The basic principle of PIXE is schematically illustrated in Fig.1.
When charged particles which is produced in a cyclotron pass through material they interact with the electrons in the atoms and occasionally an electron is ejected. When this occurs in one of the inner shells, the vacancy created is filled by an electron from an outer shell, as indicated in the figure. In this process an X-ray photon of characteristic energy to each element is emitted and by measuring the energy the atomic number can be determined.
In practice, thin target film is bombarded with 2.9MeV proton beam from the cyclotron in Takizawa (Cyclotron Research Center Iwate Medical University, Nishina Memorial Cyclotron Center Japan Radioisotope Association). Induced characteristic X-rays were detected with Silicon Lithium semiconductor detector and analyzed with a multichannel analyzer. As Shown in Fig.2, two detectors were used in our analysis to detect all elements from Na to U simultaneously. A 3-5mm-thick Mylar absorber is used for detection of elements heavier than Ca. Another detector at the opposite side is for measurement of low-atomic number elements and a small aperture made of graphite is put in front of it to reduce the counting rate of X-rays.
Fig.3 shows a block diagram of the data-taking system with two detectors. Spectrum data from the two Pulse Height Analyzer (PHA) are transferred to Japan NEC PC-9801 personal computer and the contents of elements were quantified using quantitative software package "SAPIX".
Representative PIXE spectrum of serum and the procedure of spectrum analysis are shown in Fig. 4. These spectra shows a typical fit of many KΏand Kΐ peaks.
