Chapter_3_nuclear_radiation

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    Damage done from Non-Ionizing Radiation is due to the buildup of heat
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  • Chapter_3_nuclear_radiation

    1. 1. Nuclear RadiationChapter 3
    2. 2. 1. Atoms consist of electrons, protons, and neutrons. 2. Atoms of elements are distinguished by the number of protons in the nucleus (the atomic number). 3. Isotopes of an element have different numbers of neutrons but the same number of p+ and e- . 4. Isotopes of elements react identically (in most chemical reactions). 5. Traditional chemical reactions focus primarily on interactions in the outer valence electrons of atoms. Review:
    3. 3. • A nucleus with a specified number of protons and neutrons is a nuclide. E A – mass number (number of p+ + number of n) Z – atomic number • Together, protons and neutrons are called nucleons. A Z Review of Nucleus
    4. 4. Nucleus: Particle Properties Protons, neutrons, and electrons are all fermions (spin 1/2). Protons and neutrons are “heavy” baryons (composed of 3 quarks). [proton = up, up, down quarks and neutron = up, down, down] Electrons are “light” leptons. Particle Charge amu Spin µ Proton +e 1.007276 1/2 +2.79µN Neutron 0 1.008665 1/2 – 1.91µN Electron –e 5.4858×10-4 1/2 +1.00µΒ
    5. 5. The Nucleus Let’s take a look at the nucleus, where the protons and neutrons reside. Breaking these apart can cause a large release of energy. Protons
    6. 6. What is Radioactivity? Elements that are RADIOACTIVE are UNSTABLE because they have too many nucleons or too much energy. In an attempt to become STABLE, they give up particles or energy and this is……. RADIOACTIVITY From Latin radioto (to radiate)
    7. 7. Radioactivity C 12 6 Stable C 13 6 Stable C 14 6 Unstable RADIOACTIVE
    8. 8. Radioactivity C 14 6 Unstable RADIOACTIVE The nucleus of this atom is very heavy because it contains two extra NEUTRONS In order to become stable it needs to get rid of some excess weight
    9. 9. Radioactivity Because this atom is unstable a NEUTRON begins to break down Neutron Breakdown C 14 6 Unstable RADIOACTIVE
    10. 10. Neutron Breakdown Neutrons are made up of positively and negatively charged particles C 14 6 Unstable RADIOACTIVE The positive part of the NEUTRON is actually a PROTON The negative part of the NEUTRON is called a BETA particle An anti-neutrino is also released
    11. 11. Neutron Breakdown C 14 6 Unstable RADIOACTIVE = Neutron breaking down The Negative Beta Particle is released β This energy is RADIOACTIVE Having released the β particle the NEUTRON now becomes a PROTON An anti-neutrino is also released
    12. 12. Neutron Breakdown C 14 6 Unstable RADIOACTIVE N 14 7 Stable NITROGEN Lose NEUTRON Gain PROTON
    13. 13. Neutron Breakdown Is Just one way a element can become stable Accompanied by Beta emission And the conversion of a NEUTRON to a PROTON Carbon-14 is a BETA emitter There are other ways that an element can obtain stability and this results in different types of RADIATION
    14. 14. Nuclear Chemistry Introduction Most chemical changes deal with the valence electrons Nuclear chemistry deals with changes in the nucleus, often accompanied by the release of a large amount of energy Unstable nucleus spontaneously emits a particle or energy. Radiation comes from the nucleus of an atom. Radiation is energy in transit in the form of high speed particles and electromagnetic waves Radiation cannot be tasted, felt, or smelt, but has the potential to do a great deal of damage Radioactivity, or radioactive decay, is the spontaneous change of the nuclei of certain atoms, accompanied by the emission of subatomic particles and/or high-frequency electromagnetic radiation. There are five principal particles or waves of radiation we will learn about: Alpha (α or 4 He2+ ) Beta (β− or e- ) Positron (β+ ) Gamma (γ) Neutrons (n)
    15. 15. Summary Of Decay Types γ e e symbolparticleHe 0 1 0 1- particleinneutronsandprotons particlein (NOT Charge here!) protons 4 2 + =
    16. 16. Main Types Of Radioactive Decay • An alpha (α) particle has the same composition as a helium nucleus (4 2He): two protons and two neutrons. • Beta (β− ) particles are electrons (-1 0 e). • Gamma (γ) rays are a highly penetrating form of electromagnetic radiation (0 0 γ). • Positrons are particles having the same mass as electrons but carrying a charge of 1+ (+1 0 e). A positron and an electron can annihilate each other upon colliding, producing energy as photons: -1 0 e + +1 0 e → 2 0 0 γ • Other forms of radioactive decay: • Proton emission • Neutron emission • Electron capture (EC) is a process in which the nucleus absorbs an electron from an inner electron shell, usually the first or second, thus converting a proton into a neutron, along with the release of an X-ray.
    17. 17. Radioactivity: Historical Overview 1896: Becquerel accidentally discovered that uranyl crystals emitted invisible radiation onto a photographic plate. 1898: Marie and Pierre Curie discovered polonium (Z=84) and radium (Z = 88), two new radioactive elements. 1903: Becquerel and the Curie’s received the Nobel prize in physics for radioactive studies. 1911: Marie Curie received a 2nd Nobel prize (in chemistry) for discovery of polonium and radium. 1938: Hahn (1944 Nobel prize) and Strassmann discovered nuclear fission - Lisa Meitner played a key role! 1938: Enrico Fermi received the Nobel prize in physics for producing new radioactive elements via neutron irradiation, and work with nuclear reactions.
    18. 18. Three Main Types of Radiation
    19. 19. Radioactivity • All elements have at least one radioactive isotope. • All isotopes with atomic number greater than 83 are radioactive. • Artificial and Natural sources exist. • Radioactive isotopes have same chemical properties as non-radioactive isotopes.
    20. 20. Stable and Unstable Nuclei
    21. 21. Everyday Radiation Exposure
    22. 22. Alpha (α) Particles Symbol: 2 4 He or α; Equivalent to the Helium Atom It is composed of 2 protons, 2 neutrons, has a mass of 4 amus and a charge of 2+ Since they are so large they can cause great damage if they strike tissue. But, they cannot travel very far because of their weight and they’re low energy Travel 3-4 inches in air and can be blocked by a sheet of paper Cannot penetrate the epidermal layer of the skin More of an internal hazard than an external hazard Once ingested they are usually within 3-4 inches of a vital organ 4 inches Emission of Alpha Particle 3-4 inches Because Alpha particles are so large, they are the most damaging. The probability of them coming into contact with other particles is great
    23. 23. Beta (β) Particles Symbol: -1 0 e or β; A high energy electron Can be either positively or negatively charged Usually given off when a neutron is converted to a proton or when protons convert to neutrons. Very small and can travel up to 100 feet in air Can penetrate the skin Can be stopped by a thin piece of metal or 2-3 inches of wood Since they are so small the likelihood of them striking biological tissue is much less than an Alpha particle. 100 Feet If particle strikes damage will occur Particle may pass through without touching any matter A neutron in the nucleus breaks down 1 1 0 n  H + e 0 1 -1
    24. 24. Gamma (γ) Particles and X-Rays For all practical purposes Gamma and X-rays are identical. Gamma particles are produced by atomic disintegration X-rays are produced by machines and Electron Capture Both are pure energy and travel at the speed of light 3 x 108 m/s Can travel great distances without striking other particles. If collision takes place, damage will occur Because it is electromagnetic radiation, it is deeply penetrating Takes several feet of concrete or many inches of lead to stop them It has no mass or charge  Very high energy There are very few pure gamma emitters, although gamma radiation accompanies most α and β decay In radiology one of the most commonly used gamma emitters is Tc 43 99m Tc →43 99 Tc + γ A gamma decay will have no change in the atomic number or atomic mass Much energy will pass through without any effect on biological matter Some energy may cause ionization
    25. 25. Neutron Radiation Symbol:0 1 n It has a mass of one, no protons, and no charge Very rare but very lethal Generated in the explosion of nuclear weapons Neutron Bombs Since this type of radiation is so specialized it is not usually discussed in lectures such as this
    26. 26. Types of nuclear radiation Radiation Type of Radiation Mass (AMU) Charge Shielding material Alpha Particle 4 2 Paper, skin, clothes Beta Particle 1/1836 ±1 Plastic, glass, light metals Gamma Electromag -netic Wave 0 0 Dense metal, concrete, Earth Neutrons Particle 1 0 Water, concrete
    27. 27. From: http://www.physics.isu.edu/radinf/properties.htm
    28. 28. Nuclear Physics General Rules: 1) α emitted to reduce mass, only emitted if mass number above 209 2) β− emitted to change neutron into proton, happens when have too many neutrons 3) β+ emitted (or electron capture) to change proton into neutron, happens when have too few neutrons 4) γ emitted to conserve energy in reaction, may accompany α or β. 5) Neutrons and protons emitted due to bombardment…
    29. 29. Bombardment Reaction Bombardment reaction-bombarding 2 stable atoms together, creating a radioisotope All of the known elements whose atomic number is greater than 92 were created from bombardment reactions
    30. 30. Nuclear Equations Basic principle in writing a nuclear equation : charge, mass number, and atomic number must be conserved in a nuclear reaction. The two sides of a nuclear equation must have the same totals of atomic numbers and mass numbers. Balancing Nuclear Eqns: reactants’ and products’ Atomic numbers must balance and Mass numbers must balance
    31. 31. Alpha decay
    32. 32. Beta decay 234 Th → 234 Pa + 0 e 90 91 −1 beta particle
    33. 33. Gamma radiation No change in atomic or mass number 11 B 11 B + 0 γ 5 5 0 boron atom in a high-energy state
    34. 34. Learning Check NR1 Write the nuclear equation for the beta emitter Co-60.
    35. 35. Solution NR1 Write the nuclear equation for the Beta emitter Co-60. 60 Co 60 Ni + 0 e 27 28 -1
    36. 36. Producing Radioactive Isotopes Bombardment of atoms produces radioisotopes = 60 = 60 59 Co + 1 n 56 Mn + 4 He 27 0 25 2 = 27 = 27 cobalt neutron manganese alpha atom radioisotope particle
    37. 37. Learning Check NR2 What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0
    38. 38. Solution NR2 What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He 13 N + 1 n 5 2 7 0 nitrogen radioisotope
    39. 39. Half-Life of a Radioisotope The time for the radiation level to fall (decay) to one-half its initial value decay curve 8 mg 4 mg 2 mg 1 mg initial 1 half-life 2 3
    40. 40. Half–Life (t1/2) The half-life (t1/2) of a radioactive nuclide is the time required for one-half the nuclei in a sample of the nuclide to decay. The shorter the half-life t1/2, the larger the value of λ (decay constant) and the faster the decay proceeds. The time required for one-half of the unstable nuclei to decay. (t1/2) A0 A = -------- 2n A0 = original amount n = number of elapsed half lives 1 half life 1/2 original amount left (50%) 2 half lives 1/4 original amount left (25%) 3 half lives 1/8 original amount left (13%) 4 half lives 1/16 original amount left (6.3%)
    41. 41. Selected Nuclide Half-lives
    42. 42. Learning Check NR3 The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?
    43. 43. Solution NR3 t1/2 = 13 hrs 26 hours = 2 x t1/2 Amount initial = 64mg Amount remaining = 64 mg x ½ x ½ = 16 mg
    44. 44. Radiocarbon Dating Carbon-14 is formed at a nearly constant rate in the upper atmosphere by the bombardment of nitrogen-14 with neutrons from cosmic radiation. The carbon-14 is eventually incorporated into atmospheric carbon dioxide. Carbon-14 in living matter decays by β¯ emissions at a rate of about 15 disintegrations per minute per gram of carbon. When the organism dies, no more carbon-14 is integrated into the system. Ratio of 14 C to 12 C tells how long the item has been dead. The half-life for carbon-14 is 5,730 years. This dating method works well if an object is between 5,000 and 50,000 years old.
    45. 45. Radiocarbon DatingRadiocarbon Dating Radioactive C-14 is formed in the upper atmosphereRadioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmicby nuclear reactions initiated by neutrons in cosmic radiationradiation 1414 N +N + 11 oon --->n ---> 1414 C +C + 11 HH The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through, which circulates through the biosphere.the biosphere. When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 years.= 5730 years. Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.
    46. 46. NUCLEAR vs. CHEMCIAL REACTIONS Nuclear reactions Chemical reactions 1. Atomic numbers may change 1. Atomic numbers do not change 2. Isotopes of an element have 2. Isotopes of a given element different properties behave almost identically. 3. There is a small but significant 3. There is no significant change mass change; matter is in the total quantity of matter converted to energy. in the reaction 4. Individual atoms are usually 4. Mole quantities are usually used in calculations used in calculations.
    47. 47. Summary The five types of radioactive nuclides involve emission of alpha (α) particles, beta (β) particles, gamma (γ) rays, positrons, and electron capture. All known nuclides with Z > 83 are radioactive, and many of them occur naturally as member of four radioactive decay series. In the formation of an atomic nucleus from its protons and neutrons, a quantity of mass is converted into energy.
    48. 48. Synthetic Nuclides For centuries, alchemists tried - without success - to change one element into another – alchemy – turn lead into gold. The process of changing one element into another is called transmutation. Modern scientists have learned to do this. Rutherford, in 1919, was able to convert nitrogen-14 into oxygen-17 plus some extra protons by bombarding the nitrogen atoms with α particles. This is a naturally occurring isotope of oxygen and is not radioactive. 14 7N + 4 2He  17 8O + 1 1H Phosphorous-30 was the first synthetic radioactive nuclide. Since its discovery, scientists have synthesized over a thousand others.
    49. 49. Transuranium Elements In 1940, the first of the transuranium elements - elements with a Z > 92 - was synthesized by bombarding uranium- 238 nuclei with neutrons. This first element is plutonium. 238 92U + 1 0n  239 92U 239 92U  239 93Np + 0 -1e 239 93Np  239 94Pu + 0 -1e
    50. 50. Nuclear Stability About 160 stable nuclides have an even number of protons and an even number of neutrons. About 50 stable nuclides have an even number of protons and an odd number neutrons. About 50 stable nuclides have an odd number of protons and an even number neutrons Only four stable nuclides have an odd number of protons and an odd number of neutrons. The magic numbers of protons or neutrons for nuclear stability are 2, 8, 20, 28, 50, 82, and 126.
    51. 51. Stability of Nuclides All the stable nuclides lie within the belt of stability (as do some radioactive ones). Nuclides outside the belt are radioactive. Their modes of radioactive decay are indicated.
    52. 52. Energetics Of Nuclear Reactions While working out the details of the theory of special relativity, Einstein derived the equation for the equivalence of mass and energy: E = mc2 . In a typical spontaneous nuclear reaction, a small quantity of matter is transformed into a corresponding quantity of energy. Nuclear energies are normally expressed in the unit MeV (megaelectronvolt). 1 u = 931.5 MeV : one atomic mass unit contains energy equivalent to 931.5 megaelectronvolts. 1 amu = 1 u
    53. 53. Nuclear Binding Energy The energy released in forming a nucleus from its protons and neutrons is called the nuclear binding energy and is expressed as a positive quantity. Alternatively, nuclear binding energy is the quantity of energy necessary to separate a nucleus into individual protons and neutrons. This explains why there is a mass loss of 0.0304 u in the formation of a helium nucleus from the two protons and two neutrons which comprise it. This quantity is called the mass defect of the nucleus.
    54. 54. Nuclear Binding Energy For Helium
    55. 55. Average Binding Energies
    56. 56. Nuclear Fission Fission large nuclei break up 235 U + 1 n 139 Ba + 94 Kr + 3 1 n + 92 0 56 36 0 Energy
    57. 57. Fission
    58. 58. Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n + 1 1 2 0 Occurs in the sun and other stars Energy
    59. 59. Learning Check NR4 Indicate if each of the following are (1) Fission or (2) Fusion or both: A. Nucleus splits B. Large amounts of energy released C. Small nuclei form larger nuclei D. Hydrogen nuclei react Energy
    60. 60. Solution NR4 Indicate if each of the following are (1) Fission (2) fusion A. 1 Nucleus splits B. 1 + 2 Large amounts of energy released C. 2 Small nuclei form larger nuclei D. 2 Hydrogen nuclei react
    61. 61. Geiger Counter Used to detect radioactive substances
    62. 62. Exposure vs. Contamination Exposure Contamination
    63. 63. Exposure Your body has been subjected to some type of radiation: Alpha Beta Gamma X-ray Neutrons The amount of damage done depends on the type of radiation received, the amount of time exposed, and the amount of radiation. •It does cause damage to your body •Exposure to radiation does not make you radioactive
    64. 64. Contamination Radioactive material has attached itself to you body Internally Externally You are also exposed as long as you are contaminated You are “a source”of radioactivity to others
    65. 65. Factors to Reduce Exposure Time • Distance • Shielding
    66. 66. Time If you decrease the time exposed to a given isotope you will decrease the dose of that exposure If an isotopes gives off 1 Rad/hour in .5 hours you receive .5 Rads
    67. 67. Distance Inverse Square Law If you double the distance between you and a radioactive source you reduce the amount of exposure by ¼ Mathematically I=Io/R2 • I=Intensity at Distance R • Io=Original Intensity • R=Distance from Source
    68. 68. Application of Inverse Square Law At a distance of one foot from a 14 C source you receive an exposure dose of 1 RAD. What would be your exposure if you moved 10 feet from the source? I=Io/R2 I=1RAD/102 I=1RAD/100 I=.01 RAD By increasing the distance 10 times you decrease the dose 100 fold
    69. 69. Shielding (Barrier between you and the source) Type needed depends on type of radiation produced Alpha Air Paper Beta Metal Wood Plexiglass Gamma Concrete Lead
    70. 70. Penetrating Power Alpha particles are most ionizing, but have the least penetrating power. Skin is adequate protection. Beta particles are more penetrating but can be shielded with paper or thin foil. Gamma radiation is the most penetrating. A lead barrier is needed for protection from them.
    71. 71. Types of Radiation Non-Ionizing Ionizing
    72. 72. Non-Ionizing Radiation Waves of energy that do not have the strength to break chemical bonds or alter the arrangement of atoms Lasers Microwaves Ultraviolet Light
    73. 73. Ionizing Radiation Energy is strong enough to break or alter chemical bonds
    74. 74. Sources of Ionization Alpha, beta and gamma rays from radioactive materials Cosmic rays and the solar wind (lots of protons and neutrons) Any charged particles with high energy passing through materials can strip electrons from atoms
    75. 75. Ionization & Biology The ionization can disrupt the structure of crystals in solids Can rip up proteins and other tissue molecules Tends to be bad news for living things Since ionizing radiations often start as charged particles with energies in MeV range and electron binding is in eV range, one incoming particle can create lots of problems
    76. 76. Neutron Radiation Ionization Neutrons cause ionization indirectly They primarily interact with nuclei and cause nuclear reactions These reactions change the identity of the atoms and thus the chemistry, disrupting important molecules So, similar kinds of damage to tissue
    77. 77. Radiation & Biology If individual protein molecules are damaged, most cells have plenty of protein and can recover However, too much radiation can destroy too much protein and kill the cell Worse, may change DNA and wreak all kinds of havoc Now you can start producing defective cells
    78. 78. Radiation & Biology Radiation is classified as somatic or genetic Somatic damage kills cells and can affect the functioning of systems Genetic damage is that affecting the reproductive system and can result in defective offspring All radiation carries risk of damage!
    79. 79. Measure Radiation Amounts We want to deal with measuring the amount of radiation received by a biological system Just like medications, we refer to the dose Start with the radiation source How many particles (disintegrations) per second does the source emit? Historical measure is the Curie
    80. 80. Amount & Energy of Radiation Amount of Radiation (Activity): Curie (Ci) = 3.7 x 1010 dps Becquerel (Bq) = 1 dps = 2.8 x 10-11 Ci Energy of Radiation: Roentgen (R) = 2.1 x 109 charges/cm3 = 2.58 x 10-4 coulomb/kg
    81. 81. Radiation Dosages Dose (Amount + Energy) rad = radiation absorbed dose – absorbed radiation energy per kg of material (also called gray (Gy) = 100 rad) rem = radiation equivalent man (also called sievert (Sv) = 100 rem)
    82. 82. Activity The “radioactive strength” of an isotope Measured in units called Curies (Ci) One Curie = 3.7 x 1010 disintegrations/sec Relatively speaking a Ci is a large unit so we usually deal in fractions of a Ci Millicurie (mCi) = 0.001 Ci OR Microcurie (µCi) = 0.000001 Ci This is the strength of 1 gram of Radium Many now use a new unit, the Becquerel which is one disintegration per second Manufacturers specify the activity of a radioactive source at the time of manufacture Of course, we need to know the half-life to calculate present strength
    83. 83. Absorbed Energy Amounts? We need to be concerned with how much energy is actually being absorbed by a target There has been a historical progression of units used to measure the effect of radiation The first was the Roentgen One Roentgen produces 1.6 x 1012 ion pairs in dry air at room temperature The modern unit is the rad which is the amount of radiation which deposits energy at a rate of 10-2 J/kg in any absorbing material. The RAD is the measure of absorbed radiation energy in any type of material A new SI unit is the gray which is 100 rad
    84. 84. Biological Effect of Absorbed Radiation? Finally, we need to ask if there is any difference in tissue damage between the various possible types of radiation The answer is that there is a BIG difference, so we had better take that into account as well Alpha rays cause 10 to 20 times more damage than beta rays Since they are fat and move slowly, they confine their damage to a smaller area and cause greater disruption in a single location
    85. 85. RBE We account for these differences by figuring out the relative biological effectiveness or quality factor of the radiation The quality factors vary from one to twenty depending on type of radiation and energy of the particles Radiation Type RBE (Relative Biological Effectiveness) X-rays 1 Gamma (γ) rays 1 Beta (β) rays 1 Thermal (Slow) Neutrons 1 n 3 Fast Neutrons 1 n and Protons 1 p Up to 10 Alpha (α) particles and heavy ions Up to 20
    86. 86. Measurement of Dosage: the REM The REM (Roentgen Equivalent Man) Unit used to measure the effect that radiation (the number of RAD’s) will have on human tissue. This is done by applying a correction or “quality factor” (RBE == relative biological effectiveness) to the RAD based on the type of particle the material emits rem = rad x rbe This is known as the effective dose The latest SI unit for this is the Sievert which is gray x quality factor or 100 rem
    87. 87. Units of Radiation dose rad = radiation - absorbed dose the quantity of energy absorbed per kilogram of tissue 1 rad = 1 x 10-2 J / kg rem = roentgen equivalent for man, the unit of radiation dose for a human: 1 rem = 1 rad x RBE RBE = Relative Biological Effectiveness RBE = 10 for α RBE = 1 for x-rays, γ -rays, and β’s
    88. 88. Sample Dosage Problem A man working in a nuclear power plant has received an accidental exposure. The particular isotope that he was working with emitted 30 RADS of gamma radiation, and 3 RADS of fast neutron radiation. What was the worker’s total dose equivalent it REMS? REM = RAD x Quality Factor 30 RAD’s gamma x1 = 30 REM 3 RAD’s fast neutron x 10 = 30 REM TOTAL DOSE = 60 REM
    89. 89. Maximum Permissible Dose Occupational Workers in mRem Type of Exposure Yearly Exposure Whole Body 5000 Lens of the Eye 15000 Hands and Feet 50000 Pregnant Women 500 (Dose to Fetus) Minors 10% of Adult Dose Non-Occupational Worker in mRem 100 mRem any body part
    90. 90. Radiation Rates and Radiation Amounts Note that Activity (in Bq or Ci) is a rate. It tells how fast something is decaying with respect to time. Note that Exposure (in roentgens), Absorption (in rads or Grays), and Effective doses (in rems or Sieverts) are all amounts. They do not tell how fast this is occurring with respect to time.
    91. 91. Radioactive Events are Random Unpredictable Collision with biological tissue Passes harmlessly through body
    92. 92. Biological Effects of Radiation on Living Tissue Somatic Effects Non-stochastic (immediate) Skin burns Ulcers Loss of hair Blood changes Vomiting Diarrhea Stochastic (delayed) Formation of cancers and cataracts
    93. 93. Biological Effects of Radiation on Living Tissue Genetic Effects Causes damage to chromosomes Causes mutations in future generations May take many years to determine • Examples: Hiroshima, Nagasaki, Chernobyl Teratogenic Effects Damage to developing fetus or embryo
    94. 94. Dosages Required for Certain Immediate Effects 0-100 REM’s Survival certain No obvious symptoms Maybe some clinical signs if lab tests are done 100-200 REM’s Survival probable Begins signs of light radiation sickness Nausea Vomiting Listlessness 200-1000 REM’s Survival questionable. Some will survive, some won’t. Severe radiation sickness Radiation burns Over 1000 REM’s Survival impossible
    95. 95. Natural or Background Radiation We are all being exposed daily to a variety of radiation We receive about 100 mREM/year from background The average non-occupational worker receives about 200 mREM/year of chronic radiation exposure Present at all times as a result of radiation naturally present in the environment Cosmic rays Uranium, thorium and radon in soil] Building materials We receive an additional 100 mREM/year from Medical and dental x-rays Smoke detectors Dials on watches, etc. Differs depending on geographical location
    96. 96. Sources of Background Radiation 54% 8% 11% 11% 3% 1%4% 8% Other Radon Medical X-rays External Terrestrial Cosmic Nuclear Medicine Consumer Products
    97. 97. Radioactivity: Summary of Units Activity: Becquerel (Bq) = 1 decay / s 1 curie (Ci) = 3.7×1010 decays / s (or Bq) (disintegration rate of 1g of radium) Ion Dose: Ionizing behavior of radiation is most damaging to us! Roentgen = 2.6×10–4 C/ kgair (or 0.0084 j/kg) Energy Dose: rad = 0.01 j/kg Energy Dose for Human Health Considerations: rem = # rads × RBE Dosages: 0.5 rem / yr = natural background 5 rem / yr = limit for nuclear power plant workers 500 rem = 50% die within a month 750 rem = fatal dose (5000 rem = die within 1 week)
    98. 98. Radiation Exposure Standard medical x-ray dosage is about 0.04 rem Recommended maximum annual dosage is 0.5 rem per year from all sources Occupational limits are 5 rem/year These folks have to constantly monitor with film badges or pocket dosimeters to limit exposure to prescribed levels
    99. 99. Radiation Exposure 1000 rems are fatal 400 rems and half die 400 rems over an extended time you will probably live, but not be in good shape Most hard data from Japanese exposed at the end of WW II Some data from Chernobyl accident
    100. 100. Effects of RadiationEffects of Radiation
    101. 101. Applications in Nuclear Medicine Imaging Gamma or positron emitting isotopes 99m Tc, 111 In, 18 F, 11 C, 64 Cu Visualization of a biological process Cancer, myocardial perfusion agents Therapy Particle emitters Alpha, beta, conversion/auger electrons 188 Re, 166 Ho, 89 Sr, 90 Y, 212 Bi, 225 Ac, 131 I Treatment of disease Cancer, restenosis, hyperthyroidism
    102. 102. Nuclear Medicine: Imaging consumption of Na131 I Source: Visuals Unlimited Normal Thyroid An Enlarged Thyroid
    103. 103. Radiation Therapy Radiation is used to deal with cancer and also for diagnostics (imaging) Rapidly growing cells hurt more by radiation (same as chemotherapy exploits) Cells that divide quickly are: Cancerous cells Hair follicles (loss of hair) Digestive tract epithelial cells (nausea) Try to localize radiation to the tumor
    104. 104. Radiation Therapy Methods The goal is to minimize damage to surrounding tissue by limiting exposure. Can achieve the same goal by implanting “seeds” directly into tumors. Used for prostate cancers. Use body’s natural processes for other cancers. Iodine concentrates in thyroid, so inject hot “iodine.”
    105. 105. Latest Cancer Research Carbon nanotubules (nanotechnology) attached to folate molecules, which are only found on most cancerous cells Sent into cancerous cells using this process Near-infrared light radiation is then used to kill the cells The nanotubules heat up and kill them Later, might attach nanotubules to antibodies to target specific cancer cells
    106. 106. Tracer Studies Tag molecules and introduce to the body and then watch natural processes occur You can monitor for the presence of the radiation to see where it goes Label a chemical with technetium-99 with 6 hour half life. Want to look at an organ? Pick a molecule that heads there and tag it with Tc- 99 Often done for bone scans to look for cancer
    107. 107. Emission Tomography Again, inject radioactive substance Positron emission tomography is interesting tomo = slice or section; graphy = writing or imaging Use a positive beta emitter to tag a molecule The positron annihilates with an electron to form two gamma rays Detect the gammas on an imaging basis as in CT scans
    108. 108. Emission Tomography Coincidence of signal detection establishes the originating location.
    109. 109. Nuclear Magnetic Resonance Protons have an intrinsic angular momentum called spin You can think about this for the time being as the proton is like a little planet that rotates on its axis. Since the proton has charge, this means we have a rotating charge We can consider the rotating charge to be a tiny current
    110. 110. Nuclear Magnetic Resonance We learned that a current going in a loop generates a little magnetic field. When we place the loop in an external magnetic field, the magnetic field in the loop tends to line up with the external magnetic field You can convince yourself by considering the forces on the charges in the current as they circulate in the loop
    111. 111. Nuclear Magnetic Moment Long story short, the axis of spin of the proton wants to line up with the magnetic field that we apply externally The proton’s energy is lowest when the proton’s magnetic field points in the same direction as the external magnetic field It is higher when it points in the opposite direction
    112. 112. Nuclear Magnetic Resonance The proton’s energy level splits into two states depending on whether its spin is up or down. This is just like the Zeeman effect for electrons. The energy difference between these states corresponds to hf such that the frequency is about 40 MHz if the field strength is 1T. The energy is proportional to the field strength.
    113. 113. Nuclear Magnetic Resonance If the magnetic field is modified by the presence of other things like electrons in the neighborhood, then the frequency will be slightly different. By measuring the frequency of energy absorption by the protons we can deduce its electron environment.
    114. 114. Nuclear Magnetic Resonance This environment will depend on the chemical composition of the neighborhood. The changing frequency in different chemical environments is called the chemical shift. Chemists use this idea to study the structure of molecules.
    115. 115. Nuclear Magnetic Resonance For our purposes, we want to form images, so we need to sense the chemical shifts as a function of position in the body. Since different body structures have different chemical environments, we can map the structures by mapping the chemical shifts. This is MRI.
    116. 116. Nuclear Magnetic Resonance To get position information, we apply a magnetic field with a gradient (change in intensity from one location to another. Then we can carefully determine position.
    117. 117. Low Level Effects of Radiation The effects of low level radiation are hard to determine. There are no directly measurable biological effects at the background level. Long term effects of radiation may include heightened risk of cancer, but many different things have been related to long term heightened risk of cancer. Separating out the different effects and accounting for the different amounts of low level radiation make this very difficult to determine.
    118. 118. Low Level Effects of Radiation At the cellular level, a dose of 100 millirems of ionizing radiation gives on average 1 "hit" on a cell. (So the background radiation gives about 2 hits per year to each cell.) There are five possible reactions to a “hit”. 1. A "hit" on a cell can cause DNA damage that leads to cancer later in life. Note: There are other causes of DNA damage, a relatively large amount from normal chemical reactions in metabolism.
    119. 119. Low Level Effects of Radiation 2. The body may be stimulated to produce de-toxifying agents, reducing the damage done by the chemical reactions of metabolism. 3. The body may be stimulated to initiate damage repair mechanisms.
    120. 120. Low Level Effects of Radiation 4. The cells may kill themselves (and remove the cancer risk) by a process called apoptosis, or programmed cell death (a regular process that happens when the cell determines that things are not right). 5. The body may be stimulated to provide an immune response that entails actively searching for defective cells - whether the damage was done by the radiation or by other means.
    121. 121. Low Level Effects of Radiation There are two main theories: 1. Linear Hypothesis: A single radiation “hit” may induce a cancer. Therefore, the best amount of radiation is zero, and any radiation is dangerous. The more radiation, the more the danger. This says effect #1 is always more important than effects 2-5.
    122. 122. Low Level Effects of Radiation 2. Hormesis Hypothesis: A small amount of radiation is actually good, but a large amount of radiation is certainly bad. Many chemicals behave this way - for example B vitamins: we need some to live, but too much is toxic. Vaccines are also this way: we make ourselves a little sick to build up our defenses against major illnesses. This theory says that at low levels, effects 2-5 are more important than effect 1.
    123. 123. Radiation Treatments If high doses of radiation do bad things to biological systems, can radiation be used as a treatment? Ask yourself this: does a knife do harm to biological systems? If if does, why do surgeons use scalpels? Fast growing cancer cells are more susceptible to damage from radiation than normal cells. For cancer treatment, localized (not whole- body) doses regularly exceed 10,000,000 mrems.
    124. 124. FoodFood IrradiationIrradiation •Food can be irradiated withFood can be irradiated with γγ rays fromrays from 6060 Co orCo or 137137 Cs.Cs. •Irradiated milk has a shelf life of 3 mo.Irradiated milk has a shelf life of 3 mo. without refrigeration.without refrigeration. •USDA has approved irradiation of meatsUSDA has approved irradiation of meats and eggs.and eggs.
    125. 125. Measurement of Radioactivity Devices Film badges photographic film exposed to radiation Geiger Counter number of disintegrations Scintillation counter large number of samples in lab
    126. 126. Where does chemical energy come from? If chemicals are bound, then breaking the bonds does not release energy. It requires external energy. This energy can come from the formation of stronger bonds between the atoms, such as when you burn some sort of fuel. The fuel bonds break, but stronger bonds are formed with oxygen for a net release of energy. It can also come from the thermal energy of its surroundings, such as when you break the ionic bonds in salt by dissolving it in water Those are sources of net energy change, however. At the site of the bond itself, this energy comes from the electromagnetic force (although there is some KE of the electrons in addition to the electrical PE). The charges (electrons and the nuclei) in chemicals are not perfectly evenly distributed, causing net electrostatic fields. When bonds are broken or formed, this motion of charges in the fields (which exert a force on the charges) either absorbs or releases energy because the charges are being pulled or pushed by the electric fields of all the other charges present. If you want to think of it as an exchange of something, think of it as an exchange of photons (leave virtual photons out of this, that's for much faster processes involved in particle physics), which carry the electromagnetic force.
    127. 127. How about nuclear energy source? The nucleus has its own forces, AND the electromagnetic force. Typical nuclear reactions are dictated by the strong force, which holds the nucleus together. The weak nuclear force predominantly causes beta decays. But the queston is about the force between the parts of a nucleus, what holds it together, and that is the strong force. The exact form of the strong nuclear force is still a mystery. We have what we believe to be relatively exact models for the other 3 forces (electromagnetism, the weak force, and gravitation), although there's some debate about the extent of the knowledge we have about those. But the exact nature of the strong nuclear force remains unknown. It results from the exchange of a zoo of virtual particles (gluons and mesons), and it depends on too many things (such as the spins of the protons and neutrons which are bound together in the nucleus) to go into here. But it's just another force like gravitation and electromagnetism. The reason you don't feel it personally is that it's very short-range, it essentiall ends at the boundaries of the nucleus itself. Electromagnetic forces (like what holds magnets on your refrigerator) and gravitation are long-range, so we're more familiar with them because they do operate on objects which are of lengths that we can see and touch. So, just like gravity pulls a rock towards the center of the Earth and makes it take energy to roll uphill (or pick up energy as it rolls downhill), adding nucleons (protons and neutrons) to or removing them from a nucleus requires energy. Think of the nucleus as a pit into which nucleons fall, pulled down by a strange type of gravity that suddenly gets really strong right next to and inside the hole. Now if you add a nucleon to a nucleus, it will generally just scatter unless there's some way to convert this strong force into energy that can be released. This can be in several forms, such as photons (gamma-rays are photons emmited by such processes which have very high energies) or other particles with high energies (say a proton fuses with a nucleus and a neutron is ejected). If the incoming nucleon has enough energy, that energy can be converted into new (generally unstable) particles. The nucleus is a complex place, so there's no single answer to that aspect of your question.
    128. 128. Final Nuclear Notes Mostly the energy released is in the form of kinetic energy of the products of the reaction. For example, in the proton-proton chain that powers the sun: proton + proton -> deuteron + positron + neutrino + KE of products The mass of the deuteron + positron + neutrino is less than the mass of the two protons; this excess mass was converted to energy, in the form of kinetic energy of the deuteron, positron, and neutrino. Usually, if there is electromagnetic radiation involved, it is listed explicitly (as a gamma ray), as in the next step in that chain: proton + deuteron -> helium-3 + gamma + KE of products So you get both electromagnetic radiation (the gamma ray) and energy, in the form of kinetic energy of the helium-3 nucleus and the gamma ray. Similarly, in fission reactions, the excess energy is in the form of kinetic energy of the nuclear fragments. In the following figure, this energy is referred to as "heat energy"; however, heat energy on an atomic scale is just kinetic energy
    129. 129. Measuring Health Effects Gamma rays (high energy photons) are very penetrating, and so generally spread out their ionizations (damage). Beta rays (high speed electrons) are less penetrating, and so their ionizations are more concentrated. Alphas (high speed helium nuclei) do not penetrate very far since their two positive charges interact strongly with the electrons of the atoms in the material through which they go.
    130. 130. Measuring Health Effects This difference in penetrating ability (and localization of ionization) leads us to create an RBE (radiation biological equivalent) factor and a new unit: the rem. The more localized the ionization, the higher the RBE. # of rems = RBE * # of rads . This is called an EFFECTIVE dose. RBE for gammas = 1; RBE for betas = 1 to 2; RBE for alphas = 10 to 20.
    131. 131. Levels of Radiation and Health Effects In addition to our own radioactivity (and our food), we receive radiation from: a) space in the form of gamma rays; the atmosphere does filter out a lot, but not all; b) the ground, since the ground has uranium and thorium; c) the air, since one of the decay products of uranium is radon, a noble gas. If the Uranium is near the surface, the radon will percolate up and enter the air.
    132. 132. Nuclear Physics size of atoms: take water (H2O) density = 1 gm/cc, atomic weight = 18 gm/mole, (alternately, get mass of one molecule from mass spectrograph) Avogadro’s number = 6 x 1023 /mole (1 cm3 /gm)*(18 gm/mole) / (6x1023 molecules/mole) = 3 x 10-23 cm3 /molecule, so datom = V1/3 = 3 x 10-8 cm = 3 x 10-10 m.
    133. 133. Mass Defect & Binding Energy By definition, mass of 6C12 is 12.00000 amu. The mass of a proton (plus electron) is 1.00782 amu. (The mass of a proton by itself is 1.00728 amu, and the mass of an electron is 0.00055 amu.) The mass of a neutron is 1.008665 amu. Note that 6*mproton+e + 6*mneutron > mC-12 . Where did the missing mass go to?
    134. 134. Mass Defect & Binding Energy Similar question: The energy of the electron in the hydrogen atom is -13.6 eV. Where did the 13.6 eV (amount from zero) go to in the hydrogen atom? Answer: In the hydrogen atom, this energy (called the binding energy) was emitted when the electron “fell down” into its stable orbit around the proton.
    135. 135. Mass Defect & Binding Energy Similarly, the missing mass was converted into energy (E=mc2 ) and emitted when the carbon-12 atom was made from the six protons and six neutrons: ∆m = 6*mproton + 6*mneutron - mC-12 = 6(1.00782 amu) + 6(1.008665 amu) - 12.00000 amu = .099 amu; BE = ∆m*c2 = (0.099 amu)*(1.66x10-27 kg/amu)*(3x108 m/s)2 = 1.478x10-11 J*(1 eV/1.6x10-19 J) = 92.37 MeV
    136. 136. Mass Defect & Binding Energy For Carbon-12 we have: BE = ∆m*c2 = 92.37 MeV If we consider the binding energy per nucleon, we have for carbon-12: BE/nucleon = 92.37 MeV /12 = 7.70 MeV/nucleon. The largest BE/nucleon happens for the stable isotopes of iron (about 8.8 MeV/nucleon).
    137. 137. Mass Defect and Binding Energy Be careful: The fact that isotopes of iron have the highest binding energy per nucleon is NOT related to iron being a hard metal. The fact of being a metal is determined by the ELECTRONIC shells, NOT the nuclear binding. Note: Chemical binding energies (ionization energies) are on the order of several eV. Nuclear binding energies are on the order of several MeV. Nuclear energies are thus an order of a million times stronger than electrical binding energies!
    138. 138. Plot of energy versus the separation distance
    139. 139. Nucleus: Particle Potential Wells Electron is only bound with negative total energy, and can never escape. Nucleon can be bound with positive total energy, and can escape by tunneling through the Coulomb barrier → nuclear decay processes. Leads to radioactive processes. Electron Coulombic PotentialNucleon Nuclear Potential Energy Radius r
    140. 140. Radiation Processes: β– Decay (e– Emission) Parent nucleus decays to daughter nucleus plus electron and anti-neutrino. Anti-neutrino is 3rd particle that explains range of electron kinetic energies. If atom (Z) has greater mass than its right neighbor (Z+1), then β– decay is possible. Free neutron can decay into a proton. t1/2 = 10.8 min, Q = 939.57 – (938.28 + 0.511) = 0.78 MeV ( ) ( ) 2 1 1 *electron mass included in daughter nucleus ( ) A A Z A A Z Z ZX D Q MeV Ma e v ss X Mass D c+ − +→ + +  = − 
    141. 141. Positron Emission Tomography (PET) – A new and Important Tool in Imaging Research In the technique of positron Tomography, a positron emitting isotope Is included into a molecule that is incorporated into a chemical reaction. The positron emitted during the decay of the isotope will analite with an Electron and emit two 511 kev gamma rays that can then be detected, and the location of the decaying isotope isolated accurately. B+ + e- Energy Two Gamma rays at 180o e- + B+ 511 kev 511 kev Common Positron emitting Isotopes: 15 O, T1/2 = 122s ; 18 F, T1/2 = 1.83 hr 11 C, T1/2= 20.3 min , 13 N, T1/2 = 9.97 min , ETC The two gamma rays come away at 180o .
    142. 142. Positron Emission Tomograph The Tomograph is an instrument that is a ring of gamma ray detectors that react very fast to gamma rays, and by measuring the time each detector receives the signal one can locate the point of origin of the gamma ray to a precision of + 1 cm in a human being or any other physical object, with out any in vivo investigation. The detectors must have a capability of measuring up to + 250 ps per pulse. _ _
    143. 143. Four Known Forces  Two familiar kinds of interactions: gravity (masses attract one another) and electromagnetism (same-sign charges repel, opposite- sign charges attract)  What causes radioactive decays of nuclei ? Must be a force weak enough to allow most atoms to be stable.  What binds protons together into nuclei ? Must be a force strong enough to overcome repulsion due to protons’ electric charge
    144. 144. Previously, we peered inside the atom We recalled that electrons orbit the atom’s massive nucleus and determine an element’s chemical behavior. We explored the proton and neutron content of nuclei and the phenomena of radioactivity, fission, and fusion they make possible. Today we’ll look inside the nucleons themselves. Fundamental particles in the Standard Model are: Leptons Quarks Intermediate Gauge Bosons
    145. 145. Anti-matter Each kind of elementary particle has a counterpart with the same mass, but the opposite electric charge, called its “anti-particle”. Electron: m= .0005 GeV, charge = +1, symbol e- Positron: m = .0005 GeV, charge = -1, symbol e+ The anti-particle has a bar over its symbol: Anti-proton is written , anti-neutrino is Anti-matter is rare in the explored universe It’s created in cosmic rays and particle accelerators and some radioactive decays. When a particle and its anti-particle collide, they “annihilate” one another in a flash of energy. p v
    146. 146. Where do the elements come from?
    147. 147. Stability diagram Heavy elements can fission into lighter elements. Light elements can undergo fusion into heavier elements. Elements from helium to iron were manufactured in the cores of stars by fusion. Heavier elements are metastable and were made during supernovae explosions.
    148. 148. Fission: Chain Reaction Use neutrons from fission process to initiate other fissions! 1942: Fermi achieved first self-sustaining chain reaction. For nuclear bomb, need more than one neutron from first fission event causing a second event. For nuclear power plant, need less than one neutron causing a second event.
    149. 149. Chain reaction For reaction to be self-sustaining, must have CRITICAL MASS.
    150. 150. Figure 21.11: Upon capturing a neutron, the 235 U nucleus undergoes fission to produce two lighter nuclides, free neutrons (typically three), and a large amount of energy.
    151. 151. Figure 21.12: Representation of a fission process in which each event produces two neutrons, which can go on to split other nuclei, leading to a self-sustaining chain reaction.
    152. 152. Figure 21.13: If the mass of the fissionable material is too small, most of the neutrons escape before causing another fission event; thus the process dies out.
    153. 153. Nuclear reactors
    154. 154. Fusion Light nuclei are more stable when combined Tremendous energy released Hydrogen bombs and Fusion power?
    155. 155. Schematic diagram of a cyclotron
    156. 156. Physicist works with a small cyclotron at the University of California at Berkeley. Source: Corbis
    157. 157. CERN, the world's largest particle accelerator, lies at the foot of the Jura Mountains near Geneva, Switzerland.
    158. 158. Diagram of a linear accelerator
    159. 159. Accelerator tunnel at Fermilab, a high-energy particle accelerator in Batavia, Illinois. Source: Fermilab Batavia, IL
    160. 160. Units used for Nuclear Energy Calculations electron volt - (ev) The energy an electron acquires when it moves through a potential difference of one volt: 1 ev = 1.602 x 10-19 J Binding energies are commonly expressed in units of megaelectron volts (Mev) 1 Mev = 106 ev = 1.602 x 10-13 J A particularly useful factor converts a given mass defect in atomic mass units to its energy equivalent in electron volts: 1 amu = 931.5 x 106 ev = 931.5 Mev

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