 But around that time, radioactivity was discovered by the French scientist Henri Bacorelle. Using uranium salts, he was able to blacken a photographic plate. Here's a photograph of the plate. Further research by Bacorelle, Rutherford, Curie, and others, discovered three types of radiation. Here's how they did it. A radiation source shines on a lead plate with a small hole in it to create a beam. The beam is directed at a fluorescent screen. The screen flashes when it is struck. Without any electric field present, the beam illuminates a single point on the screen. When an electric field is applied, the beam is separated into three components. One is deflected upward by the electric field, indicating that it is negatively charged. These were named beta rays. One is deflected downward, but not as far as the beta rays were deflected upward, indicating that it consists of positively charged particles that are more massive than the beta rays. These were named alpha rays. The radiation that continued to hit the center was not affected by the electric field and therefore as no charge. These emissions were named gamma rays. It turned out the beta rays are high speed electrons. The alpha particles were later found to be helium atoms without their electrons. And the gamma rays turned out to be high energy photons, more energetic than x-rays.