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ALPHA RADIATION
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Discovery of radioactivity

• In the late years of the 19th century scientists
  were interested in experiments about the rays
  that certain elements were emitting. After
  various experiments they found that there was a
  different ray then x rays which could go further
  and deeper and could pass thicker obstacles
  through experiments. Soon a scientist called
  Becquerel discovered that various substances
  containing uranium admixtures emitted such
  radiation. This new phenomenon was to be called
  radioactivity.

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• Rutherford and others began studying the nature
  of the rays emitted in radioactivity about 1898.
  They found that the rays could be classified into
  three distinct types according to their
  penetrating power. One type of the radiation
  could barely penetrate a piece of paper. The
  second type could pass through as much as 3mm of
  aluminum. The third was extremely penetrating it
  could pass trough several centimeters of lead and
  still be detected on the other side. They named
  these three types of radiation alpha (a) , beta
  (ß) and gamma (?), respectively, after the first
  three letters of the Greek alphabet.

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(http//www.ndt-ed.org/EducationResources/HighScho
ol/Radiography/radioactivity.htm)
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Alpha Decay

• The alpha decay occurs when the nucleus of an
  element emits an alpha particle which is two
  protons and two neutrons. This is a simple helium
  atom with no electron present. An example of this
  is a uranium-238 atom decaying into into a
  thorium-234 atom and an alpha particle (helium-4
  nucleus, i.e. 2 protons and 2 neutrons).

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(No Transcript)
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p Li Be 2 He proton
lithium beryllium 2 alpha
particles
(http//library.thinkquest.org/3659/nucreact/tra
nsmutation.html)
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WHY??

• As you may wonder why does alpha decay occur?
• Alpha decay occurs because the strong nuclear
  force is unable to hold very large nuclei
  together. Because the nuclear force is a
  short-range force, it acts only between
  neighboring nucleons. For every nuclei, the large
  atomic number means the repulsive force becomes
  very large (Coulomb's law) and it acts between
  all protons. The strong nuclear force, since it
  acts only between neighboring nucleons, is
  overpowered and is unable to hold the nucleus
  together.

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?

• But if there is a repelling force between the
  protons why not all the protons leave the
  nucleus? This should be explained by another
  force holding them together called as Strong
  Nuclear Force.

?
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HOW DOES THE NUCLEUS STAY TOGETHER??
Indeed, the question arises as how a nucleus
stays together at all in the view of the fact
that the electric force between protons would
tend to break it apart since stable nuclei stay
together,it is clear that another force must be
acting.
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• Because this force is stronger than the
  electric force it is called the strong nuclear
  force. The strong nuclear force is an attractive
  force that acts between all nucleons-protons and
  neutrons - alike .
• Thus,protons attract each other via the nuclear
  force and at the same time they repel each other
  via the lectric force.
• Neutrons, since they are electrically neutral,
  only attract other neutrons or protons via the
  nuclear force.
• This way, the nucleus does not break apart and
  stay together.

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SPONTANEITY OF ALPHA-DECAY

• Alpha decay is an exothermic process. As the
  nucleus becomes more stable, it liberates a net
  amount of energy due to this. Therefore, the
  tendency for minimum enthalpy is fulfilled. Also,
  the decays entropy can be said to be positive
  the places the particles can exist increase.
• Under these conditions, it can be said that Alpha
  decay is always spontaneous.

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Energy Changes in Alpha Decay

• This type of decay occurs naturally in uranium
  and is an example of "spontaneous decay".
• The uranium atom doesn't just break apart. As
  it decays, each of the two resulting elements
  (the thorium and a-particle) fly apart at high
  speed. In other words they both have kinetic
  energy.
• It is possible to measure the mass of the
  original uranium atom and the masses of the two
  resultant particles. This is done by measuring
  the momentum of each particle as it strikes a
  sensor. When these measurements are taken it is
  found that the total mass of the two smaller
  particles is less than the mass of the original
  uranium particle. Some mass must have been turned
  into (mostly kinetic) energy.
• So as we have said the mass and energy is not
  conserved during a radiation.

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QUESTIONS

• Write a balanced equation for the following
  process
• Np (Np turns into Pa)

Answer Np
Pa He
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• Write a balanced equation for the process that is
  described below
• Uranium (235) which is used in atomic bombs,
  decays initially by alpha particle production.
• U Th He

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• When an alpha decay occcurs
• 1) Mass number decreases by 2
• 2) Its chemical properties change
• 3) Neutron number decreases by 2
• Which of the following above statements are
  correct?
• Only 1 B)1 and 2
• C) 2 and 3 D) 1 and 3
• E) 1,2 and 3

Answer C
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• When the atom Ra makes 3 alpha radiation
  what would be the neutrons number of the newly
  formed element?
• A) 214 B) 164 C) 142
• D) 132 E) 82

Answer Ra 3 He
X 3 x 4 12 226-12 214 3 x 2
6 88-682 X 214
82 132 So the answer is D.
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QUESTION THAT WAS NOT ANSWERED...
Why does in alpha decay a simple helium atom is
emitted instead of saperate individual particles??
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EVALUATION
Self Evaluation

• There was a lot of verbal and written mistakes.
• I did not talked deeply about the subjects such
  as energy change during alpha radiation which can
  last for a very long time.
• I could not answer some of the questions came
  from the class.

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Peer Evaluation

• The subjects were presented in a very easy level.
• It was easy to understand the topics and contents
  but scientifically the presentation is not
  enough.
• Many subjects that should have been placed in the
  presentation was skipped so it was not sufficent.