Chapter 25
25.1

Marie Curie was a Polish
scientist whose research led
to many discoveries about
radiation and radioactive
elements. In 1934 she died
from leukemia caused by her
long-term exposure to
radiation. You will learn about
the various types of radiation
and their effects.
25.1
 Marie Curie (1867-1934) and Pierre Curie (1859-1906)
were able to show that rays emitted by uranium atoms
caused fogging in photographic plates.
 Marie Curie named the process by which materials give off
such rays radioactivity.
 The penetrating rays and particles emitted by a radioactive
source are called radiation.
25.1
 Nuclear reactions differ from chemical reactions in a
number of important ways.
 In chemical reactions, atoms tend to attain stable electron
configurations by losing or sharing electrons.
 In nuclear reactions, the nuclei of unstable isotopes, called
radioisotopes, gain stability by undergoing changes.
 In the periodic table, radioactive elements have mass
numbers in parentheses.
 Reference table N
25.1
◦ An unstable nucleus releases energy by emitting
radiation during the process of radioactive decay.
25.1

Types of Radiation
◦ What are the three main types of nuclear radiation?
25.1
 The three main types of nuclear radiation are alpha
radiation, beta radiation, and gamma radiation.
 Reference table O
25.1
◦ Alpha Radiation
Alpha radiation consists of helium nuclei that have been
emitted from a radioactive source. These emitted
particles, called alpha particles, contain two protons and
two neutrons and have a double positive charge.
Note: In a nuclear decay equation, mass and charge are
conserved!
25.1
25.1
◦ Beta Radiation
 An electron resulting from the breaking apart of a
neutron in an atom is called a beta particle.
25.1
 Carbon-14 emits a beta particle as it undergoes
radioactive decay to form nitrogen-14.
25.1
25.1
◦ Gamma Radiation
 A high-energy photon emitted by a radioisotope is
called a gamma ray. The high-energy photons are
electromagnetic radiation.
25.1
 Alpha particles are the least penetrating. Gamma rays
are the most penetrating.
25.1
25.2

Radon-222 is a radioactive isotope that is
present naturally in the soil in some areas. It
has a constant rate of decay. You will learn
about decay rates of radioactive substances.



Radioactive substances decay at a constant
rate regardless of factors such as
temperature and concentration.
Radioactive decay is a random event.
Decay continues until a stable isotope is
formed.
◦ Some radioisotopes have a long decay series.
25.2
Stable Isotope



The time it takes for half the atoms in a
sample to decay is called the half-life.
Each isotope has its own unique half-life.
The shorter the half-life, the less stable it is.
Reference table N

If a 100 g sample has a half-life of 5 days:
◦
◦
◦
◦
◦
After 5 days ½ (50g) will remain undecayed
After 10 days ¼ (25g) will remain undecayed
After 15 days 1/8 (12.5g) will remain undecayed
After 20 days 1/16 (6.25g) will remain undecayed
And so on…
25.2
 The ratio of Carbon-14 to
stable carbon in the
remains of an organism
changes in a predictable
way that enables the
archaeologist to obtain an
estimate of its age.

Radioactive decay is measured with a Geiger
counter.
◦ A Geiger counter records individual decay events.

Graphing decay allows determination of the
half-life.
25.2

Transuranium elements are synthesized in
nuclear reactors and nuclear accelerators.


The conversion of an atom of one element to
an atom of another element is called
transmutation.
What are two ways that transmutation can
occur?

Transmutation can occur naturally by
radioactive decay.
◦ a single nucleus undergoes decay

Transmutation can also occur artificially
when particles bombard the nucleus of an
atom.
◦ at least two reactants produce the target material

A nucleus is bombarded with high-energy
particles to bring about a change.

Two types:
◦ Bombarding with charged particles: protons or
alpha particles.
 Particle accelerators use magnetic or electrostatic
fields to accelerate particles towards the target.
 Cern video
◦ Bombarding with neutrons.
 Neutrons are obtained as by-products of nuclear
reactors.
 The first artificial transmutation reaction involved
bombarding nitrogen gas with alpha particles.
 The elements in the periodic table with
atomic numbers above 92, the atomic
number of uranium, are called the
transuranium elements.
◦ All transuranium elements undergo transmutation.
◦ None of the transuranium elements occur in nature,
and all of them are radioactive.
25.3

The sun is not actually
burning. If the energy
given off by the sun were
the product of a
combustion reaction, the
sun would have burned out
approximately 2000 years
after it was formed, long
before today. You will learn
how energy is produced in
the sun.
25.3

Nuclear Fission
◦ What happens in a nuclear chain reaction?
25.3
 When the nuclei of certain isotopes are bombarded
with neutrons, they undergo fission, the splitting of a
nucleus into smaller fragments.
25.3
◦ In a chain reaction, some of the neutrons produced
react with other fissionable atoms, producing more
neutrons which react with still more fissionable
atoms.
25.3
 Nuclear Fission
25.3
A Nuclear Power Plant
25.3

Nuclear Waste
◦ Why are spent fuel rods from a nuclear reaction
stored in water?
25.3
 Water cools the spent rods, and also acts as a radiation
shield to reduce the radiation levels.
25.3

Nuclear Fusion
◦ How do fission reactions and fusion reactions
differ?
25.3
 Fusion occurs when nuclei combine to produce a
nucleus of greater mass. In solar fusion, hydrogen
nuclei (protons) fuse to make helium nuclei and two
positrons.
25.3
◦ Fusion reactions, in which small nuclei combine,
release much more energy than fission reactions, in
which large nuclei split.
25.3
 The use of controlled fusion as an energy source on
Earth is appealing.
 The potential fuels are inexpensive and readily available.
 The problems with fusion lie in achieving the high
temperatures necessary to start the reaction and in
containing the reaction once it has started.
25.4

In a smoke detector,
radiation from the Americum
nuclei ionizes the nitrogen
and oxygen in smoke-free
air, allowing a current to
flow. When smoke particles
get in the way, a drop in
current is detected by an
electronic circuit, causing it
to sound an alarm. You will
learn about some of the other
practical uses of radiation.

C-14 is used to date fossils.

U-238 is used to date rocks.

Radioisotopes are used to trace chemical
pathways in biological systems.
Radioisotopes are used to determine minute
thicknesses such as plastic wrap and
aluminum foil.
 Gamma radiation is used to irradiate foods
to kill bacteria and make the foods last
longer.


Radioisotopes with short half-lives that are
quickly eliminated from the body are used as
tracers in medical diagnoses and treatments.
◦ I-131 is used to detect and treat thyroid disorders.
◦ Co-60 is used in cancer treatments.
◦ Tc-99 is used to detect tumors.
25.4
 This scanned image of a thyroid gland shows where
radioactive iodine-131 has been absorbed.



In medical treatments radiation can destroy
normal cells as well as cancerous cells.
Radiation leaking from a nuclear power plant
can cause mutations that could be inherited.
Spent fuel rods are a disposal concern. They
are still radioactive and potentially
dangerous.