Photon induced positron annihilation spectroscopy: A nondestructive method for assay of defects in large engineering materials

This paper describes a new methodology for volumetric assay of defects in large engineering materials nondestructively. It utilizes high energy photons produced by nuclear reaction to create positrons in situ whose fate is followed using conventional positron spectroscopic techniques. The photon induced positron annihilation (PIPA) spectroscopy system has been set-up using a Folded Tandem Ion Accelerator (FOTIA). Possibility of using prompt γ-rays produced in nuclear reactions 27Al(1H,γ)28Si and 19F(1H,αγ)16O has been examined. The reaction 19F(1H,αγ)16O is seen to provide higher photon flux (and positron yield) and measurements have been carried out in large samples of metals and polymers. We could establish good sensitivity of the technique as well as reproducibility in a number of measurements. This technique has been used to carry out defect studies in cold worked zircaloy-2 plates. The measured S-parameter, indicative of defect concentration, was seen to correlate well with the measured residual stress using X-ray technique. The results were validated by γ-induced positron annihilation lifetime measurements at ELBE LINAC based GiPS facility.