Atomic: Nuclear Reactions 2018

1. Atomic: Nuclear Reactions 2018 Unit 4: Physical Science 10.1-2, 4 Geo Ch21.2-4

2. Nuclear Chemistry Nuclear Decay Nuclear Reactions Alpha Decay Beta Decay Gamma Decay Fission Fusion + -

3. Smaller elements neutron to proton ratio is 1:1 to be stable isotopes • Example: Helium, Nitrogen, Oxygen • Heavier elements neutron to proton ratio is 3:2 to be stable isotopes • Example: Iron, Nickel, Copper, Zinc • Larger nuclei tend to be unstable – all nuclei containing more than 83 protons are radioactive • All elements with more than 92 protons are synthetic and decay soon after they are created (UNSTABLE) • Nuclei of any isotopes that differ much from these ratios are unstable, whether heavy or light Golden Ratio: Stable and Unstable Nuclei

4. Physics - Radioactivity: The Discovery of Radioactivity • When a nucleus becomes unstable, it is said to be radioactive. It decays releasing particles and energy called nuclear radiation • Some radiation is more powerful than others • There are four types of nuclear radiation – • alpha (α) – made of 2 p+ and 2 n0 • beta (β- and β+) • n0decays into p+ and e- (beta minus) • p+ decays into n0and e+ (beta plus) • gamma (γ) – no mass or charge, just energy Radiation Types of Radioactive Decay (great resource comparing/contrasting)

5. What kind of decay will occur?

6. γ or α β 0 0.0005 0 -1, +1 4 Types of Radiation, cont

7. Prior Knowledge Isotope Notation

8. Alpha Decay • Alpha radiation is made of alpha particles • Alpha particles are made of two protons and two neutrons (a Helium atom!) • They are represented by: α • Properties: • Large size • Cannot pierce deep into matter – easily stopped by a thin layer of material • When alpha decay occurs, the nucleus loses 2p+ and 2n0 • Atomic number is 2 less • Mass is 4 less

9. Beta Decay (+ or -) • Beta radiation is made of beta particles • Beta particles are made of a high energy electron • They are represented by: β+ or β- • Properties: • Small and light • Move fast • Can only be stopped by thick materials, like stacked sheets of metal, blocks of wood or heaving clothing • When Beta + decay: a proton turns into a neutron and a β+ is emitted • Atomic number is 1 less • Mass number is same • When Beta - decay occurs, a neutron changes into a proton and a β-is emitted • Atomic number is 1 more • Mass number is same

10. Gamma Decay • Gamma radiation is made of gamma rays • Gamma rays are a high-energy form of electromagnetic radiation • They are represented by: γ • Properties: • No mass or charge • Can pass through most types of materials – need a material thicker than blocks of concrete • When gamma radiation occurs, only energy is given off • Usually occurs along with another type of decay • Atomic number is same • Mass number is same

11. Spontaneous: you cannot predict when each atom will decay • Random: you cannot predict which atom will decay • But, each radioisotope has a predictable half-life • Half-life: amount of time it takes for half of the nuclei in a radioactive isotope to decay • Original, unstable substance = parent • New, (stable or unstable) substance = daughter • After 1 half-life 50% of parent isotopehas decayed into a daughter isotope • Overall rate of decay is constant • This allows you to predict when a given fraction of the sample will have decayed Half-Life

12. Half-Life Values and Graph

13. ½ or 1:1 ratio ¼ or 1:3 ratio 1/8or 1:7 ratio Half-Life Values and Graph

14. Carbon 14-Dating • Carbon-14 is widely used to determine the ages of fossils • All organisms take in carbon during lifetime • Most of this carbon is the isotope carbon-12 • 1 in every million is the radioisotope carbon-14 • When an organism dies, carbon is no longer being taken in • The amount of carbon-14 slowly decreases • the half-life of carbon-14 is short compared to ages of many fossils and geological formations • Objects more than 60,000 years old cannot be dated using carbon-14 radiocarbon dating

15. Check for Understanding What fraction of the parent isotope is left after 9 half-lives? What is the half-life of the element below?

16. Practice Example Problem: 228Ac has a half life of 6.0 hours. How much of a 5.0 mg sample would remain after one day (24 hours)? The first step is to determine the number of half lives that have elapsed. number of half lives = total time / half-life = 24 hours/6.0 hours = 4.0half lives For each half life, the total amount of the isotope is reduced by half. Amount remaining = Original amount x half-life % = 5.0 mg x 6.25%= 0.31 mg

17. Practice • Americium-242 has a half-life of 6.0 hours. If you started with 24 g and you now have 1.5 g, how much time has passed? 24 g  12 g  6.0 g  3.0 g  1.5 g1st ½ 2nd ½ 3rd½ 4th ½ 4.0 ½ lives x 6.0 hrs= 24 hrs • The half-life of cobalt-60 is 5.0 years. If you have 10. grams of Co-60, how much do you have after 15 years? 15 years ÷ 5.0 years = 3.0 half lives 10. g  5.0 g  2.5 g  1.25 g1st ½ 2nd½ 3rd ½

18. Nuclear Fission – the process of splitting a nucleus into two nuclei with smaller masses • Chain reaction – ongoing series of fission reactions • Critical mass – the amount of fissionable material required so that each fission reaction produce approximately one more fission reaction • Nuclear Fusion – two nuclei with low masses are combined to form one nucleus of larger mass • Fission and Fusion Video (~4 minutes) KEY TERMS:Ch 10.4 Nuclear Reactions

20. Fission means “to divide” • The process of splitting a nucleus into two nuclei with smaller masses • This occurs when a neutron hits the nucleus of an atom • Only large nuclei can undergo fission reactions • Two uses from book: generate electricity, nuclear weapons • The total mass of the products is slightly less than the mass of the original nuclear and the neutrons that break free • The missing mass is converted into large amounts of energy Nuclear Fission

21. Lighter element Neutrons + Energy Neutron Uranium - 235 Lighter element Nuclear Fission

22. Chain reactions are continuing series of reactions in which each produces a product that can react again • If chain reaction occurs too quickly, explosions occur, releasing a lot of energy all at once energy energy energy energy Nuclear Fission energy energy

23. Fission of Uranium-238

24. Nuclear Fusion • Fusion = combine • Nuclear Fusion is when two or more nuclei combine to form a larger nucleus (requires very high temps to overcome the repulsive forces) • The sun uses this process to produce energy • It fuses hydrogen into helium • The problem lies in the energy involved to start fusion • Most nuclei that can undergo fusion are fairly unreactive • Energy given off (output) does not outweigh the energy needed (input) • Hydrogen Bomb • Just like in fission, a small amount of mass is converted into a large amount of energy

25. Fusion of Hydrogen into helium

26. positron energy neutrino positron Nuclear Fusion energy neutrino

27. Think back to the law of conservation of energy • We need to include mass in this law when talking about fission and fusions reactions • This relationship is shown by Einstein’s theory of relativity • This states that energy and mass are equivalent and can be converted using the equation E=mc2 Energy to Mass Conversions

28. What type of nuclear reaction shown below? • Write an equation for the reaction. You only need to include the symbol and mass number. • What type of nuclear reaction is shown below? Extra Practice

29. Extra Practice Gold-198 has a half-life of 2.7 days. How much of a 96 g sample of gold-198 will be left after 8.1 days? What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 20.0 s? (Hint: 12.5 is 12.5% of 100.0, so figure out what fraction that is!) The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed?

30. Review: Types of Radioactive Decay and Nuclear Equations Videos: Types of Radioactive Decay and their effects on the Nucleus Balancing Nuclear Equations and Predicting Products of Nuclear Reactions