We present for the first time hourly variations of the spatial density gradient of 50 GeV cosmic rays within a sample solar rotation period in 2006. By inversely solving the transport equation, including diffusion, we deduce the gradient from the anisotropy that is derived from the observation made by the Global Muon Detector Network (GMDN). The anisotropy obtained by applying a new analysis method to the GMDN data is precise and free from atmospheric temperature

A method for enhancing the brightness of an intense slow positron beam produced by an electron linear accelerator (LINAC) in order to obtain an intense positron microbeam was developed. The developed brightness enhancement system is simple and consists only of a few beam optics and a transmission remoderator. The slow positron beam produced by the LINAC is magnetically guided from the positron source to an experimental room. The beam is extracted from the magnetic field and is focused by a lens on the remoderator to enhance its brightness. The brightness-enhanced beam is extracted from the remoderator and focused on a sample by a lens. The beam size at the sample was 90 μm, which was two orders of magnitude smaller than that in the magnetic transport system that was about 10 mm. The efficiency of the transmission remoderator was about 5%. Adiabatic rules in the magnetic transport and the paraxial-ray equation were used to estimate the beam size that could be produced using this method.

An intense positron microbeam generated by an electron accelerator has been developed for obtaining three-dimensional positron lifetime mappings in a sample to permit visual evaluation of defect distributions. The beam diameter at the sample was 80–100 μm. The counting rate of the positron annihilation γ rays used to measure positron lifetime was as large as 3×103 s−1. Three-dimensional imaging was demonstrated of positron lifetimes in a SiO2 sample, which was irradiated with ion beams through a mesh mask. The time to obtain a single image (3500 pixels for an area of 2.5×3.5 mm2) was 0.5–1 h.

Abstract. To improve the spatial resolution of positron annihilation spectroscopy (PAS), a system to produce an intense positron microbeam was developed in AIST. A slow positron beam, which was produced by an electron linear accelerator, was focused by a lens onto a remoderator to enhance its brightness. The brightness-enhanced beam with an intensity of ≈1 × 10 6 e + /s was extracted from the remoderator and focused onto the sample by a lens. The beam size at the sample was 25 µm, which is more than two and half orders of magnitude smaller than that in the magnetic transport system (≈10 mm). Hence, the spatial resolution of PAS with an AIST positron microbeam can be drastically improved relative to PAS using conventional methods.

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