Document Type

Conference Proceeding


Positron Annihilation Spectroscopy (PAS) techniques can be utilized as a sensitive probe of defects in materials. Studying these microscopic defects is very important for a number of industries in order to predict material failure or structural integrity. We have been developing gamma‐induced pair‐production techniques to produce positrons in thick samples ( ∼4–40 g/cm2, or ∼0.5–5 cm in steel). These techniques are called ‘Accelerator‐based Gamma‐induced Positron Annihilation Spectroscopy’ (AG‐PAS). We have begun testing the capabilities of this technique for imaging of defect densities in thick structural materials. As a first step, a linear accelerator (LINAC) was employed to produce photon beams by stopping 15 MeV electrons in a 1 mm thick tungsten converter. The accelerator is capable of operating with 30–60 ns pulse width, up to 200 mA peak current at 1 kHz repetition rate. The highly collimated bremsstrahlung beam impinged upon our steel tensile specimens, after traveling through a 1.2 m thick concrete wall. Annihilation radiation was detected by a well‐shielded and collimated high‐purity germanium detector (HPGe). Conventional Doppler broadening spectrometry (DBS) was performed to determine S, W and T parameters for our samples.


Doppler effect; Electron spectroscopy; Gamma ray spectrometry; Gamma ray spectroscopy; Linear accelerators; Materials – Defects; Materials – Fatigue; Materials – Testing; Materials analysis; Microscopic defects; Positrons; Public address systems; Spectrum analysis; Structural failures


Engineering Science and Materials | Materials Science and Engineering | Mechanical Engineering | Other Engineering Science and Materials


Conference held: Fort Worth, Texas, 10–15 August 2008


Copyright American Institute of Physics. Used with permission.

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