DHS 20 Nuclear Physics (Notes & Tutorial)

Dunman High School (Senior High Physics Department) For Internal Use Only Page 1 of 33 Guiding Questions • Why are some nuclei radioactive? What happens during radioactive decay? Where does the energy come from? • What is emitted during radioactive decay, and is it harmful? How do decay products interact with matter? • What are the uses of radioactivity? • How are nuclear reactions different from chemical reactions? How are they similar? • What can conservation laws tell us about nuclear processes? Content • The nucleus • Isotopes • Mass defect and nuclear binding energy • Nuclear processes • Radioactive decay • Biological effect of radiation 9749 H2 Physics Topic 20 Nuclear Physics Year 6 (2025) DUNMAN HIGH SCHOOL

Dunman High School (Senior High Physics Department) For Internal Use Only Page 2 of 33 (a) infer from the results of the Rutherford α-particle scattering experiment the existence and small size of the nucleus Rutherford’s α-particle scattering experiment: Setup Rutherford's experiment consisted of a beam of alpha particles ( ) 4 2 He , generated by the radioactive decay of radium, directed normally onto a sheet of very thin gold foil (~ 4×10–7 m thick) in an evacuated chamber (Fig. 1). Alpha particles produce a tiny, but visible flash of light when they strike the fluorescent zinc sulphide screen, which is used as a detector, at the focus of a microscope; the screen and microscope could be swivelled around the foil to observe particles deflected at any given angle. Figure 1: (Left) Schematic diagram of the apparatus used by Geiger and Marsden to test Ernest Rutherford’s atomic model. (Right) The actual apparatus. Figure 2: Possible paths of scattered α-particles most of the α- particles deviated through small angles α-particle deviated through angles > 90o [very small percentage (0.01%)] gold nucleus scatter angle θ b d

Dunman High School (Senior High Physics Department) For Internal Use Only Page 3 of 33 Rutherford’s α-particle scattering experiment: Observations 1 Most of the α-particles were deviated through small angles. 2 A small but significant percentage of the α-particles were deviated through angles larger than 90o, (Fig. 2). Rutherford’s α-particle scattering experiment: Inferences Observation Inference Most of the α-particles were deviated through small angles. A smaller but significant percentage of the α- particles deviated through large angles greater than 90°. Models for the atom Figure 3a: The quantum mechanical model of an atom, in this case, helium. The quantum mechanical model is based on mathematics. Alt