Doppler broadening measurements of positron annihilation using bremsstrahlung radiation F.A. Selim a, * , D.P. Wells a , J.F. Harmon a , W. Scates a , J. Kwofie a , R. Spaulding a , S.P. Duttagupta b , J.L. Jones c , T. White c , T. Roney c a Department of Physics, Idaho Accelerator Center, Idaho State University, Campus Box 8263, Pocatello, ID 83209, USA b Department of Electrical Engineering, Boise State University, Campus Box 2075, ID 83725, USA c Idaho National Engineering and Environmental Laboratory, P.O. Box 1625-2802, Idaho Falls, ID 83415, USA Abstract The first system to measure Doppler broadening of positron annihilation based on during electron-pulse brems- strahlung radiation has been constructed and demonstrated. No photon-induced activation or positron emitters are involved in the process. The collimated bremsstrahlung radiation from a small electron accelerator, which exhibits excellent penetrability, is used to generate positrons inside the sample via pair production. The annihilation photons are recorded by a HPGe detector. The line-shape parameters of Doppler broadening can be used to identify defects in pure metals and alloys. The dependence of these parameters on different elements has been measured and shows promise as a probe of momentum of electronic wave-functions in pure and composite materials. This method also shows promise as an additional tool for measuring elemental composition, when used in conjunction with accelerator-based X-ray flu- orescence. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 78.70.Bj; 41.75.Fr Keywords: Bremsstrahlung; Positron annihilation; Doppler broadening; Defect measurements 1. Introduction Positron annihilation Doppler broadening spectroscopy is a well established tool to probe and characterize defects [1,2]. The 511 keV peak is Doppler broadened by the longitudinal momen- tum of the annihilating pairs. Since the positrons are thermalized, the Doppler broadening mea- surements provide information about the mo- mentum distributions of electrons at the anni- hilation site. Two parameters S (for shape), and W (for wings) see e.g. [3,4] are usually used to char- acterize the annihilation peak. The S parameter is more sensitive to the annihilation with low mo- mentum valence and unbound electrons and is defined as the ratio of the counts in the central region of the peak to the total counts in the peak. The W parameter is more sensitive to the annihi- lation with high momentum core electrons and is defined as the ratio of counts in the wing regions of the peak to the total counts in the peak. A high concentration of defects, or an increase in the mean size of defects, leads to a larger contribution Nuclear Instruments and Methods in Physics Research B 192 (2002) 197–201 www.elsevier.com/locate/nimb * Corresponding author. Tel.: +208-282-5874; fax: +208-282- 5878. E-mail address: faselim@yahoo.com (F.A. Selim). 0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0168-583X(02)00868-6