Brightness enhancement method for a high-intensity positron beam produced by an electron accelerator

Abstract

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.

High-intensity positron microprobe at the Thomas Jefferson National Accelerator Facility

“…This new brightness enhancement method can be directly applied to our design. Using a single-crystal remoderator after solid Ne and taking advantage of the method utilized by Oshima et al (2008), we calculate that after remoderation our proposed positron source will provide beam brightness in the range of ≈ 10 10 − 10 11 mm −2 eV −1 s −1 at 1 keV.…”

“…As it is known that the energy bandwidth of the emitted slow e + from an RGM is higher than a W moderator, the resulting beam brightness will be lower but the brightness can be significantly enhanced with brightness enhancement methods to develop a positron microprobe. It has recently been demonstrated by Oshima et al (2008) that a positron beam can be brightness enhanced with one stage remoderation through a thin transmission foil with 5% remoderation efficiency. 45 The positron beam was produced by using a linac-driven electron beam and magnetically extracted from a solenoid channel to remod-erate in a transmission remoderator.…”

“…It has recently been demonstrated by Oshima et al (2008) that a positron beam can be brightness enhanced with one stage remoderation through a thin transmission foil with 5% remoderation efficiency. 45 The positron beam was produced by using a linac-driven electron beam and magnetically extracted from a solenoid channel to remod-erate in a transmission remoderator. The beam spot on the sample was measured to be less than 100 µm.…”

The Positron Probe Microanalyser Studies of Defect Distribution Induced by Machining of Copper, Iron and Titanium

“…It has been demonstrated by many authors that this parameter is extremely sensitive to the presence of openvolume defects, such as vacancies, their clusters and dislocation lines, and jogs at dislocation lines, where positrons can be trapped and annihilate. More technical details about the PPMA constructed at the Chiba University in Japan were given in the papers by Fujinami et al [16] and Oshima et al [20].…”

Development of Positron Microbeam in AIST

“…The advantage of such a SPM is that it can obtain two or three dimensional PAS images using the scanning lateral injection position (xy) and the implantation depth (z) of the focused beams, which allow the defect distributions to be visually evaluated. The AIST microbeam system [8] uses an electron linear accelerator (LINAC) to produce positrons [9,10], and consequently, its beam intensity (10 6 e + /s) is 10-100 times higher than those of the other SPMs [3][4][5][6], which use radioisotopes as the positron source. Therefore, the AIST microbeam system can obtain PAS images within a reasonable time (~10 3 pixels/hour) [11] and hence, SPM may be a practical tool.…”