Unit 6 Nuclear Reactions Chapter 20 (p ) Chapter 20 (p )

VocabularyVocabulary 1.Alpha particle 2.Beta particle 3.Gamma 4.Radiation 5.Transmutation 6.Nuclear decay 7.Half-life 8.Radioactive dating 9.Fission 10.Fusion 11.Chain reaction 12.Radioactive isotopes (tracers) 13.Nuclear energy

Purpose: Understand the difference between a chemical rxn and a nuclear rxn.  Purpose on ISN 122.  Notes on ISN 123.  Homework on ISN 122. WKBK 245 Compare & Contrast

Strong Force  Protons (P + ) & neutrons (n 0 ) are the particles in the nucleus.  Strong Force: force that causes p+ & n 0 to be attracted to eachother.  Short-range force  As distance increases, the force becomes weaker

Electric Force  Normally causes p+ to repel other p+  Long range force  Causes repulsion over long distances Stong (Nuclear) vs. Electric Forces Animation All 4 charges explained video

Nuclear Forces  The strong nuclear force attracts protons and neutrons.  Stronger than electric forces over short distances  Decreases with distance (like gravity)  Electric repulsions push protons apart.  When a nucleus is large enough, the electric forces can overcome the strong nuclear forces.  Nuclei are unstable at this point.  Any atom with 83 or more protons is unstable – and, therefore, radioactive. 6 Small nucleus Proton from a small nucleus Proton from a large nucleus Strong nuclear forces: Electric forces: Large nucleus

Nuclear Reactions with respect to other changes Energy drives all reactions, physical, chemical, biological, and nuclear. Physical reactions change states of material among solids, liquids, gases, solutions. Molecules of substances remain the same. Chemical reactions change the molecules of substances, but identities of elements remain the same. Biological reactions are combinations of chemical and physical reactions. Nuclear reactions change the atomic nuclei and thus the identities of nuclides. They are accomplished by bombardment using subatomic particles or photons.

Purpose: Compare & contrast alpha & beta decay to gamma radiation.  Purpose on ISN 124.  Notes on ISN 125.  Homework on ISN 124. WKBK 248 Compare & Contrast

Types of Radiation  Alpha (  )  helium nucleus paper 2+  Beta-minus (  -)  electron 1- lead  Gamma (  )  high-energy photon 0 concrete

3 Types of Nuclear Radiation  Nuclear radiation: charged particles and energy that are emitted from the nuclei of radioisotopes Radiation Type SymbolChargeMass (amu)Common Source Alpha particle ,, 2+4Radium-226 Beta particle ,, 1-Carbon-14 Gamma ray  00Cobalt-60

Alpha Decay  Alpha particle,   2 protons and 2 neutrons  Positively charged  Same as He nucleus  Least penetrating type of nuclear radiation  Travel only centimeters in air  Can be stopped by a sheet of paper or clothing

Beta Decay  Beta particle,   1 electron  Negatively charged  Produced by a neutron that decomposes into a proton and an electron  More penetrating than  particles  Pass through paper  Stopped by a thin sheet of metal

Gamma Decay  Gamma ray,   Penetrating ray of energy  Like X-rays and light, only very short wavelength  Most penetrating form of the three types discussed  Often accompanies alpha or beta decay  Several centimeters of lead or several meters of concrete required to stop it

Purpose: Compare & contrast fission & fusion.  Purpose on ISN 126.  Notes on ISN 127.  Homework on ISN 126. WKBK 249 Both of the Summarize sections & Define

F ission  splitting a nucleus into two or more smaller nuclei  some mass is converted to large amounts of energy

FissionFission Neutron (( )) (( )) (very unstable) Energy

F ission  chain reaction - self-feeding reaction

19 Fission and Chain Reactions  Fission can result in a chain reaction.  Neutrons released from the first reaction can trigger another reaction, and so on – similar to a rumor spreading. Neutron Energy

20 Chain Reactions (cont’d)  For a chain reaction to happen, each split nucleus must produce at least one neutron with enough energy to split another nucleus  This only happens when a specific mass of fissionable material is available – called the critical mass.  Controlled chain reactions are used to generate electricity in nuclear power plants.  Uncontrolled chain reactions are used in nuclear weapons  Chain Reaction Video Chain Reaction Video  Bomb Aftereffects Video Bomb Aftereffects Video

FusionFusion  combining of two nuclei to form one nucleus of larger mass  produces even more energy than fission  occurs naturally in stars

22 Nuclear Fusion  Fusion: nuclei of two atoms combine  The sun and other stars are powered by fusion of H into He  Requires extremely HIGH temperatures  What state is matter in at such high temperatures? PLASMA Fusion ++ ENERGY (17.6 MeV)

 Alpha Emission  Beta Emission TRANSMUTATIONTRANSMUTATION

 Why nuclides decay…  to obtain a stable ratio of neutrons to protons Stable Unstable (radioactive)

Purpose: Predict how mass & time are related in radioactive decay.  Purpose on ISN 128.  Notes on ISN 129. Practice Problems ½ sheet handout goes here also  Homework on ISN 128. Textbook p. 811 (6, 8-10)

 Half-life (t ½ )  time it takes for half of the nuclides in a sample to decay Example Half-lives polonium seconds lead hours iodine days carbon-145,370 years uranium billion years

 How much of a 20-g sample of sodium-24 would remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours. GIVEN: total time = 30 hours t 1/2 = 15 hours original mass = 20 g WORK : number of half-lives = 2 20 g ÷ 2 = 10 g (1 half-life) 10 g ÷ 2 = 5 g (2 half-lives) 5 g of 24 Na would remain.

 Purpose on ISN 130.  Notes on ISN 131.  Homework on ISN 130. WKBK 251 & 252 all but Describe. Purpose: 1. Discuss ways in which nuclear energy is used in society; 2. Describe how radioactive dating is used to determine the age of matter; 3. Describe health & safety issues caused by the use of nuclear energy.

Nuclear Power  Fission Reactors Cooling Tower How they work...

Nuclear Power  Fission Reactors

A. Nuclear Power  Fusion Reactors (not yet sustainable)

A. Nuclear Power  Fusion Reactors (not yet sustainable) Tokamak Fusion Test Reactor Princeton University National Spherical Torus Experiment

 235 U is limited  danger of meltdown  toxic waste  thermal pollution  Hydrogen is abundant  no danger of meltdown  no toxic waste  not yet sustainable FISSIONFISSION FUSIONFUSION vs.

Radioactive Decay During radioactive decay, the number of protons in the atom changes, and one element transforms into another. Parent isotopes decay into daughter isotopes. Radioactive Decay is like popping popcorn.

 Each radioactive parent always decays to a specific daughter.  There is no way to predict which atoms will decay first.  Radioactive atoms decay at a specific rate.  Once they decay, they can not change back.

How Long Does Radioactive Decay Take?  Half-Life - the time it takes for half of the radioactive or parent isotopes in a sample to decay to daughter isotopes.  Each parent has a 50% chance of decaying during 1 half-life.  Measured in seconds, minutes, years, etc.  Each isotope has its own unique half-life. From thousandths of a second to billions of years

 If you measure the ratio of parent to daughter isotopes, you can determine how many half-lives have passed.  Find the half-life of the parent isotope  # of half-lives  length of half-life = age of sample  Example: 3 half-lives; 1 half-life = 200 years Starting the Stopwatch

Notice original element is decreasing while new element is increasing…

Atoms Don’t Age the Way We Do e280_baby.jpg Have 70 year half-lives 4 half-lives = 280 years Each atom has a 50% chance of decaying during a half-life. Start with 16 baby aliens

How to Choose Which Isotope to Use  Estimate the age of your sample and choose an isotope with an appropriate range.  First find out what minerals are in your sample. The minerals in your rock need to have the element you want to use for dating.  Carbon-14 can only be used to date samples that were once living (organic)  Ex: Wood, bone, cloth, paper K-40: feldspar & mica Uranium: zircon

Radioactive Dating  Carbon Dating Video Carbon Dating Video

Ted Talk: Nuclear Energy Debate Ted Talk: Nuclear Energy Debate Ted Talk: Nuclear Energy Debate Ted Talk: Nuclear Energy Debate  Choose one of the following to investigate:  Irradiated Food (p.676)  Radioactive Dating (p.633)  Nuclear Medicine (p )  Make a mini-poster to display what you have learned.

Nuclear Reactions 43 Additional Interests Isotope production and distribution facilities: The U.S. Department of Energy's (DOE) national laboratories offer unique isotope production and separation facilities and processes such as reactors, associated hot cells, accelerators, and calutrons. The 250-megawatt Advanced Test Reactor (ATR) at Idaho CANDU reactors can also produce useful isotopsCanada now produces approximately 85 percent of the world's supply of Co-60 and more than 50 percent of the Co-60 medical therapy devices and medical device sterilizers. It also produces most of the world's supply of molybdenum-99, the precursor of Technetium-99m, the isotope that is the most widely used radioactive pharmaceutical.