Radiation & Radiation & RadioactivityRadioactivity

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?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 Are there different types of radiation?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 RadiationElectromagnetic RadiationRadiation 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 RadiationParticle RadiationRadiation 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 RadiationIonizing 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 RadiationIonizing vs. Non-Ionizing Radiation

Electromagnetic Radiation

Particle Radiation

Non-ionizing Radiatio

n

• Radio waves• Microwaves• Visible light

IonizingRadiatio

n

• Ultraviolet rays• X-rays• Gamma rays

• Alpha particles• Beta particles

Credit: Canadian Nuclear Association

What is radioactivity, or What is radioactivity, or radioactive decay?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 strontium-90, plutonium-239, carbon-14, uranium-235, and iodine-131.

What types of radiation are What types of radiation are emitted during radioactive decay?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 x-rays)

◦ If a person is exposed to gamma rays, severe damage can be caused to their internal organs

Credit: Wikipedia

How is radioactivity measured?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

Hear what a Geiger counter sounds like: http://www.geigercounters.com/Geiger.wav

Credit: ThinkQuest

The Radioactivity iLabThe Radioactivity iLab

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

In this lab, you can study how the intensity of radiation changes over distance.

What is strontium-90?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.

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

Credit: eHow