Radioactivity: Principles Radioactivity: Principles and Applications (14 and Applications (14 October) October) Background Background Radioactivity is natural Radioactivity is natural Quantitative analysis of radioactivity Quantitative analysis of radioactivity Principles of radioactivity and human Principles of radioactivity and human health health Application of the principles of Application of the principles of radioactivity radioactivity
Transcript
Radioactivity: Principles Radioactivity: Principles and Applications (14 and Applications (14
October)October)
BackgroundBackground Radioactivity is naturalRadioactivity is natural Quantitative analysis of radioactivityQuantitative analysis of radioactivity Principles of radioactivity and human Principles of radioactivity and human
healthhealth Application of the principles of Application of the principles of
radioactivityradioactivity
Take Home MessageTake Home Message
Radioactivity is a natural process Radioactivity is a natural process Radioactivity is due to the instability of Radioactivity is due to the instability of
atoms, resulting in the spontaneous emission atoms, resulting in the spontaneous emission of subatomic particles and/or energyof subatomic particles and/or energy
Radioactivity has unique features including Radioactivity has unique features including isotopes and radioactive decayisotopes and radioactive decay
Human health issues of radioactivity are Human health issues of radioactivity are based on the ability of emissions to affect a based on the ability of emissions to affect a cell’s biochemistry and metabolismcell’s biochemistry and metabolism
Radioactivity has been “harnessed” to Radioactivity has been “harnessed” to provide a host of applications to enhance the provide a host of applications to enhance the quality of lifequality of life
Radioactivity also has its liabilities Radioactivity also has its liabilities associated with waste disposal and misuse associated with waste disposal and misuse
Radioactivity: Principles Radioactivity: Principles and Applicationsand Applications
Radioactivity is naturalRadioactivity is natural Quantitative analysis of radioactivityQuantitative analysis of radioactivity Principles of human radioactivityPrinciples of human radioactivity Application of the atomic principles Application of the atomic principles
of radioactivityof radioactivity
IsotopesIsotopes
Atoms have specific number of protons, Atoms have specific number of protons, neutrons and electronsneutrons and electrons
88
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1616
If the number of protons is unchanged but If the number of protons is unchanged but the number of the number of neutronsneutrons goes up or down, goes up or down, what happens to the properties of that what happens to the properties of that element?element? 88
OO
1717
Isotopes ContinuedIsotopes Continued
AtomsAtoms of an element with same number of of an element with same number of protonsprotons but different number of but different number of neutronsneutrons are are isotopesisotopes
Key is the number of neutronsKey is the number of neutrons Conventional notation ( Conventional notation ( AA
ZZX)X) Not all elements have isotopes, but many Not all elements have isotopes, but many
Stable versus Unstable Stable versus Unstable IsotopesIsotopes
Stable over timeStable over time Unstable: “transmutate by releasing Unstable: “transmutate by releasing
mass and/or energymass and/or energy
Radioactivity: Principles Radioactivity: Principles and Applicationsand Applications
BackgroundBackground Radioactivity is naturalRadioactivity is natural Quantitative analysis of radioactivityQuantitative analysis of radioactivity Principles of human radioactivityPrinciples of human radioactivity Application of the principles of Application of the principles of
radioactivityradioactivity
Discovery of Discovery of RadioactivityRadioactivity
Rutherford (as in the nucleus) and Rutherford (as in the nucleus) and three forms of “transmutated” three forms of “transmutated” activity (“radioactivity”)activity (“radioactivity”) Alpha Alpha nucleus of the helium atom nucleus of the helium atom
((4422He)He)
Beta (Beta (): high energy electron): high energy electron Gamma (Gamma (): electromagnetic radiation ): electromagnetic radiation
with very short wavelengths with very short wavelengths
Principal Early Principal Early ObservationsObservations
Atom exhibits “Atom exhibits “spontaneousspontaneous” release ” release ofof mass (mass ( or or ) ) energy (energy ())
100% natural process100% natural process Spontaneous release of mass or Spontaneous release of mass or
energy is called energy is called radioactive decayradioactive decay
Radioactivity: Principles Radioactivity: Principles and Applicationsand Applications
BackgroundBackground Radioactivity is naturalRadioactivity is natural Quantitative analysis of radioactivityQuantitative analysis of radioactivity Principles of human radioactivityPrinciples of human radioactivity Application of the principles of Application of the principles of
SourcesSources Cosmic rays from outer spaceCosmic rays from outer space SoilsSoils WaterWater Building materialsBuilding materials Nuclear sourcesNuclear sources
ExamplesExamples Radon gas (Ra)Radon gas (Ra)
Radioactive DecayRadioactive Decay
Uranium – 238Uranium – 238238238
9292U (92 protons; 238-92 (146) neutronsU (92 protons; 238-92 (146) neutrons Spontaneous release of an alpha (Spontaneous release of an alpha () )
subatomic particle (helium nucleus or subatomic particle (helium nucleus or 4422He) He)
results in an atom with 90 protons and mass results in an atom with 90 protons and mass of 234of 234
2342349090? or _____ (periodic table)? or _____ (periodic table)
All isotopes of all elements with > 83 All isotopes of all elements with > 83 protons (Bismuth) are unstable and protons (Bismuth) are unstable and radioactively decayradioactively decay
Types of DecayTypes of Decay
Alpha (Alpha ()) Release of Release of 44
22HeHe Travel distance: easily stopped by sheet of paper Travel distance: easily stopped by sheet of paper
(even air)(even air) Eventually acquires electrons to yield normal He Eventually acquires electrons to yield normal He
atomatom Beta (Beta ())
Release of high energy electronRelease of high energy electron Travel distance: 10 meters; 1 cm aluminum blockTravel distance: 10 meters; 1 cm aluminum block Eventually “finds” an atom needing an electronEventually “finds” an atom needing an electron
Gamma (Gamma ()) Release of high energy electronRelease of high energy electron Travel distance: 100’s meters; 5 cm block lead Travel distance: 100’s meters; 5 cm block lead
brickbrick Eventually energy is absorbed by materialEventually energy is absorbed by material
Penetration of RadiationPenetration of Radiation
Radioactive DecayRadioactive Decay
Radioactive DecayRadioactive Decay
Rate of decay to a stable state (no Rate of decay to a stable state (no more spontaneous decay) is specific for more spontaneous decay) is specific for each isotopeeach isotope
Rate has unique terminology called Rate has unique terminology called half-lifehalf-life
Time for ½ (50%) of the nuclei to decay Time for ½ (50%) of the nuclei to decay to the stable state is abbreviated tto the stable state is abbreviated t1/21/2
Example: M&M’sExample: M&M’s
Radioactive DecayRadioactive Decay
Measurement of RadiationMeasurement of Radiation
Number of nuclear disintegrations Number of nuclear disintegrations per unit of time called a per unit of time called a curicuri (Ci); (Ci); 3.70 x 103.70 x 101010 nuclear disintegrations nuclear disintegrations secondsecond-1-1
Radiation at the Radiation at the site of absorptionsite of absorption (living tissues)(living tissues) Radiological dose in units called Radiological dose in units called remrem
Natural dose = 0.001 rem (1 millirem)/dayNatural dose = 0.001 rem (1 millirem)/day Lethal dose = 500 remLethal dose = 500 rem
Radioactivity: Principles Radioactivity: Principles and Applicationsand Applications
BackgroundBackground Radioactivity is naturalRadioactivity is natural Quantitative analysis of radioactivityQuantitative analysis of radioactivity Principles of radioactivity and Principles of radioactivity and
human healthhuman health Application of the principles of Application of the principles of
radioactivityradioactivity
Radioactivity: Human Radioactivity: Human HealthHealth
Radioactivity in biological tissues results in Radioactivity in biological tissues results in atoms being ionizedatoms being ionized Disrupts bondsDisrupts bonds DNA as primary site of actionDNA as primary site of action Fragments molecules and disrupts biochemistryFragments molecules and disrupts biochemistry
Sensitivity is greatest for actively growing Sensitivity is greatest for actively growing cells and tissuescells and tissues BloodBlood Bone marrow (Cesium-137)Bone marrow (Cesium-137) Thyroid (I-131)Thyroid (I-131)
Radioactivity: Principles Radioactivity: Principles and Applicationsand Applications
BackgroundBackground Radioactivity is naturalRadioactivity is natural Quantitative analysis of radioactivityQuantitative analysis of radioactivity Principles of radioactivity and human Principles of radioactivity and human
healthhealth Application of the principles of Application of the principles of
radioactivityradioactivity
Application of Atomic Application of Atomic Principles of RadioactivityPrinciples of Radioactivity
Radiation medicine and Radiation medicine and radiopharmaceuticalsradiopharmaceuticals
Nuclear energyNuclear energy Yucca Mountain, NevadaYucca Mountain, Nevada Three Mile IslandThree Mile Island ChernobylChernobyl Dirty bombDirty bomb
A high speed electron emitted from A high speed electron emitted from a nucleus during radioactive decay a nucleus during radioactive decay is called a (an) _____.is called a (an) _____.
A.A. AlphaAlpha
B.B. BetaBeta
C.C. GammaGamma
D.D. All of the aboveAll of the above
A sheet of paper will stop a (an) A sheet of paper will stop a (an) ____.____.
A.A. AlphaAlpha
B.B. BetaBeta
C.C. GammaGamma
D.D. All of the aboveAll of the above
Rate of radioactive decay is Rate of radioactive decay is affected by changes in ______.affected by changes in ______.
A.A. TemperatureTemperature
B.B. PressurePressure
C.C. Sample sizeSample size
D.D. Other radioactive materials nearbyOther radioactive materials nearby
E.E. None of the aboveNone of the above
What is meant by background What is meant by background radiation? radiation?
Is the dose of background Is the dose of background radiation equivalent over the radiation equivalent over the Earth’s surface?Earth’s surface?
For you as an individual, what For you as an individual, what are the most common sources are the most common sources of natural/background of natural/background radiation?radiation?
Why measure the duration of Why measure the duration of radioactivity in units of half radioactivity in units of half life (tlife (t1/21/2) versus lifetime? ) versus lifetime?
Beryllium-7 (Beryllium-7 (7744Be) is an unstable Be) is an unstable
isotope of Beryllium (isotope of Beryllium (9944Be). When Be). When
the atom “transmutates”, the the atom “transmutates”, the stable product that is formed is stable product that is formed is the element Lithium (the element Lithium (77
33Li).Li).
What was emitted in the process What was emitted in the process of radioactive decay?of radioactive decay?
Is Is 7733Li stable or unstable?Li stable or unstable?
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