Determining the Valence State of Lead in Compounds Using PIXE Andrew Voter Nuclear group July 23, 2007

Motivation Valence state is the charge on the metal ion Valence state is the charge on the metal ion Why is it important to know this? Why is it important to know this? - Synthesis of new compounds leads to new questions about chemical structure and function

Hope Ion Beam Analysis Lab (HIBAL) Accelerates ions through a large potential to high energies Accelerates ions through a large potential to high energies Can accelerate protons or alpha particles Can accelerate protons or alpha particles We observe what happens after the ions hit the target We observe what happens after the ions hit the target

Particle Induced X-ray Emission (PIXE) Accelerated protons excite inner electron shells of the target Accelerated protons excite inner electron shells of the target Other electrons fill the gap and give off large amounts of energy in the form of X-rays Other electrons fill the gap and give off large amounts of energy in the form of X-rays These X-rays are detected; their energy identifies the elemental source, and the number of x-rays identifies concentration These X-rays are detected; their energy identifies the elemental source, and the number of x-rays identifies concentration

The Goal “Influence of chemical environment on the analysis of PIXE/XRF spectra of samples containing various compounds” 1 “Influence of chemical environment on the analysis of PIXE/XRF spectra of samples containing various compounds” 1 i.e. peaks change (slightly) i.e. peaks change (slightly) A Typical Lead PIXE Spectra 1 Fazinic, S. et al.; XI Intl. Conf. on PIXE. May25-29, L  peak L β peak L Energy

What causes this change? Valence state of element in compound Valence state of element in compound Crystal structure of the compound Crystal structure of the compound Cell parameters of the compound Cell parameters of the compound Statistics Statistics Something else… Something else…

Preparation of Samples Compound mixed with organic binder Compound mixed with organic binder Pellet pressing with hydraulic press Pellet pressing with hydraulic press Pellet is then mounted onto a slide Pellet is then mounted onto a slide Slide placed in PIXE chamber Slide placed in PIXE chamber

The Procedure Tested Cu, Mn, Pb compounds Tested Cu, Mn, Pb compounds Compounds appear sorted by valence state Compounds appear sorted by valence state Pb (0) metal Pb (0) metal PbO 2 (IV) PbO 2 (IV) Size effect too? Size effect too? Energy

Future Work Double blind test of unknown element Double blind test of unknown element Testing compounds of more elements Testing compounds of more elements (more Mn, Cr, Ru?) (more Mn, Cr, Ru?) Publish results Publish results

Acknowledgements Dr. Graham Peaslee Dr. Graham Peaslee Dr. Paul DeYoung Dr. Paul DeYoung Dave Daugherty Dave Daugherty Nuclear Group Nuclear Group R.E.A.C.H. Program R.E.A.C.H. Program Hope College Hope College NSF NSF