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Nuclear and Atomic Physics
 

Nuclear and Atomic Physics

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    Nuclear and Atomic Physics Nuclear and Atomic Physics Presentation Transcript

    • Nuclear Physics
    • Shortcut to AtomicBombTest
    • RADIATION ELECTROMAGNETIC RADIATION NUCLEAR RADIATION RADIO LIGHT IR UV X ray ALPHA particles BETA particles GAMMA rays
    • Using Nuclear Radiation
    • Cancer Therapy
    • Electricity Production
    • Smoke Detectors
    • Sterilisation
    • Radiocarbon Dating
    • Radioactive Tracers
    • Thickness Monitoring
    • Understanding Atoms
      • Our understanding of what’s inside atoms has developed in the last 200 years……..
    • The Dalton Model In about 1810, James Dalton decided that matter was made of tiny, solid , spherical particles called atoms.
      • He introduced the idea of atoms as elementary particles.
    • Electron microscope picture of Carbon Atoms
    • Thomson’s Model of the Atom
      • In 1897, JJ Thomson discovered electrons, and suggested that the atom was a solid sphere of positive charge with electrons stuck in it like plums in a plum pudding.
    • Copyright © Houghton Mifflin Company. All rights reserved. 2–19 Rutherford's Experiment On α-Particle Bombardment of Metal Foil Copyright © Houghton Mifflin Company. All rights reserved. 2–19 Rutherford's Experiment On α-Particle Bombardment of Metal Foil Thomson’s Model
    • The Rutherford Model
    • Rutherford’s Experiment
      • In 1909, Ernest Rutherford wanted to carry out an experiment to test Thomson’s Model.
      • We can’t see inside an atom with our eyes, but he wanted to “see” inside.
      • “ Seeing” inside things……
      • “ Seeing” inside things……
    •  
      • “ Seeing” inside things……
      • He managed to “look inside” the atom by firing tiny particles called alpha particles at a thin gold foil to see how the alpha particles were deflected by the atoms of gold.
      • Alpha particles are the same as Helium nucleii, they are emitted from some radioactive atoms.
    • detector Rutherford’s Gold Foil Experiment
    • What they expected to happen: GOLD FOIL
    • What did happen: GOLD FOIL
      • This is what they expected to happen
      • Thomson Model
      • They expected to see small or no deflection of the alpha particles
      • This is what did happen
      • Rutherford model
    • Expected Results Actual Results
    • Rutherford’s Experiment (1911)
      • Results:
      • Most particles go straight through.
      • Some particles are deflected from straight path. A few even go backwards
      • Interpretation:
      • Most of the atom is empty space.
      • nucleus must be positive , very dense , more massive than alpha particles.
      • Negative electrons orbit the nucleus, but are much lighter
    • Rutherford’s Atom
    • Scale of the atom.
      • If an atom was enlarged to the size of a stadium, the nucleus would be the size of a plum .
      • The electrons would be the size of match heads wizzing around the stands.
      The rest is empty space
    • Size of the Atom
      • An atom is roughly 10 -10 m in diameter
      • This means a full stop is roughly ten million atoms across.
      • A small nucleus is roughly 10 -15 m in diameter
      • This is 1/100,000 ths the diameter of the atom
    • Fundamental Forces
      • What are the only two Fundamental Forces you are familiar with?
      • Gravity
      • Electric
    • How Do You Make An Atom?
      • Why don’t the electrons fall into the nucleus?
    • Physicists realised the nucleus was made of two types of nucleons . Protons and Neutrons. What stops them flying apart? The strong nuclear force!!! extension… Now we’ll look closer at the nucleus
    • Nuclear Notation
      • A nucleus can be described by two numbers:
      • Atomic or charge number (number of protons) ( Z )
      • Determines the nature of the atom and the element
      • Mass or nucleon number (Number of protons plus neutrons) ( A )
      • e.g.
    • Isotopes : Atoms of an element with different number of neutrons e.g.
    • Radioactive Decay
      • Nuclei that have too much energy are unstable.
      • They become more stable by firing out some nuclear radiation
      • There are three types of radioactive decay……
    •  
    • Write the equation for the alpha decay of Radium to Radon Alpha Decay
    • Beta Decay
    • Beta Decay
      • Write the equation for the beta decay of radium into actinium
      This is what causes beta decay beta decay is when a nucleus fires out an electron…
    •  
    • Gamma Decay
      • Write the equation for the gamma decay of……
      A gamma ray is a high energy photon emitted from a nucleus
    • Ionisation
      • When alpha particles collide with atoms, they can knock electrons off.
      • This will produce a positive ion and a free electron.
    • Positive ion
    • Sorting by Absorption Paper 1mm Lead
    • Sorting with a Magnetic Field
      • Identify each type of radiation
    • Half Life
      • The half life of an isotope is the time taken for half of a sample to decay into another isotope.
      • OR, the time taken for the activity of a sample to halve.
      • The shorter the half life, the less stable it is.
      • e.g. Uranium 238: 4,500 MY
      • Radon 218 0.04 s
      • link to half life 1
    • Radioactivity and Probability
      • Radioactivity is all about chance.
      • You can’t say when a certain nucleus will decay, but it might have a 1 in 10 chance of decaying in the next 5 seconds.
      • For the example above:
      • 1000 nuclei  100 decays in 5s
      • 100 nuclei  10 decays in 5s
      • This means there are more decays when there are more nuclei.
      • A shorter half life means a greater probability of a decay occurring
      • e.g Beryllium 11 decays to Boron 11 with a half life of 14 s
      • So If you have 16g of
      • Beryllium 11 now ,
      • after 14 s you will
      • have 8g etc.
      • link to half life 2
      8g 4g 2g 1g 56 42 28 14 16g 0 Amount of B Time(s)
    • Berillium amount Time 16 g Now 8 g after one half life 4 g after two half lifes 1 HL 2 HL 3 HL 4 HL Boron amount
      • Note that the total mass of the sample is about the same , because as the Beryllium decays, it doesn’t disappear, it changes into Boron. The Boron is still there.
    • Sample Question.
      • A radioactive isotope has a half life of 3 years.
      • A 5 g sample of the isotope produces 30 decays per sec.
      • What will the decay rate of a 1 g sample be in 9 years time?
    • Carbon Dating
      • This image shows the Shroud of Turin.
      • It was supposedly the cloth that Christ was buried in. Is it real or a medieval fake???
      • In the Atmosphere, cosmic rays hit Nitrogen 14 changing it to Carbon 14.
      • The Carbon 14 decays with a half life of 6300 years.
      • So a small fraction of CO 2 molecules contain Carbon 14. This is taken in by plants, and hence animals.
      • When the organism dies, The Carbon 12 stays the same, the Carbon 14 decays.
      • By measuring the ratio of C14 to C12, the time since it was alive can be calculated
      • Back to the shroud. The ratio of C14 to C12 showed it was about 800 years old!!!
      • Final question. A wooden axe handle has a ratio of C14 to C12 that is 1/8 times the ratio for new wood.
      • How old is it?
    • NCEA type question
      • Describe the Dalton model of the atom
      • Explain the evidence for the Thomson model
      • Explain the evidence for the Rutherford model
      • (a) Cobalt-60 undergoes radioactive decay..
      • Show how the decay of cobalt-60 ( ) results in nickel-60 ( ).
      • (a) A smoke detector contains radioactive americium  241 which emits radiation. Complete the following equation to identify the radiation emitted.
      • Explain why the radiation given out by the americium is unlikely to do any harm to the people living inside the house.
      • The alpha particles ionise atoms in the air. Explain what this means.
      • Estimate the half-life of americium-241.
      • (b) Radon-212 ( ) is a radioactive gas. Show that when radon-212 undergoes alpha decay, polonium is formed.
      • Radon-212 decays with a half-life of 24 minutes.
      • If you start with 96 mg of radon-212, find the approximate mass of polonium-208 two hours later.
      • Why is the actual mass less than your calculation?
    • State what an alpha particle is. 12 years beta particle hydrogen-3 24 minutes beta particle uranium-239 less than 1 second alpha particle polonium-213 138 days alpha particle polonium-210 74 days gamma ray iridium-192 6 days gamma ray technetium-99 Half-life Type of radiation emitted Isotope
    • Two isotopes of polonium are given in the table. How do the nuclei of these two isotopes differ? 12 years beta particle hydrogen-3 24 minutes beta particle uranium-239 less than 1 second alpha particle polonium-213 138 days alpha particle polonium-210 74 days gamma ray iridium-192 6 days gamma ray technetium-99 Half-life Type of radiation emitted Isotope
    • A doctor needs to monitor the blood flow through a patient’s heart. She injects a radioactive isotope into the patient’s bloodstream. Explain why she would choose technetium-99 instead of the other isotopes listed in the table above. 12 years beta particle hydrogen-3 24 minutes beta particle uranium-239 less than 1 second alpha particle polonium-213 5 seconds gamma ray Strontium 91 74 days gamma ray iridium-192 6 days gamma ray technetium-99 Half-life Type of radiation emitted Isotope