Transcript Electromagnetic Spectrum

The Nucleus
Nuclear Concepts to Master
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Compare the benefits and dangers of
radioactivity.
Which isotopes are used for treatments of
which illnesses?
How is background radioactivity different
from natural radioactivity?
How did the transuranium elements come
into existence?
Does fusion or fission produce more
energy?
What are the equations for fission and
fusion?
Which reaction has not been achieved and
which one is used in nuclear power plants
(fission or fusion)?
Compare fission and fusion.
What is the shielding effect?
Write and balance equations that involve
alpha, beta, neutron, positron, or proton
particles and gamma radiation.
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Which direction will alpha particles move
when placed in an electric field?
What is the band of stability?
What is the difference between and artificial
and natural transmutation?
Use table N and O to solve problems.
Solve problems involving half-life using the
equation or the “walk-the-dog” method.
Half-life is constant!
What is a Geiger counter used for?
How do scientist use uranium isotopes to date
rocks?
How do scientist use carbon isotopes to date
mummies?
Why do doctors use radioisotopes with shorter
half-lies when performing a medical procedure?
Which radioisotope is used for sterilizing things
like medical equipment?
Which isotope is used in the irradiation of meat?
Vocab
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Absorption
Alpha particle
Artificial radioactivity
Background radioactivity
Beta particle
CPM
Daughter nucleus
Decay
Emission
Endothermic
Exothermic
Fission
Frequency
Fusion
Gamma radiation
Half-life
Ionization
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Irradiated
Isotope
Natural radioactivity
Nuclides
Penetrating distance
Positron
Radioactive isotopes
Radioactivity
Radionuclide
Shielding
Transmutation
Transuranium elements
Wavelength
Labs
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Radioactive decay of Uranium
Half-Life Simulation
Electromagnetic
LESS harmful to the body
Spectrum
MORE harmful to the body
Ionization is the ability of an atom to become an ion (charged particle).
If electrons are lost a cation is formed.
If electrons are gained an anion is formed.
Ionization is the ability of an electron to jump away from or to another atom.
Ionizing Power
• The ionizing power of ionizing radiation
measures how many ions are formed in a given
area when the radiation passes through it.
• It indicates how densely packed incidents of
ionization will be. In human tissue ionization
occurring in a limited location means
concentrated tissue damage and will increase
the probability of cell death or mutations due to
DNA damage.
Radioactivity
• Unstable isotopes
• To become more stable, the atom spits out
subatomic particles and rays of energy
• This release of subatomic particles and rays
is radioactivity
3 H
1
= H31 =H3= H-3
Unstable Nucleus?
In the band of stability,
atoms are stable. The ratio
n/p is 1 for low nuclear
masses and it increases
steadily up to 1.5 for high
nuclear masses.
In region A, a
nucleus with too
many neutrons is
unstable because
not enough of
them are paired
with protons.
In region B, a
nucleus with too many
protons has too much
repulsive electrical
interactions to be
stable.
Sulfur
Isotope
Atomic
#
Mass
#
# of
Protons
# of
Neutron
s
S-32
# of
Electrons
% found
in
NATURE
94.93
0.78
4.29
S-33
S-34
Calculate ATOMIC MASS
Map of U.S. Natural Radioactivity
The colors indicate uranium concentrations: red is high, yellow is medium, blue is low.
Natural Radioactivity
•The earth is radioactive (air, water, and soil).
•Due to elements that spontaneously and
uncontrollably emit radioactivity.
•Radioactive elements are also called:
–Radioactive isotopes
–Radionuclide
–Nuclides
Types of Radiation - Beta
• A beta particle is like a fast electron.
– It’s mass is small like an electron’s.
– Since it’s small, it can penetrate your skin!
Beta Decay
Types of Radiation - Positron
• A positron is an like an electron but with a positive charge!
– It’s small like an electron
– It has a charge of +1 (opposite to an electron!)
– When it meets with an electron it annihilates it!
– Often when nuclei that release positrons also release gamma
radiation.
– Can penetrate your skin!
Positron Decay
Types of Radiation - Alpha
• An alpha particle is a particle that is made up of two protons and
two neutrons.
– It is therefore a helium nucleus with a mass number of 4 and a
atomic number of 2. 42He
– It has a mass of 4.0 amu - massive on a nuclear scale!
– Too BIG to penetrate your skin.
Types of Radiation - Gamma
• The gamma ray is a photon of high energy.
– It has no mass.
– It has no charge.
– Can penetrate your skin!
• For gamma ray emission to occur the nucleus must still be in an
unstable state after emitting an alpha, beta or positron particle. So to
become more stable, it spits out more energy.
Gamma radiation released with beta decay
Radiation in an Electric Field
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Try # 5 – 9 on your own before clicking to get the answers.
These are often referred to a SHIELDS and they
Protect you from radiation. Distance is also a shield.
Artificial Radioactivity
• Man-made
• Stable isotopes are
bombarded with particles
such as neutrons to
cause a nuclear reaction.
• Elements with atomic
numbers over 92 have
been artificially made.
They are called the
transuranium elements.
• (92 is the atomic number
of the heaviest naturally
occurring element,
Uranium.)
• Atom Smashers
• Nuclear reactors
Fission
Larger nucleus is split into smaller nuclei.
Mass is converted to energy!
Control rods needed in nuclear power plants! WHY? It’s a CHAIN REACTION
Fusion
Fusion is when two small nuclei combine to form a single bigger nucleus.
Mass is converted to energy!
Compare
• Fission
– Produces hazardous
waste since nuclear
fuel rods last about 3
years.
– The used rods are
stored underground
– As of 2000, the
amount stored is
40000 metric tons
• Fusion
– Little to no hazardous
waste (He released
and no reactor core)
– Inexhaustible energy –
1 gallon of sea water
contains enough
deuterium to support a
family of 4 for 1 year.
– Why? It’s a CHAIN
REACTION
Radiation
•Effect of
distance
•Effect of shield
•thickness
•type
Shielding
• Shielding protects you from radiation exposure.
Determining the type of rxn
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Absorption (Always Artificial)
Emission (natural DECAY)
Artificial transmutation
Natural Transmutation (DECAY)
Fission
Fusion
Half – Life of Radioisotopes
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The time taken for a given sample of a radioisotope to decay so that its
radioactivity is one half the initial amount is called the half-life, t½, of that
isotope.
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The half-life is a constant for the isotope, and shows enormous variations
from one isotope to another.
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For example, 17F (fluorine-17) has a half-life of 70 seconds, while 238U
has a half-life of 4.51 x 109 years. 14C (carbon-14) has a half-life of 5668
years.
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The long-lived nature of some waste products of nuclear reactors pose
grave ecological problems, as some of these radioisotopes remain
dangerously active for tens of thousands of years.
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Whereas the short-lived nature of some radioisotopes allow their use in
medicine.
Rate of Decay – Half Life
Number of
Halflives
Time
years
% Strontium90
remaining
% Strontium-90
that has
decayed
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0
100
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1
28
50
50
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56
25
75
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84
12.5
87.5
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112
6.25
93.75
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140
3.125
96.875
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168
1.5625
98.4375
Rate of Decay – Half Life
What’s the half-life of Sr-90?
What type of curve is the above?
What would the graph look like if the
The y-axis was % being transformed?
Calculating Half Life
How much 42K will be left in a 320 g sample
after 62 h?
Step 1: Look up the half life in Table N, the table
of Selected Radioisotopes
12.4 h
Mass
Time
Fraction
Half
Lives
320 g
0h
1
0
Step 2: Set up a table showing the mass, time
elapsed, the fraction remaining, and number
of half lives.
320/2 =
160 g
12.4 h
1/2
1
160/2 =
80 g
12.4+12.4=
24.8 h
1/4
2
80/2 =
40 g
24.8 +12.4=
37.2 h
1/8
3
40/2 =
20 g
37.2+12.4=
49.6 h
1/16
4
20/2 =
10 g
49.6+12.4=
62 h
1/32
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Step 3: Fill in the table with the starting
condition(s) and ending when the full time
has elapsed. Time will always start with 0.
Fraction will always start as 1, and Half-lives
will always start at 0.
Step 4: For each half life elapsed:
a) cut the mass in half
b) increase the time by an amount equal to
the half life
c) cut the fraction in half
d) add one to the number of half lives
Calculating Half Life
Determining Half – Life from a graph
The table below shows how the activity (in counts per second) of a sample of radioactive
material varies in time. Plot a graph of activity against time to determine the half-life
of the material.
Time (days)
0
1
2
3
4
5
6
7
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Activity (c/s)
800
655
536
439
359
294
241
197
162
Radioactivity
• Extremely Beneficial
– Nuclear power plants
– Nuclear medicine
• Cardiovascular imaging
• Bone scanning
• Detecting cancers
• Extremely Dangerous
– Nuclear power plants
released radioactive
substances into the
atmosphere during
nuclear accidents.
• Three Mile Island
• Chernobyl
– Nuclear Bomb
Radiological dating
• We can use the natural radioactivity in some
objects to date them.
• The following slide shows a rock containing
naturally occurring radioactive uranium.
• As time goes by, the uranium decays to stable
lead.
• By comparing the proportions of uranium and
lead we can determine the approximate age of
the rock.
Isotopes in Medicine
• Nuclear medicine imaging
techniques give doctors
another way to look inside
the human body. The
techniques combine the use
of computers, detectors,
and radioactive substances.
• It is very important to
consider the half-life of a
substance that is to be used
for medical purposes.
Isotopes in Medicine
• Co-60
– Beta and gamma emitter
– Sterilization of medical equipment
– Treatment of malignant tumors
• I-131
– Beta and gamma emitter
– Iodine-131 is one of the radioactive isotopes of iodine
that can be used to test how well the thyroid gland is
functioning.
http://www.uic.com.au/nip26.htm
Co-60 and Meat
• food is irradiated in an area
that is surrounded by concrete
walls at least 6-feet thick which
keep any rays from escaping.
• The radiation source, usually
Cobalt 60, is held in a resting
position in a pool of water.
• A conveyor system transports
the meat or poultry product to
the area.
• The radiation source is then
raised out of the water and the
food is exposed for a defined
period of time.
• When the source is raised,
lights and alarms are sounded
to make people aware that the
product is being irradiated.
• Once the food is irradiated, the
source automatically returns to
the resting position and the
food leaves the area for further
processing.
Detecting
Radioactivity
• Geiger Counter
– Measures radiation as CPM
– Counts per minute
– the amount of radioactive
material (counts) that is released
in one minute
• Film Badge
– Radioactivity will expose film.
– The amount of film exposed
indicates the level of exposure to
radioactivity.