The brightest gamma-ray beam ever produced — more than a quadrillion (thousand billion) times more brilliant than the sun — could open up new possibilities for medicine. Physicists have discovered that ultrashort-duration laser pulses can interact with ionized gas to give off beams so intense that they can pass through 20 cm of lead and would require 1.5 m of concrete to be completely absorbed. The ray could have several uses, such as in medical imaging, radiotherapy and radioisotope production for PET (positron emission tomography) scanning. The source also could be useful in monitoring the integrity of stored nuclear waste. Student and research associate Silvia Cipiccia with an accelerator device used to produce gamma rays. (Photos: University of Strathclyde) In addition, the laser pulses are short enough, at 1 fs, to capture the response of a nucleus to stimuli, making the rays ideal for use in lab-based study of the nucleus. The device used in the research is smaller and less costly than more conventional sources of gamma rays, which are a form of x-rays. The experiments were carried out on the Gemini laser in the Central Laser Facility at Rutherford Appleton Laboratory in Didcot, England. The research was conducted by the University of Strathclyde, which was joined by the University of Glasgow and by Instituto Superior Técnico in Lisbon, Portugal. “This is a great breakthrough, which could make the probing of very dense matter easier and more extensive, and so allow us to monitor nuclear fusion capsules imploding,” said professor Dino Jaroszynski of Strathclyde, who led the research. Professor Dino Jaroszynski “To prove this, we have imaged very thin wires — 25 μm thick — with gamma rays and produced very clear images using a new method called phase-contrast imaging,” he added. “This allows very weakly absorbing material to be clearly imaged. Matter illuminated by gamma rays only cast a very weak shadow and therefore are invisible. Phase-contrast imaging is the only way to render these transparent objects visible. It also could act as a powerful tool in medicine for cancer therapy, and there is nothing else to match the duration of the gamma-ray pulses, which is also why it is so bright.” The instrument the investigators used is a new type called a laser-plasma wakefield accelerator, which uses high-power lasers and ionized gas to accelerate charged particles to very high energies. Instead of a conventional accelerator, which is 100 m long, the laser-plasma wakefield accelerator fits in the palm of the hand, Jaroszynski said. The peak brilliance of the gamma rays was measured to be >1023 photons per second, per square milliradian, per square millimeter, per 0.1 percent bandwidth. The research has been published in Nature Physics. For more information, visit: www.strath.ac.uk