Transcript Nuclear Chemistry

Nuclear Chemistry
Fuuuuuusiiiiioooon
HA!
The Atom
• Nuclear chemistry revolves around the
nucleus of the atom
• Electrons do not really matter for these
reactions.
• E=mc2
The nucleus
• Composed of protons and neutrons
• Atomic number is number of protons
Ex. Sodium has an atomic number of 11, so
it has 11 protons
Neutrons
• Since they are neutrally charged, they do not impact
reactivity of the element.
• Protons + Neutrons = Atomic mass
• Wait…
• If sodium has 11 protons, and has a mass of 22.990…
• Then it has 11.990 neutrons? What gives?
Isotopes
• Not all atoms of an element are exactly the
same
• Isotopes are atoms of an element with different
numbers of neutrons (and thusly different
masses)
• The mass on the periodic table is the weighted
average of all the atoms of that element
Examples
• Sodium has a mass of 22.990 this
means…
– Most sodium atoms have a mass of 23
– A very small number have a mass of 22
– Other isotopes will be extremely rare
• Uranium has a mass of 238.029,
meaning…
– Most uranium atoms have a mass of 238
– Very few have the useful mass of 235
Stability
• If protons are in the nucleus, and electrons
are in the cloud around it, how can a
nucleus be stable?
• Answer is a little complex
Stability Cont.
• When protons collide, they “stick” together
to form a larger, positive charge. They quit
behaving like single positive charges.
• Neutrons aid in the “stick” together.
• Scientists are still trying to figure out why
this happens.
Instability
• If there are not enough neutrons, the atom
has an unstable nucleus.
• Unstable nuclei can and will break down
into nuclei of a different element.
– Ex. Uranium-235 will spontaneously break
down into thorium-231
• All elements on the periodic table after
Uranium are radioactive for ALL isotopes
Fission
• Fission is a natural process in which
unstable nuclei break down.
• Elements heavier than iron have energy
released with break down.
Fission
• But where does the
mass go?
– A very small part of the
nucleus will be shot off
will most of the
“missing” mass and
have much of the
energy
– This is known as
radiation.
– Not all of it is harmful
Radiation
• 3 types of particles
released
– Alpha
– Beta
– Gamma
• Not all 3 types are
produced when they decay
• Most elements only
produce 1
Alpha
• Helium-4 nucleus
• +2 charge (zero electrons)
• Nearly harmless
– A few centimeters of air will effectively block
– Used in smoke detectors
• Polonium-210 breaks down into Lead-206
by alpha emission
Beta
• Electron emitted from the nucleus
• Stopped by glass
• Used for medical purposes
• Carbon releases this when breaking down
into nitrogen.
Gamma
• This is a high-energy electromagnetic
wave
• In English, this is essentially just energy
• Will penetrate several meters through lead
• Due to its high energy this is the big one
for causing cancer.
• Uranium emits this on its way to thorium
Radiation Poisoning
Radiation poisoning
• I’d show you a picture, but I’d like to eat
sometime today
• It’s very difficult to measure exactly how
much radiation is dangerous
• Scientist cannot agree on how it should be
measured.
mrem
• We’ll be using millirem (mrem) for
comparison purposes
– Rem stands for “Roentgen equivalent in man”
and is a function of radiation dosage and
biological effectiveness of the radiation
– 15-25mrem is typical for just living normally on
Earth.
– 1mrem will come from your TV
– Living near a nuclear power plant will add a
whopping 0.01 mrem (coal delivers 0.03 mrem)
– A chest x-ray delivers 6 mrem
– The average American receives 360mrem a year
Deadly amounts
• 450,000 mrem will cause death in 50% of
people…
• Yeah, that nuclear plant is starting to
sound much safer, isn’t it?
• You’d have to live next to the plant for 45
million years to receive that much
radiation.
More Deadly Amounts
• The Chernobyl accident had a radiation
spike of 3,000,000 mrem/hr
• That hits the 50% fatality mark in under 10
minutes.
• Severe illness would begin in minutes.
Symptoms of Radiation Poisoning
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Hair loss
Skin lesions (open sores)
Teeth falling out
Nausea/vomiting
Diarrhea
Headache
Fever
Dizziness
Fatigue
Poor wound healing
Bloody vomit
Low blood pressure
Death in 2-6 days for high doses
And worst of all…
Your cable bill will be late
Media
• Why is it the media over emphasizes
amount of radioactive material?
Half-Lives
No, not the video game series.
Half-Life
• Fission happens randomly amongst unstable
nuclei.
• But it happens at a predictable rate.
• So, we know how many will be lost in a given
time, but not which ones.
• For every half-life that passes, ½ of the
remaining sample has decayed.
Half-Lives
Starting with 100g:
After 1 half life: 50g remain
After 2: 25g remain
After 3: 12.5g
After 4: 6.25g
After 5: 3.125g
After 6: 1.5625g
After 7: 0.78125g
After 10: 0.09766g
Half-Lives
• This is used to carbon-date objects.
• 10 half-lives is considered safe for most
radioactive samples.
• For uranium-235, 1 half-life is 700 million years
– 700million x10 for safety= 7billion years
– The age of the Earth is around 4.5 billion years.
C. Half-life
mf  m ( )
1 n
i 2
mf: final mass
mi: initial mass
n: # of half-lives
C. Half-life
• Fluorine-21 has a half-life of 5.0 seconds. If you
start with 25 g of fluorine-21, how many grams
would remain after 60.0 s?
GIVEN:
WORK:
t½ = 5.0 s
mf = mi (½)n
mi = 25 g
mf = (25 g)(0.5)12
mf = ?
mf = 0.0061 g
total time = 60.0 s
n = 60.0s ÷ 5.0s
=12
Fusion
Fusion
• combining of two nuclei to form one
nucleus of larger mass
• thermonuclear reaction – requires temp of
40,000,000 K to sustain
• 1 g of fusion fuel =
20 tons of coal
• occurs naturally in
stars
2
1
H H
3
1
Fusion
• Elements after Uranium have been
synthesized by fusing smaller elements
• Ex. Synthesis of Einsteinium
– Californium-249 is struck by hydrogen-2
– Products are einsteinium-248 and 3 neutrons
Practice
• Pick three trans uranium elements
• Predict a possible synthesis reaction for
them.
C. Fission vs. Fusion
F
I
S
S
I
O
N
• 235U is limited
• danger of meltdown
• toxic waste
• thermal pollution
F
U
S
I
O
N
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•
•
fuel is abundant
no danger of meltdown
no toxic waste
not yet sustainable
Nuclear Reactors
Main idea
• chain reaction - self-propagating
reaction
• critical mass mass required
to sustain a
chain reaction
Chain reactions
• One nuclei breaks down and releases
enough energy to trigger another break
down.
• If the mass is too small, the energy
escapes without colliding with another
nuclei.
Parts
• Control Rod
– Absorbs neutrons to keep decay under control
– Too fast = meltdown
– Too slow = shutdown
• Fluid to absorb heat-sodium or
pressurized water
• Cooling tower
– The part of the plant you’re probably most
familiar with
A. Nuclear Power
• Fission Reactors
Cooling
Tower
A. Nuclear Power
• Fission Reactors
A. Nuclear Power
• Fusion Reactors (not yet sustainable)
Fusion Plasma
• What might be a potential issue with using
plasmas in a fusion reactor?
Nuclear weapons
Adding the “new clear” to nuclear
And I’m so going to prison for this
Power vs. Weapon
• In a power plant, the decay is tightly
controlled. Not too fast nor too slow.
• In a weapon, the decay is forced to
happen at once.
• A power plant CANNOT be turned into a
weapon
– Fuel is not pure enough
– Not as simple as getting a lot of uranium
together and flinging it at someone.
Timing
• For a nuclear weapon to work, every atom
must decay in unison.
• If decay is not uniform, weapon will just be
a really expensive bullet.
• A hydrogen bomb uses a uranium or
plutonium bomb to trigger the fusion
reaction.
Timing continued
• Step 1: keep sub critical (mass too small
to maintain a chain reaction) masses apart
• Step 2: Smash sub critical parts together
without a neutron setting the whole thing
off prematurely
• Step 3: Introduce a neutron at peak time
• Step 4: Climb into a 1950’s fridge
Adding the “nuke you” to nuclear
Destruction
• A kiloton references how much TNT could be
used for a similar effect. 1 kiloton=1,000 tons of
TNT.
• 1megaton=1,000,000 tons of TNT
• The largest conventional weapon (non-nuclear)
is 0.15kilotons.
• Temperature of a typical explosive can reach
temperatures of 1,000 degrees Celsius, while
nuclear can exceed 1,000,000 degrees Celsius
(temperatures on the order of the sun)
Destruction of a 15 kiloton nuclear
weapon
• .75mi
– 500mph winds
– Most buildings leveled
– Zero survivors
• 1.2 mi
– 3rd degree burns
– Death likely due to lack of medical response and
capabilities.
• 1.5 mi
– 93mph winds
– Severe injuries and casualties
Tsar Bomba
• Largest yield nuclear weapon ever detonated (50megatons)
• If dropped on Sugar Land…
– Louisiana would feel the wind.
– Katy would be history
– 68 mi away, 45% of people would be injured, 5% killed
– 170 miles away, the heat would be felt.
– 560 miles away, windows would break.
– Would be seen 620 miles away (Kansas would be able to see
it)
– Mushroom cloud would be 8 times higher that Mount Everest
– Could cause an earthquake hitting 7.1 on the Richter scale
(same as the earthquake responsible for Fukushima)
– Anybody injured on our side of San Antonio and Louisiana
would have a high chance of dying from otherwise treatable
injuries due to inhibited medical response.
Warning Time
• How much warning time would be
necessary for you to get to a safe distance
from the blast?
• Assuming the flight from Cuba (they’re not
really fond of us) is 2 hours, is there
reason for alarm if such a weapon were to
be found?
Complications
• Random radiation from space can set off a
critical mass
• Random radioactive decay can set off
critical mass
• So, the entire process must be done
extremely fast (faster than a single nuclei
can decay ~4microseconds).
To complicate things even more…
• It is difficult to predict exactly how much damage
such a weapon would do.
• Terrain and weather can impact the forces.
• Modern weapons now employ the “more is
better” option
– By setting off multiple warheads, the total destruction
area can be maximized.
– Instead of “goodbye Houston,” it could be “goodbye
New York, Los Angeles, Houston, Washington D.C.
and Seattle”
On Indiana Jones…
• Would it have been plausible for him to
have survived in the lead lined
refrigerator?
• Why or why not?
Hiroshima
15 kiloton atomic bomb
Before
After
Ground Zero
The first signs of these effects were visible four miles or
so from the bomb’s dropping point. The roofs looked denuded, as
their tiles had been blown off by the blast. In places, the grass
was bleached, as if dried; the Japanese journalist explained to me
that the plants, vegetables and rice up to five or six miles from the
bomb's epicentre had lost their green colour immediately after the
explosion. They only got their colour back three or four weeks
later. However, some plants, obviously more sensitive, had died.
At three miles from the bomb's epicentre, some houses
had been flattened like cardboard. The roofs were completely
caved in; the rafters stuck out all round. This was the familiar
sight of cities destroyed by explosive bombs. At two and a half
miles, there were only piles of beams and planks, but the stone
houses seemed intact. At just over two miles from the town
centre, all houses had been gutted by fire. All that remained was
the outline of their foundations and heaps of rusty metal. This
area looked like the towns of Tokyo, Osaka and Kobe, destroyed
by incendiary bombs. At one mile or so everything had been torn
apart, blasted and swept away as if by a supernatural power;
houses and trees had disappeared.
Dr. Junod
Paint exposed to the radiation was
burned away. Unexposed areas
left behind “shadows
Tsutomo Yamaguchi
(Lucky?) Survivor of both bombs
Murphy and Nuclear Power
Why thousands can pay for a
“nobody will know”
Chernobyl Accident in 1986
• Reactor near Pripyat Ukraine
• 30 people dead
Issues
• Control rods leave a space when being
moved.
• The negative space allows steam to form
• Neutrons that would have been absorbed
by liquid water strike the reactor rods
• Reactor output actually increased as the
control rods were inserted
• Government was slow to order evacuation
The Test
• A test was to be run on the reactor to see how it
performed if it lost power.
• Automatic shutdown feature was DISABLED
• Due to some human error, the people trained to
conduct the test were NOT present
• Combined with the issue of control rods briefly
INCREASING the power of the reactor…
Graphite moderator. Notice the
control rod channel
Reactor after explosion
Reactor today with concrete containment
structure over reactor
I talked to some scientists. One told me: “I could lick your helicopter with my
tongue and nothing would happen to me.” Another said: “You’re flying without
protection? You don’t want to live too long? Big mistake! Cover yourselves!”
Eduard Borisovich Korotkov
Warning Sign
Red Forest-Trees
killed from radiation
Bumper cars left
behind
Some 3,600 soldiers worked on the roof
of the ruined reactor. They slept on the ground in tents. They were
young guys. These people don’t exist any more, just the documents
in our museum, with their names.
Sergei Vasilyevich Sobolev
Control Room-Where so many
mistakes were made
We buried trash heaps and gardens. The women in the villages watched us and
crossed themselves.
One of the poets says somewhere that animals are a different people. I killed them
(animals) by the ten, by the hundred, thousand, not even knowing what they were
called. I destroyed their houses, their secrets. And buried them. Buried them.
Arkady Filin
I took my daughter and my wife to the hospital.
They had black spots all over their bodies. These
spots would appear, then disappear.
I want to bear witness: my daughter died from
Chernobyl. And they want us to forget about it.
Nikolai Fomich Kalugin
We were newlyweds. We still walked around holding
hands, even if we were just going to the store. I would
say to him, “I love you.” But I didn’t know then how
much. I had no idea.
The only thing that saved me was it happened so fast;
there wasn’t any time to think, there wasn’t any time to
cry. It was a hospital for people with serious radiation
poisoning. Fourteen days. In 14 days a person dies.
I tell the nurse: “He’s dying.” And she says to me: “What
did you expect? He got 1,600 roentgen. Four hundred is
a lethal dose. You’re sitting next to a nuclear reactor.”
They buried him barefoot. My love.
Lyudmilla Ignatenko
I’m 12 years old and I’m an
invalid. The mailman brings two
pension cheques to our house –
for me and my grandad.
When the girls in my class
found out that I had cancer of
the blood, they were afraid to sit
next to me. They didn’t want to
touch me.
The doctors said that I got sick
because my father worked at
Chernobyl. And after that I was
born. I love my father.
Vanya Kovarov
Chemistry Classroom
Fukushima Diichi Nuclear
Disaster
Issues
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Falsification of safety records
Major design flaws ignored
Tsunami study ignored
Reactors 4,5,6 were shut down at the time
Reactors 1,2,3 were immediately shut
down during earthquake
Myth vs. Fact
• There was a lot of radiation released, but
sources vary—and may not ever agree (same
for just about every other radiation issue)
• Nobody was killed (hundreds exposed to
radiation, and projected deaths from cancer is
100)
• On a scale of 0-7, Fukushima ranks in at a 7
(same as Chernobyl) due to the reactor
explosion
• Sources STILL disagree on exactly how far the
radiation distance compares to Chernobyl
Comparison
• Which was worse, Chernobyl or
Fukushima?
• How do they compare to Hiroshima?
Common Misconceptions
Radiation
• It is not green.
– It’s actually blue
– Cherenkov radiation
• Blue glow from electrons exceeding the speed of light in
water
• Speed of light in water is .75c
• Will not generate new species overnight
– Remember evolution? Still takes a long time.
• Not necessarily dangerous (alpha is harmless)
Cherenkov Radiation
Nuclear Power
• Far safer than most power types.
• Most news stories over-hype the dangers
• Reactors now cannot sustain themselves without
power
• The uranium used is not the same as in
weapons.
• Don’t always have cooling towers looking like
the ones you are familiar with
• Lesson was learned from Chernobyl. New
safety regulations and understanding of nuclear
reactors prevent it from ever happening again.
Weapons
• Not an easy thing to build
• You’ve got a billion things to do within 4
microseconds.
• Conventional weapons cannot cause one
to go critical. Worst case scenario is the
radiation kills everyone in the room.
• President Obama does not have a big red
button. (It’s a briefcase)
AAAAND
• No, dragon ball z has nothing to do with
real world fusion.
• Quit asking.
• And yes, the power output of a nuclear
reactor is over 9,000.