Nuclear Chemistry 1 Copyright 2000 by Harcourt Inc

Comparison Of Chemical and Nuclear Reactions Chemical Reactions 1 No new elements can be produced. 2 Usually only the outer most electrons participate 3 Release or absorb relatively slight amounts of energy. 4 Rate of reaction depends on factors such as concentration, pressure, temperature, and catalysts. 2 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Comparison Of Chemical and Nuclear Reactions 1 Elements may be converted from one to another. 2 Particles within the nucleus are involved. 3 Release or absorb immense amounts of energy. 4 Rate of reaction is not influenced by external factors. 3 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Beginning of Nuclear Science 1896 - Henri Becqurel – discovers radioactivity in U salts 1898 - Marie and Pierre Curie – discover two new radioactive elements – Po and Ra 1898 - Ernest Rutherford – discovers that radioactivity has two forms a and b radiation 4 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Radioactive decay (transmutation) v During nuclear reactions atoms can change into new elements through radioactive decay v When balancing reactions make sure the mass numbers and atomic numbers before and after the arrow are equal 5 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Several types of radioactive decay 4 Nuclide too large – alpha or 4 Too many neutrons Beta minus (electron) or 4 Too many protons, Beta plus (also called positron electron capture or k-capture) or Copyright © 2000 by Harcourt, Inc. All rights reserved.

Other types of particles used during radioactive decay Ø Neutron Ø Proton or Ø

Examples 1) 218 Po + ? 2) 253 Es + ? + 3) 142

Examples 1) 218 Po 2) 253 Es + 3) 142 Pm + ? ?

Examples • 7 = instead of + + + • Try 4 10 Copyright

Main Types of Radiation 4 Alpha (2 protons and 2 neutrons) 4 Beta (electron)

Radiation Interaction with Matter Copyright © 2000 by Harcourt, Inc. All rights reserved.

Alpha particles – first to be discovered Radium-226 Radon-222 alpha particle Mass number must = 4 Atomic number must = 2 So an alpha particle is 2 protons and 2 neutrons, and has a charge of +2. The element Helium has a mass of 4 and an atomic number of 2, so the alpha particle is just like a helium atom without any electrons 13 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Beta particles Carbon-14 Nitrogen-14 beta particle Mass number must = 0 Atomic number must = -1 The electron has a mass of zero and a charge of -1, so the beta particle is just like an electron; Beta particles are produced when a neutron changes into a proton; an electron is ejected from the nucleus 14 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Gamma rays – last to be found Uranium-238 thorium-234 alpha particle gamma ray Mass number must = 0 Atomic number must = 0 The gamma ray has no mass and no charge; Gamma rays usually occur with alpha and beta radiation They account for most of the energy lost during radioactive decay 15 Copyright © 2000 by Harcourt, Inc. All rights reserved.

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Alpha particles (+ charge) deflect towards the negative plate Beta particles (- charge) deflect towards the positive plate Gamma rays (no charge) are not deflected at all 17 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Detecting Radiation What do you need in order to detect radiation? – Material for interaction – Method of measuring the interaction 4 Typical detectors include – Gas filled counters, semiconductor based (Geiger counters) – Luminescent film (Photographic detection) – Florescent detection (Scintillators absorb energy and then emit visible light) Copyright © 2000 by Harcourt, Inc. All rights reserved.

Fission and Fusion Nuclear fission (fizzing like pop rocks or shaking a coke) – splitting of a heavy nucleus into two lighter nuclei Nuclear fusion (fusing two things together) – combining two light nuclei into one heavier nucleus Both processes generate enormously large amounts of energy 19 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Fusion Fission Merge (makes heavier products) Release tremendous amounts of energy Produces no radioactive waste Hydrogen + Hydrogen Helium Involves changes in the atom at the subatomic level Currently not feasible Split up (makes lighter products) Release tremendous amounts of energy Produces radioactive waste Uranium lots of smaller radioactive elements Involves changes in the atom at the subatomic level Used at nuclear reactors 20 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Nuclear Fusion is the most energetic process in nature. – energy source of stars, fusion reaction is in the main sequence of stars – produces chemical elements – potential energy source for humans Thermonuclear or hydrogen bombs have been in existence since the 1950’s 21 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Nuclear Fusion (Thermonuclear) Energy Controlled nuclear fusion – must occur at temperatures of » 10 million o. C Fusion reactors must contain this temperature and not melt! Some fusion reactors exist around the world – Although none can currently generate a sustainable fusion reaction Possible energy source for the 21 st Century 22 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Nuclear Fission Most nuclides with atomic numbers greater than 80 are able to undergo fission – They split into nuclei of intermediate (smaller) masses and emit one or more neutrons Some fission reactions are spontaneous while others require activation, usually by neutron bombardment (hit by a neutron). 23 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Nuclear Fission – chain reaction Some possible fission paths for 235 U are (after

Nuclear fission demo 4 https: //www. youtube. com/watch? v=XIv. Hd 76 Ed. Q 4

Nuclear Reactors (Fission) Electricity can be generated from steam heated by nuclear fission reactions. Nuclear power is a cost effective and relatively safe way to produce power Greatest danger of nuclear reactors is core meltdown. 26 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Serious nuclear reactor accidents: – Three Mile Island, PA (1979) Nuclear reactor malfunctioned – no meltdown, but some radioactive contamination. Affected a 25 mile radius – Chernobyl , Russia (1986) Nuclear reactor’s cooling system failed – meltdown. Released thirty times the radioactivity of the atomic bombs dropped on Hiroshima and Nagasaki. 31 lives were lost immediately. Radiation in soil & atmosphere still presents significant health risks. 27 Copyright © 2000 by Harcourt, Inc. All rights reserved.

– Japan (2011) After the earthquake and tsunami that hit Japan in 2011. The cooling system of the nuclear power plant in Fukushima failed causing the reaction to spiral out of control. The heat produced by the reaction caused the Uranium to decay to Cesium 137, a very unstable atom that caused most of the environment to become radioactive. This has caused the area to become a dead zone. 28 Copyright © 2000 by Harcourt, Inc. All rights reserved.

On a happy note: Nature thrives in Chernobyl 4 About 30 years after the world’s worst nuclear accident blasted radiation across Chernobyl, the site has evolved from a disaster zone into a nature reserve, filled with numerous animals 4 The population rates are similar to those found in four comparable, and uncontaminated, nature reserves in the region. 29 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Animals found in the Chernobyl exclusion zone. Recent pictures of wild animals taken in Chernobyl: deer, wolf, elk, lynx, and boars The radiation contamination is still heavy but since people are mainly absent, the animals are thriving. 30 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Nuclear Reactors (Fission) Fuel - 235 UO 2 or 239 Pu Moderator – a material usually graphite or water that slows neutrons from fast to thermal Control Rods - removes neutrons and slows the chain reaction – usually made of boron, efficient neutron absorber Shielding - protection from radiation – lead and concrete are commonly used Cooling Systems - reactor core must be cooled to remove heat – possible coolants: water, helium, and liquid sodium 31 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Turning Heat into Electricity BWR: Boiling Water Reactors PWR: Pressurized Water Reactors Copyright ©

Comanche Peak Copyright © 2000 by Harcourt, Inc. All rights reserved.

Radiation all around us 4 Naturally occurring radiation – K-40, Thorium, Radium – Cosmic 4 Radiation in household products – Fiestaware • (1936 – 1959) used U • (1959 – 1973) used depleted U – Fire Detectors • Uses Americium-95 – Antique Clocks and watches • Used Radium which glows in the dark • 1917 – women who worked at the U. S. Radium Factory were told that the Ra was harmless. They ingested deadly amounts of Ra and in turn became incredibly ill. This is an important time in history for labor rights Copyright © 2000 by Harcourt, Inc. All rights reserved.

Health concerns Acute radiation to cells causes them to divide and grow without control – this creates a tumor (cancer) *More harmful to children than adults 35 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Health benefits Radiation can be used to actually destroy cancerous growths Medical Field - Wide spread use in medical imagining and diagnostics. – CT Scans – PET Scans – X-rays – Cancer Treatments – Radioactive barium used in “milkshakes” for colon exams. 36 Copyright © 2000 by Harcourt, Inc. All rights reserved.

More benefits Many uses of nuclear radiation in industry, agriculture, space research – used in archaeology, biology, physics, chemistry, cosmology Food Industry – Food is sometime irratdiated to kill the bacteria that causes food to spoil Crime Scene Investigations 37 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Radioactive Dating Carbon dating can be used to estimate the ages of items of organic origin. 14 C is produced continuously in the upper atmosphere by the bombardment of 14 N by cosmic-ray neutrons: 14 C atoms then react with O to form CO 2 2 – CO 2 then is incorporated into plant life by photosynthesis. After material dies 14 C content decreases from radioactive decay ~ 14 C half-life is 5730 years. 38 Copyright © 2000 by Harcourt, Inc. All rights reserved.

Half Life Half life the amount of time it takes for half of a sample to decay. Ex. the half life of carbon-14 is 5730 years. – This means that if you start with 24 grams of carbon 14, 5730 years later you will have 12 grams, 5730 years after that you will have 6 grams, 5730 years after that you will have 3 grams. Copyright © 2000 by Harcourt, Inc. All rights reserved.

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Mythbusters ● Myth #1 Americans get most of their yearly radiation dose from nuclear power plants Dental X-ray ~ 1 mrem ●Natural Radiation ~ 30 mrem per yr ● 3 hour flight ~ 1. 5 mrem ●Living within 50 miles of a Nuclear plant ~0. 01 mrem ● Copyright © 2000 by Harcourt, Inc. All rights reserved.

Mythbusters Myth #2 ● A nuclear power plant can explode like a nuclear bomb –It is impossible for a reactor to explode like a bomb. – Bombs require much, much higher levels of fuel enrichment and must be configured in a specific geometry – Neither of which are present in a power plant Copyright © 2000 by Harcourt, Inc. All rights reserved.

Mythbusters Myth #3 ● The smoke you can see from a cooling tower is radioactive – The `smoke' is actually water vaper. The water is very clean and has no detectible radiation Copyright © 2000 by Harcourt, Inc. All rights reserved.

Mythbusters Myth #4 ● An event similar to Chernobyl can happen in the USA The Chernobyl design is vastly different than what is operating in the US – Chernobyl used graphite as a moderator not water – Graphite has postive reactivity coefficient, water has a negative reactivity coefficient – Chernobyl did not have containment, American reactors have 3 levels of containment Fuel Rod, Reactor Vessel, and Containment building – Copyright © 2000 by Harcourt, Inc. All rights reserved.