Half-Life, Nuclear Fission and fusion

1. Half-Life, Nuclear Fission and fusion

2. Half-Life • amount of time it takes for half of a given sample to decay. • Each half-life, half of the sample decays and half remains. • Half lives vary from billionths of a second to billions of years.

3. Half-Life: Equation Form • How do we put this into equation form? • Let t1/2 = the half-life of the isotope • Ending Amount=Amount of isotope that is left at end • Starting amount= the amount of isotope at the beginning before it starts to decay • T= the amount of time that has passed ln (ending amount/starting amount) = -(0.693/t1/2)T

4. Nuclear Reactions - Fission • If nucleus too big - nuclear fission. • “fissions” (breaks up) into several smaller nuclei (and usually some extra neutrons as well). • not easily predicted. • Often initiated by absorbing a neutron. • Example: 92235U + 01n --> 56141Ba + 3692Kr + 3 01n

5. Nuclear Energy - Fission • Energy can be harnessed. 92235U + 01n --> 56141Ba + 3692Kr + 3 01n The neutrons collide with other atoms of 235U, split, producing more neutrons . . . causing a chain reaction. • The energy given off can be harnessed to produce electricity (or, unfortunately, for more destructive purposes).

8. Nuclear Energy - Fission

9. Nuclear Weapons

10. Nuclear Waste

11. Nuclear Fusion • The opposite of nuclear fission is fusion, when smaller nuclei come together to form larger nuclei. • Example: 11H + 13H --> 24He • The fusion of hydrogen to form helium is the source of energy for the sun and many other stars.

12. Nuclear Energy - Fusion • Release even more energy than fission. • emitted by stars (mostly hydrogen fusing to form helium). • no safe way yet to harness fusion • takes too much energy to get started

13. Energy in Radioactive Decay • Radioactive Decay generally gives off large amounts of energy. • Where does it come from? • The answer lies in something called “mass defect.”

14. Mass Defect • Law of Conservation of Mass • Mass cannot be created or destroyed. • Law of Conservation of Energy • Energy cannot be created or destroyed. • But, during nuclear reactions: • Mass can be converted into energy and energy can be converted into mass.

15. Mass Defect • During nuclear reaction, some mass is either lost or gained. This change in mass is called the mass defect (Dm). • Dm = mass of products - mass of reactants • The relationship between the mass defect and the amount of energy given off or absorbed (DE) is DE = Dmc2 where c = the speed of light = 3.0 x 108 m/s.

16. Mass Defect DE = Dmc2 • Example: If 0.01g of mass is converted into energy, 9 x 1011 J of energy is given off. That’s enough to heat 2.7 million liters of water from room temperature to boiling! • By comparison: you would need to burn 16 million grams of methane to give off the same amount of heat.

17. Common Uses of Radioactivity • Food Irradiation • Archaeological Dating • Medical Detection • Medical Treatment

18. Daily Exposure to Radiation • Cosmic rays • Radon gas • Smoke detectors

19. Detecting Radiation • Geiger Counters • (beta) • Scintillation Counters • (alpha, beta and gamma) • Film • (beta, gamma)