predict the dZ for projectiles of given Z and energy. The predicted and measured values of dZ show good agreement within 10%. We conclude that 4 < Z < 30 at intermediate energy can be identified with good dZ in these detectors. The predictive model will be used in designing future cross section measurement experiments.

A microbeam irradiation system, SPICE (Single Particle Irradiation system to Cell), is under completion at the National Institute of Radiological Sciences (NIRS). We have improved the beam size, which is now approximately 5 um in diameter, and the cell targeting system, which can irradiated a maximum of 400~500 cells per minute. Two types of cell dishes were specially designed. One is a Si3N4 plate (2.5 mmx2.5 mm area with 1 um thickness) supported by a 7.5 mmx7.5 mm frame of 200 um thickness, and the other is Mylar film stretched by pressing with a metal ring. These cell dishes can be placed on a voice coil stage equipped on the cell targeting system, which also includes of a fluorescent microscope and a CCD camera for capturing the cell images. This microscope system captures all the images of dyed cell nuclei, and computes the coordinates of the cell position according to the fluorescence, and synchronizes this and the voice coil motor stage with a single-particle irradiation system consisting of a scintillation counter and a beam deflector for irradiation. Irradiation of selected cells with a variable preset number of protons can be automatically performed. We employed the simultaneous detection method for visualizing the position of mammalian cells and proton traversal through CR-39 to determine whether the targeted cells are actually irradiated. An Immuno-assay was also performed against gamma-H2AX, to confirm the induction of DNA double-strand breaks in the target cells.

Selective irradiation by an ionizing particle of a targeted cell organelle may disclose such mechanisms as signal transaction among cell organelles and cell-to-cell communication in the processes toward an endpoint observed. Bystander effect, existence of which has been clearly evidenced by application of the particle microbeam to biological experiments, suggests potential deviation from the conventional risk estimation at low particle fluence rates, such as in an environment of space radiation in International Space Station.To promote these studies we started the construction of a microbeam facility (named as SPICE) by using our HVEE Tandem accelerator (3.4 MeV proton and 5.1 MeV 4He2+). For our primary goal,"irradiation of cell organelle with a single praticle with a position resolution of 2 mum in a reasonable irradiation time", special features are considered. Usage of a triplet Q-magnet for focussing the beam to micrometer levels is an out standing feature compared to facilities of other institutes. Other features are almost similar to those of other institutes. Those are precise position control of a cell dish holder, design of the cell dish, data acquisition of microscopic image of a cell oraganelle (cell nucleus), data processing, reliable particle detection, soft and hard wares to integrate all these related data and system to control and irradiate a targeted spot with exactly determined number of particles.

In March 1999, a HVEE Tandetron was installed in the Electrostatic Accelerator Building of NIRS (National Institute of Radiological Sciences) for PIXE (Particle Induced X-ray Emission) analysis. The specifications of the Tandetron accelerator system operating at NIRS are as follows: The accelerating voltage is 0.4 to 1.7MV, and the maximum beam current is 500nA at 3.4MeV. The accelerator facility incorporates three beam lines for conventional, in-air and microbeam PIXE analysis. The scanning microbeam PIXE analysis line is based around an Oxford Microbeams OM2000 nuclear microscope end stage. This system provides the ability of multi-elemental mapping over sample areas up to 2 * 2 mm area with spatial resolutions routinely at 1 * 1 micrometres. The scheduled operation of this facility started in April 2000 and is controlled by the Division of Technical Service and Development. The result of beam resolution tests carried out in 2001 are as follows: For Scanning Transmission Ion Microscopy (STIM), the estimated beam size is 100 * 200 nm, measured using a 2.6 MeV proton beam scanned over a 12.7 micrometres repeat distance copper grid. For Particle Induced X-ray Analysis (PIXE) operation at 50 pA beam current the estimated best spot size is 0.4 * 0.6 micrometres. The micro beam facility is being used for research into the elemental distribution of small biological samples such as biological cells and tissue.