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grenz rays

British  
/ ɡrɛnz /

noun

  1. physics X-rays of long wavelength produced in a device when electrons are accelerated through 25 kilovolts or less

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of grenz rays

C20: from grenz from German Grenze boundary