Werner Brandt legacy to PIXE: Past and present perspectives

Inner-shell ionization cross sections used in Particle-Induced X-ray Elemental (PIXE) analyses are routinely calculated in the ECPSSR [W. Brandt, G. Lapicki, Phys. Rev. A 23 (1981) 1717–1729] theory and/ or semiempirical formulas scaled to that theory. Thirty years after the passing of Werner Brandt, with recognition of his seminal contributions to other research on positron physics and stopping power problems, the work and articles that progressed into the ECPSSR theory for inner-shell ionization by protons and heavier ions are recalled as Brandt’s past legacy to the PIXE community. Applications of the ECPSSR and its evolution into the ECUSAR [G. Lapicki, Nucl. Instr. Meth. B 189 (2002) 8–20] theory over the last three decades are reviewed with perspectives on Brandt’s present legacy. 2013 Elsevier B.V. All rights reserved. 1. Work of Brandt and co-workers prior to 1983 1.1. Early work prior the initiation of inner-shell ionization theory and x-ray production experiments in 1966 Already in his first publication, on calculation of intermolecular force constants from polarizabilities [1], Brandt showed superb ability to scale the data so as to extract these constants in the Lennard–Jones potential for a variety of molecules. His work at DuPont followed with papers on stopping power [2], compressibilities of high-polymers [3], and a seminal article on positronium decay in molecular substances [4]. His first NYU article on Bose–Einstein condensation of excitons [5] was followed by a series of papers on atomic collective response [6] and a paper on the effect of proton channeling on x-ray production in crystals [7], which inspired Brandt to pursue a new field of research that was to become his legacy to the PIXE community. A New York Times obituary noted, inter alia, that Brandt directed New York University’s Radiation and Solid State Laboratory which since the early 1960’s had been an interdisciplinary venture that had used biochemistry and physical chemistry, as well as physics, to probe the interaction of matter and energy [8]. A program from his memorial service [9] listed and elaborated on three key areas in which Brandt has excelled during his career as an outstanding original researcher: active and definitive analysis of inner-shell excitations by atomic projectiles, studies of positron annihilation, and stopping powers of charged particles in matter. Aside from a plethora of publications on stopping powers, the titles of informal annual workshops held every January in the 1977– 1983 period [10], and continued to this day as the Werner Brandt Workshops, inform and reflect on Brandt’s leadership in the field of penetration of charged particles in matter. An obituary [11] describes Brandt’s work and in memoriams [12] vividly capture memories about him. While it would be impossible to review all his seminal and multi-facted contributions to physics, this review is written from my perspective as one of Brandt’s last students and the next-to-last post doc at the time when the Fig. 1 photo