Boston | Scientists have developed a new technique for generating electron bursts, which could pave way for shoebox-sized X-ray imaging devices that consume very little power.
Ultrashort bursts of electrons have several important applications in scientific imaging, but producing them has typically required a costly, power-hungry apparatus about the size of a car.
Ultrashort electron beams are used to directly gather information about materials that are undergoing chemical reactions or changes of physical state. They are also used to produce ultrashort X-rays.
The new technique developed by researchers at Massachusetts Institute of Technology (MIT) in the US, the German Synchrotron, and the University of Hamburg in Germany could bring the imaging power of ultrashort X-ray pulses to academic and industry labs.
While the electron bursts have a duration measured in hundreds of femtoseconds, the new approach has the potential to lower their duration to a single femtosecond.
An electron burst of a single femtosecond could generate attosecond X-ray pulses, which would enable real-time imaging of cellular machinery in action.
“We’re building a tool for the chemists, physicists, and biologists who use X-ray light sources or the electron beams directly to do their research,” said Ronny Huang, a PhD student at MIT.
“Because these electron beams are so short, they allow you to kind of freeze the motion of electrons inside molecules as the molecules are undergoing a chemical reaction,” Huang said.
“A femtosecond X-ray light source requires more hardware, but it utilises electron guns,” he said.
In particular, with a technique called electron diffraction imaging, physicists and chemists use ultrashort bursts of electrons to investigate phase changes in materials, such as the transition from an electrically conductive to a nonconductive state, and the creation and dissolution of bonds between molecules in chemical reactions.
Ultrashort X-ray pulses have the same advantages that ordinary X-rays do. They penetrate more deeply into thicker materials.
The current method for producing ultrashort X-rays involves sending electron bursts from a car-sized electron gun through a billion-dollar, kilometre-long particle accelerator that increases their velocity.
Then they pass between two rows of magnets – known as an “undulator” – that converts them to X-rays.
The researchers’ new electron gun is about the size of a matchbox and consists of two copper plates that are 75 micrometres apart at the centres.
The plates bend in opposite directions, so that they are farthest apart – 6 millimetres – at their edges.
At the centre of one of the plates is a quartz slide on which is deposited a film of copper that, at its thinnest, is only 30 nanometres thick.