21.6: Energy Changes in Nuclear Reactions

1
21.6 Energy Changes in Nuclear Reactions

• Courtney Wong Lauren Hebel

2
Energy Associated with Nuclear Reactions

• Energy and mass of nuclear reactions are related
  in Einstein's famous equation
• Emc2
• Eenergy
• Mmass
• C speed of light (3.00 x 108)
• Equation states that mass and energy are
  proportional
• If a system loses mass, it loses energy
• Vice -versa

3
Mass change, ?m

• Mass changes and associated energy changes are
  much greater in nuclear reactions when compared
  to chemical reactions
• ?m(total mass of products) (total mass
• of reactants)
• -?m exothermic spontaneous nuclear reaction

4
Example ?m Problem
Reaction

• 22688Ra --gt 22286Rn 42He
• (mass of p) - (mass of r)
• ?m Mass of one mole of 42He mass of one mole
  of 22286Rn mass of one mole of 22688Ra
• ?m 4.0015 g 221.9703 g - 225.9771 g
• ?m -0.0053 g

5
Using ?m In Einsteins Equation

• Rearranged as ?Ec2?m
• To obtain ?E in joules, ?m must be converted to
  Kg when used in the equation
• Example Continued
• ?m -0.0053 g
• ?E (2.9979 x 108)2 (-0.0053) (1kg/1000g)
• ?E-4.8x1011

6
Nuclear Binding Energies

• 1930s scientists discovered that mass of
  individual parts of the nucleus always weighs
  more that the nucleus itself
• Ex
• Helium-4 nucleus has a mass of 4.00150 amu
• Mass of two protons 2(1.00728 amu) 2.01456
  amu
• Mass of two neutrons 2(1.00728 amu) 2.01456
  amu
• Total Mass 4.03188 amu

7

• Ex (continued)
• Mass of two protons and two neutrons 4.03188
  amu
• Mass of 42He nucleus 4.00150 amu
• Mass Difference (?m) 0.03038 amu
• Mass Defect the mass difference between a
  nucleus and it individual nucleons
• Increase in mass increase in energy
• Energy 42He 211p 210n
  so
• ?Ec2?m
• (2.9979 x 108 m/s)2 (0.03038 amu) (
  ) ( )
• 4.534 x 10-12 J

1g 6.022 x 1023 amu
1kg 1000g
Nuclear Binding Energy
8
Nuclear Binding Energy

• The energy required to break apart a nucleus into
  its individual nucleons
• The larger the binding energy the more stable the
  nucleus is towards decomposition

Nucleus Mass of Nucleus (amu) Mass of Individual Nucleons (amu) Mass Defect (amu) Binding Energy (J) Binding energy per Nucleon (J)
42He 4.00150 4.03188 0.03038 4.53 x 10-12 1.13 x 10-12
5626Fe 55.92068 56.44914 0.52846 7.90 x 10-11 1.41 x 10-12
23892U 238.00031 239.93451 1.93420 2.89 x 10-10 1.21 x 10-12
9
Nuclear Binding Energy

• Binding energy per nucleon increases in magnitude
  as mass number increases, reaching 1.4 x 10-12 J
  (mass number of nuclei close to iron-56)
• Then it decreases to 1.2 x 10-12 J for a very
  heavy nuclei

10

• Trend nuclei of intermediate mass numbers are
  more tightly bound and more stable than those
  with either smaller or larger mass numbers

5626Fe
23892U
42He
11
Nuclear Binding Energy

• Trend shows that
• Heavy nuclei gain stability and split into two
  mid-sized nuclei
• Known as FISSION
• Used to generate energy in nuclear power plants
• Greater amounts of energy are released if very
  light are fused together to form a more massive
  nuclei
• Known as FUSION
• is an essential energy-producing process in the
  Sun

12
Outside Sources

• http//chemistry.about.com/od/workedchemistryprobl
  ems/a/nukerxns.htm
• http//wps.pearsoncustom.com/pcp_brown_chemistry_1
  0/34/8909/2280844.cw/index.html

13
Biological Effects of Radiation
Susanna Trost
Kelsey Mariner
14
Everyday Life

• Natural and artificial sources
• Sun gives off infrared, ultraviolet, visible
  radiation
• Television and radio stations give off radio
  waves
• Microwaves ovens give off microwaves
• Medical procedures can give off X-rays
• Natural materials like soil can have radio
  activity

15
Matter Absorbing Radiation

• Excitation is when excited electrons are moved to
  a higher energy state or the motion of molecules
  is increased as a result of absorbed radiation
• Ionization is when an electron is removed from a
  molecule or atom by radiation
• Ionizing radiation radiation that causes
  ionization, can ionize water
• Non-ionizing radiation radiation that does not
  cause ionization and has a lower energy

16
H2O H2O H3O OH

• Free Radical A substance with one or more
  unpaired electrons
• OH molecule is a highly reactive and unstable
  free radical
• Free radicals attack surrounding biomolecules
  which produces new free radicals
• One free radical can cause many chemical
  reactions disrupting normal cell operations

17
Damaging Radiation

• Based on energy and activity of radiation,
  location of source, and length of exposure
• Gamma rays and X-rays can penetrate human tissue
• The skin stops alpha rays
• If within the body, they can transfer energy to
  surrounding tissues causing damage
• Beta rays penetrate only 1 cm into the skin
• Tissues that rapidly reproduce show the most
  damage
• Examples Lymph nodes, bone marrow, and blood
  forming tissues
• Prolong exposure to radiation may lead to cancer
• Damage to a cells growth-regulation mechanism
  causes a cell to rapidly and uncontrollably
  reproduce
• Leukemia is most associated with radiation
  (excessive growth of white blood cells)

18
Radiation Doses

• Gray and Rad are units to measure radiation
  exposure
• Gray (Gy) the SI unit of absorbed dose
• One joule per kilogram of tissue
• Rad (radiation absorbed dose) 1 x 10-2 joule of
  energy per kilogram of tissue
• 1 Gy 100 rad
• Rad is the most common

19
Relative Biological Effectiveness

• Different types of radiation harm biological
  materials differently
• RBE is a multiplication factor that measures the
  relative biological damage caused by radiation
• Multiplied by the radiation dose to correct the
  differences in radiation damage
• changes with total dose, dose rate and the type
  of tissue affect
• About 1 for beta and gamma radiation
• About 10 for alpha radiation
• Rem (roentgen equivalent for man) unit for
  effective dosage, more commonly used
• Sievert (Sv) is the SI unit for effective dosage
• 1 Sv 100 rem

of rems ( of rads)(RBE)
(gray)(RBE) Sv
20
Radon-222

• Radioactive noble gas
• Radon-222 is caused from nuclear disintegration
  series of Uranium-238
• Created in soil and rock decays as uranium
• Accounts for large percentage of our exposure to
  radiation
• Does not chemically react as it escapes from the
  ground
• Because it is extremely unreactive
• Has a very short half life
• Combined with its high RBE, radon is a probable
  cause of lung cancer when inhaled

21
Radiation Therapy

• High-energy radiation is used to damage the DNA
  of cancer cells, which kills the cells
• Normal cells can also be damaged, so treatment is
  done very carefully
• Cancer cells more likely to be damaged because
  rapidly reproducing cells are very vulnerable to
  radiation damage
• Radiation can come from a machine or radioactive
  material can be injected into the bloodstream or
  placed directly in the body near the tumor cells
• Gamma rays, x-rays and charged
• particles can be used

22
Sources

• http//www.cancer.gov/cancertopics/factsheet/Thera
  py/radiation

http//www.google.com/imgres?qwave
http//www.nrc.gov/reading-rm/doc-collections/fact
-sheets/bio-effects-radiation.html
Chemistry The Central Science Textbook
23
2.1 Radioactivity

• By Margo Fox

24
Review

• Nucleons- both protons and neutron
• All atoms
• Same of protons (atomic )
• Can have different of neutrons
• Mass number- total of nucleons in nucleus
• Same atomic but different mass number- isotopes

25
Isotopes

• Uranium-235 or U
• Different natural abundances
• Different stabilities
• Nuclide- nucleus with specified of protons and
  neutrons
• Radionuclides- radioactive nuclei
• Radioisotopes- atoms containing those nuclei

235 92
26
Nuclear Equations

• Radionuclides- unstable, spontaneously emit
  particles and electromagnetic radiation
• Emit radiation to become more stable
• Emitted radiation is carrier of the excess energy

27
Nuclear Equations

• Ex Uranium-238 and helium-4
• Helium-4 particles are known as alpha particles
• Alpha radiation- stream of alpha particles
• 238 234 4
• 92 90 2
• radioactive decay and alpha decay
• 238 234 4
• 92 90 2
• Must be balanced

Th
U
He
28
Types of Radioactive Decay
Property a (Alpha) ? (Beta) ? (Gamma)
Charge 2 1- 0
Mass 6.64 10-24g 9.11 10-28g 0
Relative penetrating power 1 100 10,000
Nature of radiation He nuclei Electrons High-energy protons
4 2
29
Beta Radiation

• Beta particles- high speed electrons emitted by
  an unstable nucleus
• 0 0
• -1 -1
• 1 1 0
• 0 1 -1

e or
ß
n p e
30
Gamma Radiation (Gamma Rays)

• High-energy photons (electromagnetic radiation of
  very short wavelength)
• Does not change atomic or mass
• Represents the energy lost when remaining
  nucleons reorganize to be more stable
• Generally not shown when writing equations

31
Positron Emission

• Same mass as an electron, but opposite charge
• Converts proton to neutron and decreases atomic
  number by 1

32
Electron Capture

• The capture by the nucleus of an electron from
  the electron cloud surrounding the nucleus
• Shown on reactant side because the electron is
  consumed not formed in the process
• Converts proton to neutron

33
Further Research

• Positron Emission Tomography Scan- imaging test
  to help reveal how tissues and organs are
  functioning
• Inject, swallow, or inhale radioactive material
• Accumulates in areas with higher levels of
  chemical activity (areas of disease)
• Gamma Knife Therapy
• treatment using gamma rays, a type of high-energy
  radiation that can be tightly focused on small
  tumors or other lesions in the head or neck, so
  very little normal tissue receives radiation

34
(No Transcript)
35
What Type of Radiation
81 36
81 37
11 6
11 5
0 1
0 -1
36
Bibliography

• http//www.cancer.gov/dictionary?cdrid46396
• http//www.mayoclinic.com/health/pet-scan/MY00238

37
Detection of Radioactivity

• By A Stormy Hickey and
• The Austin McCadden

38
Discovery of Radiation

• Was discovered by Henri Becquerel
• Observed effect of radiation on photographic
  plates
• Received 1903 Nobel Prize for his works
• SI unit for expressing radiation activity was
  named becquerel (Bq)

39
Effects of radiation

• Radiation affects photographic film the same way
  it does X-rays
• Increased radiation darkens negative are on film
• Used by people who work with radiation to see
  extent of exposure

40
Ways of Detection

• Geiger counter
• detects and measures radioactivity
• Use is based on the ionization of matter caused
  by radiation
• Ions and electrons permit conduction of
  electrical current

41
Geiger Counter

• Consists of a metal tube filled with gas
• Tube has a window that can be infiltrated by
  alpha, beta, or gamma rays
• Wire in tube connected to a source of direct
  current
• Current flows between the wire and tube when ions
  are produced by entering radiation
• Records pulses that indicate presence of radiation

42
Other Indicators of Radiation

• Phosphors-
• excited by radiation give off light when
  electrons return to lower-energy states
• Ex Zinc sulfide is excited by alpha particles

43
Scintillation Counter

• Measures radiation based on tiny flashes of light
  
• Flashes of light produced when radiation strikes
  a phosphor thats suitable
• Flashes are magnified electronically and counted
  to measure radiation

44
Radioisotopes

• Radioisotopes can be detected readily, used to
  follow element through chemical reactions
• Possible because all isotopes of an element have
  essentially identical chemical properties

45
Radioisotopes Continued

• When small amounts of radioisotopes are mixed
  with the naturally occurring stable isotopes, all
  isotopes go through same reaction together
• Element can be tracked in reaction or process by
  tracing radioactivity
• Because Radioisotopes trace paths of element they
  are called Radiotracers

46
Additional Research

• Gold Leaf Electroscope
• When electroscope is charged, the gold leaf
  sticks out, because charges on gold repel charges
  on metal stalk
• Radiation ionizes air, and conducts electricity
• The charge leaks away from electroscope,
  discharging it and the gold leaf falls.

47
Additional Research Cont.

• Personal radiation detectors can be purchased at
  a relatively low price
• PDS-100G
• Sensitive Survey Meter

48
Questions

• How did Becquerel discover radiation?
• How can Radioisotopes be used to track the path
  of an element?

49
Sources

• http//www.darvill.clara.net/nucrad/detect.htm
• http//www.mirion-hp.com/portableinstruments.asp?_
  kkdetection20of20radioactivity_kt43082093-d73
  5-446c-87b0-366f3477100fgclidCMCRpffE4q4CFYuK4Ao
  d7G9bZw

50
21.8 Nuclear Fusion

• Stephanie Cho
• Abigail Wang

51
What is nuclear fusion?

• Light nuclei fuse into larger ones ? produces
  energy
• Take place on the Sun (mostly H and He)

52
Fusion as an Energy Source

• Appealing due to
• 1. Availability of light isotopes
• 2. Products are not usually radioactive
• Still, not used presently
• Requires high energies to overcome repulsion?
  high temps needed

53
Fusion as an Energy Source

• Thermonuclear reactions
• Lowest temp needed for any fusion requires
  40,000,000 K
• Temps have been achieved with atomic bomb to
  begin process
• Unacceptable for controlled power generation

54
Problems and Research

• No known structural material is known to
  withstand temperatures
• Researching to generate high temperature
• Tokamak - an apparatus for producing controlled
  fusion reactions in hot plasma
• Strong magnetic fields
• Up to 3,000,000K can be generated, but still not
  enough
• Use of powerful lasers

55
Inertial Confinement

• Lasers
• Direct drive
• Lasers focused on small deuterium-tritium pellet
• Compresses inwards? shock wave? heat
• Indirect drive
• National Ignition Facility
• Hohlraum is heated by 192 beams? X-rays heat
  pellet
• Plasma and compression
• 10-11 to 10-9 seconds

56
Magnetic Confinement

• Magnetic fields used to contain the charged
  particles composed of plasma
• Contains plasma for a long time at low density
• Two types
• Mirror
• Electric current generates a magnetic field
• Contains the plasma inside the magnetic field
• Open type
• Toroidal/Tokamak
• Closed type
• Coils magnetic field and magnetic current
  created by plasma counteracts

57
Chapter 21.3 Nuclear Transmutations

• By Jin Lee and Paul Gregotski
• And Special Appearances from
• Hannah Cherry and Kayla Seider

58
What is a Nuclear Transmutation?

• A nucleus can also change identity if it is truck
  by a neutron or by another nucleus. Nuclear
  reactions that are induced in this way are known
  as nuclear transmutations.
• The first conversion of on nucleus into another
  was performed in 1919 by Ernest Rutherford.
• He succeeded in converting nitrogen-14 into
  oxygen-17 plus a proton using high velocity alpha
  particles emitted by radium.
• Reaction 14/7 N 4/2 H --? 17/8 O 1/1 H

59
What type of Particles are They?

• This reaction demonstrated the nuclear reactions
  can be induced by striking nuclei with particles
  such as alpha particles.
• Such reactions made it possible to synthesize
  hundreds of radioisotopes in the lab.
• Nuclear transmutations are sometimes represented
  by listing, in order, the target nucleus, the
  bombarding particle, the ejected particle, and
  the product nucleus.
• Written in this fashion is 14/7 N (a,p) 17/8 O
• The alpha particle, proton, and neutron are
  abbreviated as a, p, n.

60
Charged Particles

• Charged particles such as alpha particles must be
  moving very fast in order to overcome the
  electrostatic repulsions between them and the
  target nucleus.
• The higher the nuclear charge on either the
  projectile or the target, the faster the
  projectiles must be moving to bring about nuclear
  reactions.
• Many methods have been devised to accelerate
  charged particles using strong magnetic and
  electrostatic fields.
• These particle accelerators are called cyclotron
  and synchrotron.

61
What is a Cyclotron?

• Cyclotron the hollow D-shaped electrodes are
  called dees. The projectiles particles are
  introduced into a vacuum chamber within the
  cyclotron.
• The particles are then accelerated by making the
  dees alternately positively and negatively
  charged.
• Magnets placed above and below the dees keep the
  particles moving in a spiral path until they are
  finally deflected out of the cyclotron and emerge
  to strike a target substance.
• Particle accelerators have been used mainly to
  synthesize heavy elements and to investigate the
  fundamental structure of matter.

62
Using Neutrons

• Most synthetic isotope used in quantity in
  medicine and scientific research are made using
  neutrons as projectiles.
• Because neutrons are neutral they are not
  repelled by the nucleus.
• They do not need to be accelerated as do charged
  particles in order to cause nuclear reactions.
• The necessary neutrons are produced by the
  reactions that occur in nuclear reactors.
• Cobalt-60 is used in radiation therapy where it
  is bombarded by neutrons.
• The following sequence takes place
• 58/26 Fe 1/0 n ----? 59/26 Fe
• 59/26 Fe --? 59/27 Co 0/-1 e
• 59/27 Co 1/0 n --? 60/27 Co

63
Transuranium Elements

• Artificial transmutations have been used to
  produce the elements with atomic number above 92.
• These are known as transuranium elements because
  they occur immediately following uranium in the
  periodic table.
• Elements 93, neptunium, and 94, plutonium were
  first discovered in 1940. They were produced by
  bombarding uranium-238 with neutrons
• 238/92 U 1/0 n ? 239/92 ? 239/93 Np 0/-1 e
• 239/93 Np ? 239/94 Pu 0/-1 e

64
Transmutation Elements (cont.)

• Elements with larger atomic numbers are normally
  formed in small quantities in particle
  accelerators.
• In 1994 a team of European scientists synthesized
  element 111 by bombarding bismuth target for
  several days with a bream of nickel atoms
• 209/83 Bi 64/28 NI ? 272/111 X 1/0 n
• The nuclei are very short-lived, and they undergo
  alpha decay within milliseconds of their
  synthesis.

65
Equations

• Example Carbon-11 is an example of an isotope
  that decays by positron emission
• The positron has a very short life because it is
  annihilated when it collides with an electron,
  producing gamma rays
• Electron capture is the capture by the nucleus of
  an inner-shell electron from the electron cloud
  surrounding the nucleus.

66
Chart of Particles
Particle Symbol
Neutron 1/0 n
Proton 1/1 p or 1/1 H
Electron 0/-1 e
Positron 0/1 e
Beta Particle 0/-1 e or 0/-1 ß
Alpha Particle 4/2 a or 4/2 He
67
Example Problem

• Question Balance the following equation
• 252/98 Cf 10/5 B -? 3 (1/0 n) ?
• Answer
• 25210262 CfB Lr103
• 985103
• 262-3259
• 259/103 Lr

68
Questions

• Question Write a balanced equation for
• 106/46 Pd (a,p) 109/47 Ag
• Question Fill in the missing particle
• 32/16 S 1/0n ? 1/1 p ?
• Question Write a balanced equation for
• 14/7N(p,a)11/6C

69
Answers To Questions

• Question Write a balanced equation for
• 106/46 Pd (a,p) 109/47 Ag
• 106/46 Pd 4/2 a ? 1/1 p 109/47 Ag
• Question Fill in the missing particle
• 32/16 S 1/0n ? 1/1 p ?
• 32/16 S 1/0n ? 1/1 p 32/15 P
• Question Write a balanced equation for
• 14/7N(p,a)11/6C
• 14/7 N 1/1 p ? 4/2 a 11/6 C

70
Bibliography

• http//faculty.ncc.edu/LinkClick.aspx?fileticketF
  khb0_AcPfE3Dtabid1920
• http//www.avon-chemistry.com/nuclear_lec.html
• Chemistry (The Central Science) Brown LeMay
  Bursten

71
21.3Nuclear Transmutations

• By Dakota Lieske
• Cindy Rushworth

72
What are Nuclear Transmutations?

• Nuclear transmutations are nuclear reactions that
  are caused by a nucleus being struck by either a
  neutron or another nucleus
• The result of this is a change in the nucleuss
  identity

73
Ernest Rutherfords First Conversion

• Ernest Rutherford performed the first nuclear
  transmutation in 1919, converting nitrogen-14 to
  oxygen-17 and a proton
• To do this, he used high-velocity alpha particles
  emitted by radium
• This proved that by striking nuclei with alpha
  particles or anything of the like, nuclear
  reactions can be created

74
Shorthand Notation

• Nuclear Transmutations can be listed in shorthand
  notation by listing, in order, the target
  nucleus, the bombarding particle, the ejected
  particle, and the product nucleus

Product Nucleus
Target Nucleus
Comma
Bombarding Particle
Ejected Particle
Alpha Particles will be abbreviated as
Neutrons will be abbreviated as n
Protons will be abbreviated as p
75
Charged Particles

• Charged particles (those such as alpha particles)
  must be moving extremely fast so that it can
  overcome the electrostatic repulsion between them
  and the target nucleus
• Particle accelerators are made to accelerate the
  charged particles by using strong magnetic and
  electrostatic fields
• Particle accelerators have been used in order to
  synthesize heavy elements, investigate
  fundamental structures of matter, and fail at
  creating black holes

76
Neutrons

• Most isotopes are made using neutrons as
  projectiles in nuclear transmutations they do
  not need to be accelerated in order to cause
  nuclear reactions, as they are neutral and
  therefore not repelled by the nucleus
• For the reaction in which Iron-58 is bombarded by
  neutrons to create Cobalt-60, the following
  sequence takes place

77
Transuranium Elements

• Transmutations are often used to produce elements
  with an atomic number above 92
• These elements are called Transuranium Elements
  as they occur after uranium on the periodic table
• Elements such as neptunium and plutonium were
  discovered through this in 1940 by bombarding
  uranium-238 with neutrons

78
Patterns of Nuclear Stability

• By Courtney Walker and Kelli Joerger

79
Stability of a Nucleus

• Not one single rule to determine if nucleus is
  radioactive
• Variety of factors
• Observations can help predict stability of nucleus

80
Neutron-to-Proton Ratio

• Strong nuclear force
• Attraction between nucleons
• Neutrons bind nucleus together
• All nuclei with at least 2 protons contain a
  neutron
• Nuclei up to atomic number 20 have equal protons
  and neutrons
• As exceeding this number, more neutrons than
  protons
• Neutron-to-proton ratios of stable nuclei
  increase with increasing atomic number

81
Belt of Stability Chart
All nuclei with 84 or more protons are
radioactive
82
Type of Radioactive Decay

• Depends on neutron-to-proton ratio compared to
  nearby nuclei in belt of stability
• 3 possible situations

83
Situation 1 Above

• Nuclei above belt of stability
• High neutron-to-proton ratio
• Capable of lowering ratio by emitting a beta
  particle
• Beta emissions- decrease number of neutrons and
  increase number of protons in nucleus

84
Situation 2 Below

• Nuclei below belt of stability
• Low neutron-to-proton ratio
• Capable of increasing ratio by positron emission
  or electron capture
• Both increase number of neutrons and decrease
  number of protons
• Positron emission more common in lighter nuclei
• Electron capture more common as nuclear charge
  increases

85
Situation 3 Above 84

• Nuclei with atomic numbers greater than or equal
  to 84
• Heavy nuclei
• Beyond belt of stability
• Alpha emission- decreases number of neutrons and
  number of protons by 2
• Nucleus diagonally toward belt of stability

86
Sample Exercise 21.3

•  

87
Sample Exercise 21.3

• B. Predict the mode of decay of (b) xenon- 118.

88
Sample Exercise 21.3

• B. Predict the mode of decay of (b) xenon- 118.
• - Xenon has an atomic number of 54, and 118-54
  64 neutrons giving it a neutron-to-proton ratio
  of 64/54 1.2.
• - According to the belt of stability, stable
  nuclei usually have higher neutron to proton
  ratios than xenon- 118.
• -The nucleus can increase this ratio by either
  positron emission or electron capture.
• Both modes of decay are observed.

89
Radioactive Series

• Some nuclei cannot become stable with only one
  emission
• Therefore a series of successive emissions occur
• Also called nuclear disintegration series
• Series of nuclear reactions that begins with an
  unstable nucleus and terminates with a stable one
• Examples include
• Starts with uranium-238 and ends with lead-206
• Starts with uranium 235 and ends with lead-207
• Starts with thorium-232 and ends with lead-208

90
Radioactive Series of Uranium-238
91
Additional Observations

• Magic Number- more stable
• Nuclei with 2, 8, 20, 28, 50, or 82 protons
• Nuclei with 2, 8, 20, 28, 50, 82, or 126 neutrons
• Nuclei with even numbers of both protons and
  neutrons generally more stable than those with
  odd numbers of nucleons
• Shell model of the nucleus analogous to stable
  closed shell electron configurations

92
Number of Stable Isotopes Protons Neutrons
157 Even Even
53 Even Odd
50 Odd Even
5 Odd Odd
93
Sample Exercise 21.4

•  

94
Additional Research

• http//www.youtube.com/watch?vVJZuY3_aLnI
• http//www.youtube.com/watch?voFdR_yMKOCwfeature
  related

95
Review Game

• 1. Provide an explanation for why neutrons are
  needed in the nucleus.

96
Answer

• Positive Particles repel each other, and multiple
  positive particles in the nucleus needs something
  to keep that mass together. Neutrons do this
  because they have no charge and are able to
  balance out the positive charge of the protons.

97
Review Game

• 2. What type of particle is emitted when
• a. The neutron to proton ratio is high
• b. The neutron to proton ratio is low
• c. The atomic number is above 84?

98
Answer

1. A beta particle is emitted
2. Either a positron emission or electron capture
3. An alpha particle is emitted

99
Review Game

• 3. Describe Nuclear Disintegration Series

100
Answer

• Initially begins with an unstable nucleus that
  becomes stable through emitting multiple
  particles and results in a stable one.

101
Review Game

• 4. Define the meaning of a magic number.

102
Answer

• A nucleus that involves a magic number is more
  stable than a nucleus without a magic number.
• Nuclei with 2, 8, 20, 28, 50, or 82 protons
• Nuclei with 2, 8, 20, 28, 50, 82, or 126 neutrons

103
Bonus Worth the rest of the bag of candy.

• Reiterate how you can predict a method of decay
  when given an element and its atomic number.

104
Rates of Radioactive Decay

• Steph Coyle and Rachel Sacchetti

105
What is Radioactive Decay?

• Spontaneous breakdown of an atomic nucleus
• Results in the release of energy and matter from
  the nucleus

106
Half Life

• Decay first order kinetic process
• Half-Life- time required for ½ of any given
  quantity of a substance to react
• Constant rate
• Less and less mass
• is lost at the point of
• each half life

107
Half-Life (cont.)

• Short as millionth of a second- billions of years
• Quick decay not found in nature (synthesized)
• Unaffected by temp., pressure, or state of
  chemical combination
• Cannot be made harmless via chemical rxn

108
Alpha and Beta Decay
109
Radiocarbon-dating Technique

• Assumed carbon-14 to carbon-12 has been constant
  for 50,000 yr
• Carbon-14 in atmosphere? photosynthesis? plants
  eaten by animals? carbon-14 incorporated in
  organism make-up? animal dies ?
• Ratio of C-14 to C-12 decrease, and when compared
  to ratio in atmosphere, can estimate age of
  organism

110
Carbon Dating (cont.)

• 4.5x109 yrs for Uranium-238 to decay to Lead-206
  
• Age of rocks containing Uranium-238 can be
  determined by looking at ratio U-238 to Pb-206
• Oldest rocks 3x109 yrs old

111
Carbon Dating (cont.)
112
Calculating Rate of Decay

• RatekN
• k decay constant
• N number of radioactive nuclei
• Activity- rate at which a sample decays
• Bq- becquerel, unit for expressing activity
• Ci- Curie, 3.7x1010
• Relationship between k and ½ life is
  k0.693/ t½

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Example

• 4.0 mCi sample of Co-60 undergoes (4.0x1010-3) x
  (3.7x1010) 1.5x108 disintegrations per second
• Therefore 1.5x108 Bq

114
Further Research

• Radioactivity was discovered in 1896 by the
  French scientist Henri Becquerel
• Hence Bq SI unit
• Working with phosphorescent materials, noticed
  they glowed in dark after exposure to light

115
More Research

• Wrapped photographic plate in black paper and
  placed phosphorescent salts on paper
• No result
• Placed uranium salts on plate, blackened the
  plate
• Radiations called Becquerel Rays

116
Quiz!

• What is a half life?
• Time required for ½ of any given quantity of a
  substance to react
• What is radioactive decay?
• Spontaneous breakdown of an atomic nucleus
• How does temperature affect decay?
• It doesnt

117
Quiz!

• True or false, radiocarbon-dating can be used to
  date a rock
• False
• What is the rate equation?
• RatekN
• How old is the oldest rock?
• 3x109

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Work Cited

• http//www.ndted.org/EducationResources/HighSchool
  /Radiography/radioactivedecay.htm
• http//www.dummies.com/how-to/content/nuclear-chem
  istry-halflives-and-radioactive-dating.html
• http//www.nobelprize.org/nobel_prizes/physics/lau
  reates/1903/becquerel-bio.html