Novel System for Potential Nondestructive Material Inspection Using Positron Annihilation Lifetime Spectroscopy

A new positron annihilation lifetime spectrometer consisting of a start gamma-ray detector, a stop gamma-ray detector, a digital oscilloscope, and a positron detector, which is a plastic scintillator coupled to a photomultiplier tube, is described. A (22)Na source is placed between the positron detector and a sample to be studied. gamma-ray signals related to positrons annihilating in the positron detector are rejected by anti-coincidence processing. Comparison of the positron lifetime spectrum of a steel strip collected with the new system with that collected with a conventional system using two specimens sandwiching the (22)Na source shows that accurate positron lifetime measurements are possible with the new system. The new system does not require cutting of the samples and is potentially applicable to truly nondestructive onsite inspection of various materials such as those used in nuclear power plants, aircraft and cars, etc., by positron annihilation lifetime spectroscopy (PALS). (C) 2011 The Japan Society of Applied Physics