Bellringer

1. Bellringer • Collect your homework from last week. • Save it for reference material later.

2. Objectives • Be able to explain how a nucleus stays together. • Use the mass defect principle to solve sample problems and fix the Earth’s energy crisis.

3. Light and Astronomy Tests • I have one more question to grade. • Should be done by tomorrow…maybe. • James, Lexis, Colin, Meghann, and Ryan still need to make up part(s) of the exam.

4. Homework • Complete these multiple choice questions for homework. • Due this Thursday. • If you’re not going to be here on Thursday you will turn it in on Wednesday. • Complete on your own without the help of your notes or the internet. • You will receive full credit for turning in a completed answer sheet on time.

5. Modern Physics Our Final Chapter

6. Ernest Rutherford • An atom has a positively charged small dense nucleus surrounded by a nearly massless cloud of electrons • Left no information about the actual structure of the nucleus

7. Henry Moseley • A member of Rutherford’s team • Found the magnitude of the nuclear charge during X-ray scattering experiments. • Results showed that the positively charged protons accounted for roughly half the mass of the nucleus.

8. James Chadwick (English, 1932) • Discovered the neutron, a neutral particle with a mass similar to that of a proton. • Accounted for the missing mass. • Protons and neutrons are collectively referred to as nucleons.

9. Atomic Mass Unit • Protons and neutrons have the same rest mass • 1 proton (mass) > 1800 electron (mass) • =1 atomic mass unit • It is defined as one twelfth of the mass of an unbound neutral atom of carbon-12

10. Chem refresher • Open to page 802 and start reading at the section titled “Protons and neutrons” stop reading on page 804 before “The Strong Force” • Hold onto your textbook when you’re done reading.

11. Reading Questions • If the nucleus of an atom is extremely dense why are atoms not extremely heavy? • How is it possible for atoms to have a listed mass that isn’t a whole number? • What is an isotope? • What determines which element an atom is? • What is your favorite element and why?

12. Atom Movie • Can we see an atom? • Making of the movie • https://www.youtube.com/watch?v=xA4QWwaweWA&src_vid=oSCX78-8-q0&feature=iv&annotation_id=annotation_211263 • The movie • https://www.youtube.com/watch?v=oSCX78-8-q0

13. Bellringer – 2 mins to hand in • A soccer ball is kicked into the air at an angle of 35 degrees from a level field. It has an initial vertical velocity of 15m/s. What is its final vertical velocity right before it hits the ground somewhere else on the field? DO WORK STOP

14. Objectives • Understand how to calculate the mass defect and the binding energy of nuclei. • Know the three types of radiation. • Look into a career in nuclear physics.

15. The Nucleus • Protons and electrons are attracted to each other by the electromagnetic force. • Why are protons attracted to neutrons? • Why are protons not repelled from other protons?

16. The Strong Nuclear Force • When any pair of nucleons gets within about a protons radius of each other, they experience an attraction that is more than 100 times stronger than the electromagnetic force. • Aka the strong force

17. The Strong Nuclear Force • An attractive force that keeps nucleons together in the nucleus. • The strong force has the same strength between all nucleon pairs. • See Figure 4 in the textbook.

18. Missing Mass • The mass of an assembled nucleus is less than the sum of the masses of the protons and neutrons that compose it. • An actual helium atom with four nucleons has a mass of 0.029279u less than the mass of its constituent parts.

19. Mass Defect • This difference between the sum of the masses of the individual nucleons and the actual mass is called the Mass Defect. • Why does this happen?

20. Albert Einstein • He showed that mass and energy are the same thing. • To pull a nucleon out of a nucleus, you have to do work to overcome the strong nuclear force. • Doing work adds energy to the system • So, the system of separated protons and neutrons has more energy than the assembled nucleus.

21. Albert Einstein • This energy difference between separated nucleons and the assembled nucleus is the binding energy of the nucleus. • The binding energy can be expressed in the form of an equivalent amount of mass.

22. Energy Equivalent of 1u • Hence, each atomic mass unit of mass is equivalent to 931MeV of energy.

23. Practice • I have a mass of 76kg. What is my equivalent energy?

24. Practice • I buy about 290kWh of energy every month from NYSEG. What is the mass equivalent of this energy?

25. Practice • The world uses about a year. What is the minimum amount of mass we could use to produce this energy? • That’s about the mass of 4 cars…

26. The Real Mass of Protons and Neutrons • The mass of protons and neutrons can change depending on how they are bonded. • The Atomic Mass Unit from earlier is based off of the stable carbon atom, not a single nucleon. • A single proton has a mass of 1.007276u • A single neutron has a mass of 1.008665u

27. Mass Defect and Binding Energy • Page 806, numbers 5, 6, and 8 • Mass of Hydrogen includes one proton and one electron

28. Bellringer – 2 mins to hand in • A soccer ball is kicked into the air at an angle of 35 degrees from a level field. It has an initial vertical velocity of 15m/s. What is its final vertical velocity right before it hits the ground somewhere else on the field? DO WORK STOP

29. Objectives • Understand how to calculate the mass defect and the binding energy of nuclei. • Know the three types of radiation. • Look into a career in nuclear physics.

30. Answers • a) -0.098940u b) -92.161MeV • a) -0.002388u b) -2.2244MeV • Skip it • a) -0.137005u; -0.148410u b) -127.62MeV; -138.24MeV c) The nucleus of O18 has more nucleons than O16 and therefore experiences a larger strong force. Thus, O18 is more tightly bound and has a more negative binding energy.

31. Radioactive Decay • In 1896 Henri Becquerel discovered that uranium emits some type of light that fogged his photographic plates. • In 1909 Ernest Rutherford was able to identify the radiation Becquerel found as the helium-4 nuclei.

32. Radioactive Decay • Nuclei that emit particles and energy are said to be radioactive. • A material that emits particles is also said to decay. • Nuclei decay naturally in order to become more stable.

33. Types of Radiation • Rutherford and his team found uranium produced three kinds of radiation. • Classified by how easy it was to stop. • Alpha, Beta, and Gamma Radiation

34. Alpha Radiation • Alpha particles are helium nuclei • The emission of an particle from a nucleus is a process called alpha decay. • Only occurs in nuclei with at least 106 nucleons.

35. Beta Radiation • Beta particles are electrons emitted by the nucleus. • Beta Decay occurs when a neutron changes to a proton or a proton changes to a neutron within the nucleus. • Total charge of the nucleus must be maintained. • So if a neutron becomes a proton the nucleus must also create and electron to emit and balance the charge.

36. Gamma Radiation • Gamma rays are high-energy photons emitted by the nucleus during gamma decay. • Gamma Decay occurs when there is a redistribution of energy within the nucleus and a gamma ray is emitted. • Often accompanies alpha and beta decay.

37. Checkpoint • What are the three types of radiation and how are they different?

38. Nuclear Reaction • Whenever the energy, number of neutrons, or number of protons in a nucleus changes, the resulting event is called a nuclear reaction. • Some nuclear reactions release energy, while others need energy to happen.

39. Nuclear Fission • Enrico Fermi and Emilio Segre (Italians 1934) came up with the idea of bombarding uranium with neutrons to see what happened. • Otto Hahn and Fritz Strassmann (Germans 1939) showed that the resulting atoms acted chemically like barium • One week later Lise Meitner and Otto Frisch proposed that this started a chain reaction that broke uranium into two smaller nuclei and released a large amount of energy.

40. Nuclear Fission • The division of a nucleus into two or more fragments is called fission. • The right side has a total mass 0.186u less than the left. This mass becomes of kinetic energy.

41. Nuclear Fission • Fission is causes a chain reaction because the three new released neutrons trigger further fission

42. Controlling Fission • To harness this energy in a useful form we need to control the rate of the reaction. • Speed of neutrons, amount of fissionable uranium. • Nuclear power plants use fission to create energy.

43. Bellringer – 2 mins to hand in • What is the mass equivalent (in atomic mass units) to 3204MeV? DO WORK STOP

44. Objectives • Understand the difference between fission and fusion nuclear reactions. • Explain where everything in the universe came from.

45. Nuclear Reactors • Nuclear power plant tour • https://www.youtube.com/watch?v=_AdA5d_8Hm0

46. Nuclear Reactors • Cadmium metal are placed between the uranium rods to control the reaction rate because cadmium absorbs neutrons easily. • The uranium rods need to be replaced about once a year. • Empty rods are still extremely radioactive and must be stored in very secure locations. • Methods of permanently storing these radioactive waste products are currently being developed.

47. Nuclear Bombs • All nuclear bombs use fission to release a mass amount on energy very quickly. • Some have “Fusion Fuel” in them to release even more damage. • “Little Boy” and “Fat Man” are the only two ever to be dropped during war.

48. Little Boy - Uranium • 64kg of uranium was used to cause the explosion. • It exploded with an energy of 16 kilotons of TNT

49. Fat Man – Plutonium • 6.2kg of Plutonium was used to cause the reaction. • It exploded with an energy of 21 kilotons of TNT • https://www.youtube.com/watch?v=5gD_TL1BqFg

50. Nuclear Fusion • In nuclear fusion, nuclei with small masses combine to form a nucleus with a larger mass. • In the process, energy is released • Why?