Chapter 21 : Chapter 21 The Nucleus:
A Chemist’s View
Slide2 : Chapter 21: The Nucleus: A Chemists View 21.1 Nuclear Stability and Radioactive Decay
21.2 The Kinetics of radioactive Decay
21.3 Nuclear Transformations
21.4 Detection and Uses of Radioactivity
21.5 Thermodynamic Stability
21.6 Nuclear Fission and Nuclear Fusion
21.7 Effects of Radiation
Subatomic particle tracks in a bubble charger at CERN, the European particle physics laboratory in Geneva, Switzerland. : Subatomic particle tracks in a bubble charger at CERN, the European particle physics laboratory in Geneva, Switzerland. Source: CERN, Geneva, Switzerland
Figure 21.1: Known nuclides : Figure 21.1: Known nuclides
DISTRIBUTION OF STABLE NUCLIDES : DISTRIBUTION OF STABLE NUCLIDES Protons Neutrons Stable Nuclides %
Even Even 168 60.2
Even Odd 57 20.4
Odd Even 50 17.9
Odd Odd 4 1.4 279 99.9% Total = (like table 21.1 , P 980)
PROPERTIES OF FUNDAMENTAL PARTICLES : PROPERTIES OF FUNDAMENTAL PARTICLES Particle Symbol Charge Mass
(x10 -19 Coulombs) (x10-27kg)
Proton P +1.60218 1.672623
Neutron N 0 1.674929
Electron e -1.60218 0.0005486
NUCLEAR STABILITY Modes of Radioactive Decay : NUCLEAR STABILITY Modes of Radioactive Decay Alpha Decay - Heavy Isotopes - 42He+2-
Beta Decay - Neutron Rich Isotopes - e - -
Positron Emission -Proton Rich Isotopes -
Electron Capture - Proton Rich Isotopes
x - rays
Gamma-ray emission( - Decay of nuclear
excited states
Spontaneous Fission - Very Heavy Isotopes
Slide8 : Comparison of Chemical and Nuclear Reactions Chemical Reactions Nuclear Reactions 1. One substance is converted to 1. Atoms of one element typically
another,but atoms never change change into atoms of another.
identity.
2. Orbital electrons are involved as 2. Protons, neutrons, and other
bonds break and form; nuclear particles are involved; orbital
particles do not take part. electrons take part.
3. Reactions are accompanied by 3.Reactions are accompanied by
relatively small changes in energy relatively large changes in
and no measurable changes in mass. energy and often measurable
changes in mass.
4. Reaction rates are influenced by 4. Reaction rates are affected by
temperature, concentration, number of nuclei, but not by
catalysts, and the nature of the temperature, catalysts, or the
chemical substance. nature of the chemical substance.
Slide9 : Emission and Absorption of Light by Atoms Nucleus of atom Electron Light Light Light Absorption by an
atom moves an electron
to a higher energy level. Light Light Emission occurs when an
electron drops from a higher
energy level to a lower one.
Slide10 : Absorption and Emission of Light by The Nucleus Excited state Ground state Protons and Neutrons in the nucleus are moved up to excited states
by the absorption of large amounts of energy, and they move from
excited states back to the ground states by the emission of large
amounts of energy! This energy is normally 106 times larger than
the energy emitted by electron transfers around atoms, and is in the
Gamma ray region of the electromagnetic spectrum.
Figure 12.1: Electromagnetic radiation has oscillating electric (E) and magnetic (H) fields in planes perpendicular to each other and to the direction of propagation. : Figure 12.1: Electromagnetic radiation has oscillating electric (E) and magnetic (H) fields in planes perpendicular to each other and to the direction of propagation.
Figure 12.2: The nature of waves : Figure 12.2: The nature of waves
Figure 12.3: Classification of electromagnetic radiation : Figure 12.3: Classification of electromagnetic radiation
Figure 21.7: Schematic representation of a Geiger-Muller counter : Figure 21.7: Schematic representation of a Geiger-Muller counter
Alpha Decay -Heavy Elements : Alpha Decay -Heavy Elements 238U 234Th + + E
T1/ 2= 4.48 x 10 9 yrs
210Po 206Pb + + E
T 1/ 2= 138 days
256Rf 252No + + E
T1/ 2= 7 msec
241Am 237Np + + E
T1/ 2= 433 days
Beta Decay - Electron Emission : Beta Decay - Electron Emission N P+ + + Energy
90Sr 90Y + + Energy
T1/ 2= 30 yrs
14C 14N + + Energy
T1/ 2= 5730 yrs
247Am 247Cm + + Energy
T1/ 2= 22 min
131I 131Xe + + Energy
T1/ 2 = 8 days
Slide18 : Electron Capture - Positron Emission P+ + e - n + Energy = Electron Capture P+ n + e+ + Energy = Positron Emission 51Cr + e - 51V + Energy
T1/2 = 28 days 7Be 7Li + + Energy
T1/2 = 53 days 177Pt + e - 177Ir + Energy
T1/2 = 11 sec 144Gd 144Eu + + Energy
T1/2 = 4.5 min
Slide19 : Gamma Ray Emission, the Nuclear Particles in the Nucleus dropping from excited states to their ground states. Example is the decay of cobalt – 60 to excited states in nickel – 60, which then decay to the ground state of 60Ni. Ground state of 60Ni 1.332 Mev 2.405 Mev 1.173 Mev Gamma ray 1.332 Mev Gamma ray 60Co Beta decay, e-
Slide20 : Natural Decay Series of Existing Isotopes 40K 40Ar
T1/2 = 1.29 x 109yrs
232 Th 208 Pb
T1/2 = 1.4 x 1010yrs
235U 207 Pb
T1/2 = 7 x 108yrs
238U 206 Pb
T1/2 = 4.5 x 109yrs
Figure 21.2: Decay series : Figure 21.2: Decay series
Slide23 : Natural Decay series for Uranium 238 238U 234 Th
234Pa
234U 230 Th 226Ra 222Rn 218Po 214Pb
218At 214Bi 210 Tl
214Po 210Pb 206Hg
= decay 210Bi 206Tl
= decay 210 Po 206Pb
238U -- 8 decays and 6 decays leaves you with -- 206Pb
Slide24 : Natural Decay series for Uranium 235 235U 231 Th
231Pa 227Ac 223Fr 219At 215Bi
227 Th 223Ra 219Ra 215Po 211Pb
215At 211Bi 207 Tl
211Po 207Pb = decay
= decay 235U -- 8 decays and 4 decays leaves you with -- 207Pb
Slide25 : Natural Decay series for Thorium 232 232 Th 228Ra
228Ac
228 Th 224Ra 220Rn 216Po 212Pb
212Bi 208Tl
212Po 208Pb = decay
= decay 232 Th -- 7 decays and 4 decays leaves you with -- 208Pb
Figure 21.3: The decay of a 10.0 -g sample of strontium-90 over time. : Figure 21.3: The decay of a 10.0 -g sample of strontium-90 over time.
Figure 21.4: change in the amount of Molybdenum - 99 with time : Figure 21.4: change in the amount of Molybdenum - 99 with time
Figure 21.5: Schematic diagram of a cyclotron : Figure 21.5: Schematic diagram of a cyclotron
Physicist works with a small cyclotron at the University of California at Berkeley. : Physicist works with a small cyclotron at the University of California at Berkeley. Source: Corbis
CERN, the world's largest particle accelerator, lies at the foot of the Jura Mountains near Geneva, Switzerland. : CERN, the world's largest particle accelerator, lies at the foot of the Jura Mountains near Geneva, Switzerland.
Figure 21.6: Diagram of a linear accelerator : Figure 21.6: Diagram of a linear accelerator
Accelerator tunnel at Fermilab, a high-energy particle accelerator in Batavia, Illinois. : Accelerator tunnel at Fermilab, a high-energy particle accelerator in Batavia, Illinois. Source: Fermilab Batavia, IL
Carbon-14 radioactivity is often used to date human skeletons found at archaeological sites : Carbon-14 radioactivity is often used to date human skeletons found at archaeological sites Source: University of Pennsylvania Photo Archives
Figure 21.8: Consumption of Na131I : Figure 21.8: Consumption of Na131I Source: Visuals Unlimited Normal Thyroid An Enlarged Thyroid
Figure 21.9: Binding energy per nucleon as a function of mass number. : Figure 21.9: Binding energy per nucleon as a function of mass number.
Slide39 : Units used for Nuclear Energy Calculations electron volt - (ev)
The energy an electron acquires when it moves through
a potential difference of one volt:
1 ev = 1.602 x 10-19J
Binding energies are commonly expressed in units
of megaelectron volts (Mev)
1 Mev = 106 ev = 1.602 x 10 -13J
A particularly useful factor converts a given mass defect
in atomic mass units to its energy equivalent in electron
volts:
1 amu = 931.5 x 106 ev = 931.5 Mev
Binding Energy per Nucleon of Deuterium : Binding Energy per Nucleon of Deuterium Deuterium has a mass of 2.01410178 amu. Hydrogen atom = 1 x 1.007825 amu = 1.007825 amu
Neutrons = 1 x 1.008665 amu = 1.008665 amu
2.016490 amu Mass difference = Theoretical mass - actual mass
= 2.016490 amu - 2.01410178 amu = 0.002388 amu Calculating the binding energy per nucleon:
Binding Energy -0.002388 amu x 931.5 Mev / amu
Nucleon 2 nucleons
= =
Slide41 : Calculation of the Binding Energy per
Nucleon for Iron- 56 The mass of Iron -56 is 55.934939 amu, it contains 26 protons and
30 Neutrons Theoretical Mass of Fe - 56 :
Hydrogen atom mass = 26 x 1.007825 amu = 26.203450 amu
Neutron mass = 30 x 1.008665 amu = 30.259950 amu
56.463400 amu Mass defect =Actual mass - Theoretical mass:
55.934939 amu - 56.46340 amu = - 0.528461 amu Calculating the binding energy per nucleon: Binding Energy - 0.528461 amu x 931.5 Mev / amu
nucleon 56 nucleons = =
Slide42 : Calculation of the Binding Energy per
Nucleon for Uranium - 238 The actual mass of Uranium - 238 = 238.050785 amu, and it has
92 protons and 146 neutrons Theoretical mass of Uranium 238:
Hydrogen atom mass = 92 x 1.007825 amu = 92.719900 amu
neutron mass = 146 x 1.008665 amu = 147.265090 amu
239.984990 amu Mass defect = Actual mass - Theoretical mass:
238.050785 amu - 239.984990 amu = - 1.934205 amu Calculating the Binding Energy per nucleon: Binding Energy -1.934205 amu x 931.5 Mev / amu
mucleon 238 nucleons = =
Slide43 : Mass and Energy in Nuclear Decay - I Consider the alpha decay of 212Po T1/2 = 0.3 s 212Po 208Pb + + Energy 211.988842 g/mol 207.976627 g/mol + 4.00151 g/mol Products = 207.976627 + 4.00151 = 211.97814 g/mol Mass = Po - Pb + = 211.988842
211.97814
0.01070 g/mol E = mC2 = (1.070 x 10-5 kg/mol)(3.00 x 108m/s)2
= 9.63 x 1011 J/mol 9.63 x 1011 J/mol
6.022 x 1023 atoms/mol = 1.60 x 10-12J/atom
Slide44 : Mass and Energy in Nuclear Decay - II The Energy for the Decay of 212Po is 1.60 x 10-12J/atom 1.60 x 10-12J/atom
1.602 x 10-19 J/ev = 1.00 x 107 ev/atom 1.00 x 107 ev 1.0 x 10-6 Mev
atom ev x = __________________ !!!!! The decay energy of the alpha particle from 212Po is = 8.8 Mev !!!!
Figure 21.10: Both fission and fusion produce more stable nuclides and are thus exothermic. : Figure 21.10: Both fission and fusion produce more stable nuclides and are thus exothermic.
Figure 21.11: Upon capturing a neutron, the 235U nucleus undergoes fission to produce two lighter nuclides, free neutrons (typically three), and a large amount of energy. : Figure 21.11: Upon capturing a neutron, the 235U nucleus undergoes fission to produce two lighter nuclides, free neutrons (typically three), and a large amount of energy.
Figure 21.12: Representation of a fission process in which each event produces two neutrons, which can go on to split other nuclei, leading to a self-sustaining chain reaction. : Figure 21.12: Representation of a fission process in which each event produces two neutrons, which can go on to split other nuclei, leading to a self-sustaining chain reaction.
Figure 21.13: If the mass of the fissionable material is too small, most of the neutrons escape before causing another fission event; thus the process dies out. : Figure 21.13: If the mass of the fissionable material is too small, most of the neutrons escape before causing another fission event; thus the process dies out.
Figure 21.14: Nuclear power plant : Figure 21.14: Nuclear power plant
Breeder reactor at a nuclear power plant in St. Laurent-Des Eaux, France. : Breeder reactor at a nuclear power plant in St. Laurent-Des Eaux, France. Source: Stock Boston
A Uranium "button" for use as a fuel in a nuclear reactor. : A Uranium "button" for use as a fuel in a nuclear reactor.
Figure 21.15: Schematic of a reactor core : Figure 21.15: Schematic of a reactor core
Slide54 : Neutron Induced Fission -
Bombs and Reactors There are three Isotopes with sufficiently long half-lives and a
significant fission cross-sections that are known to undergo
neutron induced fission, and are useful in fission reactors, and
Nuclear weapons. Of these only one exists on earth ( 235U which
exists at an abundance of 0.72% of natural Uranium)and that is the
isotope that we use in nuclear reactors for fuel and some weapons.
The three isotopes are: 233U T1/2 = 1.59 x 105 years sigma fission = 531 barns
235U T1/2 = 7.04 x 108 years sigma fission = 585 barns
239Pu T1/2 = 2.44 x 105 years sigma fission = 750 barns
Slide55 : Breeding Nuclear Fuel There are two relatively common heavy Isotopes that will not undergo
neutron induced fission, that can be used to make other Isotopes that
do undergo neutron induced fission, and can be used as nuclear fuel in
a nuclear reactor. Natural Thorium is 232 Th which is common in rocks.
232 Th + 10n 233 Th + Energy T1/2 = 22.3 min
233 Th 233Pa + + Energy T1/2 = 27.0 days
233Pa 233U + + Energy T1/2 = 1.59 x 105 yrs
Natural Uranium is 238U which is common in rocks as well.
238U + 10n 239U + Energy T1/2 = 23.5 min
239U 239Np + + Energy T1/2 = 2.36 days
239Np 239Pu + + Energy T1/2 = 24400 years
A schematic diagram of the tentative plan for deep underground isolation of nuclear waste. : A schematic diagram of the tentative plan for deep underground isolation of nuclear waste.
Disposal system : Disposal system Source: AP/Wide World Photos
Figure 21.16: Plot of energy versus the separation distance : Figure 21.16: Plot of energy versus the separation distance
Slide60 : Hydrogen Burning in Stars and
Nuclear Weapons 1H + 1H 2H + + 1.4 Mev
1H + 2H 3He + 5.5 Mev
2H + 2H 3He + 1n + 3.3 Mev
2H + 2H 3H + 1H + 4.0 mev
2H + 3H 4He + 1n + 17.6 Mev Easiest!
Highest
2H + 3He 4He + 1H + 18.3 Mev cross
section!
1H + 7Li 4He + 4He + 17.3 Mev
Slide61 : Helium Burning Reactions in Stars 12C + 4He 16O
16O + 4He 20Ne
20Ne + 4He 24Mg
24Mg + 4He 28Si
28Si + 4He 32S
32S + 4He 36Ar
36Ar +4He 40Ca
Image of a portion of the Cyngus Loop supernova remnant taken by the Hubble space telescope. : Image of a portion of the Cyngus Loop supernova remnant taken by the Hubble space telescope. Source: NASA
Slide63 : Positron Emission Tomography (PET) – A new and
Important Tool in Imaging Research In the technique of positron Tomography, a positron emitting isotope
Is included into a molecule that is incorporated into a chemical reaction.
The positron emitted during the decay of the isotope will analite with an
Electron and emit two 511 kev gamma rays that can then be detected,
and the location of the decaying isotope isolated accurately.
B+ + e- Energy Two Gamma rays at 180o e- + B+ 511 kev 511 kev Common Positron emitting Isotopes: 15O, T1/2 = 122s ; 18F, T1/2 = 1.83 hr
11C, T1/2= 20.3 min , 13N, T1/2 = 9.97 min , ETC The two gamma
rays come away
at 180o.
Slide64 : Positron Emission Tomograph The Tomograph is an
instrument that is a ring
of gamma ray detectors
that react very fast to
gamma rays, and by
measuring the time each
detector receives the signal
one can locate the point of
origin of the gamma ray to a precision of + 1 cm in a
human being or any other physical object, without
any in vivo investigation. The detectors must have a
capability of measuring up to + 250 ps per pulse. _ _
Slide65 : Units of Radiation dose rad = radiation - absorbed dose
the quantity of energy absorbed per kilogram of
tissue 1 rad = 1 x 10-2 J / kg
rem = roentgen equivalent for man, the unit of radiation
dose for a human:
1 rem = 1 rad x RBE
RBE = 10 for
RBE = 1 for x-rays, -rays, and ’s
Slide68 : Examples of Typical Radiation Doses
from Natural and Artificial Sources - I Source of Radiation Average adult Exposure Cosmic radiation 30 -50 mrem/yr
Radiation from the ground
From clay soil and rocks ~ 25 -170 mrem/yr
In wooden houses 10 -20 mrem/yr
In brick houses 60 -70 mrem/yr
In light concrete houses 60 -160 mrem/yr
Radiation from the air (mainly radon)
Outdoors, average value 20 mrem/yr
In wooden houses 70 mrem/yr
In brick houses 130 mrem/yr
In light concrete houses 260 mrem/yr
Internal radiation from minerals in
tap water and daily intake of food ~ 40 mrem/yr
( 40K, 14C, Ra) Natural
Slide69 : Examples of Typical Radiation Doses from
Natural and Artificial Sources - II Source of Radiation Average Adult Exposure Diagnostic x-ray methods
Lung (local) 0.04 - 0.2 rad/film
Kidney (Local) 1.5 - 3.0 rad/film
Dental (dose to the skin) < 1 rad/film
Therapeutic radiation treatment locally < 10,000 rad
Other sources
Jet flight (4 hrs) ~ 1 mrem
Nuclear tests < 4 mrem/yr
Nuclear power industry < 1 mrem/yr
Total Average Value 100 - 200 mrem/yr Artificial
Slide70 : Examples of Typical Radiation Doses from
Natural and Artificial Sources - III From Kotz & Percell, Freshman Chemistry text
Smoke detectors 1 millirem/year
Smoking Tobacco(1.5 packs a day) 9000 “
10 Airline flights 3 “
Airline Crew 160 “
Hazards equivalent to the radiation dose of 10 mrem/year
3250 km travel by car
600 km travel by velocipede
150 km motorcycle
25 liters of wine
100 cigarettes smoked
1 diagonistic x-ray
Slide71 : Acute Effects of a Single Dose of Whole-Body Irradiation - I Dose Lethal Dose
(rem) Effect Population (%) No. of Days 5 - 20 Possible late effect; possible --- ---
chromosomal aberrations
20 - 100 Temporary reduction in --- ---
white blood cells
50+ Temporary sterility in men --- ---
(100+ rem = 1 yr duration)
100-200 “Mild radiation sickness”:
vomiting, diarrhea, tiredness
in a few hours
Reduction in infection resistance
Possible bone growth retardation
in children
Slide72 : Acute Effects of a Single Dose of
Whole-Body Irradiation - II Dose Lethal Dose
(rem) Effect Population (%) No. of Days 300+ Permanent sterility in Women ---- ---
500 “Serious radiation sickness”: 50 - 70 30
marrow/intestine destruction
400 - 1000 Acute illness, early deaths 60 - 95 30
3000+ Acute illness, death in hours 100 2
to days