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Nuclear Physics and Chemistry

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Title: Nuclear Physics and Chemistry


1
Nuclear Physics and Chemistry
2
Rutherford Experiment
The existence of a nucleus was proven in an
experiment where alpha particles(helium nuclei)
were aimed at a thin layer of gold. While most
of the particles passed through to the other
side, some were deflected or even reflected.
3
Atomic radius (picometers) Nuclear radius
(femtometers)
Electron shells
Nucleon shells
Helium 31pm to
Cesium 260pm Hydrogen 1.75 fm to
Uranium 15 fm
Atomic radius (general trend)
4
Atomic Structure (particles and charge)
Electromagnetism pushes the nucleus apart
(proton to proton)
Larger nuclei unstable???
proton ()
neutron (no charge)
electron (-)
Strong force between nucleons holds the nucleus
together
(neutron to neutron neutron to proton proton
to proton)
5
Unified Atomic Mass Units (Da or u or MeV/c2)
1 dalton 1/12th mass of a Carbon atom 1.7 x
10-27 kg
6
(sum of protons and neutrons)
Atomic Mass
Atomic
(the number of protons)
7
Isotopes
Every element exists in at least a few forms,
some are stable and some are not. Since the type
of element is dependent on the number of
protons(atomic ), isotopes represent a change in
the number of neutrons, which affects atomic mass.
1 neutron
2 neutrons
Carbon - 12
(stable form)
(stable)
(unstable)
8
Radioactivity
Unstable isotopes are always changingeventually
settling as a stable isotope(transmutation).
This process is mediated by the weak force of
the nucleus. Radiation has many forms, however,
all involve the ejection of particles at very
high velocities.
proton
neutron
electron
electron antineutrino
9
Radioactive particles
10
Half Life
One by one, unstable nuclei eventually become
stable through radioactive decay. Some take
billions of years while others do so in fractions
of a second. As one of the most predictable
phenomena in nature it is surprising how
unpredictable it can be.
Half life
11
Natural Transmutation
12
Artificial Transmutation
The sum of the desires of alchemy were founded in
the elusive philosophers stone. This ethereal
substance was predicted to allow one to change
base metals into gold/silver AND provide an
elixir of longevity.
13
WIPP Waste Isolation Pilot Plant
Remember the safety precautions we had for our
labs involving radioactive materials? One of the
big problems of nuclear reactors and weapons is
the radioactive waste. One solution is to bury
the BAD stuff deep in the ground and wait for
it to decay.
14
Artificial Transmutation
Another solution lies in the transmutation of the
dangerous transUranic byproducts into STABLE
isotopes.
15
The Neutron
Clear evidence of the existence of the neutron
was not experimentally proven until 1932 by James
Chadwick. Neutrons are the magic of
transmutation. Naturally, neutrons are unstable
and turn into protons unless surrounded by
protons. Artificially, neutrons have the
potential to TRANSFORM elements. (more on this
later)
16
Fission
When large, neutron heavy, nuclei are struck by a
neutron, they may undergo fission. During this
reaction, the parent element transmutes into two
daughter elements while releasing large amounts
of energy and more neutrons.
17
Chain reaction
In a large sample of fissile material(nuclei that
can undergo fission reactions), a self sustaining
reaction can begin. The ejected neutrons from
one fission event will bring about another and
another
18
Controlled Fission Chain Reaction
In a nuclear reactor, engineers need a reaction
that can be sped up or slowed down. The secret
involves slowing down or stopping the ejected
neutrons(nuclear moderation).
Control Rods- made of neutron absorbing material
Fuel Rods- made of fissile material that
undergoes chain reaction
19
Uncontrolled Chain Reaction
The first nuclear weapons capitalized on the vast
amount of energy that can be released during an
unbridled fission reaction.
20
Gun Type Fission Bomb (Little Boy)
A conventional chemical explosive is used to
create a forceful collision between two masses of
highly enriched Uranium. Since only certain
isotopes of Uranium undergo the fission reaction,
enrichment entails increasing the concentration
of these isotopes.
21
Implosion Type Fission Bomb (Fat Man)
High explosive lenses focus the detonation of a
conventional explosive on a mass of enriched
plutonium. The force of the explosion compresses
the plutonium to many times its normal
densitysetting off the fission reaction.
22
Efficiency
The challenge of yielding the most powerful
atomic weapon lies in maximizing the fission
chain reaction before the bomb destroys itself.
Little Boy 1.38
Fat Man 13
23
Boosting
To increase the efficiency of the FISSION
reaction, deuterium and/or tritium gas can be
inserted at the core of the fissile
uranium/plutonium sphere. These heavy forms of
hydrogen are able to undergo FUSION and allow the
chain reaction to proceed at a much faster and
more efficient rate. The energy boost from
fusion itself is very small.
24
Hydrogen Isotopes
The most abundant form of hydrogen(protium) has
an atomic number AND mass of 1. Hydrogens other
flavors include isotopes with one(deuterium) and
two(tritium) additional neutrons.
Protium
Deuterium
Tritium
25
The Coulomb Barrier(challenge of fusion)
Since electromagnetism exerts its force over
longer distances and like charges repulse one
another, the difficulty involved with fusion
lies in getting the nuclei close enough to each
other so that the strong force, which works
over short distances, can take hold and pull them
together.
electromagnetism


26
Energy and Mass
Weak EM
Unopposed SNF
Equilibrium EMSNF
Strong EM
Opposed SNF
This relationship is the basis of Einsteins
equation EMC2. Essentially, nucleons have a
greater mass when they are NOT bound to the
nucleus. The increased mass outside the nucleus
is attributed to the force required to PULL the
nucleons apart when they are in a nucleus.
27
Breaking the Coulomb Barrier
The only two ways scientists on Earth can fuse
nuclei is through particle acceleration or by
thermonuclear means. Deuterium and Tritium are
the fuels of choice since their binding forces
are stronger than Protium(normal hydrogen).
Large Hadron Collider
George
28
Nuclear Fusion
By using the energy of the implosion and thermal
energy of the fission reactions, heavy isotopes
of hydrogen, in a plasma state, will undergo
thermonuclear fusion to form a helium atom. This
reaction produces a great deal of energy and fast
moving neutrons to sustain it.
Higher mass
deuterium
tritium
ENERGY
helium
neutron
Lower mass
29
Thermonuclear Weapons(hydrogen bombs)
The principle behind a fusion weapon lies in
using a boosted fission reaction to initiate a
secondary fusion reaction. In a nutshell,
expanding gases, superheated plasma,
electromagnetic radiation, and high speed
neutrons from the fission reaction are
coordinated in such a way that fuel in the
secondary stage of the bomb fuses.
30
Energy Yield
The standard for establishing the energy output
of atomic weapons is TNT(trinitrotoluene). 1
Megaton of TNT contains enough energy to power
100,000 households for one year. Modern weapons
in the United States arsenal range from .3
kilotons to 1.2 Megatons.
Little Boy 15 kilotons
Tsar Bomba 50 Megatons
Castle Bravo 15 Megatons
Supernova 1028 Megatons
31
Stellar Fusion
Only the massive gravity produced by large
collections of matter can initiate, maintain, and
control a fusion reaction of common
hydrogen(protium). Thus, the starting mass of a
star determines its lifespan, energy output, and
types of fusion that can occur.
32
These helium nuclei fuse to form a Beryllium
nucleus
The deuterium nuclei fuse with 2 hydrogen nuclei
The energy that reaches Earth comes in the form
of high energy electromagnetic radiation(photons).
4 hydrogen nuclei
fuse to form 2 deuterium nuclei.
which sheds two hydrogen nuclei
to form 2 helium isotopes.
and transmutes into helium.
33
Fission vs. Fusion energy(periodic table)
Fusion reactions with elements LIGHTER than iron
result in exothermic reactionsin other words,
they give off energy.
In fission reactions, the opposite general trend
applies. Lighter elements tend to require
energy(endothermic) to split, while heavier
elements liberate energy(exothermic).
Fusion reactions with elements HEAVIER than iron
result in endothermic reactionsit takes energy
to make the reaction occur.
Stellar nucleosynthesis refers to the fusion of
elements up to and including iron.
34
Supernova Nucleosynthesis
Although lighter elements generally undergo
fusion while heavier elements undergo fission,
there are rare events where heavier elements will
fuse. When large stars produce supernovae, the
output of energy is so great, that elements
heavier than iron are fused. Besides their
immense thermonuclear energy output, stars are
the nurseries for ALL the elements of the cosmos.
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