1. Radioactive Decay, Fission, and Fusion
Nuclear Chemistry
Radioactive Decay, Fission, and Fusion

2. Discovery of Radioactivity
William Roentgen -(1895) found that it was possible to use EM waves to produce an X- ray

3. Henri Becquerel – Found that certain materials phosphorescence (glows in the dark) after being exposed to sunlight

5. Marie and Pierre Curie – took pitch blend (uranium ore) and discovered it contained Po and Ra

6. Isotopes
Isotopes – Atoms of the same element with different number of neutrons
Radioisotopes – isotopes of atoms with unstable nuclei

7. Nuclear Fission
A very heavy nucleus splits into more stable nuclei of average mass
This process can occur spontaneously or when nuclei are hit by particles
A chain reaction can take place if the nucleus releases more neutrons
Nuclear reactors use controlled fission chain reactions to produce energy

8. Nuclear Fission
Subcritical mass – If the mass is so small that it will not sustain a chain reaction
Critical mass – A sample that has enough mass to sustain a chain reaction
Supercritical mass – Too much mass is there and the reaction escalates rapidly leading to a violent nuclear explosion

9. Nuclear Fission

10. Chernobyl
A reactor at the plant exploded on April 26, 1986; as a result of the explosion and ensuing fire, clouds of radioactive particles were released.
There were 56 direct deaths and it’s estimated that as many as 9,000 people, among the approximately 6.6 million most highly exposed, may die from some form of cancer.

11. Nuclear Fusion
Light mass nuclei combine to form a heavier, more stable nucleus
Fusion releases more energy than fission

12. Nuclear Fusion
The energy released by the sun is caused by the combining of four hydrogen nuclei to form a helium nuclei (fusion under high pressure and temperature)

13. Nuclear Fusion
Uncontrolled fusion reactions of hydrogen are the source of energy for the hydrogen bomb.

14. Radioactive Decay
The spontaneous break down of a nucleus into a lighter nucleus, followed by the release of particles, electromagnetic radiation (waves) or both.

15. 3 Types of Decay
Alpha- the release of two protons and two neutrons bound together as a helium nucleus
Beta- the conversion of a neutron to a proton and electron with the release of the electron
Gamma- the emission of high-energy electromagnetic waves as a result of an atom returning to its ground state

16. Penetration Power

17. 3 Types of Decay Alpha (ά) – a helium atom Beta (β) – an electron
Positron – a positive electron

18. Other Particles Neutron
Gamma (γ) – pure energy; called a ray rather than a particle

19. Alpha Decay

20. Beta Decay

21. Gamma Decay
Gamma emission usually occurs immediately following other types of decay. (Excess energy given off after alpha or beta decay)

22. Practice Problems Show the equation for the alpha decay of 9Be.
Show the equation for the beta decay of 239Np.

23. Practice Problems Radon – 222 under goes electron capture.
C-12 goes through positron emission

24. Practice
Radon – 222 combines with a neutron to form a proton and what else?
An unknown substance breaks apart to form C-14 and an electron.

25. Transmutation
The conversion of one atom to an atom of another element.
Particle Accelerators or atom smasher – LHC (Large Hadron Collider) is a particle accelerator that uses induced transmutation
started up on 10 September 2008
Located: outside Geneva Switzerland
LHC consists of a 27-kilometer ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way

26. 4 Miles Around

31. Half-life No two radioactive isotopes decay at the same rate
Half-life (t ½) is the time required for half of the atoms of a radioactive isotope to decay
Radioisotope
Half-life
Polonium-215
seconds
Bismuth-212
60.5 seconds
Sodium-24
15 hours
Iodine-131
8.07 days
Cobalt-60
5.26 years
Radium-226
1600 years
Uranium-238
4.5 billion years

32. Radiochemical Dating
The process of determining the age of an object by measuring the amount of a certain radioisotope remaining in that object.
Carbon 14 dating
Uranium 238 dating

33. Half-Life Problems
1) A patient was administered 20 mg of iodine. How much of the isotope will remain in the body after 40 days if the half life of iodine is 8 days?
2) Hydrogen – 3 is a radioactive isotope with a half-life of 12.3 years. How long would it take a for a 40 g sample to decay down to 2.5 g?

34. Practice Problems
Chromium-48 has a short half-life. What is the half life if the sample is out for 108 hours and the sample begins with 360 g of chromium-48 and decays to g?
U‐238 has a half‐life of 4.46 billion years. How much U‐238 was present initially if 2 grams remains after 13.4 billion years?