Radioactivity: the process by which atoms emit energy in the form of electromagnetic waves, charged particles, or uncharged particles. In 1896, Henri Bequerel discovered that uranium and other elements emitted invisible rays that can penetrate solid material. These materials are now called radioactive The most common unit for radiation is counts per second (known as a Becquerel, Bq)
Natural Sources Exposure to radiation is unavoidable because radioactive elements occur in nature. - some forms of carbon and potassium are absorbed by your body are radioactive. Alps Iceman: 5,300 years old
How ionizing radiation enters the body depends on the source of the ionizing radiation. X-rays and gamma rays can pass directly through the body when it is exposed to a source such as an x-ray machine. Most subatomic particles do not penetrate very far into the body
How ionizing radiation enters the body In the air or mixed with the dust in the air. Dissolved in water. By consumption of plants and animals that have become contaminated.
-Cosmic rays: high energy radiation coming from space. - higher exposure than normal when flying at high altitudes
- Radioactive uranium and radium are found in soil and rocks. When they disintegrate, they produce another radioactive atom: radon gas. Uranium deposits around the world
Artificial Sources Nuclear power - Electricity - Submarines -Space probes
- Nuclear bombs
-Medical applications: - X-rays are used for diagnosis - Cancer treatment In medicine: we use a unit called Sieverts (10 Sv is a lethal dose for most tissues)
Effects of Radiation - Ionizing radiation carries energy values on the order of 1000 s of electron volts (ev). - Typical chemical bonds can be broken by radiation energy of 5 or less ev. - Cells do have repair mechanisms, but they are not perfect and they can be overwhelmed. - radiation by large particles can do more damage per unit of energy.
Effects of Cell Damage: 1) Cell dies: organelles or enzymes can no longer function 2) Cell survives: Damage is passed on to daughter cells in the form of mutations (some mutations can lead to cancer). Cells undergoing division are more susceptible to damage
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 = number of particles in the nucleus Nucleon: particle found in nucleus (proton and neutron)
the isotope symbol is the element symbol with the mass number and atomic number Mass number 14 6 C Atomic number
Carbon-12 Carbon-14 12 C 6 14 C 6 Mass number = 12 p + = 6 n 0 = 6 Mass number = 14 p + = 6 n 0 = 8 Mass number = #p + + #n o Atomic number = #p + 12 C 6
ISOTOPES NAME SYMBOL hydrogen-1 1 1 H hydrogen-2 (deuterium) 2 1 H hydrogen-3 (tritium) 3 1 H
ISOTOPES NAME SYMBOL lithium-6 6 3 Li lithium-7 7 3 Li
Unstable (Radioactive) Nuclides Unstable nuclides tend to disintegrate causing: A different nuclide to be produced Energy to be released as radiation Energy released as radiation Less stable More stable
Types of Radiation Rutherford discovered three types of radiation Also discovered that elements transform into different elements during the process (called transmutation). The original element is called the parent nuclide. The newly formed element is called the daughter nuclide.
Alpha Decay 222 218 Alpha particles (α) are helium- 4 They are ejected at high speeds but can be stopped by aluminum foil Rn Po 4 86 84 He (or could be written as ) 2
Alpha particle mass number = 4 (2 protons + 2 neutrons) 4 2 He Atomic number = 2 (2 protons)
For all nuclear reactions: NUCLEONS AND CHARGE ARE CONSERVED 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 222 nucleons 222 nucleons 222 218 Rn Po 4 He 86 84 2 charge = +86 charge = +86
Beta Decay A neutron decays into a proton and an electron. The electron is ejected from the nucleus at a high speed called a beta particle (β). β particles can penetrate several mm of lead. 228 228 0 0 Th Pa e (can also be written: or ) 90 91-1 -1
Beta particle is an electron formed when a neutron changes into a proton Mass number = 0 because the mass is so small, it can be ignored Charge 0 e 1
228 nucleons 228 nucleons 228 228 0 90 91 Th Pa e -1 charge = +90 charge = +90
Gamma Decay Gamma rays can be emitted along with an alpha or beta particle. When a nucleus emits only a gamma (γ) ray, the energy of the nucleus is reduced but the mass number and the atomic numbers stay the same. γ rays can penetrate many cm of lead. 60Co* 60Co 27 27 exited unexcited
Gamma Decay Mass number = 0 because is EMR, no mass Charge = 0 0 0
Gamma Radiation Used in cancer treatment Radiation therapy can either damage DNA directly or create charged particles (free radicals) within the cells that can in turn damage the DNA.
Often, the same nuclide can undergo different decay modes
Decay Series or go through a series of decays.
Example 1: Complete the equation: 210 Bi 4 He 83 2 Nuclear charge: 83 2 = 81 According to my periodic table, that must be Nucleons: 210 4 = 206 TI What type of radiation is this? Alpha Decay
Example 2: Complete the balanced equation and identify the radiation type. 137 0 Cs e 137 55 1 56 Ba
Positron decay A positron is the antiparticle of the electron Also called beta-positive decay Sn 111 In 0 e 50 49 1 111 A proton is converted into a neutron
Example Write the reaction for the beta-positive decay of carbon-11. 11 0 C 6 1 11 C 0 11 6 1 5 B
Fission and Fusion Nuclear Fission The reaction used in all of the world s nuclear power plants. The fuel is usually uranium, but plutonium can also be used. Can be used in nuclear bombs. Involves splitting an atom into smaller nuclides. Begun when uranium absorbs a slow moving neutron
Neutron Mass number = 1 1 0 n atomic number = 0 (it s neutral!)
Example 3: Predict the missing fission product.
Nuclear Fission Chain Reaction The emitted neutrons strike more uranium atoms, causing them to undergo fission. This reaction is very hard to control. Called a chain reaction
Canada s CANDU Reactor Canadian Deuterium Uranium Reactor
control rods absorb neutrons If there are no free neutrons, the fission reactions stop
Heavy water is water where the hydrogen atoms have 1 neutron 2 H 1 The heavy water is a moderator, it slows the neutrons that are released in fission Only slow neutrons can cause fission
Heat from fission heats heavy water which is then pumped under pressure to boil normal water
There is a lot of radiation released inside nuclear reactors and by the spent fuel (but still less than is emitted by x-ray machines) Some coal-fired power plants emit more radioactivity than nuclear plants (uranium in coal ash)
Nuclear Fusion The process that made the atoms that make you. Two small nuclides with extremely high energy collide to form a bigger nuclide.
Star gone supernova: emitting energy = all the stars in the centre of galaxy. It is fusing helium into carbon, nitrogen and oxygen
Fusion In stars, gravity creates the conditions needed to bring the atoms close (very high temp and pressure) To make a fusion reactor, strong magnetic field or lasers are needed to heat the atoms to 20 million degrees or more
At large distances two nuclei repel one another because of the repulsive electrostatic force between their protons. If two nuclei can be brought close enough together, the electrostatic repulsion can be overcome by the attractive nuclear force which is stronger at close distances.
Example 3: Predict the missing reactant.
There are no operational fusion reactors Many experimental fusion reactors are under construction Would use deuterium 2 H and tritium 3 H
Advantages of Fusion Power For fusion power station, barely 0.10 tonnes of deuterium and 0.15 tonnes of tritium are required per year. Based on current prices, the costs of fuelling a fusion reactor could be 1% of the price of fusion electricity. for gas-fired power stations, fuel costs often account for 75% of the total cost of electricity production.
Advantages of Fusion Power small amounts of short-lived nuclear waste The nuclear waste is mainly limited to slightly radioactive material that must be disposed of when dismantling the installation. After a few decades, its radiation would decay to 0
Albert Einstein discovered that mass could be converted into energy. A tiny loss of mass corresponds to a gigantic gain in energy. ΔE = Δmc 2
E mc 2 Energy released in nuclear reaction Change in mass between reactant & product side Speed of light squared
CANDU CANDON T In a CANDU reactor, 1 kg of fuel (natural uranium) produces 340 000 MJ of heat that is converted to electricity. In oil and coal power plants, 1 kg of fuel produces about 4 MJ of heat that is converted to electricity.
Example In a nuclear reaction, the mass of the products is 2.45 x 10-27 kg less than the mass of the reactants. Determine the energy released. ΔE = Δmc 2 ΔE = 2.45 x 10-27 kg (3.00 x 10 8 m/s) 2 = 2.21 x 10-10 J
Example Determine the energy released when 1 mole of helium-3 absorbs neutrons.
Solution Need the masses of the reactants and products Use tables on page 8
He mass 3.01603 x 10 kg / mol 3-3 2 n mass 1.00866 10 kg / mol 1-3 0 He mass 4.00151 10 kg / mol 4-3 2 Mass of reactants = 4.02469 x 10-3 kg/mol Mass of product = 4.00151 x 10-3 g/mol m = reactants - products = 0.02319 x 10-3 kg/mol
ΔE = Δmc 2 = 0.02319 x 10-3 kg/mol(3.00 x 10 8 ) 2 = 2.09 x 10 12 J/mol
Practice Determine the energy released per mole in the reaction 235 1 3 1 92 141 92 0 0 36 56 U n n Kr Ba
Solution Mass of reactants (on left) 235 U = 235.04392 x 10-3 kg/mol Neutron = 1.00866 x 10-3 kg/mol Total = 236.05258 x 10-3 kg/mol
Solution Mass of products (on right) 3 neutrons = 3.02598 x 10-3 92 Kr = 91.92611 x 10-3 141 Ba = 140.91441 x 10-3 Total = 235.8665 x 10-3 m = reactant mass product mass m =0.18608 x 10-3 kg/mol (1.8608 x 10-4 )
ΔE = Δmc 2 ΔE =0.18608 x 10-3 x (3.00 x 10 8 ) 2 ΔE = 1.67 x 10 13 J/mol I mole of uranium-235 (mass 235 g) releases 1.67 x 10 13 J of energy
Radioactive Fallout Fallout is radioactive material spread through the environment by wind, etc. ingesting, inhaling, or otherwise absorbing radioactive material into your body is worse than just standing close to a source
Example: radioactive iodine isotopes are formed in many reactions Iodine is easily absorbed by the body (essential nutrient) iodine pills flood the thyroid with normal iodine so the radioiodine won t be absorbed
Unit is the sievert (Sv) Radiation Dose Measure of energy per kg of mass
A dose which is acute (received over a short period of time) has a much greater biological effect than one received over a longer period of time. This is because radiation acts by depositing energy in tissue, damaging your cells. Very minor damage, repeated often, will be better repaired than a large dose
Radiation Safety Avoid radiation Reduce the amount of time exposed to radiation
Radiation Safety Shielding: lead to block gamma rays Steel to block alpha, beta particles
Neutrons from fission can cause cell damage too Water and boron compounds absorb neutrons (used in reactors as moderators and emergency systems)
Radiation hazards radiation sickness: ionization causes cell damage or death genetic damage: DNA can be damaged by radiation, rapidly dividing DNA has a high probability of being damaged
Nuclear waste storage pool
Penetrating Ability of Radiation