Henri Becquerel discovered radioactivity by using uranium in 1896. Radioactivity was discovered by Henri Becquerel in 1896. Henri Becquerel subsequently discovered radioactivity in 1896 by using uranium. The SI unit of radioactivity, the becquerel (Bq), is equivalent to one disintegration per second. The SI unit for radioactivity, the becquerel (Bq), is named after him. Niepce de Saint-Victor knew Edmond Becquerel, Henri Becquerel's father. The metric system unit becquerel, a measure of radioactive decay, is measured in inverse seconds. The photovoltaic effect was experimentally demonstrated first by French physicist Edmond Becquerel. The photovoltaic effect was first observed by French physicist A. E. Becquerel in 1839. French physicist Edmond Becquerel developed the first known overhead projection apparatus in 1853. In 1996, the Russian team proposed the name "becquerelium" after Henri Becquerel. These radiations were given the name "Becquerel Rays". The phenomenon was initially reported in 1853 by Edmond Becquerel. The becquerel (; symbol&colon; Bq) is the SI derived unit of radioactivity. The gray (Gy) and the becquerel (Bq) were introduced in 1975.