XRF and PIXE Research in the period 1982 – 2002
By: Tang Seung Mun
The XRF (X-Ray Fluorescence) and PIXE (Proton-Induced X-ray Emission) research facilities were developed from the teaching equipment acquired for establishing the nuclear teaching laboratory when the Department of Physics moved from the Bukit Timah campus to the Kent Ridge Campus in 1981. With the funding for setting up the nuclear teaching laboratory, the following major instruments were purchased: a 2.5 MeV van de Graaff accelerator, several types of radiation detectors (Si(Li), Ge(Li), NaI(Tl), surface barrier) with associated electronics, a multi-channel analyzer, a number of radioisotope excitation sources (Co-57, Fe-59, Cd-109 and Am-241). With these instruments, a number of nuclear experiments for teaching purpose were set up for the second-year, third-year and the honours-year students. For secondyear students, there was the experiment for the detection of charged particles using a surface barrier detector. Two experiments were designed for thirdyear students. They were the Compton scattering experiment and the Mossbauer spectroscopy experiment. An experiment on x-ray fluorescence spectroscopy and another on coincidence spectroscopy were available for honours-year students. The van de Graff accelerator was mainly used for honours-year projects on neutron activation analysis with fast neutrons generated from bombarding a tritium target with a deuteron beam.
Shortly after the setting up of the radioisotope source excited XRF facility, Prof C T Yap realized that this facility was very suitable for the authentication of Chinese porcelains made in different periods in because the kaolin clay and the glaze of porcelains contain elemental signatures which depended on the time and the place where they were made. With the XRF facility, he carried out an extensive study of his own vast collections of Chinese porcelains made in the past 300 years and published many research papers in the nineteen eighties on his studies. The XRF facility was also used by other faculty members of the Department of Physics for the development of XRF techniques for precision elemental analysis.
In the early 1980s, the use of the van de graaff accelerator for research was confined to the study of conversion coefficients in decays of radioisotopes produced using the fast neutrons generated by the accelerator by the (d,n) reaction. In 1983, at the request of the International Atomic Energy Agency (IAEA), the Physic Department hosted an IAEA regional workshop on Particleinduced X-ray Emission (PIXE) training workshop. The van de Graaff acceleration was re-configured for PIXE applications with equipment (a PIXE chamber, a Si(Li) detector, a multichannel analyzer and some signal counting electronics) given by IAEA for conducting the workshop. Since then, the PIXE facility was further developed and used by Prof S M Tang and members of his research team for numerous research projects on elemental/stoichiometric analysis of gemstones, coastal waters, marine sediments, aerosol particles and Y-Ba-Cu-O superconductors.
In 1992, a quadrupole focusing magnet was acquired with the teaching laboratory upgrading fund to upgrade the broadbeam PIXE system to a nuclear microscope capable of delivering 100-pA of proton beams with a sub-micron spot size. This nuclear microscope was used for student projects and a wide range of research works (such as micromachining, microanalysis of various types of specimens) for a decade until it was replaced by a new nuclear microscope purchased under a research grant of Prof Frank Watt in 2003.