Outline Chapter 8a The Nucleus
8-1. Rutherford Model of the Atom
8-2. Nuclear Structure
8-3. Radioactive Decay
8-4. Half-Life
8-5. Radiation Hazards
8-6. Units of Mass and Energy
8-1. J.J. Thompson’s Plum
Pudding Model of the Atom
In 1898, British physicist J. J. Thompson described
atoms as positively charged lumps of matter with
electrons embedded in them.
8-1. Rutherford Model of
the Atom
In 1911, an experiment
suggested by British
physicist Ernest
Rutherford shows that
alpha particles striking
a thin metal foil are
deflected by the strong
electric fields of the
metal atom's nuclei.
8-2. Nuclear Structure
The nucleus of ordinary hydrogen is a single positively charged
proton; other nuclei contain electrically neutral neutrons as well
as protons. The number of protons is the atomic number.
8-2. Nuclear Structure
Isotopes are atoms of the same element that differ in the number
of neutrons in their nuclei. A nucleus with a particular composition
is called a nuclide and is represented by
A
ZX
where X = chemical symbol, Z = atomic number, and A =
mass number or the number of protons and neutrons in the
nucleus. A nucleon is a neutron or proton; the mass number of a
nucleus is the number of nucleons (protons and neutrons) it
contains.
Isotope Notation
Protons Neutrons Electrons
6
6
6
6
7
6
6
8
6
How many protons, neutrons and electrons in
each of the following:
protons neutrons electrons
23Na
11
12
11
7
7
7
14N
38Ar
18
20
18
35Cl
17
18
17
36Cl-1
17
19
18
56Fe
26
30
26
8-3. Radioactive Decay
In 1896, Henri Becquerel
discovered that uranium
gives off a penetrating
radiation, a property
called radioactivity.
Soon after Becquerel's
discovery, Pierre and
Marie Curie discovered
two more radioactive
elements: polonium and
radium. Radioactive
decay occurs when a
nucleus emits particles or
high frequency em
waves.
Band of Stability
The stable nuclides
have approximately
equal numbers of
protons and
neutrons (N/Z ratio
= 1) in the lighter
elements (Z = 1 to
20) and more
neutrons than
protons in the
heavier elements
(N/Z ratio > 1).
Figure 15.4
15-
8-3. Radioactive Decay
Nuclear Decay
After Decay
• When an atomic nucleus is unstable, decay
brings the nucleus to a more stable state
• The final product of nuclear decay is a stable
element
• This may require numerous decay steps
– Uranium 238 requires 8 alpha decays and 6 beta
decays to eventually become Lead 206, a stable
element
238
92
U
206
82
Pb
Discovery of Po and Ra
Marie Skłodowska
Curie (1867-1934)
Marie, and her husband
Pierre, analyzed a ton of
Uranium ore. After removing
the uranium the radioactivity
increased. This led to the
discovery of Polonium, more
radioactive than uranium,
named after here home
country of Poland. After
removing the Polonium the
radioactivity increased
again. This led to the
discovery of a small amount
in their hand of Radium, so
radioactive that it glowed in
the dark.
(1943 Marie Currie Movie 2hrs)
8-4. Half Life
The half-life of a radionuclide (radioactive nuclide) is
the time needed for half of an original sample to decay.
http://www.eserc.stonybrook.edu/ProjectJava/Radiation/
http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html
8-5. Radiation Hazards
The SI unit of radiation dosage is the sievert (Sv); 1 Sv is the
amount of radiation having the same biological effects as
those produced when 1 kg of body tissue absorbs 1 J of xrays or gamma rays. Maximum dose is 20 mSv per year.
Predicted Indoor Radon Levels
red zones-greater than 4 pCi/L
orange zones-between 2 and 4 pCi/L
yellow zones-less than 2 pCi/L
Santa Barbara/
Ventura Counties
highest levels
15-
Preventing Radon in Homes
15-
Fig.8.6
A radionuclide tracer can be seen here. The
different colors are different amount of tracer
absorption. Cancerous bone absorbs more
tracer. The white spot indicates a tumor.
8-6. Units of Mass and the
Electronvolt
The atomic mass unit (u) is the standard unit of atomic
mass:
1 atomic mass unit = 1 u = 1.66 x 10-27 kg
The electronvolt (eV) is the energy unit used in atomic
physics:
1 electronvolt = 1 eV = 1.60 x 10-19 J
The megaelectronvolt (MeV) is equal to 1 million eV:
1 megaelectronvolt = 1 MeV = 106 eV = 1.60 x 10-13J
The energy equivalent of a rest mass of 1 u is 931 MeV.
8-7. Binding Energy
All atoms have less
mass than the
combined masses of
the particles of which
they are composed.
The energy equivalent
of the missing mass of
a nucleus is called the
binding energy; the
greater the binding
energy of a nucleus,
the more the energy is
needed to break it
apart.
8-8. Binding Energy per
Nucleon
The binding energy per nucleon is found by dividing the
total binding energy of the nucleus by the number of nucleons
(protons and neutrons) it contains; the greater the binding
energy per nucleon, the more stable the nucleus.
8-9. Nuclear Fission
Lise Meitner
(1878-1968)
Enrico Fermi
(1901-1954)
A chain reaction is a series of fission reactions spreading
through a mass of an unstable radionuclide such as uranium.
When a nucleus undergoes fission, two or three neutrons are
released and can cause other nuclei to split and begin a chain
reaction. The first chain reaction was demonstrated by the
Italian physicist Enrico Fermi in Chicago in 1942.
8-10. How a Nuclear Reactor
Works
A nuclear power plant transforms nuclear energy into electricity.
The chain reaction within a nuclear reactor is controlled by a
moderator which slows down neutrons. Reactors use
enriched uranium as a fuel.
ENCLOSED water circulates around fuel—gets HOT HOT HOT
Super
heated water (enclosed)
LAST, and VERY IMPORTANT is the COOLING of the whole
system. This is the ONLY WATER THAT IS NOT COMPLETELY
ENCLOSED. Usually comes from a nearby lake or river,
recirculated back into the river…
Nuclear
fuel
More ENCLOSED water is heated to boiling,
producing steam,
which turns a turbine—causing the coils of an ELECTRIC
GENERATOR to rotate---remember Ampere’s law?
NUCLEAR DECAY PRODUCES HEAT
8-11. Plutonium
When nonfissionable U-238 captures a fast
neutron, it eventually forms the fissionable
nuclide of plutonium, Pu-239, which can support
a chain reaction. Plutonium is a transuranium
element, meaning that it has an atomic number
greater than the 92 of uranium. The fissionable
plutonium produced in a uranium-fueled reactor
can be used as a fuel or in nuclear weapons.
Little Boy
Fat Man
Nuclear Bombs
Trinity Bomb Test
First nuclear bomb
http://www.metacafe.com/watch/400
824/trinity_nuclear_weapon_test/
25
Nuclear Bombs
Hiroshima bomb- Little Boy
Equivalent to 12-15 kilotons of TNT 70,000 killed immediately
and 70,000 died afterward. Half from blast, a third radiation and
rest from radioactivity
Enola Gay
Hiroshima before the bomb.
Hiroshima after the bomb.
26
Hiroshima after the blast.
The sky turned pink from gamma
rays and abut 15 seconds later the
shock wave hit.
27
Imprint of sitting person from
gamma ray incineration.
Nagasaki-Fatman bomb
Equivalent to 20-22 kilotons of TNT.
About 20,000 killed immediately and
another 20,000 died afterward. A military
target that contained a weapons factory.
28
A Nuclear World?
Nuclear energy generates about 21 percent of
the electricity produced in the United States.
Questions of safety, costs, and nuclear waste
disposal have halted construction of nuclear
reactors in the United States.
http://en.wikipedia.org/wiki/Chernobyl_disaster
A Nuclear World?
Nuclear Power plants locations
throughout the world.
Fig. 8.22
Disposal of
nuclear
wastes is a
problem.
Here a tunnel
is being
prepared to
store nuclear
waste in
Yucca
Mountain in
Nevada.
8-12. Nuclear Fusion.
Here an experimental fusion reactor at Princeton University.
This uses powerful magnetic fields to confine the fusion
material. This is called a tokamak reactor based on a Soviet
reactor.
8-12. Nuclear Fusion.
Nuclear fusion produces tremendous quantities of energy and
has the potential of becoming the ultimate source of energy on
earth.
Pons and Fleishmann at the
University of Utah
8-13. Antiparticles
An antiparticle has the same mass and general behavior as its
corresponding elementary particle, but has a charge of opposite
sign and differs in certain other respects. When an antiparticle and
its corresponding elementary particle come together, they undergo
annihilation, with their masses turning entirely into energy. In the
process of pair production, a particle-antiparticle pair materializes
from energy. Quarks make up protons/neutrons.
8-14. Fundamental Interactions
1. The strong interaction, which holds protons and neutrons
together to form atomic nuclei.
2. The electromagnetic interaction, which gives rise to electric
and magnetic forces between charged particles.
3. The weak
interaction, which, by
causing beta decay,
helps determine the
compositions of
atomic nuclei.
4. The gravitational
interaction, which is
responsible for the
attractive force one
mass exerts on
another.
8-15. Leptons and Hadrons
Leptons, which are
not affected by the
strong interaction,
have no internal
structure. Electrons
are leptons.
Neutrinos are
leptons that have no
charge and very little
mass. Hadrons,
which are affected by
the strong interaction,
are composed of
quarks; protons and
neutrons are hadrons.
8-15. Leptons and Hadrons
Physics is trying
to bring all
theories together
into one
THEORY OF
EVERYTHING.
Large Hadron Collider at the CERN laboratory between France and
Switzerland, the most powerful particle accelerator in the world.