Transcript Atomic and Nuclear Physics

Atomic and Nuclear Physics
Mrs. B-Z
Early Atomic Theory and Structure
Chapter 5.1 Early Thoughts
• Roots of atomic theory are
as old as 440 B.C. with
Democritus’ idea of the
atom
• It took 2 000 years for us
to expand on this idea.
The new theory was to be
done by an English
schoolmaster John Dalton
in the early 1800s.
Dalton’s
Atomic
Theory
His theory included 6 postulates
•
• 1. Elements are made up of atoms
• 2. Atoms of the same element are alike
• 3. Atoms of different elements are different by
virtue of their size and mass
• 4. Chemical compounds are formed by the union
of two or more atoms of different elements
• 5. Atoms combine to form compounds in whole
number ratios (1:2 or 2:2, etc]
• 6. Atoms of two elements may combine in
different ratios to form more than one compound
5.4 - 5.8 Subatomic Particles
• Through the years of the late 1800s and into
the early 1900s it was determined that there
are three subatomic particles
• Electrons (discovered first)
• Protons (reasoned to exist if elements are
neutral)
• Neutrons (discovered last)
Electrons
• 1. Electron which occupies the area
outside the nucleus and has a
negative charge, relative to the other
subatomic particles it has negligible
(so small that it can be ignored) mass.
Protons
• 2. Proton which exists in the nucleus,
has a positive charge and has mass
roughly equal to neutrons
Neutron
• 3. Neutrons (discovered last] functions
as the glue that holds the nucleus
together so that the protons don’t repel
each other, it has no charge and
roughly the same mass as the proton
Create a Timeline of the Atomic
Model
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•
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•
•
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You should include the major players such as
John Dalton
J. J. Thomson
Neils Bohr
Rutherford
James Chadwick
Henri Bacquerel
Einstein
http://www.cartage.org.lb/en/themes/Sciences/Physics/At
omicphysics/Atomicstructure/AtomicTimeline/AtomicTim
eline.htm
Alpha Particle a
Characteristics
Range
Shielding
Hazards
Sources
• +2 charge
• 2 protons
• 2 neutrons
• Large mass
• Very short
range
• 1" -2" in air
• Paper
• Outer layer
of skin
• Internal
• Plutonium
• Uranium
• Radium
• Thorium
• Americium
a
a
a
a
a
Beta Particle b
Characteristics Range
Shielding
Hazards
Sources
• -1 charge
• Small mass
• Plastic
safety
glasses
• Thin
metal
• Skin and
eyes
• Can be
internal
• Radioisotopes
• Activation
Products
• Sealed
sources
• Short range
• About 10'
in air
Gamma Ray g
Characteristics Range
Shielding
Hazards
Sources
• No charge
• No mass
• Similar
to x-rays
• Lead
• Steel
• Concrete
• External
(whole body)
• Can be
internal
• X-ray
machines
• Electron
microscopes
• Sealed
sources
• Accelerators
• Nuclear
reactors
• Radioisotopes
• Long range
• About 1100'
in air
Paper Plastic Lead
Neutron Particle h
Characteristics Range
Shielding
Hazards
Sources
• No charge
• Found in
nucleus
• Water
• Plastic
• External
(whole body)
• Fission
• Reactor
operation
• Sealed
sources
• Accelerators
• Extended
range
Paper Lead
Water
Tumbling Further Down the Rabbit
Hole, Alice (or Neo)?
• By the mid 1930s, the understanding of the fundamental
structure of matter seemed almost complete. Decades
before, Rutherford had shown that atoms have relatively
tiny but massive nuclei. The quantum theory had made
sense of atomic spectra and electron orbitals. The
discovery of the neutron had explained nuclear isotopes.
So protons, neutrons, and electrons provided the
building blocks of all matter. Some puzzles remained,
however:
What holds the protons and neutrons together to form
the nucleus?
What are the forces involved in the radioactive decays of
nuclei that make alpha, beta, and gamma rays?
Enter the Accelerator!
• To study the nucleus and the interactions of
neutrons and protons that form it, physicists
needed a tool that could probe within the tiny
nucleus, as earlier scattering experiments had
probed within the atom. The accelerator is a tool
that allows physicists to resolve very small
structures by producing particles with very high
momentum and thus short wavelength. The
wavelength (l ) of the associated wave is
inversely proportional to the momentum (p) of
the particle (l = h/p), where h = Planck's
constant.
• Particle experiments study collisions of
high energy particles produced at
accelerators. In modern experiments,
large multi-layered detectors surround the
collision point. Each layer of the detector
serves a separate function in tracking and
identifying each of the many particles that
may be produced in a single collision.
Outside view of a particle
accelerator
Heavy Ion Accelerator (40 m)
Early Particle Accelerator—helped
to build the first atomic bomb on
view at the National Science
Museum in London
The Particle Explosion
• To the surprise of the physicists, accelerator
experiments revealed that the world of particles
was very rich; many more particle types similar
to protons and neutrons (called baryons) - and a
whole new family of particles called mesons were discovered. By the early 1960s a hundred
or so types of particles had been identified, and
physicists still had no complete understanding of
the fundamental forces.
The Quark Proposal
• In 1964, two physicists - Murray Gell-Mann and George
Zweig - independently hit upon the idea that neutrons
and protons and all those new particles could be
explained by a few types of yet smaller objects; GellMann called them quarks. They could explain all the
observed baryons and mesons with just three types of
quarks (now called up, down, and strange) and their
antiquarks. The revolutionary part of their idea was that
they had to assign the quarks electric charges of 2/3 and
-1/3 in units of the proton charge; such charges had
never been observed!
Anti• Antiquarks are the antimatter partners of
quarks; they have the same masses as,
but the opposite charge from, the
corresponding quarks. When a quark
meets an antiquark, they may annihilate,
disappearing to give some other form of
energy.
The Standard Model
• Nearly thirty years and many experiments later, the
quark idea has been confirmed. It is now part of the
Standard Model of Fundamental Particles and
Interactions. New discoveries have shown that there are
six types of quarks (given the odd names of up, down,
strange, charm, bottom, and top, in order of increasing
mass). Also, there are six types of particles including the
electron, called leptons. The Standard Model accounts
for the strong, weak, and electromagnetic interactions of
the quarks and leptons, and thus explains the patterns of
nuclear binding and decays.
The particles made from quarks
• The reason that fractional electric charges like those of
quarks have not been seen is that the quarks are never
found separately, but only inside composite particles
called hadrons. There are two classes of hadrons:
baryons, which contain three quarks, and mesons, which
contain one quark and one antiquark. The sample
hadron tables on the Standard Model chart give a few
examples of the many known particles. Particles made
from the first five quark types have been produced and
studied at accelerators. The top quark is so massive it
took many years and very high-energy accelerators to
produce it. The top quark was finally discovered in April
1995 at Fermilab.
The Leptons
• In contrast to the quarks, any of the six
leptons may by found by itself. The
electron is the best known lepton. Two
other charged leptons, the muon,
(discovered in 1936) and the tau
(discovered in 1975) differ from the
electron only in that they are more
massive than it.
• The other three leptons are very elusive
particles called neutrinos, which have no
electric charge and very little, if any, mass.
There is one type of neutrino
corresponding to each type of electrically
charged lepton. For each of the six leptons
there is an antilepton with equal mass and
opposite charge.
Forces and Interactions
• Now we know the building blocks of matter, but
we must also ask: What holds it together? All
forces are due to the underlying interactions of
the particles. Interactions come in four types:
gravitational, electromagnetic, strong, and weak.
Gravity is perhaps the most familiar force to us,
but it is not included in the Standard Model
because its effects are tiny in particle processes
and, furthermore, physicists have not yet figured
out how to include it.
Electromagnetic Forces
• Electromagnetic forces are also familiar; they
are responsible for binding the electrons to the
nucleus to form electrically-neutral atoms. Atoms
combine to form molecules or crystals because
of electromagnetic effects due to their charged
substructure. Most everyday forces, such as the
support of the floor or friction, are due to the
electromagnetic forces in matter that resist
displacement of atoms or electrons from their
equilibrium positions in the material.
• In particle processes the forces are
described as due to the exchange of
particles; for each type of force there is an
associated carrier particle. The carrier
particle of the electromagnetic force is the
photon; gamma ray is the name given a
photon from a nuclear transition.
Far, Far Away
• For distances much larger than the size of
an atomic nucleus, the remaining two
forces have only tiny effects -- so we never
notice them in everyday life. But we
depend on them for the existence of all the
stuff from which the world is made, and for
the decay processes that make some
types of matter unstable.
Gluons—finally a science term
that’s EASY to remember!
• The strong force holds quarks together to
form hadrons; its carrier particles are
whimsically called gluons because they so
successfully "glue" the quarks together.
The binding of protons and neutrons to
form nuclei is a residual strong interaction
effect due to their strongly-interacting
quark and gluon constituents. Leptons
have no strong interactions.
Bosons
• Weak interactions are the only processes in which a
quark can change to another type of quark, or a lepton to
another lepton. They are responsible for the fact that all
the more massive quarks and leptons decay to produce
lighter quarks and leptons. That is why stable matter
around us contains only electrons and the lightest two
quark types (up and down). The carrier particles of weak
interactions are the W and Z bosons. Beta decay of
nuclei was the first observed weak process: in a nucleus
where there is sufficient energy a neutron becomes a
proton and gives off an electron and an antielectron
neutrino. This decay changes the atomic number of the
nucleus. Beta ray is the name given to the emerging
electron.
• So now we have explained beta and
gamma rays; what about the alpha? The
alpha particle is a helium nucleus - one of
the products of a nuclear fission. Fission is
the breakup of a massive nucleus into
smaller nuclei; this occurs when the sum
of the masses of the smaller nuclei is less
than the mass of the parent nucleus. This
is a residual strong interaction effect.
What questions remain?
Are we done yet?
Not by a long shot!
• The Standard Model answers many of the
questions of the structure and stability of
matter with its six types of quarks, six of
leptons, and the four force types.
The big BUT!
• But the Standard Model leaves many other
questions unanswered: Why are there three
types of quarks and leptons of each charge? Is
there some pattern to their masses? Are there
more types of particles and forces to be
discovered at yet higher-energy accelerators?
Are the quarks and leptons really fundamental,
or do they, too, have substructure? How can the
gravitational interactions be included? What
particles form the dark matter in the universe?
• Questions such as these drive particle
physicists to build and operate new
accelerators, so that higher-energy
collisions can provide clues to their
answers.
Fission
• The process of splitting heavier nuclei into
lighter nuclei
• Neutrons released in fission reactions can start a
chain reaction
• This can lead to uncontrolled reactions.
• To control nuclear chain reactions, we use
critical mass—minimum amount of a substance
that can undergo a fission reaction and also
sustain a a chain reaction.
Nuclear Power Plant
• In a nuclear power plant, fission is used to
create power.
• The nuclear energy is transformed to heat
energy which is transformed to mechanical
energy which is transformed to make
electricity (electrical energy).
• Remember energy cannot be created nor
destroyed. It can only change forms.
Fusion
• Energy obtained from very light nuclei
combining
• At high temperatures like those of a star,
the H nuclei combine
• But there is an initial outlay of a lot of
energy to overcome the repelling forces of
the protons of the two hydrogen atoms
Fusion
• In nuclear fusion four hydrogen nuclei are
fused into a helium nucleus and two
positrons.
• Positrons are positive electrons
Negatives for Fusion
• Requires 100,000,000 K
• The sun has this temperature and that’s
where fusion occurs continually
• The sun is able to do this with extreme
pressure due to high gravity
Comparing Fission and Fusion
•Reactions
•Availability of Resources
•Safety
•Waste Material
Reactions
•Fission
–Divides a
large nucleus
•Fusion
–Combines
four nuclei
into one
helium
nucleus
Available Resource Material
• Fission
–Requires
radioactive
substances
like
uranium
• Fusion
– Currently requires an
isotope of hydrogen
called tritium which is
also radioactive
– Future: may use
hydrogen (not
radioactive)
Safety
• Fission
–Has proven
track record of
safety although
disasters like
Chernobyl
make us
realize how
dangerous it
could be
• Fusion
–Eventually if
feasible it
would be able
to produce
more energy
than fission
and have no
radiation
danger
Products
(end result of the reaction)
• Fission
– Although the
radioactive cores last
a very long time, they
eventually after nearly
100 years need to be
disposed of
– Usually we put them in
mountains to shield us
from the radiation
• Fusion
– Product is helium
which is not
radioactive nor
dangerous.
Timeline Websites -http://www.nuclearfiles.org/menu/timeline/flash_index.htm
Einstein’s Special Theory of
Relativity
• 1. Laws of physics are the same in all
frames of reference
• 2. The speed of light is the same for all
inertial observations independent of their
motion or of motion of the sources of light.
KE = w mc2 – mc2
w= time dilation
E=
2
mc
Who cares?
• This is important because it proves that the
particle has energy by virtue of its mass alone. A
stationary particle with zero kinetic energy has
potential energy that is proportional to its mass.
• Small mass is proportional to lots of energy
• Or energy and particles are interchangeable or
have a quantifiable relationship.
Large Scale (Big Picture)
• Nuclear power plants and nuclear
generators could be created
• Small amounts of radioactive uranium
would yield great amounts of energy
• The sun loses mass and turns it into
energy
• Half life is the amount of time it takes for
half of the atoms in the sample to decay
Quantum Physics
• Introduced by Plank around 1900
• Black Body – ideal system that absorbs all
radiation around it
• Produced by microscopic, charged
oscillators called resonators (only allowed
to have certain energies
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