Nuclear Physics

1. Nuclear Physics EQ: How can the nucleus of an atom have the power to Be both destructive and advantageous to the world as we know it? Pg.88 https://www.youtube.com/watch?v=6lbjxk1Lexs

3. Where might we see radioactive materials in everyday life? Nuclear Energy Nuclear power plants use fission to make electricity. By splitting uranium atoms into two smaller atoms, the extra energy is released as heat. Uranium is a mineral rock, a very dense metal, that is found in the ground and is non-renewable. It is a cheap and plentiful fuel source. Power plants use the heat given off during fission as fuel to make electricity. Fission creates heat which is used to boil water into steam inside a reactor. The steam then turns huge turbines that drive generators that make electricity. The steam is then changed back into water and cooled down in a cooling tower. The water can then be used over and over again.

4. Where might we see radioactive materials in everyday life? Agricultural applications-radioactive traces Food irradiation Gamma rays of a radioisotopes (Cobalt-61) destroy many disease-causing bacteria as well as those that cause food to spoil Helps scientists to understand the detailed mechanism of how plants utilize phosphorous to grow an reproduce But what is radioactivity?

5. Nuclear Medicine Imaging is a test that produces pictures (scans) of internal body parts using small amounts of radioactive material. This test is used to provide images of organs and areas of the body that cannot be seen well with standard X-rays. • Some examples include: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT) and Cardiovascular Imaging.

6. What’s in a Nucleus • The nucleus of an atom is made up of protons and neutrons • each is about 2000 times the mass of the electron, and thus constitutes the vast majority of the mass of a neutral atom (equal number of protons and electrons) • proton has positive charge; mass = 1.007276 a.m.u. • neutron has no charge; mass = 1.008665 a.m.u. • proton by itself (hydrogen nucleus) will last forever • neutron by itself will “decay” with a half-life of 10.4 min • size of nucleus is about 0.00001 times size of atom • atom is then mostly empty space

7. Nuclear Notation

9. What holds it together? • If like charges repel, and the nucleus is full of protons (positive charges), why doesn’t it fly apart? • repulsion is from electromagnetic force • at close scales, another force takes over: the strong nuclear force • The strong force operates between quarks: the building blocks of both protons and neutrons • it’s a short-range force only: confined to nuclear sizes • this binding overpowers the charge repulsion

10. Strongest Weakest There are four fundamental forces in nature • Strong nuclear • Electromagnetic • Weak nuclear • Gravitational

11. Strong nuclear force • Binds the neutrons and protons in the nuclei of atoms together • Very strong, but only over very, very, very short distances (within the nucleus of the atom)

12. Electromagnetic force • Causes electric and magnetic effects • Like charges repel each other • Opposite charges attract each other • Interactions between magnets • Weaker than the strong nuclear force • Acts over a much longer distance range than the strong nuclear force

13. Weak nuclear force • Short range nuclear interaction that is involved in beta decay

14. Gravitational force • Weakest of all fundamental forces, but acts over very long distances • Always attractive • Acts between any two pieces of matter in the universe • Very important in explaining the structure of the universe

15. Remember… • The weak nuclear force is NOT the weakest of the fundamental forces. • GRAVITY is the weakest force, but most important in understanding how objects in the universe interact.

16. Einstein – Energy/Mass Equivalence In 1905, Albert Einstein publishes a 2nd major theory called the Energy-Mass Equivalence in a paper called, “Does the inertia of a body depend on its energy content?”

17. Einstein – Energy/Mass Equivalence states that mass is concentrated energy. In his theory of special relativity Einstein formulated the equation E=mc^2. There is a tremendous amount of energy in mass. A 20g marble contains as much energy as a 500 kiloton hydrogen bomb, but this energy is very difficult to release.. The large amount of energy comes from the fact that the speed of light is squared.

18. Mass Defect The nucleus of the atom is held together by a STRONG NUCLEAR FORCE. The more stable the nucleus, the more energy needed to break it apart. Energy needed to break the nucleus into protons and neutrons is called the Binding Energy Einstein discovered that the mass of the separated particles is greater than the mass of the intact stable nucleus to begin with. This difference in mass (Dm) is called the mass defect.

19. Mass Defect - Explained The extra mass turns into energy holding the atom together.

20. Discovery of Radioactivity In 1897, Becquerel accidentally discovered radioactivity in pitchblende (a uranium mineral). He found photographic plates that had been covered to keep light out had become partially exposed. This mineral was found to produce a photographic image, even through black paper. Radioactive Nuclei that emit particles and energy Henri Antoine Becquerel French Professor of Applied Physics Nobel Prize in Physics 1903 (1852 – 1908)

21. Some Important Terminology • Nuclear reactions involve the atomic nucleus (i.e., protons and neutrons). • Regular chemical reactionsinvolve only the outer electrons of atoms. • An atom is the smallest entity that retains the properties of an element. • Atoms are composed of one or more electrons and a nucleus. • The nucleus is the central portion of an atom and contains one or more protons and zero or more neutrons.

22. Element= The simplest stable building blocks of materials, consisting of protons, neutrons and electrons. • Isotope = An atom of an element with the same number of protons, but a different number of neutrons.* • Radioisotope = An unstable isotope that undergoes nuclear decay. *Note:Atomic weights given on the periodic table are the weighted average of all the natural isotopes of each element, as determined using mass spectrometry.

23. Radioactive Decay • When an unstable nucleus releases energy and/or particles. • For an element with an atomic number over 83, repulsive forces between protons can not be balanced by the strong nuclear forces by the addition of more neutrons

24. Types of Radiation • Nuclear Reaction • Whenever the energy or the number of neutrons or protons in a nucleus changes

25. All particles produced by the decay of an atomic nucleus have the energy needed to penetrate substances - but to very differing distances.

26. Alpha Decay

27. Alpha Decay Applications Americium-241, an alpha-emitter, is used in smoke detectors. The alpha particles ionize air between a small gap. A small current is passed through that ionized air. Smoke particles from fire that enter the air gap reduce the current flow, sounding the alarm.

28. Beta Decay • In a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transformed into the other. • In beta minus decay, a neutron decays into a proton, an electron, and an antineutrino • In beta plus decay, a proton decays into a neutron, a positron, and a neutrino

29. Beta Plus Decay Application - Positron emission tomography (PET) Positron emission tomography (PET) is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Images of tracer concentration in 3-dimensional space within the body are then reconstructed by computer analysis.

30. Gamma Decay

31. Gamma Decay Applications Gamma rays are the most dangerous type of radiation as they are very penetrating. They can be used to kill living organisms and sterilize medical equipment before use. They can be used in CT Scans and radiation therapy. Gamma Rays are used to view stowaways inside of a truck. This technology is used by the Department of Homeland Security at many ports of entry to the US.

32. Half-Life • The half-life of a radioactive element is the TIME it takes for HALF of the radioactive atoms to decay to stable ones. • If there are 80 grams of a radioactive element that has a half-life of 1000 years, then after 1000 years half of the element, or 40 grams of the element, will remain. • Now that there are only 40 grams left, how many grams will be left after another 1000 years has passed? • There will be only 20 grams remaining.

34. Carbon-14 and Half-Life? • Carbon-14 dating is a method of determining the age of an object containing organic material by using the properties of radiocarbon C a radioactive isotope of carbon • Unstable carbon-14 gradually decays to carbon-12 at a steady rate. • The ratio of these carbon isotopes reveals the ages of some of Earth's oldest inhabitants. • The half-life of C-14 is 5,730 years

35. 2 nuclear reactions Examples

36. 2 nuclear reactions Nuclear process Condition Fuel Energy production Energy released Energy requirement Waste products

37. Review Nuclear fission: A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process Nuclear fusion: Several small nuclei fuse together and release energy.