Radioactivity

1. Radioactivity

2. Radioactivity: the process by which atoms emit energy in the form of electromagnetic waves, charged particles, or uncharged particles. • In 1896, Henri Bequerel discovered that uranium and other elements emitted invisible rays that can penetrate solid material. These materials are now called “radioactive” • The most common unit for radiation is counts per second (known as a Becquerel, Bq) CBC archives - radioactivity

3. Applications & Exposure

8. Natural Sources • Exposure to radiation is unavoidable because radioactive elements occur in nature. • - some forms of carbon and potassium are absorbed by your body are radiactive. • C  600 Bq/kg of body mass • K  110 Bq/kg “ “ “ Alps Iceman: 5,300 years old

9. Cosmic rays: high energy radiation coming from space. • higher exposure than normal when flying at high altitudes

10. - Radioactive uranium and radium are found in soil and rocks. When they disintegrate, the produce another radioactive atom: radon gas. Uranium deposits around the world

11. Artificial Sources • Nuclear power • Electricity • Submarines • - Space probes February 1, 2005—The U.S. Navy released this photograph last Thursday of the nuclear submarine San Francisco, which crashed headlong into an uncharted undersea mountain near Guam on January 8. Standing more than three stories high and with classified technology veiled by a tarp, the fast-attack submarine is shown awaiting repairs in a Guam dry dock. The impact shredded the submarine's nose, killed one sailor, and injured 60 more. The sailors were largely protected by the vessel's reinforced inner hull, which did not rupture. After the wreck, the crew quickly ascended and sailed along the ocean's surface back to their base in Guam.

12. The Cassini space probe is powered by energy released from 28.8 g of radioactive Pu. The radiation is absorbed by ceramic surronding the Pu and the heat is converted ot electricity. Each Kg of Pu emits 556 J each second.

13. There is a lot of radiation released inside nuclear reactors and by the spent fuel (but still less than is emitted by x-ray machines) • Some coal-fired power plants emit more radioactivity than nuclear plants (uranium in coal ash)

14. - Nuclear bombs

15. In medicine: we use a unit called Sieverts (10 Sv is a lethal dose for most tissues) • Medical applications: • X-rays are used for diagnosis • Cancer treatment

16. Effects of Radiation • Ionizing radiation carries energy values on the order of 1000’s of eV. • Typical chemical bonds can be broken by radiation energy of 5 or less eV. - Cells do have repair mechanisms, but they are not perfect and they can be overwhelmed. - Large particle radiation (such as α particles) can do more damage per unit of energy.

17. Effects of Cell Damage: • 1) Cell dies: organelles or enzymes can no longer function • 2) Cell survives: Damage is passed on to daughter cells in the form of mutations (some mutations can lead to cancer). • Cells undergoing division are more susceptible to damage

18. Radiation Strength • Depends on three factors: • The kind of particles/EMR emitted • Amount of radioactive material present • The rate at which atoms disintegrate to emit radiation (1 count/second = 1Bq) – depends on the isotope.

19. The Nucleus and Nuclear Reactions

20. Structure of the Nucleus - Review Which elements are these? (protons are shown in red and neutrons in white.) They are both carbon. Both have 6 protons. i.e. they both have an atomic number of 6. These are two isotopes(varieties) of carbon. - same chemical properties, but different physical properties (e.g. how they behaving in nuclear reactions) - different number of neutrons, therefore different atomic masses In nuclear physics, we often call atoms nuclides.

21. Carbon-12 Carbon-14 Mass number = 12 p+ = 6 n0 = 6 Mass number = 14 p+ = 6 n0 = 8 Mass number = #p+ + #no Atomic number = #p+

22. SYMBOL NAME ISOTOPES hydrogen-1 hydrogen-2 (deuterium) hydrogen-3 (tritium)

23. SYMBOL NAME ISOTOPES lithium-6 lithium-7

24. The Strong Nuclear Force • Using accelerators, scientists have discovered the forces that hold nuclei together The big circle marks the location of the Large Hadron Collider (LHC) at the European particle physics laboratory in CERN. The tunnel where the particles are accelerated is located 100 m (320 ft) underground and is 27 km (16.7 mi) in circumference. The smaller circle is the site of the smaller proton-antiproton collider. The border of France and Switzerland bisects the CERN site and the two accelerator rings.

25. Nuclear forces act over very small ranges. (3 x 10-15 m) • Over 100 times greater than the electrostatic force. • The strong nuclear force is independent of the charge • The attraction is the same between: • p+ - p+ • n0 - n0 • n0 – p+

26. Unstable (Radioactive) Nulcides • Unstable nuclides tend to disintegrate causing: •  A different nuclide is to be produced • Energy to be released as radiation • Unstable nuclides have too few neutrons in relation to the number of protons. •  In general, the more protons in a nucleus, the more neutrons that are required to overcome the electrostatic repulsion. • All elements with atomic numbers greater than 82 exist only as unstable nuclides.

27. Types of Radiation • Rutherford discovered three types of radiation • Also discovered that elements transform into different elements during the process (called transmutation). • The original element is called the parent nuclide. The newly formed element is called the daughter nuclide.

28. Alpha Decay • Alpha particles (α) are helium- 4 • They are ejected at high speeds but can be stopped by aluminum foil

29. For all nuclear reactions: NUCLEONS AND CHARGE ARE CONSERVED i.e. The sum of the mass numbers on both sides of the arrow must be equal and the sum of the atomic numbers on both sides of the arrow must be equal 222 nucleons 222 nucleons charge = +86 charge = +86

30. Beta Decay • A neutron decays into a proton and an electron. • The electron is ejected from the nucleus at a high speed – called a beta particle (β). • β particles can penetrate several mm of lead.

31. 228 nucleons 228 nucleons charge = +90 charge = +90

32. Gamma rays can be emitted along with an alpha or beta particle. • When a nucleus emits only a gamma (γ) ray, the energy of the nucleus is reduced but the mass number and the atomic numbers stay the same. • γ rays can penetrate many cm of lead. Gamma Decay exited unexcited

33. Often, the same nuclide can undergo different decay modes…

34. Decay Series … or go through a series of decays.

35. Example 1: Complete the balance equation: Nuclear charge: 83 – 2 = 81 81 TI According to my periodic table, that must be Nucleons: 210 – 4 = 206 206 What type of radiation is this? Alpha Decay

36. Example 2: Complete the balanced equation and identify the radiation type. Neptunium-237 Beta Decay

37. Other Decay Modes • Some radionuclides can transmutate by capturing an electron from the lowest energy level. • A proton is converted into a neutron • Positron emission: (same mass as an electron, but a positive charge)

38. Fission and Fusion Nuclear Fission • The reaction used in all of the world’s nuclear power plants. The fuel is usually uranium, put plutonium can also be used. • Can be used in nuclear bombs. • Involves “splitting” an atom into smaller nuclides. • Initiated by a slow moving neutron. Fission Animation More animations

39. Example 3: Predict the missing fission product.

40. Nuclear Fission Chain Reaction • The emitted neutrons strike more uranium atoms, causing them to undergo fission. • This reaction is very hard to control. http://www.spacekid.net/nuclear/fission.html

41. Canada’s CANDU Reactor • Canadian Deuterium Uranium Reactor

43. Nuclear Fusion • The process that made the atoms that make you. • Two nuclide with extremely high energy collide to form a bigger nuclide. animation

44. Example 3: Predict the missing reactant.

45. Nuclear fusion as an energy source on earth is still experimental

47. Radioactive Dating • A sample of radioactive material consists of vast number of nuclei that don’t all decay simultaneously. • We can’t predict when a single nucleus will decay (it is governed only by probability) • The decay from parent nuclide to daughter nuclide follows a characteristic decay curve.

48. Radioactive Decay Curve 100% • Rutherford noticed that the radioactivity of a sample of radon gas was reduced by half every ~1 minute. • This called the half-lifeof the isotope. • half-lives can vary from 10-22s to 1028 s, depending on the isotope. Radioactivity 50% • Half-lives are always a uniform interval of time for a particular isotope. 25% 12.5% Time