Radioactivity DA Physics

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Key Points

Atoms are naturally electrically neutral

Radioactivity = Unstable Nucleus

Plum Pudding Model

Radioactivity, Isotopes & Atoms

Plum Pudding Model Electrons are dotted throughout the atom like currents in a bun.

The positive charge was spread throughout like the dough.

Alpha - Scattering Particle Experiment Rutherford tested Thomson's theory. He fired alpha particles at a strip of gold foil. Most of the alpha particles went straight through but some were deflected which told him there must be something hard inside to cause this: the nucleus.

Isotopes An isotope is an atom of an element which has the same number of protons but a different number of neutrons.

Radioactivity Radioactivity is caused by an UNSTABLE NUCLEUS, which is caused by extra electrons which makes the nucleus break up. In short, radioactivity is the spontaneous decay (break - up) of an atomic nucleus.

3 Types of Radiation Alpha Particles (a): strongest ionising power, mass of 4, charge positive

Beta Particles ( ): Mid ionising power, mass of 1/1840, charge negative

Gamma Radiation (y): Weakest ionising power, mass of 0, charge neutral

Background Radiation Radiation is measured using a Geiger - Muller Tube.

To measure background radiation:

Make sure the counter is at zero.

Switch on the counter and the detector for 30 mins.

Read the result and divide by 30 to give counts/min.

The background count must be subtracted from any reading of a radioactive source.