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I. Nuclear Radiation

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(2) I. Nuclear Radiation A common misconception is that radioactivity is new in the environment, it has been around much longer than the human race..

(3) A. The Discovery of Radioactivity 1. W. Roentgen (1895) • produced and discovered X-rays.

(4) A. The Discovery of Radioactivity 2. H. Becquerel (1896) • uranium salts produce X-ray-like radiation. Image of Becquerel's photographic plate which has been fogged by exposure to radiation from a uranium salt. The shadow of a metal Maltese Cross placed between the plate and the uranium salt is clearly visible..

(5) A. The Discovery of Radioactivity 3. Marie & Pierre Currie • isolated components of pitchblende that give off rays • coined the term ‘radioactivity’ • discovered Po & Ra • helped develop nuclear medicine • died because of exposure to radiation Curie in a mobile X-ray vehicle.

(6) B. Types of Radiation • Radioisotope – an isotope that has an unstable nucleus and undergoes radioactive decay Stable elements Radioactive elements with very long-lived isotopes Radioactive elements that may present low health hazards. Radioactive elements that are known to pose high safety risks. Highly radioactive elements. Extremely radioactive elements..

(7) 1. Alpha (α or • 5% speed of light • E = 5 MeV. 4 2 He).

(8) 2. Beta (β. 0 or -1 e). • 75% speed of light • E = 0.05 to 1 MeV • produced when neutrons decompose into p+ and e-.

(9) 3. Gamma (γ) • 100% speed of light • E = 1 MeV • high E EM radiation. Gamma rays are emitted during nuclear fission in nuclear explosions..

(10) 4. X-rays • very similar to gamma rays (lower E) • not produced by radioactive sources • produced when a beam of electrons strikes a metal target • produced by exploding stars and black holes • passes through soft tissue but blocked by bones X-rays are part of the electromagnetic spectrum, with wavelengths shorter than visible light. Different applications use different parts of the X-ray spectrum..

(11) II. Radioactive Decay.

(12) 4. Radioactive Decay • an unstable nucleus loses energy by emitting radiation.

(13) A. Nuclear Stability • Transmutation – the conversion of an atom from one element to an atom of a different element • can occur by radioactive decay or when an atom is bombarded by high energy particles.

(14) A. Nuclear Stability • Nucleon – particles found in the nucleus • p+ and n0 • protons repel each other due to electrostatic forces.

(15) A. Nuclear Stability • Strong Nuclear Force (SNF) – a force that acts on subatomic particles that are extremely close together • Range = 1-3 fm (femto = 10-15) • overcomes the p+ repulsion • binds the nucleus together.

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(17) B. Neutron-to-Proton Ratio • for ‘light’ elements the n:p ratio is 1:1 • Ex: He 2:2 (1:1).

(18) B. Neutron-to-Proton Ratio • for ‘heavy’ elements the n:p ratio is 1.5:1 • Ex: Pb 126:82 (1.54:1).

(19) B. Neutron-to-Proton Ratio • as more p+ are added to the nucleus the repulsive forces increase • more neutrons are needed to produce the SNF required to stabilize the nucleus The two opposing forces in a nucleus are the electrical repulsion between the positively charged protons and the residual strong nuclear force which pulls the protons and neutrons together and, if the numbers of protons and neutrons are not too different, overpowers the electrical forces..

(20) C. The Band of Stability (BoS) • location of stable nuclei on a n0 vs. p+ plot • all elements beyond atomic #82 are radioactive • too few neutrons and protons repel protons The neutron-vs-proton plot of all the known stable nuclei forms a pattern called the "Band of Stability"(shown in red). For isotopes with low atomic number, the stability ratio is about 1:1. For heavier isotopes the ratio increases to about 1:1.5.. Neutrons Protons. 1.5 = 1. Neutrons Protons. 1 = 1.

(21) D. Types of Decay 1. Beta Decay • isotopes above the BoS • too many neutrons and the n0 split apart into a p+ and an e-.

(22) D. Types of Decay 2. Alpha Decay • isotopes > atomic # 82 • need to reduce the # of p+ and n0.

(23) D. Types of Decay 3. Positron Emission and Electron Capture • isotopes below the BoS • Positron (e+ or β+) – particle with the same mass as an e- but an opposite charge.

(24) D. Types of Decay 3. Positron Emission and Electron Capture • Positron Emission – a decay process that transforms a p+ in the nucleus into a n0 • atomic # decreases by 1 • Ex: p+ n0 + e+.

(25) D. Types of Decay • Electron Capture – occurs when the nucleus of an atom draws in a surrounding e• this captured e- combines with a p+ to form a n0 • Ex: p+ + en0 • atomic # decreases by 1.

(26) E. Radioactive Decay Series • a series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus.

(27) F. Radioactive Decay Rates • Half-Life (t1/2) – time required for half of the nuclei of a radioisotope to decay • different isotopes have different half-lives • shorter half-lives represent greater radioactivity.

(28) F. Radioactive Decay Rates • N = N0 • • • • •. 1 2. t / t1/2. N = remaining amount N = remaining amount N0 = initial amount t = elapsed time t1/2 = half-life.

(29) F. Radioactive Decay Rates • ex: Rn-222 has a half-life of about 4.0 days. If you start with 10.0 g of Rn-222, how much will be left after 12 days? (get your calculator ready!) • N0 = 10.0 g • t = 12 days • t1/2 = 4.0 days.

(30) F. Radioactive Decay Rates • ex: Rn-22 has a half-life of about 4.0 days. If you start with 10.0 g of Rn-222, how much will be left after 12 days? (get your calculator ready!). N = 10.0 g. 1 2. 12 d / 4.0 d.

(31) F. Radioactive Decay Rates • ex: Rn-22 has a half-life of about 4.0 days. If you start with 10.0 g of Rn-222, how much will be left after 12 days? (get your calculator ready!) • the exponent could be reduced to 3.0. N = 10.0 g. 1 2. 3.0.

(32) F. Radioactive Decay Rates • ex: Rn-22 has a half-life of about 4.0 days. If you start with 10.0 g of Rn-222, how much will be left after 12 days? (get your calculator ready!) • the exponent could be reduced to 3.0 • N = 1.25 g = 1.3 g N = 10.0 g. 1 2. 3.0.

(33) G. Radiochemical dating • the process of determining the age of an object by measuring the amount of certain radioisotopes remaining in the object • Ex: C-14 dating.

(34) G. Radiochemical dating After years of discussion, the Holy See permitted radiocarbon dating on portions of a swatch taken from a corner of the shroud. Independent tests in 1988 at the University of Oxford, the University of Arizona, and the Swiss Federal Institute of Technology concluded with 95% confidence that the shroud material dated to 1260–1390 AD. This 13th to 14th century dating is much too recent for the shroud to have been associated with Jesus of Nazareth. The dating does on the other hand match the first appearance of the shroud in church history.[64] This dating is also slightly more recent than that estimated by art historian W.S.A. Dale, who postulated on artistic grounds that the shroud is an 11th-century icon made for use in worship services..

(35) III. Nuclear Reactions.

(36) A. Induced Transmutation • the process in which nuclei are bombarded with high-velocity charged particles in order to create new elements 17 14 4 1 • Ex: 7 N + 2 He O + H 8 1.

(37) A. Induced Transmutation • Transuranium Elements - elements with atomic numbers 93 and above • made in a laboratory • all are radioactive • named after people and places.

(38) B. Nuclear Reactions and Energy • • • • •. Einstein's Equation: E = mc2 E and m are equivalent c2 is a very large # a small Δ is m produces a large Δ in E.

(39) C. Fission • splitting of a (large) nucleus into smaller fragments • releases a LARGE amount of E 141 92 1 1 • Ex: 235 U + n Ba + Kr + 3( n) + E 56 92 36 0 0 •.

(40) C. Fission • Chain Reaction - self-sustaining reaction in which the products of one reaction stimulate further reactions.

(41) C. Fission • Critical Mass - a sample massive enough to sustain a chain reaction.

(42) D. Nuclear Reactors • use controlled fission to produce useful energy • energy is released as heat that produces steam, drives a turbine, and generates electricity • care must be taken to not let the reactor overheat • (meltdown).

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(44) D. Nuclear Reactors • Nuclear Waste - a byproduct of fission that is difficult to dispose of and remains radioactive for thousands of years.

(45) D. Nuclear Reactors • Breeder Reactors - produce more fuel than they use.

(46) E. Atomic Bombs • uncontrolled fission chain reaction that releases energy in an instant • 1 kg (2.2 lbs) of U-235 releases the same amount of energy as 20,000 tons of dynamite.

(47) Diagram of a gun-type fission weapon.

(48) Fat Man, the Nagasaki bomb, used 13.6 lb (6.2 kg, about 12 fluid ounces or 350 ml in volume) of Pu-239, which is only 39% of bare-sphere critical mass. Surrounded by a U-238 reflector/tamper, the pit was brought close to critical mass by the neutron-reflecting properties of the U-238. During detonation, criticality was achieved by implosion. The plutonium pit was squeezed to increase its density by simultaneous detonation of the conventional explosives placed uniformly around the pit..

(49) The first nuclear weapons, though large, cumbersome and inefficient, provided the basic design building blocks of all future weapons. Here the Gadget device is prepared for the first nuclear test: Trinity..

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(54) F. Fusion (Thermonuclear Reaction) • combination of (small) atomic nuclei • releases a HUGE amount of E 4 1 • Ex: 21H + 31H He + n + E 2 0.

(55) F. Fusion (Thermonuclear Reaction) • • • •. fuel is plentiful occur at very high T byproducts are not radioactive difficult to contain and control At short distances the attractive nuclear force is stronger than the repulsive electric force. As such, the main technical difficulty for fusion is getting the nuclei close enough to fuse. Distances not to scale..

(56) F. Fusion (Thermonuclear Reaction) • Hydrogen (Thermonuclear) Bomb - achieve the high T needed for fusion by using a fission bomb as a trigger.

(57) The basics of the Teller–Ulam configuration: a fission bomb uses radiation to compress and heat a separate section of fusion fuel..

(58) The only fusion reactions thus far produced by humans to achieve ignition are those which have been created in hydrogen bombs, the first of which, Ivy Mike, is shown here. Equivalent to 10.4 megatons of TNT.

(59) A photograph of Operation Castle thermonuclear test, Castle Romeo shot. This bomb had a yield of 15 megatons (2.5 times higher than expected) and is the largest U.S. bomb ever tested..

(60) Mushroom cloud f Soviet 50-megato Bomba, the most nuclear weapon e detonated (1961).

(61) • every second the sun converts 657 million tons of hydrogen into 653 million tons of helium • every second the sun converts 4 million tons of mass into radiant energy --> that's our sunshine!.

(62) Questions ▪ How are we exposed to radiation? ▪ How can we detect radiation? ▪ How is radiation used?.

(63) IV. Application and Effects of Nuclear Reactions.

(64) Ionizing Radiation • Radiation that carries enough energy to liberate electrons from atoms or molecules • Cannot be detected by your 5 senses • Dangerous to living things • Photons: γ-rays, X-rays • Subatomic particles from radioactivity: α, β- (e-), n0, β+ (e+).

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(66) A. Detecting Radiation • Geiger Counter - mainly used to detect β radiation • Gas-filled metal tubes used to detect radiation.

(67) A. Detecting Radiation • Scintillation Counter – can detect α, β, and γ • Photons generated in presence of radiation and converted to electrical signal.

(68) A. Detecting Radiation • Film Badge – Personal dosimeter used to monitor cumulative radiation exposure.

(69) B. Using Radiation ▪ Analyze composition of materials • Si wafers • Petroleum products • Pollution • Chemicals.

(70) Irradiation ▪ Certain types of radiation kill germs without harming the object • Foods take much longer to spoil • Medical equipment can be sterilized ▪ Does not make it radioactive.

(71) Radioactive Tracers • Labeling substances to track their paths – – – –. Air, water pollution Industrial leaks Medical uses Research.

(72) Agriculture ▪ Test the effects of pesticides, herbicides and insecticides ▪ Study plant growth and reproduction. A solution of phosphate, containing radioactive phosphorus-32, is injected into the root system of a plant. A Geiger counter is then used to detect the movement of the radioactive phosphorus-32 throughout the plant. This information helps scientists understand the detailed mechanism of how plants utilized phosphorus to grow and reproduce..

(73) Medicine ▪ Detect certain diseases ▪ PET, SPECT ▪ X-rays, CT scans. Positron emission tomography (PET scan) has seen markedly increased usage by doctors over the past 10 to 15 years. PET is a nuclear imaging technique, used in conjunction with a CT scanner to image for possible cancer and/or metastases. Using FDG, an analog of glucose, the PET scan detects tissue with increased metabolic activity..

(74) Medicine ▪ Treat certain types of cancer ▪ Iodine-131 treats thyroid cancer. A ring of hair loss is one of the symptoms of the radiation overexposure..

(75) Ionizing Smoke Detectors • Very, very small amount of americium-241 Outside and inside view of an americium-base d smoke detector.

(76) C. Biological Effects of Radiation Average annual dose: 0.1-0.3 rem (100-300 mrem) Dose 0-25 rem. Effect No detectable effect. 25-50 rems. Slight decrease in white blood cell count. 50-100 rems. Headache, nausea, drop in white cells, increased cancer risk. 100-200 rems. Nausea, vomiting, major drop in white cells, fatigue, 10% fatal after 30 days. 200-300 rems. Vomiting, hair loss, diarrhea, loss of appetite, listlessness, sterility, 35% fatality after 30 days. 300-600 rems. Hemorrhaging, 50-60% chance of death within 30 days. 600-1000 rems. Destruction of bone marrow, internal bleeding, near 100% fatality after 14 days. 1000-5000 rems. Symptoms within 30 minutes, massive diarrhea, internal bleeding, delirium, coma, death within hours or days. 5000-8000 rems. Coma in seconds or minutes, fatal within hours. Over 8000 rems. (Usually) instant, or nearly instant, death.

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