7. The Scanning Micro-Beam PIXE Analysis Facility at the Electrostatic Accelerator Building

Hitoshi Imaseki, Masae Yukawa,Takahiro Ishikawa, Frank Watt¹⁾ and Hiroyuki Iso²⁾
(¹⁾National University of Singapore; ²⁾Neos Tech, Chiba)

Keywords: PIXE, micro-beam scanning, mapping, elemental distribution

In March 1999, a HVEE Tandetron was installed in the Electrostatic Accelerator Building 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 5 A at 3.4MeV. The accelerator facility incorporates three beam lines for conventional, in-air and microbeam PIXE analysis. The conventional beam line has two types of X-ray detecting devices, Si (Li) and CdZnTe detectors, and elements from Na (Z=11) to U (Z=92) are detectable. Fifteen samples can semi automatically be measured at one time using a proton beam of optical beam size from 0.5 to 2.0 mm at 100 nA beam current. The in-air beam line is used for irradiation of wet sample using a proton beam of optical beam size from 2 mm . The proton beam, thru out of Kapton film, is introduced into a chamber filled with helium gas of 1 atmosphere.

The scanning microbeam PIXE analysis line is based around an Oxford Microbeams OM2000 nuclear microscope endstage. This system provides the ability of multi-elemental mapping over sample areas up to 2×2mm area with spatial resolutions routinely at 1µm×1µm. The scheduled operation of this facility started in April 2000. The results of beam resolution tests carried out in 2001 are as follows: For Scanning Transmission Ion Microscopy (STIM), the estimated beam size is 100 x 200 nm, measured using a 2.6 MeV proton beam scanned over a 12.5µm repeat distance copper grid (Fig.8). For Particle Induced X-ray Analysis (PIXE) operation at 50 pA beam current, the estimated best spot size is 0.4 x 0.6 microns (Fig.9). The micro-beam facility apparatus is being used for research into the elemental distribution of small biological samples such as biological cells and tissue.

The operation of this machine is controlled by the Technical Service and Development Section.

Publications:
1) Imaseki, H., Yukawa, M.: International Journal of PIXE, 10[3-4], 77-90, 2001.
2) Imaseki, H., Yukawa, M.: Tandem kasokuki oyobi sono syuhengijyutu no kenkyukai (in Japanese), 14, 105-107, 2001.

Fig.8. STIM tests using 2000 lines per inch Cu grid. Proton energy 2.6 MeV protons; scan sizes 50 microns; resolution estimated visually approximately 100 nm (horizontal) and 200 nm (vertical).

Fig.9. PIXE scan of 2000 lines per inch mesh gold grid. Proton energy 3 MeV protons; scan size 50 microns; estimated beam size 0.4x0.6 microns.