2.5 Atomic & Nuclear Physics

1. 2.5 Atomic & Nuclear Physics 3 Credits - Internal

2. Rutherford’s Model of the Atom Planetary Model Ernest Rutherford (1871 – 1937)

3. Rutherford’s Model of the Atom Protons have a positive charge which is equal to the negative charge of the electron. The neutron has no charge. Protons and neutrons are nuclear particles called nucleons.

4. Rutherford’s Model of the Atom In a stable nucleus, nucleons are bound together by very strong balanced forces. Attraction: Nuclear Force Repulsion: Electric Force

5. Rutherford’s Model of the Atom Splitting a nucleus frees up a large amount of energy (nuclear Power) Adding or removing electrons within their orbits (ionisation) also involves energy but much less than nuclear energy. (chemical energy)

6. Composition of the Atom - Nuclides the number of nucleons in the nucleus Mass Number A A = Z + N Chemical Symbol Atomic Number Z the number of protons in the nucleus (determines the type of element) The neutron number Nis the number of neutrons

7. Composition of the Atom Mass Number A Examples of Nuclides: 4 20 Chemical Symbol He Ne 2 10 Atomic Number Z A nuclide is a symbolic way of showing mass number and atomic number A = Z + N

8. Periodic Table of the Elements

9. Complete the following data table isotopes 4He 14N 24Mg 32S 40Ar 38Ar 2 7 18 18 12 16 4 24 32 38 14 40 18 18 2 7 12 16 20 2 7 12 16 22 7 12 16 18 2 18 A A = Z + N Ch Z

10. atoms of the same element that have a different number of neutrons

11. Nuclei of three naturally occurring isotopes of the element hydrogen 1 2 3 H H H 1 1 1

12. Electrons are arranged in orbital shells (energy levels) The innermost shell can take up to 2 electrons. The next two shells can take up to 8 electrons each 23 Na 11 The centripetal force holding the electrons in circular orbit is the electric force

13. Electrons are arranged in orbital shells (energy levels)

14. Draw a diagram of the structure of the following atoms 24Mg 32S 14N 12 16 7

15. Radioactivity Some elements or isotopes are less stable than others and can spontaneously emit particle or wave radiations from their nuclei 4 240 236 + He Pu U 2 94 92 Nuclear Equation

16. Radioactivity Conservation of Mass Number (A) Conservation of Atomic Number (Z) 4 238 234 + + γ He U Th 2 92 90 heavy nucleus new element alpha particle gamma radiation

17. Radioactivity Complete the following Nuclear Reaction Equations 214 4 218 + He Alpha particle Po Pb 2 84 82 99 99 0 + Beta particle Tc Ru β 43 44 -1

18. Radioactivity Complete the following Nuclear Reaction Equations 6 1 4 9 1 + + He Li Alpha particle Be H 2 4 1 3 42 42 0 Beta particle + K Ca β 20 19 -1

19. 3 Types of Radiations 4 Alpha particle α a high speed helium nucleus Beta particle β a high energy electron formed when a neutron splits into a proton and an electron Gamma waveγ a very short wavelength (high frequency) electromagnetic wave. He 2 0 β -1

20. Ionization and Radioactivity These radiations have the ability to ionise atoms (knock out electrons from their orbits) to produce ions Alpha particleα strong ionisers (heavy and slow) but can be stopped by paper Beta particle β less ionising, more penetrating (lighter, faster) can be stopped by metal foil Gamma particle γ least ionising but travel quickly. Dense materials such as concrete or lead can stop them To prevent radiation, shielding of varying thickness is used

21. Ionising Radiation Sources These radiations are charged particles that can cause the atoms they encounter to become charged

22. can travel a few cm in air, absorbed by paper particulate radiation 4 He High 2 up to 1 m in air, absorbed by aluminum sheet 0 particulate radiation Med e -1 hardly affected by air, partially absorbed by concrete, lead γ electromagnetic radiation Low

23. Half Life The half life of a radioactive element is the time it takes for half of the atoms in a sample to decay 0 – all nuclei are intact. Sample is most active 1 – after 1 half life (8 days), one half of the nuclei have decayed (16 g) leaving the other half intact. Radiation emitted is now half its initial level. 2 – after 2 half lives (16 days) three quarters of the nuclei have decayed (24g) leaving a quarter intact. e.g. Consider a 32g sample of iodine – 131 with a half life of 8 days.

24. Half Life Result is an exponential decay curve 0 – all nulei are intact. Sample is most active (32g) 1 – after 1 half life (8 days), one half of the nuclei have decayed (16 g) leaving the other half intact. Radiation emitted is now half its initial level. 2 – after 2 half lives (16 days) three quarters of the nuclei have decayed (24g) leaving a quarter intact. 8 days

25. Nuclear Fission The process of splitting an atomic nucleus. Can be achieved by bombarding a nucleus with a high speed particle e.g. an alpha particle collides with a nitrogen nucleus to produce an oxygen atom & hydrogen atom 1 4 17 14 + + He O H N 8 7 2 1

26. Nuclear Fission e.g. a chain reaction where the neutrons produced in the first fission produce further fissions 92 1 141 1 235 + + + 3 n Ba Kr n U 56 92 0 0 36