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A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 2 0 1 1 DENSEST OBJECT ON EARTH CREATED WITH COMPRESSED COPPER A collaborative team from Law- rence Livermore National Laboratory (LLNL), Calif., and Johns Hopkins Uni- versity, Baltimore, are researching the structure of copper in different atmo- spheric conditions. The team discov- ered that copper maintains its crystal- line structure at pressures ranging from one atmosphere to more than 30 mil- lion atmospheres. Using LLNL’s National Ignition Facility, the team compressed micro- scopic copper samples to pressures of 30 million atmospheres in less than a billionth of a second. These extreme conditions tripled the sample’s density, creating the densest object on the plan- et for a brief moment in time. The researchers used diamond- turning machines to generate micro- scopic copper “stair steps,” whose surface roughness surpassed optical qualities, and precision metrology to measure sample thickness to 1 billionth of a meter. During the experiment, they tracked the copper sample traveling at 50,000 miles per hour using a velocity interferometer—the world’s most so- phisticated radar gun. To determine how copper stiff- ness responded to increasing pressure, the research team took a series of x-ray images to monitor the crystalline struc- ture as the copper compressed. They also measured how the speed of sound waves changed as the copper was squeezed. From these measurements, the team benchmarked the behavior of copper at extreme conditions and de- veloped a microscopic interpretation of its quantum behavior. The researchers say their exper- iments have shown that they are able to accurately predict the behavior of copper to extreme conditions, and they suspect that this behavior may be com- mon amongst the other noble metals. llnl.gov. The National Ignition Facility’s Target Chamber at LLNL.