Positron analysis based on high energy X-ray source

Positron analysis can reveal the information of atomic level defect of materials like metals or polymers through the study of Doppler broaden 511keV ¿ spectra of positron with electrons that have different momentum distributions relating with the inner defect of materials. The usually used positrons come from isotope or accelerator positron source that irradiates the materials with positrons from outside. Because of the short range of positron in matter, only the surface of millimeter depth inside metals or polymers could be analyzed. To fulfill the demand of positron analysis inside the materials, high energy X-ray is used to produce positron. Two kinds of reaction is feasible, (1) is positron decay after the (¿, n) reaction of high energy photon with low photoneutron threshold nuclide, like N or Fe; (2) is the pair production. We use the first reaction in this paper. The algorithm to analyze the broaden 511keV ¿ spectra is S factor or FWHM method. Maximum likelihood expectation method is also researched to deconvolute the spectra to remove the detector response for more precise electron momentum information extraction. We setup the facility with 15MeV LINAC and HPGe detector, and then test several specimens including low carbon steel, cast iron, aluminium and copper. The experimental results of five low carbon steel specimens show appreciable correspondence between positron analysis result and tensile elongation. This indicates that the atomic level defect of low carbon steel is within the range of positron analysis. On the other hand, cast iron, aluminium and copper do not show such relation. This is perhaps due to the void in these materials is so much that positron analysis method is saturated.