Journal 14. What is so dangerous about nuclear energy?

Transcription

1 Journal 14 What is so dangerous about nuclear energy?

2 Nuclear Chemistry Nuclear Chemistry Bravo 15,000 kilotons

3 Discovery of Radiation Wilhelm Conrad Roentgen had discovered X rays Pierre & Marie Curie Discovery of several radioactive elements Coined Radioactive Nobel Laureates Brainpop- marie curie

4 Radioactive decay All nuclei with atomic numbers greater than 83 are radioactive These nuclei have too many neutrons and too many protons to be stable So most undergo decay losing energy by emitting radiation

5 CA Standards Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know how the nucleus changes in each type of decay. Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in matter and have different penetrations. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in nuclear reactions.

6 Types of Radiation Radiation Alpha particles Beta particles Positron Gamma particles When we are looking at any type of radiation or radioactive decay we must remember that matter is conserved!

7 Nuclear Symbols Mass number (p + + n o ) Element symbol 235 U 92 Atomic number (number of p + )

8 Alpha Particle Emission 0 1 Beta Particle Emission 4 Symbol He 4 2 or α e 2 or β 0 1 Gamma Ray Emission 0 0 γ How it changes the nucleus Mass Heavy Light No Mass Decreases the mass number by 4 Decreases the atomic number by 2 Contains 2 protons and 2 neutrons Converts a neutron into a proton Send off a fast moving e- (β) Increases atomic number by 1 -High energy radiation just energy! (gamma rays) -No change to the nucleus -emitted with alpha & beta radiation Penetration Low Medium High Protection provided by Paper, clothing Cardboard, wood Lead Danger Low, slow moving Medium, fast High

9 Types of Radioactive Decay v alpha production (α, He): helium nucleus U He Th v beta production (β, e): Th Pa e v gamma ray production (γ): U He + Th γ

10 Alpha Radiation Alpha decay is limited to VERY large, nuclei such as those in heavy metals. (α, He): helium nucleus

11 Alpha particles in a reaction Alpha radiation is emitted from U U Th He Is matter conserved? Yes! Now you try! Alpha radiation is emitted from Rn Rn 84 Po+ 4 2 He Is matter conserved? Yes

12 Gamma particles in a reaction Th Ra He + γ When the alpha particle is released a huge amount of energy is also released (the gamma particle)!

13 Beta Radiation Beta decay converts a neutron into a proton and an e- (β) is released

14 Beta particles in a reaction C-14 is a beta emitter, show the decay process 14 6 C 14 7 N β What Happened? nàp+; so atomic mass is still 14 a new p+= atomic number of 7 (now N) A β-particle flies out of the atom 0-1 β is the same as 0-1 e

15 Now you try K Ca β What Happened? nàp+; so atomic mass is still 40 a new p+= atomic number of 20 (Ca) A β-particle flies out of the atom 0-1 β is the same as 0-1 e

16 Positron Particle Same mass as an electron Neutrons can be formed by protons that emit a positron They have a negligible mass Consequently they are more penetrating than alpha particles They have a charge of +1

17 Positrons in a reaction Potassium-38 will emit a positron, show the decay K Ar β What Happened? p+ à n; atomic mass is still 38 p+ à n; atomic number decrease by 1; 18 (Ar) A positron flies out of the nucleus Now you try 13 7 N 13 6 C β

18 CA Standards Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons. Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc 2 ) is small but significant in nuclear reactions.

19 Fission- big to small Fission - Splitting a heavy nucleus into two nuclei with smaller mass numbers.

20 Fusion Reaction- small to big Example:Deuterium Tritium Fusion - Combining two light nuclei to form a heavier, more stable nucleus.

21 Energy and Mass Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein s equation: ΔE = Δmc 2 Δm = mass defect ΔE = change in energy c = speed of light Because c 2 is so large, even small amounts of mass are converted to enormous amount of energy.

22

23 A Fission Reactor

24 Nuclear Stability Isotopes with low atomic numbers The stable ratio is 1 neutron to 1 proton Isotopes with high atomic numbers The stable ratio is 1.5 neutrons to 1 proton This creates the band of stability fig 28.6

25 Nuclear Stability and Decay Unstable isotopes will undergo decay to achieve a more stable ratio of neutrons to protons The type of decay depends on the ratio of neutrons to protons

26 Nuclear Stability Isotopes in Region A Have too many n, use beta decay to turn neutrons à protons Region C fig 28.6 Alpha decay Region A beta decay Isotopes in Region B Have too many p+, use positrons to turn p+ à neutrons Isotopes in Region C Have too many p+ & n use alpha decay to reduce the numbers Region B positron

27 Practice band of stability p 703 # 9 & 10

28 How can we use fission energy? We need to control the energy released 1) By converting energy to heat (power plant) The plant generates energy as heat Coolant removes heat from reactor core Steam is generated to drive a turbine The spinning turbine generates electricity 2) By releasing energy slower Neutron Moderation: slows the neutrons down Neutron Absorption: decrease neutrons that react This creates a manageable amount of useable power!

29 Nuclear Fusion small to big Fusion occurs when nuclei combine to produce a nucleus of greater mass Usually release more energy than fission Only take place at temps greater than 40,000,000 C Ex H e 4 2He + energy

30 Radiation in your life! Where do we use radiation? Energy Sources Disease Diagnosis Disease Treatment Biotech Tracers & Research Criminal Investigations Anthropological/Geological Dating

31 Radiation in your life! How do we measure your exposure level? Geiger counter Film badges