Name: ______________________________________
Chapter 10 Notes
A. Radioactivity – the process in which an unstable atomic nucleus emits charged particles and
energy
a. Radioisotope – any atom containing an unstable nucleus
i. Unlike stable isotopes, radioisotopes spontaneously change into other isotopes
over time. When the composition of a radioisotope changes, it is said to
undergo nuclear decay. During nuclear decay, atoms of one element can
change into atoms of a different element altogether.
b. Nuclear radiation – charged particles and energy that are emitted from the nuclei of
radioisotopes. Common types of nuclear radiation include alpha particles, beta
particles, and gamma rays.
Radiation Type
Alpha particle
Beta particle
Gamma ray
Description
Nucleus emits 2 p+ and 2 n0 (like a
helium nucleus).
Electron emitted from unstable nucleus
(a neutron decomposes into a p+ and e-).
Energy waves traveling through space at
the speed of light. They are emitted when
a nucleus loses energy.
Symbol Charge
Shielding

+2
Paper or clothing

-1
Thin sheet of metal
0
Several centimeters
of lead or several
meters of concrete

c. Background radiation – nuclear radiation that occurs naturally in the environment.
Radioisotopes in air, water, rocks, plants, and animals all contribute to background
radiation but levels are generally low enough to be safe
d. Nuclear radiation can ionize atoms. When cells are exposed to nuclear radiation, the
bonds holding together proteins and DNA molecules may break. As those molecules
change, the cells may no longer function properly.
i. Radon gas is a potentially dangerous natural source of alpha particles because
it can be inhaled. Radon with an atomic mass of 222 is formed through a series
of nuclear decay that begins with uranium in rocks deep underground. As
radon is produced it seeps upward toward the surface. It sometimes collects in
the basements of buildings that lack proper ventilation and prolonged
exposure to radon can lead to lung cancer.
B. Nuclear Decay
a. One clue that can reveal the age of an object is how many radioactive nuclei it
contains. Because most materials contain at least trace amounts of radioisotopes,
scientists can estimate how old they are based on rates of nuclear decay.
b. Half-life – the time required for one half of a sample of a radioisotope to decay. Every
radioisotope decays at a specific rate that can be expressed as a half-life and this
value can vary from fractions of a second to billions of years.
c. Unlike chemical reaction rates, which vary with the conditions of a reaction, nuclear
decay rates are constant (they do NOT depend on temperature, pressure, or surface
area).
d. Artifacts are dated by measuring levels of carbon-14 (6 protons, 8 neutrons), which
has a half-life of 5730 years. Carbon-14 is formed in the upper atmosphere due to the
effects of cosmic rays. Carbon reacts with oxygen in the atmosphere and forms carbon
dioxide. As plants absorb carbon dioxide during photosynthesis, they maintain the
same ratio of carbon-14 to carbon-12 as in the atmosphere. Likewise, animals have
the same ratio of carbon isotopes as the plants they eat. When a plant or animal dies,
however, it can no longer absorb carbon. From this point on, the organism’s carbon14 levels decrease as the radioactive carbon decays. In radiocarbon dating, the age of
an object is determined by comparing the object’s carbon-14 levels with the carbon14 levels in the atmosphere. For example, if the ratio of carbon-14 to carbon-12 in a
fossil is half the ratio in the atmosphere, then the organism lived about 5730 years
ago. Radiocarbon dating can be used to date any carbon-containing object less than
50,000 years old but objects older than that contain too little carbon-14 to be
measurable.
C. Transmutation – the conversion of atoms of one element to atoms of another. It involves a
nuclear change, not a chemical change.
a. Nuclear decay is an example of a transmutation that occurs naturally. Scientists can
perform artificial transmutations by bombarding atomic nuclei with high-energy
particles such as protons, neutrons, or alpha particles.
b. Transuranium elements – elements with atomic numbers greater than 92
(uranium). These elements are radioactive and generally not found in nature.
Scientists can synthesize these elements by the artificial transmutation of a lighter
element.
i. Although most transuranium elements have only been produced for research,
some are synthesized for industrial or consumer use. Americium is a
transuranium element used in smoke detectors. As it decays, it emits alpha
radiation that ionizes the air inside a smoke detector to produce an electric
current. When smoke enters the detector, it disrupts the current and the alarm
sounds.
c. Sometimes transmutations will not occur unless the bombarding particles are moving
at extremely high speeds. Scientists use particle accelerators where charged particles
can be accelerated to speeds very close to the speed of light. The fast-moving particles
are guided toward a target where they collide with atomic nuclei. With the help of
particle accelerators, scientists have produced more than 3,000 different isotopes.
i. Scientists also conduct collision experiments in order to study nuclear
structure and more than 200 different subatomic particles have been detected.
The main three particles (p+, n0, e-) are made up of smaller particles called
quarks.
D. Fission and Fusion
a. Strong nuclear force – the attractive force that binds protons and neutrons together
in the nucleus. It does not depend on charge and over very short distances it is much
greater than the electric forces among protons.
i. A nucleus becomes unstable, or radioactive, when the strong nuclear force can
no longer overcome the repulsive electric forces among protons (this happens
in nuclei with 83 or more protons)
b. Fission – the splitting of an atomic nucleus into two smaller parts. In nuclear fission,
tremendous amounts of energy can be produced from very small amounts of mass.
i. Chain reaction – a series of fission reactions triggered by neutrons released
during the fission of a nucleus
1. Nuclear weapons are designed to produce uncontrolled chain reactions.
The heat from controlled chain reactions can be used to generate
electricity but this also generates radioactive waste.
c. Fusion – a process in which the nuclei of two atoms combine to form a larger nucleus.
A small fraction of the reactant mass is converted into energy.
i. The sun and stars are powered by the fusion of hydrogen into helium.
ii. Fusion requires extremely high temperatures. Within the sun, temperatures
can reach 10,000,000 ˚C and matter exists as plasma.
iii. Plasma – a state of matter in which atoms have been stripped of their
electrons. It is like a gas containing nuclei and electrons.
iv. Fusion may someday provide an efficient and clean source of electricity but
scientists need to achieve high temperatures to start the reaction and they
must contain the plasma.