National Aeronautics and Space Administration. Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Krause et al. Electromagnetic Spectrum Series Series Homepage. Infrared Waves. Reflected Near-Infrared. Visible Light. Ultraviolet Waves. Earth's Radiation Budget. Diagram of the Electromagnetic Spectrum. Recommended Articles. September 24, What is more, while the index of refraction is negative for X-rays, it becomes positive for gamma rays.
Habs is an experimental physicist and does not claim to have a detailed theoretical explanation for the phenomenon, but he believes the results provide tantalizing hints of quantum electrodynamics beyond the Schwinger limit — the point at which traditional perturbative treatments of quantum electrodynamics break down and the mathematics becomes incalculable with current techniques.
Now those textbooks may have to be rewritten. Nuclear physicist Norbert Pietralla of the University of Darmstadt in Germany is impressed by the results.
He explains that this could lead to lenses for gamma rays. Habs is also excited about the breadth of the possible applications the technology might offer. He suggests medical imaging as just one possibility, saying that gamma rays could be used to track lithium in the brains of patients being treated for bipolar disorders.
On a broader note, he believes that the discovery could lead to a revolution in gamma-ray optics much like that initiated by the invention of the telescope and the microscope in the 17th century. Materials with nuclei that have a large positive charge — such as gold — should be ideal for making gamma-ray lenses, and the team are currently studying gold lenses. The research is published in Physical Review Letters. Close search menu Submit search Type to search. However, it could be boosted using lenses made of materials with larger nuclei such as gold, which should contain more virtual electron-positron pairs.
With some refinement, gamma-ray lenses could be made to focus beams of a specific energy. Such focused beams could detect radioactive bomb-making material, or radioactive tracers used in medical imaging. That's because the beams would only scatter off certain radioisotopes, and stream past others unimpeded. The beams could even make new isotopes altogether, by "evaporating" off protons or neutrons from existing samples.
That process could turn harmful nuclear waste into a harmless, nonradioactive byproduct. By Jon Cartwright, Science NOW Lenses are a part of everyday life—they help us focus words on a page, the light from stars, and the tiniest details of microorganisms. Topics gadgets physics ScienceNOW.
Reflection, classically, needs a very flat surface so that the phases of the reflected waves are retained. Depending on the material the classical beams may be absorbed, decohered in reflecting from many point sources, or reflected coherently if the scattering is elastic mirrors elastically and coherently scatter incoming light.
Gamma rays though force us to go to the micro level, because of the very small wavelength that describes them as a light beam. One has to look at the details of the surface, and whether a classical smooth surface for classical reflections can be modelled for gammas, and the answer is, no it cannot.
For micron wavelengths optical light the fields built up by atoms with angstrom distances in the lattice appear smooth and can be classically modelled. Gamma rays considered as a classical light beam, with their picometer wavelengths see mostly empty space between the atoms of the solid. For the small wavelengths of gamma rays, the photons see mostly empty space.
The reason why is based in something called the plasma frequency of the metal of a mirror. A metal, as you may know, is composed of a series of atom ion, effectively cores - nuclei, together with some, but not all, of their bound electrons - which contribute the remaining outermost electrons of their unbound forms to a communally shared "electron sea" - kind of like a giant, distributed omnidirectional covalent bond that extends all throughout the whole metal crystal here we're just considering a single crystal for simplicity.
The electrons are quantumed out all over the full extent of the crystal and effectively form a sort of "gas" throughout and permeating the metal.
When an electromagnetic wave approaches that gas, the free charges within it - the electrons - start oscillating, and as they do so, they set up another wave going outward at the same time as the first is going in. This begins as soon as the first wave begins to impinge. However, if the wave oscillation is fast enough, the electrons can't keep up due to their mass, and thus they are unable to form the reflected wave. The frequency at which this occurs is called the metal's plasma frequency and is inversely proportional to the square root of the mass, so that a high mass particle would have a lower plasma frequency.
The name comes from the fact that the metal can be thought of in a sense as a kind of "solid plasma" - ions with free electrons, the difference with what most people think of as a "plasma" being here the ions are not free to move about of their own accord.
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