Download - Nuclear chemistry
Nuclear ChemistryNuclear Chemistry
RadioactivityRadioactivity
• One of the pieces of evidence for the fact One of the pieces of evidence for the fact that atoms are made of smaller particles that atoms are made of smaller particles
came from the work of Marie Curie came from the work of Marie Curie (1876-1934). (1876-1934).
• She discovered radioactivity: the She discovered radioactivity: the spontaneous disintegration of the spontaneous disintegration of the nucleus of some elements into smaller nucleus of some elements into smaller pieces.pieces.
Nuclear Reactions vs. Normal Nuclear Reactions vs. Normal Chemical ChangesChemical Changes
• Nuclear reactions involve the nucleusNuclear reactions involve the nucleus
• The nucleus loses particles, and protons and The nucleus loses particles, and protons and neutrons are rearrangedneutrons are rearranged
• The disintegration of the nucleus releases a The disintegration of the nucleus releases a tremendous amount of energy that holds the tremendous amount of energy that holds the nucleus together – called binding energynucleus together – called binding energy
• ““Normal” Chemical Reactions involve Normal” Chemical Reactions involve electrons, not protons and neutronselectrons, not protons and neutrons
Types of RadiationTypes of Radiation
e01
He42
• Alpha (Alpha (άά) – a positively ) – a positively charged helium isotopecharged helium isotope - - we usually we usually ignore the charge because it involves electrons, ignore the charge because it involves electrons, not protons and neutronsnot protons and neutrons
•Beta (Beta (ββ) – an electron) – an electron
•Gamma (Gamma (γγ) – pure energy; ) – pure energy; called a ray rather than a called a ray rather than a particleparticle
00
6Alpha Decay
When a radioactive nucleus emits an alpha particle, a new nucleus forms that has:
• a mass number that is 4 less than that of the initial nucleus.
• an atomic number that is decreased by 2.
7
Alpha Decay Nuclear Equation
Copyright © 2005 by Pearson Education, Inc.Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin CummingsPublishing as Benjamin Cummings
In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers for the nuclei of the reactant and the products must be equal.
MASS NUMBERS Total = 251 = 251
251Cf 247 Cm + 4 He 98 96 2
Total = 98 = 98
ATOMIC NUMBERS
Balancing Nuclear Equations
Equation for Alpha DecayWrite an equation for the alpha decay of 222Rn.
STEP 1 Write the incomplete equation 222Rn ?s + 4He 86 2
STEP 2 Determine the mass number 222 – 4 = 218
STEP 3 Determine the atomic number 86 – 2 = 84
STEP 4 Determine the symbol of element 84 = Po
STEP 5 Complete the equation
222Rn 218 Po + 4He 86 84 2
10Beta Decay
A beta particle• is an electron
emitted from the nucleus.
• forms when a neutron in the nucleus breaks down.
1n 0e + 1H0 -1 1
STEP 1 Write an equation for the decay of42Potassium,a beta emitter.
42K new nucleus + 0e 19 -1
STEP 2 Mass number : (same) = 42
STEP 3 Atomic number: 19 + 1 = 20
STEP 4 Symbol of element 20 = Ca
STEP 5 42K 42Ca + 0e 19 20 -1
Writing An Equation for Beta Decay
Other Nuclear ParticlesOther Nuclear Particles
e01
n10• NeutronNeutron
• Positron – a positive Positron – a positive electronelectron
• Proton – usually referred Proton – usually referred to as Hydrogento as Hydrogen+1+1
• Any other elemental Any other elemental isotopeisotope
H11
Half Life
The time required for half of the nuclei in a The time required for half of the nuclei in a sample of a specific isotope to undergo sample of a specific isotope to undergo radioactive decay.radioactive decay.
Radioactive Parent
Stable Daughter Half life
Potassium 40 Argon 40 1.25 billion yrs
Rubidium 87 Strontium 87 48.8 billion yrs
Thorium 232 Lead 208 14 billion years
Uranium 235 Lead 207 704 million years
Uranium 238 Lead 206 4.47 billion years
Carbon 14 Nitrogen 14 5730 years
Half Lives for Radioactive Elements
Half Life and radioactive dating
Half-LifeHalf-Life
Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 O. What remains after 3 half-lives? After 5 half-lives?half-lives? After 5 half-lives?
Learning Check!
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?
In gamma radiation• energy is emitted from an unstable
nucleus, indicated by m following the mass number.
• the mass number and the atomic number of the new nucleus are the same.
99mTc 99Tc + 43 43
Gamma () Radiation
In position emission,• a proton is converted to a neutron and a
positron.
1 p 1n + 0e 1 0 +1
• the mass number of the new nucleus is the same, but the atomic number decreases by 1.
49Mn 49Cr + 0e 25 24 +1
Positron Emission
Why radiation is dangerous
Radiation ionizes atoms in cell tissue and causes Radiation ionizes atoms in cell tissue and causes chemical reactions akin to decomposition / chemical reactions akin to decomposition / combustion. combustion. disrupts nucleotide sequences (your DNA is mutated)disrupts nucleotide sequences (your DNA is mutated)
Why radiation is dangerousWhy radiation is dangerous
Measuring Radiation•How radioactive a substance is refers to the How radioactive a substance is refers to the number of nuclear disintegrations per second number of nuclear disintegrations per second that occur in a sample. that occur in a sample.
•SI unit is the Becquerel (Bq) which is 1 SI unit is the Becquerel (Bq) which is 1 disintegration/seconddisintegration/second
•The older unit, the Curie(Ci) :The older unit, the Curie(Ci) :1 Ci = 3.7 x 101 Ci = 3.7 x 101010 disintegrations per second disintegrations per second
Measuring Radiation
•The The 'rad'rad' is used to describe the energy quantity ' is used to describe the energy quantity or dose of radiation absorbed. or dose of radiation absorbed.
•radrad (rd) stands for “radiation absorbed dose” (rd) stands for “radiation absorbed dose”
•One One radrad defined as 10 defined as 10-5-5 J/g of material. J/g of material.
Measuring Radiation Damage
•The rad does not account for the kind of damage The rad does not account for the kind of damage done, only for how much radiation goes in.done, only for how much radiation goes in.
•To take into account this fact the REM was To take into account this fact the REM was derivedderived
•To find the dose in REMS the dosage in rads is To find the dose in REMS the dosage in rads is multiplied by a conversion factor that reflects the multiplied by a conversion factor that reflects the effectiveness of the effectiveness of the kindkind of radiation causing the of radiation causing the damagedamage
Dosage in REMS Biological Effect : 25 notable change in blood cell components 25 notable change in blood cell components 100 radiation sickness - nausea, vomiting, 100 radiation sickness - nausea, vomiting, decrease in white blood cell count, diarrhea, decrease in white blood cell count, diarrhea, dehydration, prostration, hemorrhaging and loss dehydration, prostration, hemorrhaging and loss of hair of hair 200 the same as above but more pronounced in a 200 the same as above but more pronounced in a shorter period of time shorter period of time
400 ½ of any population exposed to this dosage 400 ½ of any population exposed to this dosage will be dead in 60 days will be dead in 60 days
600 all exposed to this level will be dead in one 600 all exposed to this level will be dead in one week week
Chernobyl
Anyone near the Chernobyl plant when it melted Anyone near the Chernobyl plant when it melted down received 400 rems also immediately. down received 400 rems also immediately.
The day after 1 rem/hr was found in the nearest The day after 1 rem/hr was found in the nearest city. city.
Normal background radiation is 1,000 times lower Normal background radiation is 1,000 times lower than thisthan this
Detecting radiation
Detecting radiation
Protection from radiation•Wear lead infused suit.Wear lead infused suit.•Keep your distance.Keep your distance.• Inverse square law.Inverse square law.• Intensity of radiation is inversely proportional Intensity of radiation is inversely proportional to the square of the distance from the sourceto the square of the distance from the source
Nuclear Fuel
Uranium “Yellow Cake” UUranium “Yellow Cake” U33OO88
FissionNeutronNeutron
Fission Chain Reaction
Representation of a fission process.
Nuclear FissionNuclear Fission
Diagram of a nuclear power plant.
Nuclear Fission & POWERNuclear Fission & POWER
• Currently about 103 Currently about 103
nuclear power plants in nuclear power plants in
the U.S. and about 435 the U.S. and about 435
worldwide.worldwide.
• 17% of the world’s 17% of the world’s
energy comes from energy comes from
nuclear.nuclear.
Fusion
• A process by which multiple like-charged atomic nuclei join together to form a heavier nucleus
Nuclear Fusion
Fusion: small nuclei combine
2H + 3H 4He + 1n +
1 1 2 0
Occurs in the sun and other stars
Energy
What radioactive isotope is produced in the following bombardment of boron?
10B + 4He ? + 1n
5 2 0
Fusion
Nuclear Fusion
Fusion • Excessive heat can not be
contained• Attempts at “cold” fusion have
FAILED.• “Hot” fusion is difficult to contain
Artificial Nuclear ReactionsArtificial Nuclear Reactions
New elements or new isotopes of known New elements or new isotopes of known elements are produced by bombarding an elements are produced by bombarding an atom with a subatomic particle such as a atom with a subatomic particle such as a proton or neutron -- or even a much heavier proton or neutron -- or even a much heavier particle such as particle such as 44He and He and 1111B.B.
Reactions using neutrons are called Reactions using neutrons are called
reactionsreactions because a because a ray is usually ray is usually emitted.emitted.
Radioisotopes used in medicine are often made Radioisotopes used in medicine are often made by by reactionsreactions..
Artificial Nuclear ReactionsArtificial Nuclear Reactions
Production of radioactive Production of radioactive 3131P for use P for use
in studies of P uptake in the body.in studies of P uptake in the body.
31311515P + P + 11
00n ---> n ---> 32321515P + P +
Transuranium ElementsTransuranium Elements
Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made
starting with a starting with a reactionreaction
2382389292U + U + 11
00n ---> n ---> 2392399292U + U +
2392399292U U ---> ---> 239239
9393Np + Np + 00-1-1
2392399393Np Np ---> ---> 239239
9494Pu + Pu + 00-1-1
Nuclear Medicine: ImagingNuclear Medicine: Imaging
Thyroid imaging using Tc-99mThyroid imaging using Tc-99m
Food Food IrradiationIrradiation
•Food can be irradiated with Food can be irradiated with rays from rays from 6060Co or Co or 137137Cs.Cs.•Irradiated milk has a shelf life of 3 mo. Irradiated milk has a shelf life of 3 mo.
without refrigeration.without refrigeration.•USDA has approved irradiation of meats USDA has approved irradiation of meats
and eggs.and eggs.