Transcript Document 7807224

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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 atom’s 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
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Consist of 2 protons and 2 neutrons
Mass of an alpha particle is 4 amu
Charge = +2
The isotope’s 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
• 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
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)
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
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
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 the
photons 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?
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2.
3.
4.
Positron
Negatron
Megatron
Photon
Which form of radiation penetrates the
least?
1.
2.
3.
4.
Alpha Decay
Beta Decay
Gamma Decay
Delta Decay
Which radioactive particle increases
the Parent Nucleus’s atomic number?
1.
2.
3.
4.
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
Which form of radiation penetrates the
most?
1.
2.
3.
4.
Alpha Decay
Beta Decay
Gamma Decay
Delta Decay
Which particle drops the Parent
Nucleus’s atomic number by two?
1.
2.
3.
4.
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
Which particle resembles a Helium
nucleus?
1.
2.
3.
4.
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
Which particle isn’t a particle but a
photon?
1.
2.
3.
4.
Alpha Particle
Beta Particle
Gamma Particle
Delta Particle
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• End of Part 1 
Turn to page 5
• the first answer you should have
for box set #3 is:
Turn to page 6
• the last answer you should have
for box set # 12 is:
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
Half-life
• The amount of time it
takes for HALF of an
amount of a radioactive
material to decay
• One symbol for half-life
is  (lambda)
Original
Amount
# of 
Current
Amount
100g
1
50g
100g
2
25g
100g
3
12.5g
100g
4
6.25g
100g
5
3.125g
A Decay System
showing half-lives
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)
(2)
(3)
1.0mg
 0.5mg
 0.25mg
 0.125mg
30yrs
60yrs
90yrs
Practice
• The half-life of Po-218 is three minutes. How
much of a 2.0 gram sample remains after 15
minutes?
(2)
(3)
(4)
(4)
(1)
2.0g  1.0g  0.5g  0.25g  0.125g  0.0625g
6min
9min
12min
15min
3min
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
(2)
(1)
2.5g  1.25g  0.625g
56yrs
28yrs
0.625 grams…
started in
1960…
1960 +56 = 2016
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?
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”
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
Chernobyl Disaster
• April 26, 1986 –
flawed reactor design
was operated by
inadequately trained
personnel and w/o
regard to safety
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
TERMS TO REVIEW
Radiation
Alpha particle
Negatron
X-ray
Gamma ray
Half-Life
Decay Systems
Mother Nucleus
Fission
Alpha decay
Radioactive decay
Negative beta decay
Photon
Daughter Nuclei
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?
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?
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 actinium226 will remain?
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?
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?
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?
Half-life
• 10. Three grams of Bismuth-218 decay to
0.375 grams in one hour. What is the half-life
of this isotope?
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?
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 onesixteenth of the original activity?