Energy

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RADIATION

• Energy
• in the form of particles
• or electromagnetic waves
• emitted from the nuclei of unstable atoms

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RADIATION

• The term really includes all forms of
  electromagnetic radiation
• Radio Waves, Infrared, Visible Light
• Ultraviolet, X-rays, ?-rays
• Commonly used today to describe particle radiation

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NUCLEAR REACTIONS PRODUCE RADIATION

• Protons and neutrons determine nuclear reactions
• One must understand atomic structure to
  understand radiation

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NUCLEAR PARTICLES
Protons and Neutrons are the two basic nuclear
particles. Together they contain practically all
the mass of an atom and are determinants of an
atoms nuclear characteristics.
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RADIOACTIVE DECAY

• Radioactive decay refers to the spontaneous
  emission of radiation from the nucleus of an
  unstable atomic nucleus

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DEFINITION OF RADIOACTIVE DECAY
Radioactive decay is the process of spontaneous
emission of radiation in the form of particles or
photons from the nuclei of unstable atoms
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CHARACTERISTICS OF RADIOACTIVE DECAY

• It is a natural process in our universe
• It is spontaneous we cannot predict when an
  atom will undergo decay

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BASIC TYPES OF RADIOACTIVE DECAY

• Alpha (?) decay
• Occurs when atomic nuclei have too many protons
  and neutrons (i.e., Are heavy)

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ALPHA PARTICLE
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CHARACTERISTICS OF ALPHA PARTICLES

• Consist of 2 protons and 2 neutrons
• Mass of an alpha particle is 4 amu
• Charge 2
• The isotopes Atomic Mass goes down four
• The Atomic Number goes down two
• Are highly ionizing
• Have low penetrating abilities
  (only cm in air and mm in water)

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MORE ABOUT ALPHA PARTICLES

• Easily shielded common types of shielding are
  paper, cardboard, air, clothing will not
  penetrate skin
• Health hazard when taken internally
• Not commonly used in medicine
• Common sources smoke detectors
  (Am-241) and lantern mantles (thorium nitrate)

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ALPHA PARTICLE DECAY
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• Changes both the mass and identity of the nucleus
  of the parent radionuclide
• This means that the decay results in the
  formation of a new element as the daughter
  product

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QUESTIONS?
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NEGATIVE BETA (ß-) DECAY
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Occurs when atoms have too many neutrons (i.e.,
Are neutron-rich) and decay by emitting a
negative beta particle (ß-)
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WHAT ARE NEGATIVE BETA PARTICLES?
During negative beta decay, neutrons are
converted into protons and electrons. The protons
remain in the nucleus but the new electrons are
emitted as negative beta particles (ß-) or
negatrons. You may wish to think of them as
nuclear electrons.
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CHARACTERISTICS OF NEGATIVE BETA DECAY

• Less ionizing than alphas due to decreased mass
  of negatrons
• Changes the identity of the nucleus but not the
  mass
• The Atomic Number is increased by one due to
  conversion of
  neutrons
  into protons

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CHARACTERISTICS OF NEGATIVE BETA PARTICLES
(NEGATRONS)
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• Negatrons consist of nuclear electrons
• The mass is the same as electrons
• There is a charge of 1 in negatrons
• More penetrating than alpha particles 12
  meters in air
• They can penetrate skin
  best shielding is wood,
  plastics, thick
  cardboard, etc.

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QUESTIONS?
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GAMMA (?) EMISSION
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Is a form of pure electromagnetic radiation
emitted from nuclei that have excess energy. It
is sometimes called gamma photon radiation.
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GAMMA RAYS
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Are photons emitted from unstable nuclei to rid
themselves of excess energy. Gamma photons are
subatomic packets of pure energy. They are
higher in energy and more penetrating than
thephotons that make up visible light.
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PROPERTIES OF GAMMA (?) RAYS

• Charge is 0 (no charge)
• Mass is 0 (no mass)
• Low ionization
• Penetration abilities can be extremely high
  penetrating power is
  dependent upon the
  energy of the
  emitted photons

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QUESTIONS?
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What is a packet of light energy that behaves
like a particle?

1. Positron
2. Negatron
3. Megatron
4. Photon

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Which form of radiation penetrates the least?

1. Alpha Decay
2. Beta Decay
3. Gamma Decay
4. Delta Decay

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Which radioactive particle increases the Parent
Nucleuss atomic number?

1. Alpha Particle
2. Beta Particle
3. Gamma Particle
4. Delta Particle

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Which form of radiation penetrates the most?

1. Alpha Decay
2. Beta Decay
3. Gamma Decay
4. Delta Decay

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Which particle drops the Parent Nucleuss atomic
number by two?

1. Alpha Particle
2. Beta Particle
3. Gamma Particle
4. Delta Particle

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Which particle resembles a Helium nucleus?

1. Alpha Particle
2. Beta Particle
3. Gamma Particle
4. Delta Particle

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Which particle isnt a particle but a photon?

1. Alpha Particle
2. Beta Particle
3. Gamma Particle
4. Delta Particle

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5

• End of Part 1 ?

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Turn to page 5

• the first answer you should have for box set 3
  is

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Turn to page 6

• the last answer you should have for box set 12
  is

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Decay Systems

• Each radioactive element will undergo various
  forms of radiation until it becomes stable
• The particular elements that a Parent Nucleus
  changes into are always the same
• This path is a Decay System

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Half-life
Original Amount of ? Current Amount
100g 1 50g
100g 2 25g
100g 3 12.5g
100g 4 6.25g
100g 5 3.125g

• The amount of time it takes for HALF of an amount
  of a radioactive material to decay
• One symbol for half-life is ? (lambda)

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A Decay System showing half-lives
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Practice

• 1. An isotope of cesium (cesium-137) has a
  half-life of 30 yrs. If 1.0 mg of cesium-137
  disintegrates over a period of 90 yrs., how many
  mg of cesium-137 would remain?

(1) 1.0mg ? 30yrs
(2) 0.5mg ? 60yrs
(3) 0.25mg ? 90yrs
0.125mg
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Practice

• The half-life of Po-218 is three minutes. How
  much of a 2.0 gram sample remains after 15
  minutes?

(2) 1.0g ? 6min
(3) 0.5g ? 9min
(4) 0.25g ? 12min
(4) 0.125g ? 15min
0.0625g
(1) 2.0g ? 3min
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Practice

• 3. A 2.5 gram sample of an isotope of
  strontium-90 was formed in a 1960 explosion of an
  atomic bomb at Johnson Island in the Pacific Test
  site. The half-life of strontium-90 is 28 yrs.
  In what year will only 0.625 grams of this
  strontium-90 remain?

56yrs to get to 0.625 grams started in 1960
1960 56 2016
(2) 1.25g ? 56yrs
0.625g
(1) 2.5g ? 28yrs
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Practice

• 5. Sodium-25 was to be used in an experiment,
  but it took 3.0 minutes to get the sodium from
  the reactor to the laboratory. If 5.0 mg of
  sodium-25 was removed from the reactor, how many
  mg of sodium-25 were placed in the reaction
  vessel 3.0 minutes later if the half-life of
  sodium-25 is 60 seconds?

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Nuclear Processes

• Fission
• The splitting of a large, unstable nucleus into
  two or more stable nuclei
• Scientists can cause fission by injecting a
  neutron at high speed
• These are the uses associated with nuclear
  fission
• Power plants / reactors
• Bombs
• Dirty bombs

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Nuclear Processes

• Fusion
• The joining of two or more smaller nuclei into
  one larger, more stable nucleus
• Scientists are working on fusion using high
  pressures, temperatures, and lasers
• The only place that fusion occurs naturally is
  stars

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Chernobyl Disaster

• April 26, 1986 flawed reactor design was
  operated by inadequately trained personnel and
  w/o regard to safety

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Chernobyl Disaster

• Result steam explosion and fire released at
  least 5 of the radioactive reactor core into the
  atmosphere downwind
• 28 people died within 4 months from radiation or
  thermal burns
• 19 subsequently died and 9 deaths from thyroid
  cancer

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TERMS TO REVIEW

• Radiation Alpha decay
• Alpha particle Radioactive decay
• Negatron Negative beta decay
• X-ray
• Gamma ray Photon
• Half-Life
• Decay Systems
• Mother Nucleus Daughter Nuclei
• Fission Fusion

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Half-life

• 4. Thallium-201 has a half-life of 73 hours. If
  4.0 mg of thallium-201 disintegrates over a
  period of 6.0 days and 2 hours, how many mg of
  thallium-201 will remain?

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Half-life

• 6. The half-life of isotope X is 2.0 years. How
  many years would it take for a 4.0 mg sample of X
  to decay and have only 0.50 mg of it remain?

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Half-life

• 3. Actinium-226 has a half-life of 29 hours. If
  100 mg of actinium-226 disintegrates over a
  period of 58 hours, how many mg of actinium-226
  will remain?

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Half-life

• 7. Selenium-83 has a half-life of 25.0 minutes.
  How many minutes would it take for a 10.0 mg
  sample to decay and have only 1.25 mg of it
  remain?

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Half-life

• 8. Element-106 has a half-life of 0.90 seconds.
  If one million atoms of it were prepared, how
  many atoms would remain after 4.5 seconds?

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Half-life

• 9. The half-life of Po-218 is three minutes.
  How much of a 2.0 gram sample remains after 15
  minutes? Suppose you wanted to buy some of this
  isotope, and it required half an hour for it to
  reach you. How much should you order if you need
  to use 0.10 gram of this material?

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Half-life

• 10. Three grams of Bismuth-218 decay to 0.375
  grams in one hour. What is the half-life of this
  isotope?

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Half-life

• 11. The half-life of francium is 21 minutes.
  Starting with 4 x 1018 atoms of francium, how
  many atoms would disintegrate in 1 hour and 45
  minutes? What fraction of the original sample
  remains?

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Half-life

• 12. The half-life of a radioactive element is 30
  seconds. In what period of time would the
  activity of the sample be reduced to
  one-sixteenth of the original activity?