Chapter 8
Nuclear Chemistry
Radiation
• The emission of energetic particles
• The study of it and the processes that
produce it is called nuclear chemistry.
• Unlike the chemistry we have studied to
this point, nuclear chemistry often results
in one element changing into another one.
Tragedy
•
•
•
•
•
April 26, 1986, 1:24 am
V.I. Lenin nuclear power plant
Chernobyl, USSR
Explosions in reactor 4
31 immediate deaths, 230 hospitalizations,
countless exposures to high level radiation
• The aftermath continues to this day.
• Ordinary chemistry
– Atomic and molecular changes involving
electrons
– Attainment of the stable octet configuration
• Nuclear chemistry
– Atomic changes involving the nuclei
– Nuclei emit energetic particles we call
radiation
Becquerel
• Discovered that his paper-wrapped
photographic plate was exposed by
uranium-containing crystals…
• Which disproved his hypothesis linking the
exposure to UV light and
phosphorescence…
• But it revealed a brand new phenomenon
which he termed the emission of uranic
rays
Curie
• Discovered two new emitters of uranic
rays, one was a new element (polonium)
• Since the rays were not unique to
uranium, a new term – radioactivity
Radioactivity
• Characterized by Rutherford
• The result of nuclear instability
Alpha Radiation
• Composed of two protons and two neutrons
• Represented by the symbol for a helium
nucleus
• High ionizing power
• Low penetrating power
Beta Radiation
• An energetic electron represented by the
symbol (beta particle symbol here)
• Smaller than alpha particles, so more
penetrating
• But this also means less ionizing power
In beta decay, a neutron converts to a proton,
emitting an electron and increasing the atomic
number by 1.
Gamma Radiation
• An energetic photon emitted by an atomic
nucleus
• Represented by the symbol 
• Gamma rays are electromagnetic
radiation, not matter.
• Highest penetrating power, lowest ionizing
power
ISOTOPE STABILITY
• some isotopes are more stable than others
•
-nuclear stability correlates with the ration of protons
in the isotope (proton/neutron ration of 1 is stable)
•
-nuclei with greater than 84 protons tend to be
unstable
•
-isotopes containing 2, 8, 20, 50, 82, or 126 protons
or neutrons are stable (indicate energy levels in nucleus)
•
-isotopes with even numbers of protons or neutrons
are generally more stable than those with odd numbers
Half-Life
• The time required for half of the nuclei in a
sample to decay
Half-Life
• What does At-212 become if a beta and a
gamma particle are both emitted?
• Answer:
212
At
85
212
0
+
Rn
-1
86
e
+

Balance this:
Gallium 64 emits a beta particle
Answer:
64
Ga
31
64
Ge
32
0
+
e
-1
Balance this:
Polonium 210 loses an alpha particle
Answer
210
Po
84
206
Pb
82
+
4
2
He
Nuclear Fission
• General idea: If
nuclei emit particles
to form lighter
elements, they might
also absorb particles
to form heavier
elements.
• The result would be a
synthetic element.
• Fermi hoped to make a synthetic element
with atomic number 93.
• He detected beta emission following his
neutron bombardment of uranium.
• Subsequent experiments by Hahn,
Meitner, and Strassman seemed to
confirm Fermi’s work.
Puzzling Evidence
• Just before the outbreak of WWII, Hahn,
Meitner, and Strassman reported that no
heavier element was detected, rather two
lighter ones.
• Previous nuclear processes had always
been incremental.
• Contradicting all previous experiments in
nuclear physics, they proposed a model
for the fission of uranium atoms on
absorption of neutrons.
Large amounts of energy were also emitted
during fission.
• Weeks later, U-235 fission was proposed
as the basis for both a chain reaction and
a bomb of inconceivable power.
The Manhattan Project
• Could Nazi Germany develop a fission
bomb?
• Albert Einstein communicated this
possibility to President Roosevelt.
• The largest scientific endeavor of its time,
the race to beat Germany to the atomic
bomb was code named “Manhattan
Project”.
Enrico Fermi and Leo Szilard constructed the
first nuclear reactor at the University of
Chicago; they achieved a self-sustaining
controlled fission reaction lasting 4.5 minutes.
Critical Mass
• Lesser masses of fissionable material will
not undergo self-sustaining fission; too
many neutrons are lost to the
surroundings instead of being absorbed by
other U-235 nuclei.
• After the successful controlled reaction,
the goal became the construction of a
device where fission would spiral out of
control.
Collection and synthesis of fissionable fuel (U-235
and Pu-239) were pursued at Oak Ridge, TN and
Hanford, WA. J. Robert Oppenheimer directed
bomb design at Los Alamos, NM.
Two designs were constructed and a successful
test carried out on July 16, 1945. Two atomic
bombs (one uranium and one plutonium) were
dropped on Japan only weeks later.
Nuclear Power
• Bombs are designed such that fission escalates
to produce an explosion.
• Nuclear reactors are designed to produce a
controlled fission reaction.
– Uranium rods are interspersed with control rods of
neutron-absorbing material, usually boron or
cadmium.
• Heat of fission boils water to produce steam
which turns the turbine to produce electricity.
Nuclear vs. Coal-burning
Power Plants
• Nuclear
– Uses 100 lb. of fuel
per day
– Produces enough
electricity for a city of 1
million people
– Does not produce air
pollution, greenhouse
gases, or acid rain
– Problems include
waste disposal and
accidents
• Coal-burning
– Uses 5 million lb. of
fuel to produce an
equivalent amount of
energy
Waste Disposal
• Uranium oxide pellet fuel assemblies are
replaced with fresh fuel every 18 months.
• Most spent fuel is currently stored on site.
• 1982 Nuclear Waste Policy Act
– Established a program to build an
underground nuclear waste repository
• Yucca Mountain, NV is the controversial
site of this much-delayed project.
Nuclear Accidents
• Nuclear power plants cannot detonate like
nuclear explosions.
– Enriched uranium at 3% U-235 vs. 90% U235
• Three Mile Island – March 28, 1979
• Chernobyl – April 26, 1986
• Superior power plant design in the U.S.
has meant no accidental nuclear deaths,
nevertheless public support for nuclear
power is chilly.
Mass Defect
• Mass defect is the difference between the
experimentally measured mass of an atom, and
the sum of the masses of individually measured
protons, neutrons, and electrons.
• The missing mass was converted to energy
when elements form from constituent protons
and neutrons.
• This energy is related to the mass defect by
Einstein’s equation E = mc2.
Nuclear Binding Energy
• Einstein’s equation E = mc2, represents the
energy that holds a nucleus together.
• The highest values for this binding energy are
for elements with mass numbers close to 56.
• The products have higher binding energy
than the reactants; it follows that the
products weigh less.
• The missing mass is converted to energy
according to E = mc2.
• This difference in binding energy is the
source of the energy liberated in fission.
Fusion
• Like fission reactions, the products of fusion
have higher nuclear binding energies, so energy
is released.
• Fusion releases ten times more energy per gram
than fission.
• Fusion is responsible for the sun’s energy and is
the basis of modern nuclear weapons.
Controlled Fusion
• Advantages
– Potential for an almost limitless source of
energy for society
– Less radioactive waste products
– Naturally occurring deuterium in water
• Disadvantages/Obstacles
– High temperatures required and a lack of
materials available to contain them
– Current production methods consume more
power than they produce.
Radiation and Human Life
• Radiation can destroy biological
molecules.
• Low-level alpha emitters present little
danger externally but, once ingested, have
access to internal organs.
• Danger is usually overstated by the
popular press.
Measuring Exposure
• rem – most common unit for measuring
human exposure
• Exposure, on average, per year, is 1/3 rem
Possible Effects
• The human body can repair itself and suffer
no adverse effects.
• Abnormal growth can begin that leads to
cancerous tumors.
• Damage of intestinal lining leads to radiation
sickness, hampering the intake of nutrients
and water.
• Damage to the immune system allows
infection to go unchecked.
• Genetic defects in offspring have occurred in
laboratory animals.
Radon
• Radon is the single greatest source of human
radiation exposure.
• Naturally occurring uranium deposits in the
earth lead to the collection of radon in
residential basements.
• Significance of radon as a health threat is
controversial.
Carbon Dating
• Carbon-14 is made in the upper
atmosphere: p. 235 equation here
• The half-life of C-14 is 5730 years.
• Levels of C-14 in carbon-based artifacts
are compared to modern levels as an age
signature.
The Age of the Earth
• U-238 is used to measure longer periods
of time.
• It decays to lead with a half-life of 4.5 X
109 years.
• Lead levels in artifacts are used as an age
signature.
Nuclear Medicine
• Diagnosis
– Radioactive elements (like technetium-99m)
will concentrate in specific areas of interest in
the body.
– Gamma emitters will expose photographic
film, allowing images of organs to be
recorded.
• Therapy
– Radiation can destroy cancerous tumors.
– Minimizing exposure of healthy tissue is a
challenge.