Analytical Sciences

Production of a Positron Microprobe Using a Transmission Remoderator

Masanori FUJINAMI,* Satoshi JINNO,* Masafumi FUKUZUMI,* Takumi KAWAGUCHI,* Koichi OGUMA,* and Takashi AKAHANE**

*Department of Applied Chemistry, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan
**National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan

A production method for a positron microprobe using a β⁺-decay radioisotope (²²Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was mounted at the focal point of the magnetic lens and was used as a remoderator for brightness enhancement in a transmission geometry. The remoderated positrons were accelerated by an electrostatic lens and focused on the target by an objective magnetic lens. As a result, a 4-mm-diameter positron beam could be transformed into a microprobe of 60 µm or less with 4.2% total efficiency. The S parameter profile obtained by a single-line scan of a test specimen coincided well with the defect distribution. This technique for a positron microprobe is available to an accelerator-based high-intensity positron source and allows 3-dimensional vacancy-type defect analysis and a positron source for a transmission positron microscope.

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