1. Rutherford’s gold foil experimentsimulation Beam of alpha particles Fluorescent screen Thin gold foil

3. Rutherford’s Model of the Atom 1. The positive charge is concentrated in the nucleus. This is a very small part of the atom. 2. Almost all the mass of the atom is concentrated in the nucleus. 3. Most of the volume of the atom is empty space as 99% of the alpha particles go straight through.

4. Symbol for element Atomic number – the number of protons (this is also the number of electrons) Mass number – the number of nucleons ( protons + neutrons) 235 92 U The atom

5. particle Electromagnetic wave Unstable nucleus Atoms which emit electromagnetic radiation or a particle by the spontaneous transformation of their nucleus are called radioactive.

6. Types of radiation Beta Particle (β) Gamma Ray (γ) - Alpha Particle (α)

7. Alpha particle is a helium nucleus. It has a positive charge. 4 2 He Beta particle is a fast moving electron. It has negative charge 0 e Gamma radiation is part of the electromagntic spectrum. No charge. neutron 1 0 n

8. Radioactive Decay 238 92 U 4 2 He + 234 90 Th parent daughter 234 90 Th 0 e + Pa 234 91 234 90 Th 0 0 γ + 234 90 Has less energy

9. E = mc 2 Mass can be changed into energy and vice versa. Fission – when a large atom breaks into smaller atoms which have less total mass and so releases energy. Eg. 238 U  234 Th + 4 He + energy. How much energy is released? The mass of 238 U = 3.9508 x 10 -25 kg 234 Th = 3.8843 x 10 -25 kg 4 He = 6.64 x 10 -27 kg 92902 92 90 2 This is a spontaneous emission of an alpha particle

10. A stimulated fission, where a neutron makes a large atom unstable and it breaks into smaller atoms releasing energy. Eg. 239 Pu + 1 n  137 Te + 100 Mo + 3 1 n 0 0 94 52 42 Fusion, where two small atoms join to become one larger atom with less mass. ( need very high pressures and temperatures for this to happen ie in the sun) Eg. 3 H + 2 H  4 He + 1 n 1120 Click here

11. Activity, A, number of decays per second, measured in Bequerels, Bq. A = N ÷ t Absorbed dose, D, the energy absorbed per unit mass, measured in Grays, Gy. D = E ÷ m Radiation weighting factor, w R, a measure of the biological effects of that type of radiation. Equivalent dose, H, the effect that the absorbed dose has on the tissue, measured in Sieverts,Sv H = Dw R Equivalent dose rate, H, the equivalent dose per unit time, measured in Svh -1 etc H = H ÷ t.. Average equivalent dose = 2mSv