Transcript Radiation & Radioactivity

Radiation &
Radioactivity
In preparation for the Radioactivity iLab
on iLabCentral.org
Created by: Northwestern University, Office of STEM Education Partnerships
Some information was provided by the United States Environmental Protection Agency, U.S. Dept.
of Labor Occupational Safety & Health Administration, Radiation Answers, and the Non-Destructive
Testing Resource Center.
What is radiation?

Radiation is the emission of energy from a
source that travels in the form of either:
1) waves
2) high-speed particles

As the root word “radiate” implies, when energy
travels via radiation, it spreads out in all
directions from a central point.

Many types of energy radiate through space
including light and heat.
Are there different types of
radiation?
Yes there are different types of radiation, which
can generally broken down into two
categorizations:
Electromagnetic vs. Particle radiation
Ionizing vs. Non-ionizing radiation
Electromagnetic Radiation

Radiation in the form of waves is called
electromagnetic radiation.

Electromagnetic
radiation is used in
microwave ovens,
TVs, cell phones,
power lines, and
even sunshine.

These types of
radiation have
different
wavelengths &
frequencies along
the
electromagnetic
spectrum (right).
Particle Radiation

Radiation in the form of high-speed particles is
called particle radiation.

Particle radiation happens when an
unstable nucleus releases energy in
the form of fast-moving sub-atomic
particles, in order to become more
stable.

The main examples of particle
radiation are alpha and beta
particles, which are released from
certain radioactive materials as they
decay over time.
Ionizing vs. Non-Ionizing
Radiation

Ionizing radiation has enough energy to break chemical
bonds in molecules, or remove tightly bound electrons
from atoms, which creates charged molecules or atoms (ions).
 The ionization releases energy that is absorbed by material
surrounding the ionized atom.
 Ionizing radiation can be both electromagnetic and particle
radiation.
 Exposure to this type of radiation is dangerous to humans, because
it can cause damage to living tissue.

Non-ionizing radiation has enough energy to move atoms
in a molecule, but not enough energy to remove electrons.
 Non-ionizing radiation is not as harmful to people as ionizing
radiation.
Ionizing vs. Non-Ionizing
Radiation
Electromagnetic
Radiation
Nonionizing
Radiation
• Radio waves
• Microwaves
• Visible light
Ionizing
Radiation
• Ultraviolet rays
• X-rays
• Gamma rays
Particle
Radiation
• Alpha
particles
• Beta
particles
Credit: Canadian Nuclear Association
What is radioactivity, or
radioactive decay?

Radioactivity is the spontaneous emission of
energy from an unstable nucleus of an atom
by radiation, in the form of particles or rays.

This process is also known as radioactive decay,
in which an unstable (radioactive) nucleus emits
ionizing radiation and becomes more stable.

Examples of radioactive materials are strontium90, plutonium-239, carbon-14, uranium-235,
and iodine-131.
What types of radiation are
emitted during radioactive decay?

Alpha () particles
◦ Made up of two protons and two neutrons
bound together
◦ They move slowly and can be stopped by a
sheet of paper or human skin

Beta () particles
◦ Made up of electrons
◦ They move faster than alpha but lose their
energy when they collide with other atom
◦ Some beta particles can be stopped by human
skin, but if they are ingested, the particles can
be absorbed into the bones and cause damage

Gamma () rays
◦ High-frequency photons with no charge
◦ Can penetrate paper and aluminum, but are
stopped by a thick layer of lead or concrete
(think of wearing lead vests when getting xrays)
◦ If a person is exposed to gamma rays, severe
damage can be caused to their internal organs
Credit: Wikipedia
How is radioactivity measured?

Radioactivity is measured by a Geiger counter,
which measures ionizing radiation by counting the
number of particles or rays (photons) it detects.

Geiger counters usually consist of three parts:
◦ 1) Geiger-Mueller tube – a gas-filled tube whose gas
ionizes when charged particles or photons from radioactive
material pass through the gas
◦ 2) Visual readout – a meter that keeps track of the
number of radioactive particles or photons being detected
by the Geiger counter
◦ 3) Audio readout – a meter that makes one “click” sound
for each radioactive particle or photon detected by the
Geiger counter
Credit: ThinkQuest

Hear what a Geiger counter sounds like:
http://www.geigercounters.com/Geiger.wav
The Radioactivity iLab
 In this lab, you can study how the intensity of radiation
changes over distance.

The lab equipment consists of:
◦ 1) A Geiger counter
◦ 2) A radioactive strontium-90 sample

You can set:
◦ 1) The distances in mm from the
strontium-90 source, at which radiation
can be measured (in units of “particle
counts”)
◦ 2) The measurement time in seconds
that each measurement of particle
counts will last
◦ 3) The number of trials that will be
conducted
What is strontium-90?

Strontium (Sr) is a silvery metal, and turns
yellow quickly when exposed to air.

Strontium-90 emits beta particles as it
decays. It is found in nature and often in
waste from nuclear reactors. It is
considered one of the more hazardous
components of nuclear wastes.

Credit: eHow
Strontium-90 has a half-life of 29.1 years,
meaning it takes 29.1 years for half of a
sample of strontium-90 to decay by emitting
radioactive particles.
Credit: Ricarose Roque