Nuclear Processes

1. Nuclear Processes

2. In chemical reactions, electrons in atoms are responsible for bonds forming and being destroyed. The identity of the atoms involved does not change

3. This is not true for nuclear processes. These reactions involve the protons and neutrons in the nucleus – too large or too small of a ratio between protons and neutrons

4. There are two types of nuclear reaction Fission and Fusion Reactions

5. Fission Reactions • Usually involve atoms with large nucleii such as the Lathanides and Actinides • They produce ,  and  emissions. • Involve a nucleus collapsing to form a smaller nucleus

6. Fusion Reactions • These involve nuclei joining together to make larger ones. • These type of reactions are what go on inside stars and provide the energy that causes them to shine.

7. The  particle • Is emitted from a nucleus during radio active decay due to too many protons • Consists of 2 protons and 2 neutrons (a helium nucleus) • Decreases mass by 4 and atomic # by 2

8. 241Am95 237Np93 + 4He2 • 4.0 cm of air • Low penetration -protected by skin • Is the most destructive radiation because it ionizes atoms it bumps into • Relative danger is low unless ingested • Used in smoke detectors

9. An  decay reaction The Uranium atom U23892 decays by  particle emission 238 234 4 U He ? + 2 92 90 What is represented by ?

10. An  decay reaction The Uranium atom U23892 decays by  particle emission 238 234 4 U He Th + 2 92 90 Th is thorium – we can work it out by using the periodic table and looking up the atom with atomic number 90. The mass number does not matter – it is simply an isotope of Th.

11. More  decay reactions The Thorium atom Th22790 decays by  particle emission 227 Th Complete the equation 90

12. More  decay reactions 227 223 4 Th He Ra + 2 90 88

13. More  decay reactions The Actinium atom Ac22589 decays by 3  particle emissions 225 Ac Complete the equation 89

14. More  decay reactions 213 225 4 Ac 3He Bi + 2 89 83

15.  Particle emissions  Particles are electrons but they do not come from the electron shells which surround the nucleus – they come from the nucleus itself. Due to neutron to proton ratio being too great. The electron is emitted when a neutron sheds its negative charge and becomes a proton. (Bet you didn’t know it could do that!) 10N 11 p 0-1

16. Tritium decay (beta)

17.  Particle emissions The effect of  Particle emission is to increase the proton count by 1 while leaving the overall mass unchanged. 231 0 231 Th  Pa + -1 90 91 Notice how  particle emission raises the atomic number by 1

18.  Particle emissions • Can penetrate 6-300 cm of air • Blocked by clothing and paper • Moderate danger • Excessive exposure can be harmful • Used in many medical diagnostic tests and treatments

19. Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma radiation.

20. Gamma Ray Emission • Gamma rays have no mass and no charge – may accompany  and/or  emissions • High energy and very penetrating • May be stopped with very thick (6 ft. or so of concrete) or 3-5 cm of lead (think about the dentist) • γ00 or 00γ • Used for medical tests and treatments • Sterilization of equipment & foods

21. Electron Capture • Sometimes a nucleus will capture an electron and a proton converts to a neutron. • This decreases the atomic number but does not change the mass • 201Hg80 + 0-1e  201Au79 + γ00

23. Positron Emission • A positron has the mass of an electron and the charge of a proton – it’s kind of like a “positive electron” • It may be emitted when a proton turns into a neutron • Atomic number decreases and mass stays the same. • 22Na11 0+1e + 22Ne10

25. Decay Series When a radioactive nucleus such as 238U92 decays it often produces another radioactive isotope which goes on to decay further. You are going to construct a decay series on graph paper for the element 238U92to show how it eventually forms a stable isotope of lead 206Pb82

26. GET A PIECE OF GRAPH PAPER • Draw a vertical axis representing atomic mass. It will need to run from 200 to 240 • Draw a horizontal axis representing atomic number. It will need to run from 78 to 93. • Position the isotope U23892 on your graph and mark it clearly.

27. 240 * 238U92 Mass 200 78 93 Atomic Number

28. Plotting an  decay • The nucleus gives off an alpha particle first to form a new nucleus • Work out what the new nucleus is • Find the nucleus on your graph and add it in • Join the points with an arrow

29. 240 * 238U92 234Th90 * Mass 200 78 93 Atomic Number

30. Plotting a beta emission • The Thorium next loses a Beta particle • Work out what would be formed • Add the nucleus onto your chart

31. 240 * U23892 Th23490 * * Pa23491 Mass 200 78 93 Atomic Number

32. Building up the decay series Continue to build up the series using the following emissions. Each alpha emission is shown as a diagonal to the left and each beta emission is a horizontal line to the right. If you are successful you should end up with Pb20682 Good Luck !

33. Emission sequence (including the first two example emissions) •  •  •  •  •  •  •  8.  9.  10.  11.  12.  13.  14. 