Application of Positron Annihilation Lifetime Spectroscopy

Author:  Naoya UESUGI | toyo seiko Co., Ltd.
Source:  The Shot Peener magazine, Vol 31, Issue 3, Summer 2017
Doc ID:  2017023
Year of Publication:  2017
Abstract:  
INTRODUCTION The positron annihilation lifetime spectroscopy (PALS)has been widely used for probing open volume defects in various materials 1). PALS has been applied for detecting the fatigue damages and is considered to be an effective method to evaluate fatigue damages 2), 3). In previous studies, it was required to cut the specimens into two pieces, although PALS is essentially a non-destructive method. This is because PALS requires two same specimens to sandwich the positron source. In case of sandwiching a positron source with a specimen and another material, half of the positron wouldn’t annihilate in the specimen and the positron lifetime spectrum is seriously contaminated by the false signals. Therefore it was difficult to continuously evaluate the accumulation of fatigue damages of the identical specimen by conventional PALS. As a technique to solve this problem, a novel method of PALS that does not require cutting out the specimen was developed by Yamawaki et.al.4). Briefly, the positron source is sandwiched between the specimen and a plastic scintillator which is a positron detector. The γ-ray signals relevant to the positron annihilation in the plastic scintillator are eliminated by application of anti-coincidence processing with the signal positron detected in the plastic scintillator. This technical paper describes the principle of the PALS system which is Positron Surface Analyzer developed by TOYO SEIKO and the results of several applications.