Discovery of Radioactivity Roentgen Xrays Becquerel Uranium emits

Discovery of Radioactivity

Roentgen X-rays Becquerel Uranium emits Something! Right at the end of the 1800’s … Curie Radioactivity

Roentgen discovered X-rays: 1895 Roentgen discovered that cathode ray tubes emit x-rays

Roentgen quickly discovered uses for X-rays

Natural Radioactivity - 1896 Becquerel discovered that uranium substances emit radiation

Marie Curie found emission of rays by uranium compounds was atomic property of element uranium 1898 discovered thorium also gave off radiation 1898: Curies reported 2 new elements polonium & radium discovered by their radioactivity

Radioactivity Nucleus of element emits subatomic particles & electromagnetic waves Nucleus changes into different element Original nucleus is called “unstable” Process is called nuclear “decay” or “transmutation”

Natural Radioactivity Becquerel and Curie believed that more than 1 kind of radiation was emitted by substances 1899 alpha rays and beta rays discovered 1900 gamma rays discovered

Radioactivity – Rutherford again!

Radioactivity • 3 radiations behave differently in magnetic & electric fields • different penetration power • or alpha rays stopped by paper • or beta rays stopped by thin metal foil • or gamma rays only partially blocked by lead and concrete

Penetration & Shielding

Type of Radiation Symbol Mass Charge (amu) Alpha Beta Gamma 4 He 2 or 24 4 +2 0 -1 1/1836 (0. 0005) -1 0 0