A –Level Physics: Nuclear Physics Atomic Structure and Accelerators

1. A –Level Physics: Nuclear PhysicsAtomic Structure and Accelerators

2. Objectives:

3. FLASHBACK FLASHBACK: Calculate the force of friction acting upon an 80kg mass descending a 42° slope at a constant speed.

4. Starter Activity Using your knowledge from GCSE physics, outline the similarities and differences between (10mins): • Alpha radiation • Beta + radiation • Beta – radiation • Gamma radiation

5. You will have 60 secnds to attempt memorise this slide. Get ready!c Atomic Theory Timeline Democritus -400BC Existence of atoms first suggested. Atoms can be determined by their mass and combine to make compounds Dalton 1803 Plum pudding model. Negative electros are scattered throughout a positive ‘dough’ Thomson 1906 Nuclear model. Charge mostly concentrated in a central core. Most of the space is empty with electrons orbitting 1911 Rutherford 1913 Electrons limited to specific energy orbits they can jump between Bohr

6. You can speed up the motor by: • Increasing the current • Increasing the length of wire (number of turns) • Increasing the magnetic field Now attempt to recreate it! Atomic Theory Timeline Democritus -400BC Existence of atoms first suggested. Atoms can be determined by their mass and combine to make compounds Dalton 1803 Plum pudding model. Negative electros are scattered throughout a positive ‘dough’. Disproved by rutherford Thomson 1906 Nuclear model. Charge mostly concentrated in a central core. Most of the space is empty with electrons orbitting 1911 Rutherford 1913 Electrons limited to specific energy orbits they can jump between Bohr

7. Alpha Particle Scattering Experiment

8. Alpha Particle Scattering Experiment Rutherford (Geiger and Marsden) • Fired Alpha Particles at a thin piece of gold foil • Different deflection angles proved the structure of atoms Most of atom is empty space 0-10° Deflection Central concentration of charge 10-90° Deflection Most mass is concentrated in centre 90-180° Deflection

9. Chadwick’s Discovery of the Neutron The alpha particle experiment proved the existence of a centralised ball of mass and charge. However, this experiment did not explain why the mass number was so much greater than the proton number. In 1930, Irene Joliot-Curie and her husband found that alpha particles striking berrylliumwould cause it to give off unknown radiation. This radiation could then knock off protons out of paraffin. What does this observation tell us about this unknown radiation? They thought that the radiation could be gamma. Why could this not be the case? What law does this breach? By considering the conservation of momentum and kinetic energy in the collisions. They concluded that the radiation was a neutral particle with a mass 1% greater than a proton. A neutron

10. Nuclear Structure MINI quiz • Label the Atomic Mass • Label the Atomic/Proton Number • Explain what an Isotope is • Which quantity is labelled ‘Z’ and which is labelled ‘A’? • Explain why the atomic mass of chlorine is 35.5

11. Exam Question Discuss the experimental findings that lead to the modern understanding of nuclear structure (8 marks)

12. Exam Question Discuss the experimental findings that lead to the modern understanding of nuclear structure (6 marks) • MARK SCHEME: • Dalton determined atoms can be distinguished by their mass • Reference to (Thompson’s) plum pudding model • Alpha Particle Scattering Experiment aimed alpha particles at gold nuclei/thin gold foil • Different deflection angles AND an explanation of the result (proved a centralised mass and charge) • Chadwick’s discovery of the neutron AND explanation of alpha particles striking berryllium

13. Electron Beams (Cathode Ray) Energy= ½ mv2 = eV Remember electrons can be accelerated . We often have to look at the acceleration by an electric field, just like in a particle accelerator! ½ mv2 = eV This can be rearranged into: How fast would an electron move if accelerated from rest through a p.d. of 1200V? NB: mass of electron= 9.11x10^7ms-1

14. Electron Probes Electron beams can be fired at crystal structures producing a scattering pattern which tells us about the structure of the crystal. Davisson and Germer proved that unlike the alpha particle scattering experiment, a beam through a crystal forms a diffraction pattern. This was experimental evidence to support De Broglie law as the beam (of particles) was behaving as a wave! The experiment proved that this diffraction pattern only gets produced when the beam’s electrons have a wavelength coinciding with the DeBroglie wavelength (wavelength=h/p)