Each element has different number of protons.
Nuclear Energy and radiation
Atom ingredients:
Proton (positive charge) – charge = 1.6 x 10-19 Coulombs
mass = 1.66 x 10-27 kg.
Neutron (no charge) – no charge
mass = 1.66 x 10-27 kg.
Electron (negative charge) – charge = -1.6 x 10-19 Coulombs
mass = 9.10 x 10-31 kg.
"I am become Death, the destroyer of worlds.“
–J. R. Oppenheimer (quoting Bhagavad Gita)
Phys 1010, Day 14:
Questions?
Nuclear Weapons 16.1
Nuclear Power 16.2
Reminders:
HW Today
Review next Tues
Exam Next Thursday 7:30 PM
Oxygen has 8 protons, 8 neutrons:
hydrogen
1p
deuterium
1 p, 1n
helium
2 p, 2 n
Uranium 238
92 p, 146 n
Oxygen has 8 protons, 8 neutrons
Consider a nuclei with 7 protons, 7 neutrons (nitrogen atom)… what if we want to
add another proton to make oxygen (8 protons):
Consider a nuclei with 7 protons, 7 neutrons… what if we want to add another
proton to make oxygen:
What will we need to do to get proton stuck to nucleus:
b. the closer it gets, the harder you have to push, will take lots of work ... Lots
of energy
What will we need to do to get proton stuck to nucleus:
a. just give it a little push so it will hit nucleus dead on and it will drift
towards nucleus and stick.
b. the closer it gets, the harder you have to push, will take lots of work
c. you’ll need to push really hard at first and then less as you get closer
d. you’ll have to push the proton towards the nucleus with a fixed amount
of force (constant force).
Like charges repel:
7 positives
One positive
Big repelling force
Bigger repelling force
Force on proton given by Coulomb’s law (k = Coulomb’s constant):
In general: Force = k x charge of object #1 x charge of object #2
(distance between objects)2
F = k x charge of nucleus in coulombs x charge of proton in coulombs
(distancenucleus-proton)2
The smaller the distance the larger the force!
What if threw proton so starts out going towards nitrogen nucleus with a
lot of speed (lots of kinetic energy)?
Starts with lots of kinetic energy 
Repelling force from nucleus slows down proton 
Proton’s kinetic energy converted into electrostatic potential energy,
as it gets closer to nucleus
Potential energy curves- represent energy to bring particles
r, separation distance
together. Gravity energy analogy.
Potential energy
Kinetic energy
r, separation distance
Potential energy curvesrepresent energy to bring
particles together.
separation
distance, r
Potential energy = k x charge of 7 proton nucl. x charge of single proton
Potential energy
at separation
distance of r
Kinetic energy
Gravity energy analogy.
separation distance, r
if at center, want to roll down hill/fly apart … lots of electrostatic potential energy
5
(separation distance)
Charge of 1 proton = 1.6 x 10-19 Coulombs; Charge of 7 protons=11.2 x 10-19 C
So at 10-15 m away (~ radius of nucleus),
Potential energy = 8.99 x 109 N m2/C2 x 11.2 x 10-19 C x 1.6 x 10-19 C
(10-15 m)
= 1.61 x 10-12 Joules = 10 million electron Volts.
(1 electron volt = energy gained 1 chemical reacction. So this is 10 millions times
bigger/atom)
1
potential energy curve for bringing electron in to proton
Potential energy curve (Energy vs. separation distance)
for bringing electron in to proton
a. This curve would be flat, not going up or down
b. look like bringing a proton into a proton except upside down so going
down instead of up.
c. would look same as proton on proton
b. look like proton on proton except upside down so going
down.
r
r
Lots of EPE
when separated
Electron and proton get pulled together,
curve tells us that must add energy to separate electron and proton.
electron wants to roll into center as close as possible.
7
How can a bunch of repulsive positively charged protons stick together?
Like hopper toy- really strong nuclear force between protons
and neutrons overwhelms electrical force if really close together.
Electrical force is like gravity, pushes over distance.
like nuclear force, only strong when very close (protons and
neutrons only feel this if they can hold hands).
like double sticky tape… only works if in close contact.
Neutrons help with this force (more neutrons further up
the table
suction cup or springNuclear force- Why like this?
That is the way nature is!
Stabilizing effect of neutrons in the nucleus …
why do you need them?
Add neutrons
They don’t repel anyone.
They still have the Strong force
The bind protons and neutrons
They let the protons stay a bit further apart
without adding + charge
Like putting a bunch of neutral people
between that can hold hands but don’t
cause anyone to run away… MORE
STABLE SITUATION…
(more or less)
What about a neutron? No electrostatic repulsion!
8
Stabilizing effect of neutrons in the nucleus …
why do you need them?
Protons
Repel from electrostatic force (all distances)
Protons also attract some from Strong force
(very short distances <nuclear radius)
Quickly the Strong force can’t win over the
size of the nucleus
Like putting a bunch of people who find each
other repulsive in same room. They can only
keep from falling apart if they can clasp
hands… The crowd quickly becomes an
UNSTABLE SITUATION
Potential energy curve for proton approaching nucleus
Energy scale gigantic compared
to chemical energy.
Why? Simple coulomb’s law.
electrostatic
repulsion
separation distance, r
attractive
nuclear
combination--real nucleus
separation distance, r
F= k (charge of #1)(charge of #2)
r2
Chemistry- forces between
electrons and protons on distance
scale of atomic size (> 10-10 m).
Nuclear forces- forces between
protons on distance scale
10-100,000 times smaller.
10,000 times closer means forces
have to be 100,000,000 times
bigger to hold nucleus together
(have to beat 1/r2). Lots more
potential energy stored!!!
2
Gets deeper until iron
(26 P, 30 N) less deep if
bigger.
Atomic nuclei
beryllium
harder to push together,
but bigger drop when do.
helium
Nuclear decay- one kind of nucleus changes into another.
alpha decay, (beta decay), induced fission
A. alpha decay- alpha particle = 2p and 2n. They escape together.
Most radioactivity is this type (e.g. radon).
“tunnel” out.
If alpha particle, finds
itself outside, lots of PE,
zooms away PEKE
Not real tunnel it doesn’t lose
energy.
Quantum physics says
Tiny objects are spread out
Very small fraction of time
appear outsidewhen happens-- run for it!!
2protons-2neutrons stuck
together.
(chained together prisoners
escaping!)
Really stable:
Have to add a whole bunch of
energy to break up!
Really big nucleus, >100 P, >100 N,
like Uranium or plutonium
2P-2N
14
B. Radioactive decay-fission
tunneling difficulty = width x depth of tunnel
Neutron Induced fission- key to atomic bombs
•two smaller nuclei
Neutron
E
nucleus1
hard- takes long time,
billions of years!
3
2
medium
How much energy released?
a. 1 most, 2 second, 3 least
b. 2 most, 1, 3 least
c. 3 most, 2, 1 least
d. 3 most, 1, 2 least
easy!,
happens in
millionths of
a second!
•few extra free neutrons
•LOTS OF ENERGY!!
“parent” nucleus
“daughter” nuclei
•(+sometimes other bad stuff)
“daughter” nuclei – come out in excited nuclear energy state
…. Give off gamma rays as drop to lower energy.
energy is difference from
bottom of crater to outside.
3 is most, 2 second, 1 is least
Jumps down in energy …
Gives off gamma ray…
VERY HIGH ENERGY PHOTON
16
B. Radioactive decay-fission
Neutron Induced fission- key to atomic bombs
Neutron Induced fission- key to atomic bombs
N
“parent” nucleus
•two smaller nuclei
Neutron
“daughter” nuclei
•few extra free neutrons
“parent” nucleus
“daughter” nuclei
•LOTS OF ENERGY!!
•two smaller nuclei
•LOTS OF ENERGY!!
•It is a messy process with lots of
•few extra free neutrons
N
•(+sometimes other bad stuff)
Found in strange results from Enrico Fermi’s lab
Otto Hahn saw similar results and called to his
former student for help
Lise Meitner came to his aide and explained what
was happening.
Uranium 235
92 p, 143 n
Neutron absorbed 
Excites U235 nucleus up above potential
barrier 
Splits into two smaller nuclei…
which zoom apart due to electrostatic
repulsion! (there is even more energy
from other sources)
3
Fission Nuclear explosion
“atomic bomb”
neutron induced fission
Fermi first did it, it was very hard to figure out how this could be.
If don’t get swallowed
the 3 free neutrons can go
induce more fission.
Ur 235
2nd generation
3rd generation
BOOM!
1st generation
Chain reaction: neutrons making fission that makes more neutrons, that makes more
fission that makes more neutrons, that makes more fission that makes
more neutrons, that makes more fission that makes more
Uranium 235
or plutonium
100 generations
per microsecond!
2 x 2 x 2 .…x2 fissions
each with LOTS of
energy.
that makes more
neutrons, that makes more fission that
neutrons, that makes more fission
makes more neutrons, that makes more
This is very similar to a
conventional explosion
Recipe for fission bomb.
Methane + 2 Oxygen
mainly stable
combining will release energy (heat)
Heat+CH4+2 O2 they combine immediately
releasing more heat
100 generations
per microsecond!
2 x 2 x 2 .…x2 reactions
with a lot of energy
each.
Each one is a millionth
of a fission reaction.
3rd generation
1. Find neutron induced fissionable material that produces bunch of extra
free neutrons when fissions.
2. Sift it well to remove all the other material that will harmlessly
swallow up the extra neutrons. (THE HARDEST STEP.)
3. Assemble “supercritical mass”, really fast!. Need enough stuff that the
neutrons run into other nuclei rather than just harmlessly leaving
sample.
If your mass tends to melt with a small
fizzle you are not assembling fast enough
to be supercritical. Put together faster.
1st generation
2nd generation
BOOM!
4. Let sit for 1 millionth of a second- will bake itself!
22
Fusion bomb (simple picture)
chemical explosive
hydrogen isotopes
tritium,deuterium
Plutonium “trigger”
chemical explosive
Plutonium reaches
supercritical, explodes.
(fission bomb)
Shaped plutonium and assembled bombs at Rocky Flats.
4
Al Bartlett
CU professor 1950-2013
Energy:
1 fission of Uranium 235 releases:
~10-11 Joules of energy
1 fusion event of 2 hydrogen atoms:
~10-13 Joules of energy
Burning 1 molecule of TNT releases:
~10-18 Joules of energy
Was a CU professor
from 1950-2013
Had a lot of interesting
ideas about population,
sustainability, fuel use,
etc
Photographed atomic
explosions at Los
Alamos with nano
second resolution 19441945
In the first plutonium bomb a 6.1 kg sphere
of plutonium was used and the explosion
produced the energy equivalent of
22 ktons of TNT = 8.8 x 1013 J
88,000,000,000,000 J
How does 6.1 kg relate to 22 ktons?
(the 22 k tons is 10 million times more
massive)
Dropping 1 quart of water 4 inches ~ 1J of energy
Useful exercise… compare this volume of TNT, H2, and U235
The hardest part of getting a nuclear bomb is the
material
“Front End”
- obtain 235U (HEU=at least 80%) by the
same methods used to make Low Enriched
Uranium (LEU), 3-4%.
Have to use tiny mass difference very hard
Would have to drop that quart of water from
1 billion kilometers (our model of gravity
fails first).
Gas centrifuge (use inertial difference between
masses).
Bohr told his American colleagues
that a bomb couldn't be made without
turning the entire country into a giant
factory. When he saw Los Alamos he
said, “I told you so.”
5
The hardest part of getting a nuclear bomb is the
material
“Back End”
-obtain 239Pu from Spent Nuclear Fuel: chemistry
238U loves neutrons: grabs them and converts to
239Pu (another process called beta decay)
239Pu is very much like 235U
Chemical separation of Pu is much easier.
Fusion bomb or “hydrogen bomb”
Basic process like in sun. Stick small nuclei together.
Deuterium on
Tritium
Deuterium on
Deuterium
Which will release more energy during fusion?
a. Deuterium combining with deuterium
b. Deuterium combining with tritium
Answer is b. Incoming deuterium particle has comparatively more potential
energy!
Fusion bomb or “hydrogen bomb”
Basic process like in sun. Stick small nuclei together.
activation energy of 100 million degrees
push together
energy required
Stick hydrogen isotopes
together to make helium.
+
energy released if
push over the hump
=
helium
Plutonium reaches
supercritical, explodes.
Simple if can push hard enough- just use sun or fission bomb.
More energy per atom than fission. Can use LOTS of hydrogen.
End up with GIGANTIC bombs
1000 times bigger than first fission bombs
Tritium etc. nuclei pushed together
and combine to form helium.
Fission bomb- chain reaction, hideous amounts of energy
comes off as heat and high energy particles (electrons,
neutrons, x-rays, gamma rays) “Radiation”. Heats up air that
blows things down.
In atomic bomb, roughly 20% of Pl or Ur decays by induced fission
This means that after explosion there are
a. about 20% fewer atomic nuclei than before with correspondingly fewer
total neutrons and protons,
b. 20% fewer at. nucl. but about same total neut. and protons.
c. about same total neutrons and protons and more atomic nuclei,
d. almost no atomic nuclei left, just whole bunch of isolated Neut.s and
prot.s.,
e. almost nothing of Ur or Pl left, all went into energy.
ans. c. Makes and spreads around lots of weird radioactive “daughter”
nuclei (iodine etc.) that can be absorbed by people and plants and decay
slowly giving off damaging radiation.
Lots of free neutrons directly from explosion can also induce radioactivity in
some other nuclei.
6
U235 and U238 atoms are placed into a container, which are likely to result in a
chain reaction (resulting in explosion) when a free neutron triggers fission of one of
the U235:
Lots of uranium in the ground… why not just
blow up or heat up until it melts?
U235 and U238
It did once (at least once).
Now
#5
#1
a.
b.
c.
d.
e.
#2
#2 only
#1, #2, and #5
#2 and #4
#2, #3, and #4
#2, #4, and #5.
#3
#4
Lots of uranium in the ground… why not just
blow up or heat up until it melts?
Correct answer is c. (#2 and #4) Analysis:
#1 is too sparse .. most neutrons will leave box before hitting another U235.
#2 is good.. Pure U235, densely packed, large package
#3 has too many U238’s… more U238’s than 235’s. Free neutrons more likely to be
absorbed by 238’s than to hit and fission another 235.
#4 is OK … More U235’s than 238’s, still densely packed, large package
#5 is too small of package … neutrons likely to escape package before hitting another
U235.
4 BY ago
U235 is less stable than U238. So 1.8 billion years ago natural
Uranium ore had about 3% U235.
This is how much we enrich Uranium for a reactor
Why didn’t it happen earlier? Uranium too diffuse.
For 2 BY after earth’s formation the Uranium
remained diffuse.
Then life released Oxygen.
Oxygen reacted with the Uranium making it mobile
and in Gabon it concentrated.
There was water present which acted to slow down
neutrons that were too fast.
There were no other elements that soaked up the
neutrons and…?
It didn’t explode. Instead it slowly burned for millions
of years.
Alpha particles: helium nuclei
Radioactive materials and “radiation”
Daughters often have too few neutrons
to stick together, so radioactive, divide more.
Other bad/energetic stuff that comes out.
Neutrons
electrons (“beta particles”)
photons (“gamma rays”)
helium nuclei (“alpha particles”)
- most of radiation is this type
- common is Radon (comes from natural decay process of U 238), only really
bad because Radon is a gas .. Gets into lungs, if decays there bad for cell.
In air: Travels ~2 cm ionizing air molecules and slowing down …
eventually turns into He atom with electrons
If decays in lung, hits cell and busts up DNA and other molecules:
++
Why radiation bad?
Jocell
Usually doesn’t get far -- because it hits things
Beta particles:
energetic electrons … behavior similar to alpha particles, but
smaller and higher energy
41
Sources of Gamma Radiation
42
gamma rays: high-energy photons
- So high energy can pass through things (walls, your body) without being
absorbed, but if absorbed really bad!
•two smaller nuclei
Neutron
•few extra free neutrons
•LOTS OF ENERGY!!
“parent” nucleus
“daughter” nuclei
In air: Can travel long distances until absorbed
In body, if absorbed by DNA or other molecule in cell …
damages cell… can lead to cancer.
•(+sometimes other bad stuff)
“daughter” nuclei – come out in excited nuclear energy state
…. Give off gamma rays as drop to lower energy.
Jumps down in energy …
Gives off gamma ray…
VERY HIGH ENERGY PHOTON
43
+ +
Most likely
If pass through without interacting with
anything in cell then no damage.
44
7
An odd world…
+ +
Also break DNA cancer
a) a hand, b pocket, g eat
b) b hand, g pocket, a eat
c) g hand, a pocket, b eat
d) b hand, a pocket, g eat
e) a hand, g pocket, b eat
But also can cure cancerConcentrate radiation on
cancer cells to kill them.
45
Results of radiation
You find yourself in some diabolical plot where you are
given an alpha (a) source, beta (b) source, and gamma
(g) source. You must eat one, put one in your pocket
and hold one in your hand. You …
~4,000 counts/min =
.002 Rem/hr
dose in rem = dose in rad x RBE factor (relative biological effectiveness)
RBE = 1 for g , 1.6 for b, and 20 for a.
a - very bad, but easy to stop -- your skin / clothes stop it
b - quite bad, hard to stop -- pass into your body -- keep far away
g- bad, but really hard to stop--- rarely rarely gets absorbed
Me--- I pick (d)--46
How much energy do we use?
on what?
A rad is the amount of radiation which deposits 0.01 J of energy into 1 kg of absorbing material.
domestic
Renew + nuclear.
foreign
+ primarily due to atmospheric testing of nuclear weapons by US and USSR in the 50’s and early
60’s, prior to the nuclear test-ban treaty which forbid above-ground testing.
How do you get “power” out of
Uranium.
How do you get “power” out of
Uranium.
The same way to get useful power from carbon based
fuels
The same way to get useful power from carbon based
fuels
Carbon things can
explode
Nuclei can explode
Or you can burn
them slowly
Or you can burn
them slowly
8
U.S. Oil Curves
What about US oil?
'03 DOE-EIA
2.1E9 bbl/yr
51
What does this mean?
52
What is inevitable?
Of course this is an estimate (and perhaps worst case); what is best
case?
53
57
“Paying Attention Quiz”
1. A chain reaction as it occurs in atomic bombs is
a. the chemical reaction used to form the metal used in making chains.
b. a series of chemical reactions where each one triggers the next.
c. the sequence of one nucleus splitting up and causing another to split up followed by
another etc.
d. the set of steps required to assemble an atomic bomb.
1. c, 2.c
1
2
2. To the left are energy profiles for
various atoms. Which decays most
rapidly and which never decays?
3
4
a. 3 most rapid, 4 never
b. 1 most rapid, 2 never
c. 2 most rapid, 1 never
d. 4 most rapid, 3 never
e. 4 most rapid, 1 never
59
9