Nuclear Power - Santa Rosa Junior College
Transcript of Nuclear Power - Santa Rosa Junior College
The unleashed power of the atom has changed everything save our modes of thinking and we thus drift toward unparalleled catastrophe.
-Albert Einstein
Bronze Buddha at Hiroshima
Nuclear Power
Atomic Notation
A
Z X
Atomic Mass Number
A = # protons + neutrons
Atomic #
1 3 238
1 1 92H, H, U
Atomic Number
Z = # protons
Neutron Number N
N = # neutrons
N = A - Z
E = mc2
Energy Released: The Mass DefectParent atoms have more mass than product atoms.
The difference is released in the form of Kinetic energy.
parents productsm m m
Heavy elements FISSION into lighter elements, releasing energy
in the process by E = mc2, where m is the difference in mass
between the parent and products.
~ 4.3 MeV is released in this reaction
Most of the Energy is released in the form of Kinetic Energy (heat).
Fission
Atomic Mass Units1u = 1/12 mass of Carbon-12
27 21 1.6605 10 931.5 /u x kg MeV c
238.0508u 234.0436u 4.0026u
238.0508 234.0436 4.0026 0.0046m u u
2 2 2.0.0046 (931.5 / ) 4.3E mc u MeV c c MeV
Super Useful
ANN m
M
(M is the atomic mass which is also the number of
moles in 1 gram. Avogadro’s Number is the number
of particles in a mole, N is the number of particles
present with Activity A)
Number Particles:
All Elements Have IsotopesSame # of protons - different # of neutrons
Atomic Mass of an Element is an average of all Isotopes
Isotopes have the same chemistry as the atom.
This is why radioactive isotopes can be so dangerous.
The body doesn’t see the difference between water made
with hydrogen and water made with tritium.
If Helium loses a proton,
it becomes a different element
Isotopes and Elements
If Helium loses one of its
neutrons, it becomes an
isotope
p
nn
e
3He
p
pn
e
e
3H =T
The Hydrogen Atom
• One electron orbiting a nucleus
• 1 proton = Z = atomic number
• 0 neutrons = N
• Total mass = A = Z+N =1
• Singly ionized Hydrogen is missing one electron = 1H+
• Add a neutron and you have Deuterium = 2H = D
• Add 2 neutrons and you have Tritium = 3H = T
p
e
1H
The Helium Atom
• Two electrons orbiting a nucleus with:
2 protons = Z = atomic number
2 neutrons = N
• Total mass = A = Z+N
• Singly ionized Helium is missing one
electron = 4He+
• Doubly ionized Helium is missing both
electrons = a particle = 4He++
p
pn
n
e
e
4He
Nuclei• The volume of the nucleus (assumed to be spherical) is directly proportional to the total number of nucleons
• This suggests that all nuclei have nearly the same density– Since r3 would be proportional to
A
• Nucleons combine to form a nucleus as though they were tightly packed spheres
• Average radius is
• ro = 1.2 x 10-15 m
• A is the mass number
1 3
or r A
Strong Force is STRONGER than
the Coulomb Force over short
distances: Short Range Force
~100Strong CoulombF F
Over a range of 10-15 m.
Why are Atoms Not Stable?
Why do Atoms Decay?
As nuclear size
increases, the distance
between nucleons
increases and the strong
force becomes too weak
to overcome the
Coulomb electrical
repulsion.
The nucleus is unstable
and can decay.
Stable Nuclei
Neutrons:
Nuclear Glue
With few exceptions,
naturally occurring stable
nuclei have N Z.
For Z 20, N = Z is stable.
Elements with Z 83 are
unstable and spontaneously
decay until they turn into
stable lead with Z = 82.
Binding EnergyIt takes energy to break up an atom.
Energy must be put into a system to break it apart.
That energy is converted to mass.
That energy is called the Binding Energy.
Eb = (Zmp + Nmn – MA) x 931.494 MeV/u
The masses are expressed in atomic mass units.
Add the atomic mass of the electron to the proton.
Binding Energy per NucleonThe most stable atoms have the most Binding Energy per nucleon.
Radioactive Atoms mutate by fission or fusion until they have
maximum Binding Energy per nucleon which occurs at Ni-62.
Eb = (Zmp + Nmn – MA) x 931.494 MeV/u
Mass per NucleonThe smaller the mass per nucleon, the greater the binding energy.
Elements fission down or fuse up to Iron, the most stable element,
releasing energy by E = mc2.
Fission
Fusion
Binding Energy per Nucleon
For energy release in fusion or fission, the products need to have a
higher binding energy per nucleon (proton or neutron) than the
reactants. As the graph above shows, fusion only releases energy for
light elements and fission only releases energy for heavy elements.
https://www.youtube.com/watch?v=UkLkiXiOCW
U
https://www.youtube.com/watch?v
=HCRBPZM0O1E&index=13&list
=PLaSHX1Y3kE0yjGNcRSsPhA_
ZEHIXYIE0Z
The Liquid Drop Model
1936 Bohr: Provides good agreement with observed nuclear
binding energies
2
2 3
1 2 3 41 3
1b
Z Z N ZE C A C A C C
A A
For A 15, C1 = 15.7 MeV; C2 = 17.8 MeV; C3 = 0.71 MeV; and C4 = 23.6 MeV
Magic Numbers
• The disagreement between the semiempirical formula and
experiments is plotted
• The peaks are reminiscent of the peaks in graphs of
ionization energy of atoms and lead to the shell model of
the nucleus
• These peaks are at the magic numbers of
Z or N = 2, 8, 20, 28, 52, 82
The shell model of
the nucleus, using
multielectron atoms
as an analogy, was
proposed in 1949 by
Maria Goeppert-
Mayer.
The shell model
considers each
nucleon to move
independently with an
average potential
energy due to the
strong force of
all the other nucleons.
The Shell Model
Slide 42-52
Maria Goeppert-Mayer received the
1963 Nobel Prize in Physics for her
work in nuclear physics.
The figure shows the energy diagram for 12C.
Exactly six protons are allowed in the n 1 and n 2
energy levels.
Likewise for the six
neutrons.
Thus 12C has a
closed n 2
proton shell and
a closed n 2
neutron shell.
Low-Z Nuclei
Slide 42-56
The figure shows the energy diagram for 12B.
The sixth neutron fills the n 2 neutron shell, so the
seventh neutron has to go into the n 3 energy level.
The n 2 proton shell
has one vacancy
because there are
only five protons.
12B has significantly
more nuclear energy
than 12C.
Low-Z Nuclei
Slide 42-58
Marie Curie
• 1867 – 1934
• Polish scientist
• Shared Nobel Prize in 1903 for
studies in radioactive
substances
– Prize in physics
– Shared with Pierre Curie and
Becquerel
• Won Nobel Prize in 1911 for
discovery of radium and
polonium
– Prize in chemistry
Our Friend The Atom
https://youtu.be/QDcjW1XSXN0?t=34m00s
Nuclear RadiationAtomic decay by Alpha and Beta radiation causes atomic transmutation.
Gamma radiation does not transmutate the atom, it changes its energy.
Alpha Decay• Decay of 226 Ra
• If the parent is at rest before the decay, the
total kinetic energy of the products is 4.87
MeV
• In general, less massive particles carry off
more of the kinetic energy
H eR nR a 4
2
2 2 2
8 6
2 2 6
8 8
In Fission, the alpha
particle escapes the
nucleus by Quantum
Tunneling.
In Fusion, protons fuse
to form helium by
Quantum Tunneling
through the repulsive
coulomb barrier.
Quantum
Tunneling
Beta DecayA neutron turns into a proton by emitting an electron!
Neutrino: Weak Force
1
1
X Y e
X Y e
A A
Z Z
A A
Z Z
ν
ν
Neutrino• Properties of the neutrino
– Zero electrical charge
– Mass much smaller than the electron, probably not zero
– Spin of ½ - it is a lepton.
– Very weak interaction with matter and so is difficult to detect
– in beta decay, the following pairs of particles are emitted
1
1
X Y e
X Y e
A A
Z Z
A A
Z Z
ν
ν
–An electron and an antineutrino
–A positron and a neutrino
Gamma Decay• Gamma rays are given off
when an excited nucleus decays to a lower energy state
• The decay occurs by emitting a high-energy photon
– The X* indicates a nucleus in an excited state
X X*A A
Z Z γ
12 12
5 6
12 12
6 6
B C e
C C
*
*
ν
γ
https://www.youtube.com/watch?v=aJkx6hAD-4E
The half life of a
radioactive
element is the time it
takes for a quantity
to decay to 1/2 its
original amount, N0.
Half Life ( ) λt
oN t N e
Activity: Rate of Disintegration
( )( )
dN tA N t
dt
N(t) is the # of radioactive atoms in the sample at time t.
The activity, A, is the rate at which they decay.
is the “decay constant”.
( ) 1 disintegration/secondA Becquerel Bq
A CURIE is the activity of 1 gram of Radium.
101 3.7 10 ~ Ci x Bq billion Bq
Example: Activity of 1Kg of Carbon is ~250 Bq ~ 7nCi
Inhaling a sample with 1Ci of activity will kill you.
Chernobyl released 50 million curies into the atmosphere.
The decay rate R of a sample is defined as the number of decays per second:
Ro = Noλ is the decay rate at t = 0.
( ) λt
oR t R e
( ) λt
oN t N e
The amount of undecayed radioactive particles present in the
sample at any time t is:
•λ is called the decay constant and determines the rate at which the material will decay•No is the number of undecayed nuclei at time t = 0
( )( )
dN tA N t
dt
From the activity we derive the following useful items:
Activity & Half Life dNA N
dt
0( ) tN t N e The # of radioactive nuclei present at any
time t since t = 0 when the # was N0:
0( ) / 2N t N
Decay Constant:
1/ 2 1/ 2t
e
1/ 2ln ln1/ 2t
e
1/ 2 ln 2t
1/ 2
ln 2
t (ln2=0.693)
Carbon DatingWhile alive, an organic material absorbs
radioactive C-14 from the atmosphere
and has a fixed percent of C-14 in it with
a fixed rate of radioactivity. Once the
plant dies, it stops absorbing C-14 and so
the radioactivity is reduced. Measuring
the Activity gives a measure of the
amount of C-14 remaining and thus the
date when the object died.
Carbon Half-LifeCarbon-14 decays with a halflife of about 5730 years by the
emission of an electron of energy 0.016 MeV. At equilibrium with
the atmosphere, a gram of carbon shows an activity of about 15
decays per minute.
There is 1 atom of C-14 for every 8.3x1011 atoms of C-12.
14 14
6 7C N
Activity: Rate of DisintegrationDetermine the activity of C-14 in a gram of a living organism.
There is 1 atom of C-14 for every 8.3x1011 atoms of C-12.
# C-14 atoms in 1 gram of C:
2310
11
6.02 10 12 1 141 6.0 10 14
12 8 10 12
mol x C Cg x C atoms
g mol x C
A N
10
7
0.693 16 10
5730 3.15 10
yrx atoms
yr x s
0.23Bq
1/ 2
0.693
t
0.693
5730yr
Neolithic IcemanMaterial found with the body had a C-14
activity of about 0.121 Bq per gram of carbon.
Determine the age of the Iceman’s remains.
0 0.23 @ 0A Bq t Given:
0.121 @ A Bq t now 1/ 2 5730t yr
5730ln.23/ .121 5310
0.693
yryr
0
tA A e
0ln / ln tA A e t
0
1ln /t A A
1/ 2
0.693
t
Natural Transmutation
Spontaneous FissionElements with Z 83 are
unstable and spontaneously
decay by alpha and beta
radiation until they turn into
stable lead with Z = 82.
Note: some elements can
decay by both modes.
Decay Series for U-238
Decay Series of 232Th
• Series starts with 232Th
• Processes through a
series of alpha and beta
decays
• The series branches at 212Bi
• Ends with a stable
isotope of lead, 208Pb
Radioactive SeriesNatural radioactivity: Unstable nuclei found in nature
Artificial radioactivity: Nuclei produced in the laboratory by bombarding atoms with energetic particles in nuclear reactions.
https://www.youtube.com/watch?v=9gERUtbtkRc&index=12&l
ist=PLaSHX1Y3kE0yjGNcRSsPhA_ZEHIXYIE0Z
Nuclear Reactions The structure of nuclei can be changed by bombarding
them with energetic particles
The changes are called nuclear reactions
As with nuclear decays, the atomic numbers and mass
numbers must balance on both sides of the equation
A target nucleus, X, is bombarded by a particle a, resulting in a daughter nucleus Y and an outgoing particle b
a + X Y + b
The reaction energy Q is defined as the total change in mass-energy resulting from the reaction
Q = (Ma + MX – MY – Mb)c2
Q Values for Reactions
The Q value determines the type of reaction An exothermic reaction
There is a mass “loss” in the reaction
There is a release of energy
Q is positive
An endothermic reaction
There is a “gain” of mass in the reaction
Energy is needed, in the form of kinetic energy of the incoming particles
Q is negative
The minimum energy necessary for the reaction to occur is called the threshold energy
Nuclear Reactions
• If a and b are identical, so that X and Y are
also necessarily identical, the reaction is
called a scattering event
– If the kinetic energy before the event is the
same as after, it is classified as elastic
scattering
– If the kinetic energies before and after are not
the same, it is an inelastic scattering
a + X Y + b
Our Friend The Atom
https://youtu.be/QDcjW1XSXN0?t=34m00s
Nuclear Magnetic Resonance
(NMR)
A nucleus has spin angular momentum
Shown is a vector model giving possible orientations of the spin and its projection on the zaxis
The magnitude of the spin angular momentum is
For a nucleus with spin ½,
there are only two allowed
states
Emax and Emin
It is possible to observe
transitions between two spin
states using NMR
( 1)I I h
MRI
An MRI (Magnetic Resonance Imaging) is based on NMR
Because of variations in an external field, hydrogen atoms in different parts of the body have different energy splittings between spin states
The resonance signal can provide information about the positions of the protons
https://www.youtube.com/watch?v=hlR
pl_GMPPc
Beta Decay & The Neutrino•The emission of the electron or positron is from the nucleus
•The process occurs when a neutron is transformed into a
proton or a proton changes into a neutron
•The electron or positron is created in the process of the
decay
•Energy must be conserved BUT it wasn’t! Experiments
showed a range in the amount of kinetic energy of the
emitted particles
•To account for this “missing” energy, in 1930 Pauli proposed the existence of another particle
•Enrico Fermi later named this particle the neutrino, meaning, “little neutron”
Detecting Neutrinos
50 trillion solar neutrinos pass through your body
every second. Can you detect them?
Because of the reluctance of neutrinos to react with
atomic nuclei and thus allow themselves to be captured,
very large number of neutrinos and very large detector
volumes are required.
Frederick Reines and his colleage Clyde L. Cowan, Jr.
proposed in 1953 a reactor experiment to capture
neutrinos through the reaction:
antineutrino + proton –› neutron + positron.
The target in the Reines-Cowan experiment consisted of approximately 400 litres of
water containing cadmium chloride placed between large liquid scintillation
detectors. The neutrino collides with a proton in the water and creates a positron and
a neutron. The positron is slowed down by the water and destroyed together with an
electron, whereupon two photons are created. These are recorded simultaneously in
the two detectors. The neutron also loses velocity in the water and is eventually
captured by a cadmium nucleus, whereupon photons are emitted. These photons
reach the detectors a microsecond or so later than those from the destruction of the
positron and give proof of neutrino capture.
The Nobel Prize in Physics 1995
Solar Neutrino Measurement
Detecting solar neutrinos
would be PROOF that the sun
shines from nuclear fusion.
Raymond Davis Jr’s detector, which for the first time in history
proved the existence of solar neutrinos. Over a period of 30 years
he succeeded in capturing a total of 2,000 neutrinos from the Sun
and was thus able to prove that fusion provided the energy from
the Sun. The tank, which was placed in a gold mine, contained
more than 100,000 gallons of tetrachloroethylene. A neutrino
interacts with a chlorine nucleus to produce an argon atom.
The Nobel Prize in Physics 2002
Solar Neutrino Problem
From the Davis experiment, it became clear that the
number of solar neutrinos detected was lower than that
predicted by models of the solar interior. In various
experiments, the number of detected neutrinos was
between one third and one half of the predicted number.
This came to be known as the solar neutrino problem.
The solution to the
problem is called
Neutrino Oscillations:
The neutrinos change
into each other!
According to quantum mechanics, particles sometimes behave
like waves (and vice versa). When neutrinos "mix" as described
above, they combine in the same way that waves combine. When
sound waves combine, they "beat", as depicted in the picture to
the right. Neutrinos do a similar sort of thing, except we say that
they "oscillate".
It is the flavor of the neutrino that oscillates. If a neutrino
starts out as 100% νe, as it moves along its "νe-ness" will begin
to fade, while its νμ-ness or ντ-ness grows. The νe-ness soon
reaches a minimum, and begins to increase again. Then the
neutrino once again becomes a pure νe before fading away
again. The amplitude and frequency of the oscillation depends
on the particular values of the three masses and the mixing
parameters, which are still being studied.
The Main Injector Neutrino Oscillation Search (MINOS) experiment studies a neutrino beam using two detectors. The MINOS near detector, located at Fermilab, records the composition of the neutrino beam as it leaves the Fermilab site. The MINOS far detector, located in Minnesota, half a mile underground, again analyzes the neutrino beam. This allows scientists to directly study the oscillation of muon neutrinos into electron neutrinos or tau neutrinos under laboratory conditions.
Super Kamiokande
Super-K is located 1,000 m underground in Mozumi Mine in
Japan. It consists of 50,000 tons of pure water surrounded
by about 11,200 detectors. A neutrino interaction with the
electrons or nuclei of water producing a flash of light which
can be detected. In 1998 discovered neutrino oscillations and
mass. The Nobel Prize in Physics 2002
Masatoshi Koshiba
Koshiba confrimed Davis’s results
and in 1987 detected the first cosmic
neutrinos from a supernova
explosion, capturing twelve of the
total of 1016 neutrinos that passed
through the detector.
The Oscillation Project with Emulsion-
Racking Apparatus (OPERA)
OPERA is an instrument used
in a scientific experiment for
detecting tau neutrinos from
muon neutrino oscillations.
The experiment is a
collaboration between CERN in
Geneva, Switzerland, and the
Laboratori Nazionali del Gran
Sasso (LNGS) in Gran Sasso,
Italy and uses the CERN
Neutrinos to Gran Sasso
(CNGS) neutrino beam.
Cosmic GallJohn Updike
Neutrinos they are very small.
They have no charge and have no mass
And do not interact at all.
The earth is just a silly ball
To them, through which they simply pass,
Like dustmaids down a drafty hall
Or photons through a sheet of glass.
They snub the most exquisite gas,
Ignore the most substantial wall,
Cold-shoulder steel and sounding brass,
Insult the stallion in his stall,
And, scorning barriers of class,
Infiltrate you and me! Like tall
And painless guillotines, they fall
Down through our heads into the grass.
At night, they enter at Nepal
And pierce the lover and his lass
From underneath the bed – you call
It wonderful; I call it crass.
http://www.youtube.com/watch?v=dhkCMO1lG7g