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Nuclear Physics

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Title: Nuclear Physics


1
Nuclear Physics
  • Chapter 29

2
Fossils
  • How are scientists able to determine the age of
    fossils?
  • The iceman

3
Nuclear Physics
  • The year 1896 marked the birth of nuclear physics
  • Henri Becquerel accidentally discovered natural
    radioactivity in uranium compounds.
  • Researchers tried to identifythe radiation from
    atomic nuclei.
  • 1 Thorite -------gt

4
Rutherfords Discovery
  • Rutherford showed that there were three types of
    nuclear radiation.

5
  • Alpha (a)
  • Helium nuclei
  • Least penetrating
  • Positively charged

6
  • Beta (b)
  • Electrons or positrons
  • More penetrating than alpha particles
  • Negatively or positively charged

7
  • Gamma (g)
  • High-energy photons
  • Most penetrating
  • No charge

8
Rutherfords Experiment
  • Rutherford bombarded gold foil with alpha
    particles and disproved the Thompson model of the
    atom..

9
The Strong Nuclear Force
  • Rutherford and his students discovered the
    nuclear strong force in 1911
  • It explained why the protons dont go flying off
    from the nucleus.

10
Milestones in Nuclear Physics
  • Nuclear reactions were observed in 1930.
  • The neutron was discovered in 1932.
  • Artificial radioactivity was produced in 1933.
  • Nuclear fission was discovered in 1938.
  • Nuclear fission was first controlled in 1942.

11
Atomic Nuclei
  • All nuclei are composed of two types of
    particles.
  • The atomic number, Z, equals the number of
    protons in the nucleus.
  • The neutron number, N, equals the number of
    neutrons n the nucleus.
  • The mass number, A, equals the number of
    nucleons. (A Z N)
  • A nucleon can be either a proton or a neutron

12
Nuclear Symbols
  • The symbol we use to represent nuclei is
  • Sometimes Z is not shown when the chemical symbol
    is obvious.

13
Isotopes
  • Isotopes have the same number of protons but
    different numbers of neutrons.
  • There are four isotopes of carbon.

14
  • has a 98.9 natural abundance.

15
Hydrogen Isotopes
  • Hydrogen has three isotopes.
  • Protium
  • Deuterium
  • Tritium

16
Symbols for Other Particles
  • alpha
  • beta or
  • gamma
  • neutron

17
Artificial Isotopes
  • Artificial isotopes do not occur naturally and
    are produced in the laboratory.
  • 17-1, 17-2

18
Charge and Mass
  • The proton and electron have charges that are
    equal in magnitude but opposite in sign.
  • The neutron has no charge.
  • The masses of the proton and neutron are nearly
    equal. (See Table 29.1) on pg. 914.
  • The masses of selected isotopes are in Appendix B
    on pg. A.14.

19
Unified Mass Units
  • Unified mass units (u) are based upon the
    carbon-12 atom which has a mass of exactly 12 u.
  • 1 u 1.660540 x 10-27 kg
  • The proton and neutron each have a mass of
    approximately 1 u.
  • The mass of the electron is much less.

20
Particle Masses
  • Proton mass 1.007276 u
  • Neutron mass 1.008665 u
  • Electron mass 0.000549 u

21
Mass Energy Conversion
  • The energy equivalent of one atomic mass unit is
    931.494 MeV.

22
Rutherfords Experiment
23
  • Rutherford found that an alpha particle on a
    head-on collision with a nucleus will stop
    instantaneously at a distance d from the nucleus
    because of Coulomb repulsion.
  • 29.1

24
  • A neutron has the best chance of causing a
    nuclear reaction because it has no charge.

25
Nuclear Radii
  • The average radius of most atomic nuclei can be
    found by using
  • ro 1.2 x 10-15 m
  • A is the mass number
  • 285

26
Nuclear Density
  • All nuclei have nearly the same density.

27
Nuclear Stability
  • Why dont the protons in the nucleus fly apart
    because of the repulsive Coulomb forces?

28
The Strong Nuclear Force
  • The strong nuclear force is an attractive force
    between all nuclear particles.
  • The strong nuclear force dominates the Coulomb
    force over short distances.

29
Nuclear Stability
  • There are over 260 stable nuclei.
  • Hundreds more are unstable
  • Light nuclei are stable when N Z.
  • Heavier nuclei are stable when N gt Z.
  • Elements with more than 83 protons are always
    unstable (radioactive).
  • 29.3

30
Nuclear Mass
  • The total mass of the nucleus is always less than
    the sum of the masses of its nucleons.

31
Nuclear Energy
  • The total energy of the bound nucleus is always
    less than the combined energy of the separated
    nucleons.
  • The difference is called the binding energy of
    the nucleus.
  • 290

32
Splitting a Nucleus
  • In order to break apart a nucleus, energy must be
    added to the system.

33
Binding Energy
  • Nuclei with an atomic mass near 60 are the most
    stable.
  • The average binding energy per nucleon is about
    8 MeV / nucleon.
  • 29.4, 291

34
Natural Radioactivity
  • Natural radioactivity was accidentally discovered
    by Becquerel in 1896.
  • It was later named radioactivity by Marie Curie.

35
Radioactive Elements
  • Marie and Pierre Curie discovered radium and
    polonium after years of separating the
    radioactive elements from tons of pitchblende, a
    radioactive ore.
  • Experiments indicated that the radiation was the
    result of nuclear decay.
  • Marie Curie died of leukemia in 1934.

36
The Weak Nuclear Force
  • The weak nuclear force is responsible for
    radioactivity.

37
Anti Matter
  • What is a positron?
  • It is an antiparticle with the mass of an
    electron and the charge of a proton.
  • Symbol

38
Identifying Nuclear Particles
  • A magnetic field can be used to identify the
    particles involved in nuclear radiation.
  • 29.5, 292

39
Rutherfords Mousetrap
  • Rutherfords mousetrap experimentally proved that
    alpha particles were composed of helium nuclei.
  • T-41

40
The Decay Constant
  • The decay constant (l) determines the rate at
    which isotopes decay
  • A large value for l indicates a rapid rate of
    decay.

41
Activity
  • The activity (R) is defined as the number of
    decays per second
  • 1 Bq 1 decay / second
  • 1 Ci 3.7 x 1010 decays / second 3.7 x 1010
    Bq
  • This is the approximate activity of 1 gram of
    radium.
  • The mCi and the mCi are most commonly used.

42
Remaining Nuclei
  • The number of nuclei (N) remaining after a given
    amount of time can be found by using

43
Decay Rate
  • The decay rate (Ro) can be found by using

44
Activity
  • The activity (R) after a given amount of time can
    be found by using

45
Half Life
  • Halflife
  • The time it takes or half of a given number of
    radioactive nuclei to decay is given by
  • 6, 294, 29.6

46
Questions
  • 1, 12
  • Pg. 933

47
The Decay Processes
  • Alpha decay
  • The parent nucleus emits a helium nucleus.
  • The remaining nucleus is called the daughter.
  • The daughter nucleus has two less protons and two
    less neutrons.
  • Examples

48
Transmutation
  • Transmutation is the spontaneous decay of of one
    element into another.
  • In the decay process, excess mass is converted
    into energy of other forms, mostly into the KE of
    the nuclei.
  • 39-1

49
Artificial Transmutation
  • Rutherford accomplished the first artificial
    transmutation.
  • He bombarded nitrogen-14 with alpha particles and
    produced Oxygen-17.

50
  • Beta decay
  • The parent nucleus emits an electron or a
    positron. How are these particles produced?
  • The daughter nucleus has the same number of
    nucleons as the parent nucleus.
  • The atomic number increases by 1 or decreases by
    1.
  • Examples
  • 32-1

51
The Decay Chain
  • Radioisotopes undergo a series of decays which
    eventually result in the formation of a stable
    isotope of lead.
  • Radioisotopes may decay by either alpha or beta
    emission.
  • Various half-lives are involved. 295, 74

52
  • The neutrino
  • No charge
  • Little if any mass
  • A spin of 1/2
  • Very little interaction with matter
  • There is also an antineutrino.

53
  • Gamma decay
  • The parent nucleus emits a gamma ray photon.
  • This results when the nucleus is in an excited
    state () after a collision or previous decay.
  • The atomic number and the mass number do not
    change.
  • Example

54
Summary of the Three Decay Processes
55
Penetrating Ability
  • Which type of particle would have the best chance
    of reaching the nucleus?

56
  • A gamma ray has the best chance of reaching the
    nucleus because it has no charge.

57
Applications Involving Gamma Rays
  • Baggage scanners at airports
  • 294

58
Natural Radioactivity
  • There are two groups of radioactive nuclei
  • Natural
  • Found in nature
  • Nature continuously resupplies us with
    radioactive isotopes with short half-lives
  • Artificial
  • Produced in the laboratory

59
Radon Hazzard
  • Radon is produced by the decay of radium in the
    soil.
  • Which type of decay isresponsible?
  • Health concerns?
  • 13

60
The Carbon 14 Cycle
61
Carbon Dating
  • Carbon dating depends upon the beta decay of
    carbon-14
  • Carbon-14 is produced when cosmic rays bombard
    nitrogen-14 in the atmosphere.
  • The ratio of carbon-14 to carbon-12 in the
    atmosphere remains constant.
  • All living things have the same ratio.
  • When organisms die, the ratio begins to change
    because of the beta decay of carbon-14.

62
The Shroud of Turin
  • The Shroud of Turin is a centuries old linen
    cloth that bears the image of a crucified man. A
    man that millions believe to be Jesus of
    Nazareth. Is it really the cloth that wrapped his
    crucified body, or is it simply a medieval
    forgery, a hoax perpetrated by some clever
    artist?

63
Positive Image of the Shroud
64
Negative Image of the Shroud
65
(No Transcript)
66
Biological Damage
  • Radiation damage in matter
  • The amount of damage depends upon the type of
    radiation and upon the absorbing material.
  • Cancer or death may result
  • In cells, ionization is the primarycause of
    damage.
  • Ions and free radicals may beformed.

67
Cancer Treatment
  • Radiation can be used to kill cancer cells.
  • Cancer cells are more vulnerable to damage from
    radiation than are normal cells.
  • 293

68
Cyberknife

69
Biological Damage
  • Somatic damage
  • Radiation damage to any cells but the
    reproductive organs
  • Genetic damage
  • Damage to the reproductive cells
  • Birth defects may result

70
Natural Radiation
  • Low level radiation from natural sources
  • Cosmic rays
  • Air
  • Soil
  • Food
  • Water
  • Building materials

71
Biological Units of Radiation
  • Roentgen (R)
  • The amount of radiation that deposits 8.6 x 10-3
    J of energy into 1 kg of air
  • Rad
  • The amount of radiation that deposits 10-2 J of
    energy into 1 kg of absorbing material

72
RBE
  • Relative Biological Effectiveness is the number
    of rad of x-radiation or gamma radiation that
    will produce the same biological damage as 1 rad
    of the radiation being used. (Table 29.3) on pg.
    930.

73
rem
  • A rem (roentgen equivalent man) is the product of
    the dose in rad and the RBE factor.

74
Radiation Exposure Standards
  • Government limits
  • 0.5 rem/year for the general population
  • Roentgen Equivalent Man
  • 5.0 rem/year for those in occupations involving
    higher levels of exposure
  • Higher limits are allowed for certain parts of
    the body
  • Hands and forearms

75
Lethal Dose
  • 400 to 500 rem results in a 50 mortality rate.
  • This is called lethal dose 50 (LD 50).

76
Radiation Exposure
  • Ingestion is the most dangerous form of exposure.
  • Strontium-90 is present in the radioactive
    fallout from above ground nuclear testing.
  • Behaves like calcium chemically
  • Iodine-131(also in radioactive fallout)
  • Affects the thyroid gland

77
The Chernobyl Disaster
  • Radioactive isotopes were released into the
    environment.

78
Chernobyl (after the fire)
79
  • Applications
  • Involving
  • Radiation

80
  • Sterilization of food by radiation exposure
    kills
  • Bacteria
  • Worms
  • Insects and their eggs
  • Exposing food to radiation is very controversial.

81
  • Sterilization in medicine reduces the chance of
    infection.
  • Surgical equipment
  • Grafts
  • Bone
  • Cartilage
  • Skin

82
  • Chromium-53 is used as a radioactive tracer to
    locate hemorrhages.
  • Cholangiogram, radithor capsules

83
  • Radioactive tracers in medicine must have a short
    half-life!
  • Examples
  • Iodine-131
  • Evaluating theperformanceof the thyroid

84
  • Radioactive tracers in agriculture are used to
    evaluate the effectiveness of fertilizers
  • Nitrogen use is tracked

85
  • Smoke detectors use an isotope of americiumto
    ionize air molecules
  • Smoke particles interfere with this ionization.

86
  • Radioactive tracers in industryare used to check
    for pistonring wear.

87
  • Computerized Axial Tomography (CAT Scan) images
    have greater clarity and detail than a normal
    x-ray picture.
  • X-rays enter the body from different directions
    and the results are evaluated by a computer.
  • A brain scan can be made in about 2 seconds.
  • A full body scan requires about 6 seconds
  • X-rays do present health risks to the patient.
  • CAT scan

88
CAT Scan Images
89
Magnetic Resonance Imaging
  • Very strong magnetic fields are used to affect
    proton spin for 30 min.
  • Changes can be detectedand used to form a
    highlydetailed image.
  • MRI is much less damaging to cells.

90
MRI Image
  • Magnetic ResonanceImaging (MRI) of thespine

91
PET Scans
  • A PET scan involves injecting a very small dose
    of a radioactive chemical, called a radiotracer,
    into the vein of your arm. The tracer travels
    through the body and is absorbed by the organs
    and tissues being studied. 299

92
  • Next, you will be asked to lie down on a flat
    examination table that is moved into the center
    of a PET scannera doughnut-like shaped machine.
    This machine detects and records the energy given
    off by the tracer substance and, with the aid of
    a computer, this energy is converted into
    three-dimensional pictures.

93
  • A physician can then look at cross-sectional
    images of the body organ from any angle in order
    to detect any functional problems.

94
Particle Counters
  • The Geiger counter
  • Radiation ionizes a confined gas which has a
    large potential difference applied.
  • 292

95
  • The semiconductor diode detector
  • Uses a reverse biased p-n junction

96
  • The scintillation counter
  • Counts flashes of light produced by impacts

97
Particle Track Detectors
  • Photographic emulsion
  • Uses photographic film

98
  • Cloud chamber
  • Uses a super cooled gas
  • Particles form vapor tracks

99
  • Bubble chamber
  • Uses liquid hydrogen orliquid helium.
  • Particles form tracks inthe liquid.

100
Your Annual Exposure
  • Calculate your own yearly exposure.

101
Questions
  • 2 - 4, 6 - 9, 11
  • Pg. 933
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