The Atomic
Nucleus     

Chapter 14








Joseph F. Alward, PhD
Department of Physics
University of the Pacific
     "I am become Death, the
         shatterer of worlds."
                Hindu god Shiva

 

 

  Isotopes
Same number
of protons, but
different
numbers of
neutrons.
Electrical and
chemical
properties are
the same, but
nuclear
properties
are different.

 

 

   Quarks and the Strong Force
Quarks are responsible for the
nuclear force between nucleons.

The nuclear force is also known
as the strong force.

The strong force is extremely
short-range compared to the
electric force.

  Unstable Nuclei
Neutrons 1-4 provide
strong forces of
attraction for the
indicated proton, but
other neutrons are too
far away to help
balance the longer-
range forces of
repulsion provided by
the many protons to
the right of the proton.

The larger the nucleus,
the more unstable it is.

 

 

 

   Uranium Decays via Alpha-Particle Emission

The first particle ejected from an unstable nucleus was called an alpha particle
because alpha is the first letter of the Greek alphabet.   It's now known to consist of
two protons and two neutrons, which is the same as a helium nucleus.

 

 

   Balancing Nuclear Disintegration Equations

   Total number of nucleons is conserved:    238 =====> 234 + 4

   Total charge is conserved:                            92 =====> 90 + 2

 

 

   Carbon-14 Decays by Beta Emission
The beta particle
is now known to
be just an electron.
Is the nucleon
count conserved?

Is the total charge
conserved?

 

 

  

   Reaching Stability Through Gamma Ray Emission
Nuclei with excess
energy emit
gamma-rays, which
are extremely short-
wavelength electro-
magnetic waves, i.e.,
very high energy
photons.

 

 

 

  

  The Geiger Counter

 

 

 

  

  The Geiger Counter

 

 

    The Cloud Chamber
Charged
particles
ionize the air.

When the
vapor is
expanded, it
cools and
droplets
condense
on the ions.

    Blocking Radiation
Alpha particles are 8,000 times
as heavy as beta particles.

Paper or clothing will block
alpha particles, while beta
particles require a few sheets
of aluminum foil.

Gamma radiation is extremely
dangerous--a thousand times
more potent than xrays.

 

  

  Radiation Sources in the United States

 

 

 

  Radioactivity in Radium Killed Marie Curie

                            88Ra226   ======> 86Rn222  + 2He4

 

 

 

 

  Marie Curie

        Marie Sklodowska Curie
                      (1867-1934)
Lithograph entitled "Radium"
appeared in the December 22,
1904 issue of Vanity Fair.		 Marie and Pierre Curie
isolated 1/30 ounce of
radium from one ton of
uranium ore.

Marie died from
radiation-induced
leukemia.

The pages of her lab
notebook were later
found to be
contaminated with
radioactive
fingerprints.

 

  Smoke Detector
Alpha particles emitted from
source ionize the air and
provide the charge necessary
to conduct current through
the air.

Charges stick to the heavy
smoke particles and the
current decreases, causing
the alarm to buzz.

 

 

 

 

    Leak Detection
Drag counter
above ground
over pipe.  
When the
counter stops
clicking, the
leak has been
found.

 

 

  

 

 Brain Surgery with the Gamma Knife

 

 

 

  Half-Life
The half-life of a radioactive
sample is average the amount
of time required for half of
the sample to disintegrate
(decay, disappear, transmute).

 

 

    Half-Life 
T1/2 = time for half the sample
            to disintegrate
----------------------------------

Suppose  a particular nucleus
has a half life T1/2   =  5 years.

If there are 1000 nuclei now,
how many will there be in 5
years?  

In 10 years, 15 years?

.

 

 

 

 

   Carbon-14 Dating


          The half-life of carbon-14 is 5730 years.

 

 

  Measuring the Age of Organic Matter
A German tourist in the
Italian Alps discovered
the remains of the
"Iceman" in the ice of a
glacier in 1991.  

 

 


  Calculating the Iceman's Age
The current activity per gram of
carbon half what it would be if
the Iceman were alive.

Since the half-life of carbon-14
is about 5700 years, the
Iceman's remains are about
5700 years old.

 

 

 

 

 

 The Shroud of Turin
Since the1354 AD, a
yellowing piece of linen
14-ft long has been
stored in Turin, Italy.  
It bears the image of a
person who seems to
be wearing a crown of
thorns.

Could the Shroud of
Turin have been the
burial cloth of a person
who died two thousand
years ago?

 

 

 

 

  Dating of the Shroud of Turin
At the time of the public exhibition of the shroud
in 1354, a bishop declared it to be fraud.  Most
religious bodies take a neutral stance on the
shroud's authenticity.

In 1988, three laboratories were given four
pieces of fabric; three were control pieces
similar in appearance, and one was a piece
from the shroud.  The labs all agreed that the
shroud was 608-728 years old, which means
that it came into existence sometime between
1260 and 1380 AD, a time span which
includes the year the shroud was first shown
to the public.

 

  

  Uranium Dating   

 

 

 

 

  Uranium Dating
Uranium-238 decays with a
half-life of 4.5 billion years,
with an end-product of
lead-206.

By measuring  the lead-206
content, the age of rocks may
be determined.

 

 

     Radon Poisoning
Uranium in earth's crust decays to
radium, which decays to radon.

Radon is an odorless, tasteless,
lighter-than-air gas which rises
from the ground through cracks
and fissures in the earth into
homes.

When breathed, the alpha-
emitting radon can cause cancer
of the lung.

Radon is the single greatest
source of radiation for humans.


 

 

    Transmuting Elements

 

 

 

 Neutron Bombardment

"Saint Rosalie Interceding for the Plague-Stricken of Palermo",
Anthony Van Dyke.		 Neutron bombardment reveals
absence of beta-emitting
manganese, once commonly
found in the brown pigment
umber.


0n1  +  25Mn55 ==> 25Mn56
                                               
 25Mn56 ===>  26Fe56  +  -1e0

 

 

  

 

 Transmuting Uranium to Neptunium

  Neutron enters nucleus and is transformed into a proton
  and an electron (which leaves the nucleus).

 

 

 

     Carbon-14 Production

  Neutron enters nucleus and kicks out a proton.
     
              0n1  +  7N14 --------->  6C14  + 1p1    		Protons and electrons (cosmic rays)
streaming into the atmosphere from
the sun cause atoms in the upper
atmosphere to transmute and release
neutrons, which convert nitrogen to
carbon-14.  

 

 

 

   Albert Einstein and Mass-Energy Equivalence

        Albert Einstein
             (1879-1955)
Mass is energy:  E = mc2   
Energy is mass:  m = E /c2		 When a uranium nucleus
splits, the mass of the
remnants is less than the
original mass. The difference
appears as light, heat, and
kinetic energy.

 

 

 Nuclear Fission
Average number of neutrons
released is 2.5.

Combined kinetic energy of
particles is about 200 MeV.

100,000,000 times more
energy than is released when
coal is burned:

C + O2 => CO2
 (about 2 eV)

 

 

 

  

 (Slow neutrons cause fission)
Slow neutrons are required.
A chain reaction occurs if
more than one neutron
goes on to cause another
fission.
Neutrons can be slowed by
bouncing them off of small
objects, such as carbon
nuclei.
One pound of U-235, if
completely fissioned, yields
the same energy as
100,000,000 pounds of coal.

 

 

 

 Cadmium Control Rods Absorb Neutrons

Enrico Fermi
supervised
construction of the
world's first nuclear
reactor.
 Cadmium is a good absorber of neutrons.

 

 

 

 

 World's First Controlled Nuclear Chain Reaction

 Handball court under the bleachers at the University of Chicago, 1942.  Uranium-235 is at
 the center of the stack of graphite blocks; the carbon acts as a moderator, slowing neutrons.

 

  

  The Manhattan Project 

 Oak Ridge, Tennessee.  60,000 workers worked for three
 years to separate 2 kilograms of uranium-235 from
 uranium-238.

 

 

  Critical Mass

  The smaller the sphere, the greater the ratio of surface area to volume, and the
  greater the percentage of neutrons which escape the sphere before causing
  fission.  
 
  Critical mass--or, critical size--is that mass value at which an average of more
  than one neutron per fission is used to cause another fission.

 

 

  Fission Bomb Idealized
Two sub-critical masses
are smashed together to
create a super-critical
mass.

 

  Trinity Test Site

5:30 am, July 16, 1945, Alamogordo, New Mexico.
Dr. Robert J. Oppenheimer and
Maj. Gen. Leslie L. Groves,

 

 

  

 The First Atomic Bomb

  "Little Boy", two feet in diameter, ten feet long, 9000
  pounds, dropped on Hiroshima, Japan, was a uranium
  bomb, equivalent to 20,000 tons of explosive.

 

 

 

 

 

 

 Little Boy and Fat Man

  Little boy is on the left.

 

 

 

 

 

   Atomic Bomb Targets

The only nuclear weapons used in anger were the two atomic bombs dropped in 1945.

 

 

     

 

  

   The Scorched Remains

  Nagasaki, Japan
    Nagasaki survivor. (Click here for panoramic view of  Hiroshima.)

 

 

 

    Atomic Cannon

Test Site:  Frenchman Flat,  Nevada, May 25, 1953.

Equivalent to 15,000 tons of TNT.

Height of blast:  524 feet.

History of the Bomb

 

 

  Atomic Blast
  (Before playing, turn off CD player and turn up volume.)

On May 25, 1953, a 280 mm cannon fired an atomic
projectile a distance of 7 miles at the Nevada Test Site.
Twenty 280 mm cannons were manufactured. None
were used in battle.

 

   

   Radiation Sickness
Dose
(rems)		          Effect
50-300 Sickness
400-500 Lethal   50%   (LD50)
Above 600 Lethal 100%   (LD100)

 

   The Reactor Vessel
The water in the reactor vessel has
three purposes.

The water, being composed of
relatively light molecules, acts as a  
moderator.  In Fermi's reactor,
carbon in the form of graphite was
the moderator.

Water also acts to remove heat
from fuel rods which otherwise
would melt.

The heated water, converted to
steam, is then converted into
electrical energy. 

 

 

 

 A Nuclear Reactor
Heat generated by fission
in uranium rods creates
steam which turns turbine
blades connected to a
coil of wire in magnetic
field.

 

 

 

   Nuclear Power in Germany

 

 

 

 

   The China Syndrome

What would happen if the water was lost?

 

 

 

 

 Discoverer of Nucleus Was Wrong about Nuclear Power

Rutherford at 1911 Solvay Conference

 

 

 

 

   

    Fusion 

 Fusion is the opposite of fission.  Deuterium must be
 moving extremely fast to fuse.

 

 

    Fusion in Stars

10 million degrees at the core
 causes fusion of hydrogen into
 helium.

 

 

 

  Deuterium-Tritium Fusion
Laser evaporates D-T, creating
a "plasma" of charged particles
which push away from one
another.  The reaction force
compresses and heats core.

 

 

 

  Fusion Reactor

NOVA Laser Facility, Lawrence         Plastic target shells to contain
Livermore Laboratory.                         D-T fuel shown on a quarter.

 

 

 Thermonuclear Weapons
The hydrogen bomb uses an atomic bomb as the heat source to
to fuse hydrogen into helium.  The so-called H-bomb is vastly
more destructive than fission bombs.  The Hiroshima bomb had
had explosive power of about 20,000 tons of TNT; H-bombs
commonly have 50-500 times the power (1-10 megatons).

Several hydrogen warheads are mounted on some of our
missiles, and each warhead, upon re-entering the atmosphere,
is independently targeted at a different city.

 

  Mass is Energy and Energy is Mass
The work done per nucleon
adds energy to each nucleon,
which appears as increased
mass.

Nucleons broken out of the
nucleus weigh more outside
than they do inside.

 

 

 Fusion versus Fission

  If the final products have less mass than the reactants, energy is released.

 

 

 

    Fission versus Fusion