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WASHINGTON, June 28 (Xinhua) — American researchers have recorded the most detailed atomic movie of gold melting after being blasted by laser light.
The findings reported on Thursday in the journal Science may aid the development of fusion power reactors, steel processing plants, spacecraft and other applications where materials have to withstand extreme conditions for long periods of time.
“Our study is an important step toward better predictions of the effects extreme conditions have on reactor materials, including heavy metals such as gold,” said Stanford Linear Accelerator Center (SLAC) postdoctoral researcher Mo Mianzhen, one of the paper’s lead authors.
Nuclear fusion is the process that powers stars like the sun. Scientists want to copy this process on Earth as a relatively clean and safe way of generating virtually unlimited amounts of energy.
But to build a fusion reactor, they need materials that can survive being exposed to extremely high temperatures and intense radiation produced in the fusion reaction.
“The atomic-level description of the melting process will help us make better models of the short- and long-term damage in those materials, such as crack formation and material failure,” said Mo.
The study used SLAC’s high-speed electron camera that is capable of tracking nuclear motions with a shutter speed of about 100 millionths of a billionth of a second, or 100 femtoseconds.
The team discovered that the melting started at the surfaces of nano-sized grains within the gold sample and at the boundaries between them.
They focused the laser beam onto a sample of gold crystals and watched how the atomic nuclei in the crystals responded.
By stitching together snapshots of the atomic structure taken at various times after the laser hit, they created a stop-motion movie of the structural changes over time.
“About 7 to 8 trillionths of a second after the laser flash, we saw the solid begin turning into a liquid,” said SLAC postdoctoral researcher Chen Zhijiang, one of the study’s lead authors.
“But the solid didn’t liquefy everywhere at the same time. Instead, we observed the formation of pockets of liquid surrounded by solid gold. This mix evolved over time until only liquid was left after about a billionth of a second,” said Chen.

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