Gamma ray refraction could launch nuclear photonics

Ashley N. Paddock, ashley.paddock@photonics.com

An experiment in which gamma rays were bent like ordinary light overturns decades of theoretical predictions and opens the door to a new field of research called nuclear photonics.

Gamma rays are essentially a highly energetic form of light. Able to penetrate almost any material, they now can bend and focus, which could lead to powerful new medical applications, including imaging techniques and targeted cancer treatments.

Using a version of a common classroom experiment with glass prisms, scientists from Laue-Langevin Institute (ILL) and Ludwig Maximilian University of Munich refracted the rays at the highest energies ever recorded.

At the high-resolution gamma ray facility GAMS at ILL, gamma rays now can bend and focus; this couldlead to new medical applications such as targeted cancer treatments and novel imaging techniques. Image: ©ILL/Bernhard Lehn Fotodesign Studio@bernhardlehn.de.

In the same way that light beams can be bent and split with glass prisms, the researchers used a silicon prism to bend gamma rays. They analyzed the gamma rays produced using ILL’s PN-3 facility through two silicon crystals, the first preselecting them as they came out of the reactor and directing them into a very narrow and parallel beam. Farther along the instrument, a silicon prism was placed at a height where it refracted half of the gamma ray beam. The refraction of this half-beam was then detected by a second silicon crystal and compared with the half consisting of unrefracted gamma rays.

They discovered that the energy of the gamma rays increased the falling refraction values, then suddenly increased to larger positive refraction values, similar to those of visible light. These were much higher values than anyone expected.

The researchers now believe that by replacing the silicon prisms with higher-refracting materials such as gold, they can increase refraction to a level where it can realistically be manipulated for optical techniques.

“Twenty years ago, many people doubted you could do optics with x-rays – no one even considered that it might be possible for gamma rays, too,” said Dr. Michael Jentschel, an ILL research scientist. “This is a remarkable and completely unexpected discovery, with significant implications and practical applications. These include isotope-specific microscopy with benefits across the scientific disciplines, through to direct medical treatment and even tools to address major national security issues.”

Potential applications include more selective, less destructive medical imaging techniques achieved by enriching a particular isotope in a cancer and monitoring where it goes, improved production and trialing of new, more targeted radioisotopes for cancer treatment, and remote characterization of nuclear materials or radioactive waste.

The work appeared in Physical Review Letters (doi: 10.1103/PhysRevLett.108.184802).