Radioactivity Ch 10. Radioactivity is the process in which an unstable atomic nucleus emits charged...
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Transcript of Radioactivity Ch 10. Radioactivity is the process in which an unstable atomic nucleus emits charged...
![Page 1: Radioactivity Ch 10. Radioactivity is the process in which an unstable atomic nucleus emits charged particles & energy Any atom containing an unstable.](https://reader035.fdocuments.net/reader035/viewer/2022081506/56649e1b5503460f94b08d44/html5/thumbnails/1.jpg)
RadioactivityRadioactivity
Ch 10Ch 10
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Radioactivity• is the process in which an
unstable atomic nucleus emits charged particles & energy
• Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope
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How is the Atom Unstable?• The nuclear “glue” that holds
the nucleus together sometimes isn’t strong enough.
• Over time the atom “drops” some of it’s subatomic particles …called radioactive decay!
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New Way of WritingNew Way of WritingNuclides & IsotopesNuclides & Isotopes
3919 K ; 40
19 K• Superscript is the mass
number• Subscript is the atomic
number• 14
6C ; 126 C
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IsotopesIsotopes• have the same number of p+,
different number of no
• Another way to show an isotope is to have the mass number follow the name of the element (Carbon-14 or C-14)
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Types of Nuclear RadiationTypes of Nuclear Radiation
1. Alpha 2.Beta 3. Gamma
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Alpha DecayAlpha Decay
• Alpha particle—a positively charged particle made up of two p+ & two no
• the least penetrating
• can be stopped by a sheet of paper
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Alpha DecayAlpha Decay• An alpha particle looks like a
helium atom (42He)
• massmass reduces by 4
• atomicatomic # reduces by 2
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• Examples:238238
9292 U 209209
8484 Po
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Beta DecayBeta Decay
• A beta particle is an e- emitted by an unstable nucleus
• can be stopped by a thin sheet of metal such as aluminum
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Beta DecayBeta Decay
• A beta particle is written 0-1 e
• mass remains the same & the atomic # increases by one
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• Examples:214
82 Pb218
84 Po
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Gamma decayGamma decay
• A gamma ray is a penetrating ray of energy emitted by an unstable nucleus
• Gamma rays are energy waves that travel through space at the speed of light
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Gamma Gamma decaydecay
• atomic # and mass remain the same, but the energy of nucleus decreases
• Gamma rays can be stopped by several centimeters of lead or by several meters of concrete
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Thanks Cambridge Physics Outlet for amazing graphics!
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STAR Questions
• U-238 loses 4 total subatomic particles, 2 being protons.– What elements are formed?
• Thorium and Helium
– What type of decay has it undergone?• Alpha decay
• What is the most penetrating decay?• Gamma rays
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Background radiation• is nuclear radiation that
occurs naturally in the environment (levels are low enough to be safe)
– Radioisotopes in the air, water, rocks, plants, & animals all contribute
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Background RadiationBackground Radiation
– Cosmic rays (streams of Cosmic rays (streams of charged particles) from outer charged particles) from outer space that collide with the space that collide with the EarthEarth’’s atmosphere also s atmosphere also contributecontribute
– When nuclear radiation When nuclear radiation exceeds background levels, exceeds background levels, cells in your body can mutatecells in your body can mutate
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Detecting Detecting RadiationRadiation
• Devices used to detect radiation include Geiger counters & film badges
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RATES OF NUCLEAR DECAYRATES OF NUCLEAR DECAY
A half-life is the time required for one half of a sample of radioactive sample of a radioisotope to decay
– Unlike chemical reactions, nuclear decay rates are constant regardless of temperature, pressure or surface area
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• C-14 has a half life of 5730 years.– What fraction of a sample will be remaining
after 1 half life?• After 2 half lives?
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• C-14 has a half life of 5730 years.– If you have a sample of 50 grams. How much of the
sample will be remaining after 1 half life?• After 2 half lives?
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RATES OF NUCLEAR DECAYRATES OF NUCLEAR DECAYTransmutation is the conversion of
atoms of one element to atoms of another
Transuranium elements are elements with atomic numbers higher than 92 (Uranium)
A quark is a subatomic particle theorized to be among the basic units of matter
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FISSION AND FUSIONFISSION AND FUSION• Fission is the
splitting of an atomic nucleus into two smaller parts
• Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus
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FissionFission• A chain reaction is a chain of fission reactions triggered by neutrons released during the fission of a nucleus
About 20% of the electricity in the US comes from fission reactions
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FissionFission• A tremendous amount of energy
is produced during a fission reaction
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FissionFission• Advantages: is the
lack of air pollution.
• Disadvantages: include the risk of exposure & radioactive waste
Harris plant, near Raleigh
Lake Harris
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Not in my backyard…
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Then sealed and transported by way of trucks and trains for more permanent storage. Low-level wastes will stay above ground until they become “stable”.
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If high-level, the wastes are stored deep underground, where they wait for hundreds to thousands of years to become “stable”.
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FusionFusion• release huge
amounts of energy
• occur in the sun and stars (plasma)
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FusionFusion
• We do not use fusion reactions for energy b/c of the extremely high temperatures needed to start the reaction & because the plasma would need to be contained.
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THREE MILE ISLAND• Three Mile Island power station is near Harrisburg,
Pennsylvania • In 1979 at Three Mile Island nuclear power plant a
cooling malfunction caused part of the core to melt in the # 2 reactor. The TMI-2 reactor was destroyed.
• Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents.
• There were no injuries or adverse health effects from the Three Mile Island accident.
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CHERNOBYL• The Chernobyl accident in 1986 was the result of a
flawed reactor design that was operated with inadequately trained personnel & without proper regard for safety.
• The resulting steam explosion & fire released at least five percent of the radioactive reactor core into the atmosphere and downwind.
• 28 people died within four months from radiation or thermal burns, 19 have subsequently died, & there have been around nine deaths from thyroid cancer apparently due to the accident: total 56 fatalities as of 2004.
• An authoritative UN report in 2000 concluded that there is no scientific evidence of any significant radiation-related health effects to most people exposed. This was confirmed in a very thorough 2005-06 study.
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Examples
• Iodine-131 has a half-life of 8.07 days. What fraction of a sample of iodine-131 is left unchanged after 16.14 days?
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Examples
• The radioactive isotope Ni-63 has a half-life of 100 yrs. How much of a 10g sample remains after 300 yrs?
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Examples
• How long will it take a sample of Po-194 to decay to 1/8 of its original amount, if Po-194 has a half life of 0.7 seconds?
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Examples
• A sample of Cl-38 is observed to decay to 25% of its original amount in 74.4 min. What is the half-life of Cl-38?
• sorry…no time for Star cards this time :o)