Brightest gamma ray on Earth- for a safer, healthier world
Press Release
19 September 2011
The brightest gamma ray beam ever produced- more than a thousand billion times
more brilliant than the sun- has been produced in research led at
Strathclyde- and could open up new possibilities for medicine.
Physicists have discovered that ultra-short duration laser pulses can
interact with ionised gas to give off beams that are so intense that
they can pass through 20 cm of lead and which would take 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 could also be useful in monitoring the integrity of stored nuclear waste.
In addition, the laser pulses are short enough- lasting a quadrillionth of a
second- 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 the Science and Technology Facilities Council’s
Rutherford Appleton Laboratory. Strathclyde was also joined in the
research by University of Glasgow and Instituto Superior Técnico in Lisbon.
Professor Dino Jaroszynski of Strathclyde, who led the research, said:
“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.
“To prove this we have imaged very thin wires - 25 microns thick - with gamma rays
and produced very clear images using a new method called phase-contrast imaging.
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 could also 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.
“In nature, if you accelerate charged particles, such as electrons, they radiate.
We trapped particles in a cavity of ions trailing an intense laser pulse and
accelerated these to high energies. Electrons in this cavity also interact with
the laser and pick up energy from it and oscillate wildly - much like a child being pushed on a swing.
The large swinging motion and the high energy of the electrons allow a huge increase
in the photon energy to produce gamma rays. This enabled the gamma ray photons
to outshine any other earthbound source.
"The accelerator we use is a new type called a laser-plasma wakefield accelerator
which uses high power lasers and ionised gas to accelerate charged particles to
very high energies - thus shrinking a conventional accelerator, which is 100m long,
to one which fits in the palm of your hand.”
The peak brilliance of the gamma rays was measured to be greater than 1023 photons per second,
per square milliradian, per square millimetre, per 0.1% bandwidth.
The research was supported by the Engineering and Physical Sciences Research Council,
the Science and Technology Facilities Council, the Laserlab-Europe Consortium and the
Extreme Light Infrastructure project. It is linked to SCAPA (Scottish Centre for
the Application of Plasma-based Accelerators), which is based at Strathclyde and
is run through the Scottish Universities Physics Alliance.
The research has been published in the journal Nature Physics.
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