Radioactivity. Radioactivity : the process by which atoms emit energy in the form of electromagnetic waves, charged particles, or uncharged particles.
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Radioactivity: the process by which atoms emit energy in the form of electromagnetic waves, charged particles, or uncharged particles.
CBC archives - radioactivity
Applications & Exposure
Alps Iceman: 5,300 years old
- Radioactive uranium and radium are found in soil and rocks. When they disintegrate, the produce another radioactive atom: radon gas.
Uranium deposits around the world
February 1, 2005—The U.S. Navy released this photograph last Thursday of the nuclear submarine San Francisco, which crashed headlong into an uncharted undersea mountain near Guam on January 8. Standing more than three stories high and with classified technology veiled by a tarp, the fast-attack submarine is shown awaiting repairs in a Guam dry dock.
The impact shredded the submarine's nose, killed one sailor, and injured 60 more. The sailors were largely protected by the vessel's reinforced inner hull, which did not rupture. After the wreck, the crew quickly ascended and sailed along the ocean's surface back to their base in Guam.
The Cassini space probe is powered by energy released from 28.8 g of radioactive Pu. The radiation is absorbed by ceramic surronding the Pu and the heat is converted ot electricity. Each Kg of Pu emits 556 J each second.
- Nuclear bombs
In medicine: we use a unit called Sieverts
(10 Sv is a lethal dose for most tissues)
Effects of Radiation
- Cells do have repair mechanisms, but they are not perfect and they can be overwhelmed.
- Large particle radiation (such as α particles) can do more damage per unit of energy.
The Nucleus and Nuclear Reactions
Structure of the Nucleus - Review
Which elements are these?
(protons are shown in red and neutrons in white.)
They are both carbon. Both have 6 protons. i.e. they both have an atomic number of 6.
These are two isotopes(varieties) of carbon.
- same chemical properties, but different physical properties (e.g. how they behaving in nuclear reactions)
- different number of neutrons, therefore different atomic masses
In nuclear physics, we often call atoms nuclides.
Mass number = 12
p+ = 6
n0 = 6
Mass number = 14
p+ = 6
n0 = 8
Mass number = #p+ + #no
Atomic number = #p+
The Strong Nuclear Force
The big circle marks the location of the Large Hadron Collider (LHC) at the European particle physics laboratory in CERN. The tunnel where the particles are accelerated is located 100 m (320 ft) underground and is 27 km (16.7 mi) in circumference. The smaller circle is the site of the smaller proton-antiproton collider. The border of France and Switzerland bisects the CERN site and the two accelerator rings.
Unstable (Radioactive) Nulcides
Types of Radiation
For all nuclear reactions: NUCLEONS AND CHARGE ARE CONSERVED
i.e. The sum of the mass numbers on both sides of the arrow must be equal and the sum of the atomic numbers on both sides of the arrow must be equal
charge = +86
charge = +86
charge = +90
charge = +90
… or go through a series of decays.
Example 1: Complete the balance equation:
Nuclear charge: 83 – 2 = 81
According to my periodic table, that must be
Nucleons: 210 – 4 = 206
What type of radiation is this?
Example 2: Complete the balanced equation and identify the radiation type.
Other Decay Modes
Fission and Fusion
Example 3: Predict the missing fission product.
Nuclear Fission Chain Reaction
Canada’s CANDU Reactor
Example 3: Predict the missing reactant.
Nuclear fusion as an energy source on earth is still experimental
Radioactive Decay Curve
Original amount of parent nuclide
Amount or mass of the parent nuclide remaining
Number of half-lives that have passed
Effect of Strontium-90 on Squamous Cell Carcinoma in an Eastern Box Turtle (Terrapene carolina); Discussion of Alternative Treatment Modalities
Cheryl B. Greenacre, DVM, Dipl. ABVP - Avian and Royce Roberts, DVM, MS, Dipl. ACVR
If a 2.00 g sample of strontium-90 is produced in a reactor, how much will remain after 10.0 years have passed. (The half-life of Sr-90 is 29.1 years.)
A baby mammoth found frozen in a glacier is found to contain one quarter of its original carbon-14. Determine its age if the half life for the radioactive decay of carbon-14 is 5.73 x 103 years.
1.15 x 104 years
A pregnant ichthyosaur fossil is located just below a volcanic ash layer containing a ratio of uranium-235 to lead-207 of 4:1. Determine the minimum age of the fossil in years. (The half-life of U-235 is 7.13 x 108 a)
230 million years
E = mc2
Determine the mass defect of an alpha particle.
alpha particle mass (2 protons, 2 neutrons) = 6.65 x 10-27kg
massprotons =2(1.67 x 10-27kg) = 3.34 x 10-27 kg
massneutrons = 2(1.67 x 10-27kg) = 3.34 x 10-27 kg
total mass of separate nucleons = 6.68 x 10-27 kg
mass defect = - = 0.03 x 10-27kg
E = mc2
Calculate the energy produced in the reaction
mass2H = 3.34341 x 10-27 kg
mass3H = 5.00661 x 10-27 kg
masstotal = 8.35002 x 10-27 kg
massα = 6.6463 x 10-27 kg
massn = 1.6749 x 10-27 kg
masstotal = 8.3212 x 10-27 kg
Mass defect = 8.35002x10-27 kg – 8.3212x10-27 kg
= 2.882 x 10-29 kg
2.882 x 10-29 kg
E = mc2
E = (2.882 x 10-29 kg)(3.00 x 108 m/s)2
E = 2.59 x 10-12 J
In a CANDU reactor, 1 kg of fuel (natural uranium) produces 3.4 x 105 MJ of heat that is converted to electricity.
In oil and coal power plants, 1 kg of fuel produces about 4 MJ of heat
A 8.50 x 1020 Hz photon produces an electron and an anti-electron. Determine the total kinetic energy of the particles.
Law of Conservation of Energy:
Photon energy = energy to make 2 particles + Ek
Ephoton =Eelectron + Eantielectron + Ek
hf = mc2 + mc2 + Ek
hf = 2(mc2) + Ek
Ek= hf – 2(mc2)
Ek= (6.63 x 10-34 J•s)(8.50 x 1020 Hz) – 2(9.11 x 10-31kg)(3.00 x 108 m/s)2
Ek= 4.00 x 10-13 J