Radioactivity

Radioactivity

Discovery of the Nucleus J.J Thomson's original 'Plum pudding' model, suggested the atom consisted of a positive charge with electrons dotted throughout like currents in a bun.This model was improved by Ernest Rutherford: he fired alpha particles (emitted with the same kinetic energy (to ensure deflection was constant) from a radioactive source (with a long half-life) held within a lead collimator - to ensure a narrow beam in one direction) at a thin metal foil in a vacuum (to prevent interference with air particles) the alpha particles were scattered by the metal foil; the angle of deflection from their original direction was detected by a detector moved at a constant distance from the metal foil. the detector had a florescent screen that emitted a photon of light when struck by an alpha particle, these photons were observed and counted and the angle of deflection was recorded.

Rutherford's experiment showed that; most alpha particles passed straight through the foil with little/no deflection a small percentage of alpha particles were deflected through angles of more that 90 degrees. From these results, he concluded; most of the atoms mass is concentrated in a small central region - the nucleus. the nucleus is positively charged as it repels alpha particles that pass closely to it from testing different metals , the magnitude of the charge of the nucleus was calculated to be +Ze where e is the charge of an electron and Z is the atomic number of the element.

Alpha, Beta and Gamma Radiation Alpha Radiation: