Nikola Tesla film in his laboratory in previous experiments (later identified as ""Roentgen rays"" or "X-Rays"). His early experiments were with Crookes tubes, a cold cathode electrical discharge tube. Tesla may have inadvertently captured an X-ray image—predating, by a few weeks, Wilhelm Röntgen's December 1895 announcement of the discovery of X-rays when he tried to photograph Mark Twain illuminated by a Geissler tube, an earlier type of gas discharge tube. The only thing captured in the image was the metal locking screw on the camera lens. In March 1896, after hearing of Wilhelm Röntgen's discovery of X-ray and X-ray imaging (radiography), Tesla
Roentgen equivalent man sievert in 1980, but never accepted the use of the rem. The US National Institute of Standards and Technology (NIST) recognizes that this unit is outside the SI, but temporarily accepts its use in the US with the SI. The rem remains in widespread use as an industry standard in the US. The United States Nuclear Regulatory Commission still permits the use of the units curie, rad and rem alongside SI units. The following table shows radiation quantities in SI and non-SI units: Roentgen equivalent man The roentgen equivalent man (or rem) is an older, CGS unit of equivalent dose,