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Transcript
Unit 4 Chapter 16
Atomic Energy
Radioactivity
• 1896
• Henri Becquerel
• Hypothesized that fluorescent minerals gave
off X-rays
• Placed a fluorescent mineral on top of a
photographic plate wrapped in paper
• Put it in sunlight and got an image of mineral
Radioactivity
• Next day was cloudy, so no sun
• Put experiment in desk drawer, where there
was no light
• Image still showed up on paper, due to energy
from minerals
• This energy is nuclear radiation
Radioactivity
• Nuclear radiation
– High energy particles emitted by the nucleus of
some atoms
• Marie Curie named the process by which
nuclei give off energy radioactivity
• Radioactivity is also called radioactive decay
Radioactivity
• There are three types of radioactive decay
– Alpha
– Beta
– Gamma
Radioactivity
• Alpha decay - α
– Release of alpha particle (2 protons and 2
neutrons, no electrons)
– Alpha particle is same as Helium nucleus
– Many large radioactive nuclei give off alpha
particles and become different elements
– Radium-226 does this
– Mass number and total charge of starting
materials is same as ending materials
– Can be stopped by paper
Radioactivity
• Beta decay – β
– Release of beta particle
– Beta particle is an electron
– Has no mass
– With beta decay, a neutron breaks into a proton
and electron, element becomes a different
element
– Mass number and total charge remain the same
– Beta radiation can be stopped with few mm of
aluminum
Radioactivity
• Gamma decay – γ
– Is basically pure energy
– Has no mass or charge
– Cannot cause change into different element
– VERY high energy = VERY dangerous!
– Cannot be stopped by clothes or aluminum foil
– Needs lots of lead or uranium to stop gamma rays
Power of radiation
• Exposure to radiation can lead to radiation
sickness (fatigue, hair loss, loss of appetite)
• Can cause damage to living and non-living
matter, such as burns and even death
• Atoms get destroyed, so cells get destroyed
• Chemoradiation kills cancer cells
Radiation
• You can find how old something is by its rate
of nuclear decay
– Iceman in Italian Alps, found to be 5300 years old
– Some carbon atoms (C-14) are radioactive and
break down over time
– C-14 atoms will break down after an organism dies
– Half of the atoms will decay after a certain
amount of time, this is called half-life
Half-life
• Half-life is amount of time it takes for half of
the nuclei of a radioactive isotope to decay
• Carbon-14 = 5730 years
• Uranium-238 = 4.5 billion years
• Hydrogen-3 = 12.3 years
• Calcium-36 = .1 seconds
• Nitrogen-13 = 10 minutes
Half-life
• We can use half-life to figure out how old
things are, based on how much of a
radioactive element is left in the object
• With Iceman, scientists found that almost one
half of C-14 had changed, so Iceman was
almost 5730 years old.
• Fossils can be dated this way
Half-life
• The half life of Nitrogen-13 is 10 minutes
• A 20 gram N-13 sample is prepared for an
experiment. If a scientist is late and starts the
experiment 20 minutes later, how many grams
of N-13 are left?
• If only 2.5 grams of N-13 are left at the end of
the experiment, how much time has gone by?
Uses of radioactivity
• Radioactive materials are used in everyday
things
• Smoke alarms have very small amounts of
radioactive material to detect fires
• Doctors use tracers (radioactive elements
used to follow a path) in patients to find
things inside the body
• Microwaves cook using radiation
• X-rays/MRIs/CT scans all use radiation
Energy from the nucleus
• Nuclei from some atoms decay into smaller,
more stable nuclei
• Nuclear fission: process by which a nucleus
splits into two smaller nuclei and releases
energy
• Uranium can undergo this naturally
• Humans can throw neutrons at other atoms to
force them to split (Large Hadron Collider)
Energy from the Nucleus
• Nuclear fission in fuel pellet of U can release
as much energy as burning 1000 kg of coal
• This is due to the chain reaction
• When one nucleus splits, the neutrons
released hit another nucleus and split that
one, causing a domino effect
Chain reaction
• Domino demo
Chain reaction
• Uncontrolled
– Large amounts of energy released very quickly
– Atomic bombs
• Controlled
– Energy released over longer periods of time
– Nuclear power plants
Nuclear Power (Fission)
• Advantages
– Very clean compared to coal
– Relatively inexpensive
– No greenhouse gases released
– More electricity produced
Nuclear Power (Fission)
• Disadvantages
– Accidents release dangerous radiation (Chernobyl,
Fukushima, Three Mile Island*)
– Nuclear waste that is still radioactive
– Limited amount of nuclear material to start with
Nuclear Power (Fusion)
• Fusion
– Two or more single nuclei combine to form one larger
nucleus
– Hydrogens join to form helium
– Must overcome the repelling charges (remember,
positive repels positive)
– Need VERY high temperatures to do this
– Temperature of 100,000,000 °C (like the middle of the
sun)
Nuclear Power (Fusion)
• Can make virtually unlimited amounts of
energy
• Very little radiation produced
• However, we simply do not have the
technology yet to make fusion reactors
capable of powering nations (remember, need
to have VERY high temperatures, and
materials strong enough to withstand those
temperatures)