Radioactivity: Principles and Applications (14 October) Background Background Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of radioactivity and human health Principles of radioactivity and human health Application of the principles of radioactivity Application of the principles of radioactivity

Take Home Message Radioactivity is a natural process Radioactivity is a natural process Radioactivity is due to the instability of atoms, resulting in the spontaneous emission of subatomic particles and/or energy Radioactivity is due to the instability of atoms, resulting in the spontaneous emission of subatomic particles and/or energy Radioactivity has unique features including isotopes and radioactive decay Radioactivity has unique features including isotopes and radioactive decay Human health issues of radioactivity are based on the ability of emissions to affect a cell’s biochemistry and metabolism Human health issues of radioactivity are based on the ability of emissions to affect a cell’s biochemistry and metabolism Radioactivity has been “harnessed” to provide a host of applications to enhance the quality of life Radioactivity has been “harnessed” to provide a host of applications to enhance the quality of life Radioactivity also has its liabilities associated with waste disposal and misuse Radioactivity also has its liabilities associated with waste disposal and misuse

Radioactivity: Principles and Applications Background Background Isotopes Isotopes Stable Stable Unstable = radioactive Unstable = radioactive Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of human radioactivity Principles of human radioactivity Application of the atomic principles of radioactivity Application of the atomic principles of radioactivity

Isotopes Atoms have specific number of protons, neutrons and electrons Atoms have specific number of protons, neutrons and electrons 8 8 O If the number of protons is unchanged but the number of neutrons goes up or down, what happens to the properties of that element? If the number of protons is unchanged but the number of neutrons goes up or down, what happens to the properties of that element? 8 O 17 17

Isotopes Continued Atoms of an element with same number of protons but different number of neutrons are isotopes Atoms of an element with same number of protons but different number of neutrons are isotopes Key is the number of neutrons Key is the number of neutrons Conventional notation ( A Z X) Conventional notation ( A Z X) Not all elements have isotopes, but many do: Not all elements have isotopes, but many do: Hydrogen (common isotope: 1 1 H; 3 1 H or tritium) Hydrogen (common isotope: 1 1 H; 3 1 H or tritium) Nitrogen (common isotope: 7 14 N; 15 7 N) Nitrogen (common isotope: 7 14 N; 15 7 N) Oxygen (common isotope: 8 16 O; 18 8 O) Oxygen (common isotope: 8 16 O; 18 8 O) Sulfur (common isotope: S; S Sulfur (common isotope: S; S

Isotopes of Hydrogen Hydroge n 1 1 H Stable Deuterium 2 1 H Stable Tritium 3 1 H Unstable ProtonNeutron

Stable versus Unstable Isotopes Stable over time Stable over time Unstable: “transmutate by releasing mass and/or energy Unstable: “transmutate by releasing mass and/or energy

Radioactivity: Principles and Applications Background Background Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of human radioactivity Principles of human radioactivity Application of the principles of radioactivity Application of the principles of radioactivity

Discovery of Radioactivity Rutherford (as in the nucleus) and three forms of “transmutated” activity (“radioactivity”) Rutherford (as in the nucleus) and three forms of “transmutated” activity (“radioactivity”) Alpha  nucleus of the helium atom ( 4 2 He) Alpha  nucleus of the helium atom ( 4 2 He) Beta (  ): high energy electron Beta (  ): high energy electron Gamma (  ): electromagnetic radiation with very short wavelengths Gamma (  ): electromagnetic radiation with very short wavelengths

Principal Early Observations Atom exhibits “spontaneous” release of Atom exhibits “spontaneous” release of mass (  or  ) mass (  or  ) energy (  ) energy (  ) Nucleus changes identity simpler atomic structure Nucleus changes identity simpler atomic structure 100% natural process 100% natural process Spontaneous release of mass or energy is called radioactive decay Spontaneous release of mass or energy is called radioactive decay

Radioactivity: Principles and Applications Background Background Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of human radioactivity Principles of human radioactivity Application of the principles of radioactivity Application of the principles of radioactivity

Natural/Background Radioactivity Sources Sources Cosmic rays from outer space Cosmic rays from outer space Soils Soils Water Water Building materials Building materials Nuclear sources Nuclear sources Examples Examples Radon gas (Ra) Radon gas (Ra)

Radioactive Decay Uranium – 238 Uranium – U (92 protons; (146) neutrons Spontaneous release of an alpha (  ) subatomic particle (helium nucleus or 4 2 He) results in an atom with 90 protons and mass of 234 Spontaneous release of an alpha (  ) subatomic particle (helium nucleus or 4 2 He) results in an atom with 90 protons and mass of ? or _____ (periodic table) All isotopes of all elements with > 83 protons (Bismuth) are unstable and radioactively decay All isotopes of all elements with > 83 protons (Bismuth) are unstable and radioactively decay

Types of Decay Alpha (  ) Alpha (  ) Release of 4 2 He Release of 4 2 He Travel distance: easily stopped by sheet of paper (even air) Travel distance: easily stopped by sheet of paper (even air) Eventually acquires electrons to yield normal He atom Eventually acquires electrons to yield normal He atom Beta (  ) Beta (  ) Release of high energy electron Release of high energy electron Travel distance: 10 meters; 1 cm aluminum block Travel distance: 10 meters; 1 cm aluminum block Eventually “finds” an atom needing an electron Eventually “finds” an atom needing an electron Gamma (  ) Gamma (  ) Release of high energy electron Release of high energy electron Travel distance: 100’s meters; 5 cm block lead brick Travel distance: 100’s meters; 5 cm block lead brick Eventually energy is absorbed by material Eventually energy is absorbed by material

Penetration of Radiation

Radioactive Decay

Rate of decay to a stable state (no more spontaneous decay) is specific for each isotope Rate of decay to a stable state (no more spontaneous decay) is specific for each isotope Rate has unique terminology called half-life Rate has unique terminology called half-life Time for ½ (50%) of the nuclei to decay to the stable state is abbreviated t 1/2 Time for ½ (50%) of the nuclei to decay to the stable state is abbreviated t 1/2 Example: M&M’s Example: M&M’s

Radioactive Decay

Measurement of Radiation Number of nuclear disintegrations per unit of time called a curi (Ci); 3.70 x nuclear disintegrations second -1 Number of nuclear disintegrations per unit of time called a curi (Ci); 3.70 x nuclear disintegrations second -1 Radiation at the site of absorption (living tissues) Radiation at the site of absorption (living tissues) Radiological dose in units called rem Radiological dose in units called rem Natural dose = rem (1 millirem)/day Natural dose = rem (1 millirem)/day Lethal dose = 500 rem Lethal dose = 500 rem

Radioactivity: Principles and Applications Background Background Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of radioactivity and human health Principles of radioactivity and human health Application of the principles of radioactivity Application of the principles of radioactivity

Radioactivity: Human Health Radioactivity in biological tissues results in atoms being ionized Radioactivity in biological tissues results in atoms being ionized Disrupts bonds Disrupts bonds DNA as primary site of action DNA as primary site of action Fragments molecules and disrupts biochemistry Fragments molecules and disrupts biochemistry Sensitivity is greatest for actively growing cells and tissues Sensitivity is greatest for actively growing cells and tissues Blood Blood Bone marrow (Cesium-137) Bone marrow (Cesium-137) Thyroid (I-131) Thyroid (I-131)

Radioactivity: Principles and Applications Background Background Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of radioactivity and human health Principles of radioactivity and human health Application of the principles of radioactivity Application of the principles of radioactivity

Application of Atomic Principles of Radioactivity Radiation medicine and radiopharmaceuticals Radiation medicine and radiopharmaceuticals Nuclear energy Nuclear energy Yucca Mountain, Nevada Yucca Mountain, Nevada Three Mile Island Three Mile Island Chernobyl Chernobyl Dirty bomb Dirty bomb

Chernobyl Reactor

Chernobyl

Yucca Mountain Waste Repository

A high speed electron emitted from a nucleus during radioactive decay is called a (an) _____. A. Alpha B. Beta C. Gamma D. All of the above

A sheet of paper will stop a (an) ____. A. Alpha B. Beta C. Gamma D. All of the above

Rate of radioactive decay is affected by changes in ______. A. Temperature B. Pressure C. Sample size D. Other radioactive materials nearby E. None of the above

What is meant by background radiation? Is the dose of background radiation equivalent over the Earth’s surface? For you as an individual, what are the most common sources of natural/background radiation?

Why measure the duration of radioactivity in units of half life (t 1/2 ) versus lifetime?

Beryllium-7 ( 7 4 Be) is an unstable isotope of Beryllium ( 9 4 Be). When the atom “transmutates”, the stable product that is formed is the element Lithium ( 7 3 Li). What was emitted in the process of radioactive decay? Is 7 3 Li stable or unstable?