On August 25, 1908, the French physicist and natural radioactivity discoverer Henry Becquerel died. Radioactivity refers to an element that spontaneously emits radiation (such as ¦Á-rays, ¦Â-rays, g-rays, etc.) from an unstable atomic nucleus, and disintegrates into a stable element and stops radiation (degradation product), a phenomenon discovered by Anthony Henry Becquerel (Antoine Henri Becquerel, December 15, 1852 and August 25, 1827). The energy emitted by the decay is called decay energy. The elements that have atomic sequence of 83 () or more are radioactive, but some elements below the atomic sequence of 83 (such as) are also radioactive. Anthony Henry Becquerel (Antoine Henri Becquerel, December 15, 1852 and August