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Radioactivity and Nuclear Reactions

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Title: Radioactivity and Nuclear Reactions


1
Radioactivity andNuclear Reactions
2
Who is credited with discovering radioactivity?
  • Henri Becquerel
  • left uranium salt on a photographic plate in a
    desk drawer
  • developed the plate found outline of salt on
    plate
  • hypothesized uranium emitted some invisible
    energy
  • received Nobel Prize for physics in 1896

3
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4
Who else discovered radioactivity?
  • Marie and Pierre Curie
  • used Becquerels finding and discovered polonium
    and radium
  • Ra and Po are more radioactive than U
  • Received the Nobel Prize for physics in 1896
    along with Becquerel

5
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6
Which elements are radioactive?
  • Each element with atomic s higher than 83 is
    radioactive
  • The atoms nucleus is held together by the strong
    force
  • prevents protons from pushing each other out of
    the nucleus
  • only acts across very small distances

7
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8
What is a radioactive substance?
  • The atoms of radioactive elements are held
    together less securely than nonradioactive
    elements
  • Particles of energy can escape from all nuclei
    with atomic numbers 84 or higher (radioactive
    decay)
  • The nuclei of these elements are unstable

9
What is radioactivity?
  • Emission of high energy radiation or particles
    from the nucleus of a radioactive atom

10
What are nuclides?
  • The nucleus of an isotope with a certain atomic
    number and mass
  • Some isotopes are radioactive and some are not
  • Isotope atoms of the same element with
    differing atomic masses

11
What affects a nuclides stability?
  • Ratio of neutrons to protons affects stability of
    nucleus
  • Stability ratios (neutrons protons)
  • less massive elements 11
  • more massive elements 32
  • if differ from these ratios, are unstable
  • Nuclei with too many or too few neutrons are
    radioactive

12
How do you write the symbol for a nuclide?
  • The symbol gives atomic , mass , and chemical
    symbol

39
mass
N
chemical symbol
19
atomic
13
What is nuclear radiation?
  • Radiation given off by radioactive nuclides
  • There are three types
  • alpha particles (? particles)
  • beta particles (? particles)
  • gamma rays (? rays)
  • Only gamma rays are a type of electromagnetic
    radiation!!

14
What are alpha particles?
  • Given off when a nucleus releases 2 neutrons and
    2 protons
  • Same thing as a helium nucleus
  • Has a charge of 2 and an atomic mass of 4
  • Largest and slowest form of radiation
  • Least penetrating can be stopped by a sheet of
    paper
  • Used by smoke alarms (americium)

15
What are beta particles?
  • Neutrons can spontaneously decay into a proton
    and an electron
  • The electron is the beta particle
  • The proton can decay into a neutron and a positron

16
What is a positron?
  • A positron is similar to an electron, only with a
    positive charge
  • Positrons are considered beta particles too
  • Beta particles are much faster and more
    penetrating than an ? particle

17
What are gamma waves?
  • Most penetrating and potentially dangerous form
    of radiation
  • Not made of particles
  • Are electromagnetic waves with high frequency and
    energy
  • Have no mass, no charge, and travel at the speed
    of light
  • Usually released along with ? and ? particles
  • thick blocks of lead and concrete are commonly
    used for barriers

18
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19
What is transmutation?
  • Process of changing one element to another
    through nuclear decay
  • Atomic mass of the decayed nuclide equals the
    sum of the mass of the newly formed nuclide and
    the emitted particle

20
How do you determine the mass of the new nuclide?
  • If the particle is an alpha particle, subtract
    the mass of the ejected particle from the mass of
    the old nuclide.

Alpha particle emission
Pb
He
214
218
Po

4
82
2
84
21
How do I calculate the mass of the nuclide when
it loses a beta particle?
  • Because a beta particle is the product of the
    decay of a neutron, a proton will be left behind
    when the e is ejected.

e
214
Bi

0
214
Pb
83
-1
82
22
What is half life?
  • Some nuclides of radioactive isotopes may require
    a long time to decay
  • Half life is the amount of time it takes for half
    the nuclides in a sample of a given radioactive
    isotope to decay
  • It can vary widely among the radioactive isotopes
  • Can determine amount of a radioactive sample that
    will remain after a given amount of time with the
    half life

23
Example
  • Carbon 14
  • At the beginning, there is 100. Its half life
    is 5730 years. So, after 5730 years, there will
    be only half, or 50, left. After another 5730
    years (11,460 total), there will be half of 50
    left, or 25. After another 5730 years (17,190
    total), there will be half of 25 left, or only
    12.5 of the original amount remaining.

24
Is there a formula for half-life calculations?
  • Amount remaining (initial amount)(1/2)n
  • n number of half-lives that have passed
  • n also can equal t/T, where t the elapsed time,
    T length of half-life
  • Both t and T have to be in the same units

25
What is carbon 14 dating?
  • There are always radioactive materials in your
    body, because they are incorporated into your
    body tissues from the environment while you are
    alive.
  • Carbon 14 emits beta particles and decays into
    nitrogen
  • Measuring percent carbon 14 to carbon 12 allows
    determination of approximate age of material

26
How can you measure radioactivity?
  • Electroscope device that consists of a metal
    rod with two thin metal leaves at one end. If an
    electroscope is given a negative charge, the
    metal leaves separate.
  • Geiger counter produces an electric current in
    the presence of a radioactive substance.

27
What are some other ways?
  • Cloud Chamber contains a gas cooled to a
    temperature below its condensation point
    droplets of the gas condense around the
    radioactive particles, which leave a trail that
    shows up along the chamber lining.
  • Bubble Chamber contains a superheated liquid
    radioactive particles cause the liquid to boil,
    leaving a trail of bubbles that trace path of
    radioactive particle.

28
How is the nucleus of a radioactive element
different?
  • The strong force in nuclides is powerful enough
    to keep the nucleus together permanently (stable)
  • Strong force is not sufficient to hold unstable
    nuclides together permanently
  • unstable nuclides decay to produce matter and
    energy

29
What is fission?
  • Nuclear fission is the splitting of an atomic
    nucleus into two smaller nuclei of about equal
    mass
  • Word fission means to divide
  • Large nuclei with atomic numbers above 90 can
    undergo nuclear fission
  • U 235, when bombarded by a neutron, splits to
    produce Ba 141, Kr 92, three neutrons and ENERGY!

30
What is fusion?
  • Nuclear fission is the joining of 2 less sable
    atomic nucleus (mass number lt 60) into one more
    stable nuclei
  • Word fusion means to bind together
  • Example The Sun
  • 4 ?H? 2ß a energy
  • A temperature of 5,000,000 K is needed to
    overcome the electrostatic repulsions between the
    nuclei WOW!!

31
What is a nuclear chain reaction?
  • Neutrons released from one fission reaction
    collide with another atom to cause another
    fission reaction.
  • A continuous series of fission reactions is
    called a chain reaction.
  • Huge quantities of energy are released with many
    simultaneous nuclear reactions.
  • An uncontrolled chain reaction causes a nuclear
    explosion.

32
Nuclear Reactor
  • Uncontrolled nuclear reaction controlled with
    cadmium and boron control rods that absorb
    neutrons
  • Generate heat (energy) from U-235 and heats the
    coolant water
  • The hot coolant water then heats water that is
    used to drive steam-driven turbines, which
    produce electricity
  • Problem Spent fuel rods are VERY hazardous
    waste and buried underground

33
Uses for Radiation
  • Treating Cancer Kills cancer and healthy cells
    as well
  • Radiotracers emits non-ionizing radiation and
    is used to signal the presence of an element
  • Used in studying blood flow patterns, uptake of
    thyroid gland, emptying rate of gallbladder
  • Used in research experiments to trace amounts of
    chemicals in the system ( tertiary oil recovery)
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