Delbrück Scattering, Non-perturbative QED and possible Applications, by: Prof. Dr. Dietrich Habs, emerit., from LMU Garching, Experimental Nuclear Physics

Monday 25 Jun 2012, 14:15 → 15:45 Europe/Berlin

Seminarroom 3344, T 30 (Physics Dept. Theoretical Physics)

Abstract In a recent Phys. Rev. Lett. [1] we measured the index of refraction n = 1+δ of γ rays up to two 2 MeV in Silicon and found to our surprise that it changed from small negative values (expected for X-rays) at 0.7 MeV to a positive δ, which can only be explained by Delbrück scattering of the γ quanta from the high electric field of a nucleus. However, in contrast to all former predictions, which used 1. order Born approximation the measured values were about 105 times larger than predicted [2]. Knowing that the electric fields at the nucleus are about 1000 times the Schwinger limit of 1.3 • 1018V/m and that perturbative QED has to be replaced by non-perturbative QED in the range of the Schwinger field it is now surprise, that all former predictions are wrong. I will describe carefully how we measured this index of refraction very carefully at the ILL in Grenoble. Then I will discuss two consequences: we want to measure other-perturbative QED effect like photon splitting. At the same time several theoretical groups are making good progress to calculate these non-perturbative QED effects. A second consequence is that a new γ optics becomes possible. We have built gold lenes, where we expect a δ of 10-4 -10-5 and then hopefully we can focus γ beams very well. Since at present also very brilliant γ beams are under development [3] a new field of nuclear photonics will be developed, where we can address with very monochromatic, brilliant γ beams individual nuclear levels. In this way e.g. a very sensitive diagnostics with microscopic resolution can be performed for isotopes; but also e.g. about 50 new medical radioisotopes can be produced.