Introducing Radioactive Decay
• This diagram could almost
illustrate a pinball game. It
actually illustrates the
process of radioactive
decay. This is a process
that occurs all around you.
It may even occur inside
your body.
• Bellwork: Based on the
diagram, what happens
during radioactive decay?
• A: The nucleus of a
radioactive atom gives off
radiation in the form
of energy and a particle of
matter.
Radioactive Decay
• Radioactive decay is the process in which the
nuclei of radioactive atoms emit charged
particles and energy, which are called by the
general term radiation.
• Radioactive atoms have unstable nuclei, and
when the nuclei emit radiation, they become
more stable.
• Radioactive decay is a nuclear—rather than
chemical—reaction because it involves only the
nuclei of atoms. In a nuclear reaction, one
element may change into another.
Types of Radioactive Decay
• There are several
types of
radioactive decay,
including alpha,
beta, and gamma
decay. In all three
types, nuclei emit
radiation, but the
nature of the
radiation differs.
• The Table shows
the radiation
emitted in each
type of decay.
Type
Alpha decay
Beta decay (Two types,
beta-plus and betaminus)
Gamma decay
Radiation Emitted
alpha particle
(2 protons and
2 neutrons) + energy
beta particle (1 electron
or 1 positron) and either
a proton or a neutron
that changes into the
other + energy
energy (gamma ray)
It’s Elemental
• Both alpha and beta decay change the number of protons in
an atom’s nucleus, thereby changing the atom to a different
element. In alpha decay, the nucleus loses two protons. In
beta decay, the nucleus either loses a proton or gains a
proton. In gamma decay, no change in proton number occurs,
so the atom does not become a different element.
• Q: If the radioactive element polonium (Po) undergoes alpha
decay, what element does it become?
• A: From the periodic table, the atomic number of polonium is
84, so it has 84 protons. If it loses two protons through alpha
decay, it will have 82 protons. Atoms with 82 protons are the
element lead (Pb).
Dangers of Radioactive Decay
•
•
•
•
The charged particles and energy
emitted during radioactive decay
can harm living things, but the
three types of radioactive decay
aren’t equally dangerous. That’s
because they differ in how far they
can travel and what they can
penetrate.
Alpha particles can travel only a
few centimeters through air. They
can burn the skin but not
penetrate it.
Beta particles can travel up to a
meter through air. They can
penetrate and damage skin.
Gamma rays can travel thousands
of meters through air. They can
penetrate and damage cells deep
inside the body.
Summary
•Radioactive decay is the process in which
unstable nuclei of radioactive atoms become
stable by emitting charged particles and
energy.
•There are three types of radioactive decay:
alpha decay, beta decay, and gamma decay.
Alpha and beta decay change one element into
another. Gamma decay does not.
•Radioactive decay can damage living things.
Alpha decay is the least damaging, and gamma
decay is the most damaging.