POSITRON ANNIHILATION SPECTROSCOPY

My current research focus is the characterization of materials using positron annihilation spectroscopy (PAS). PAS is a non-destructive nano-scale tool that is very useful in physics, chemistry and materials science. Materials of current interest include Zinc Oxide, tumor (cancer) cells and normal cells and other biological samples, rubber and rubber composites, polyimide and other porous polymer films, spherical and deformed magnetic alloy particles, and shale formation core and other samples of geological interest.

One recent Ph.D. graduate completed a variety of PAS studies of rubber-carbon black composites. A significant result has been to understand the behavior of rubber in composites as similar to a constrained viscous liquid. Other work includes investigation of vulcanization and cross link density, temperature measurements to below the glass transition of the rubber composite, correlation of PAS parameters with other physical properties of carbon black. Additionally, recent studies have included the investigation of Glioma brain tumor by comparing normal and tumor cells in a rat brain model.

Other recent research has included investigation of polarizational bremsstrahlung (PB). PB is distinct from ordinary bremsstrahlung. It occurs when an electron, passes by an atom, and the dynamic induced dipole moment causes the atom to radiate coherently with the accelerated electron. Two somewhat conflicting experimental results have recently been obtained : (1) the first observations of a PB contribution in experiments with 25 - 50 keV electrons on rare gas targets; (2) a measurement of bremsstrahlung from gold solid films of various thicknesses for which there is no observed PB contribution. Thus an essential theoretical problem is to explain why PB is seen from free atoms, but not from atoms in a solid lattice.

Absolute bremsstrahlung yields for 53 keV electrons on gold film targets, Scott Williams and C. A. Quarles, Physical Review A 78, 062703 (2008).

Positron study of carbon black parameters: Structure and Surface Area, J. Wang, V. O. Jobando, and C. A. Quarles, Materials Science Forum  607 (2009) 186-188.

Application of Positron Doppler Broadening Spectroscopy to the Measurement of the uniformity of Composite Materials,  C. A. Quarles, Thomas Sheffield, Scott Stacy and Chun Yang, CP1099 Applications of Accelerators in Research and Industry: 20th International Conference, edited by F.D. McDaniel and B.L Doyle, 2009 American Institute of Physics, pp 940-943.

Positron Spectroscopy Investigation of Normal Brain Section and Brain Section with Glioma Derived from a Rat Glioma Model,   SH. Yang, C. Ballmann and C. A. Quarles, CP1099 Applications of Accelerators in Research and Industry: 20th International Conference, edited by F.D. McDaniel and B.L Doyle, 2009 American Institute of Physics, pp 948-951.

Positron Annihilation Lifetime Studies of ZnO Nanopowders,  Raul M Peters, J. A. Paramo, C. A. Quarles, Y. M. Strzhemechny, CP1099 Applications of Accelerators in Research and Industry: 20th International Conference, edited by F.D. McDaniel and B.L Doyle, 2009 American Institute of Physics, pp 965-969.

Positron annihilation lifetime and Doppler broadening correlations for a variety of polymers, cross linked rubbers and organic liquids, C. A. Quarles , Vincent Jobando, Paul Arpin, Nuclear Instruments and Methods in Physics Research B261 (2007) 875, doi:10.1016/j.nimb.2007.03.048.
 
Target thickness dependence of 50 keV electron bremsstrahlung, Scott Williams, Keith Hayton and C. A. Quarles, Nuclear Instruments and Methods in Physics Research B261 (2007) 184.
 
Positron Lifetime Studies on the free volume changes during curing of Rubber- Carbon Black Composites, V.O. Jobando and C.A. Quarles, physica status solidi (c) 4 (2007) 3763-3766.
 
Effect of Cross-Linking on the Free-Volume Properties of Natural Rubber studied by Positron Annihilation Lifetime Spectroscopy, V.O. Jobando and C.A. Quarles, physica status solidi (c) 4 (2007) 3759-3762.
 
Positron Lifetime Studies on the free volume changes during deformation of Rubber- Carbon Black Composites, V.O. Jobando and C.A. Quarles, physica status solidi (c) 4 (2007) 3767-3770.
 
Forward to the Special Issue on Bremsstrahlung, C. A. Quarles and R. H. Pratt, Radiation Physics and Chemistry 75 (2006) 1113-1114.

Review of absolute doubly differential cross section experiments and cross section ratios for electron bremsstrahlung from rare gas atom and thin-film targets, C. A. Quarles and Sal Portillo, Radiation Physics and Chemistry 75 (2006) 1187-1200.
 
Target thickness dependence of bremsstrahlung from solid films, Scott Williams, Ryan Haygood and C. A. Quarles, Radiation Physics and Chemistry 75 (2006) 1707-1710.
 
Bremsstrahlung from gas atom targets: study of background processes, Ryan Haygood, Scott Williams and C. A. Quarles, Radiation Physics and Chemistry 75 (2006) 1688-1692.
 
Absolute doubly differential cross sections for electron bremsstrahlung from rare gas atoms at 28 and 50 keV, S. Portillo and C. A. Quarles, Physical Review Letters 91, 173201 (2003).