Radioactivity and Nuclear Reactions

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Radioactivity andNuclear Reactions
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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

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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

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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

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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

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What is radioactivity?

• Emission of high energy radiation or particles
  from the nucleus of a radioactive atom

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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

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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

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How do you write the symbol for a nuclide?

• The symbol gives atomic , mass , and chemical
  symbol

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mass
N
chemical symbol
19
atomic
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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!!

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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)

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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

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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

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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

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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

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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
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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
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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

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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.

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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

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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

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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.

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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.

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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

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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!

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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!!

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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.

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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

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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)