Section 11-4

DETECTING AND USING RADIOACTIVITY

LEARNING TARGETS

• List and describe the tools used to detect radioactivity

• Explain some of the uses and potential dangers of radioactivity

INTRODUCTION• Radioactivity cannot be seen or felt

• The instruments scientists use to detect and measure radioactivity include the electroscope, the Geiger counter, the cloud chamber, and the bubble chamber

DETECTING AND MEASURING RADIOACTIVITY1. Electroscope•Made of a metal rod with two thin metal leaves at one end• If an electroscope is given a negative charge, the leaves

separate•Radioactive substances remove electrons from molecules of air•When a radioactive substance is brought near a charged electroscope, the air molecules that have become positively charged attract the negative charge on the leaves• This causes the leaves to collapse

1. Geiger Counter• An instrument that produces an electric current in the

presence of a radioactive substance• Consists of a tube filled with a gas such as argon or helium • When radiation enters the tube through a thin window at

one end, it removes electrons from the atoms of the gas• The gas becomes positively charged and sets up an

electric current that is amplified and fed into a recording device• The number of clicks or flashes per unit time indicates

the strength of radiation

3. Cloud Chamber• Contains a gas cooled to a temperature below its

usual condensation point• When a radioactive substance is put inside the

chamber, droplets of the gas condense around the particles

4. Bubble Chamber• Contains a superheated liquid which is hot enough

to boil but does not• When radioactive particles pass through the

chamber, they cause the liquid to boil

PUTTING RADIOACTIVITY TO WORK• In industry, radioactive isotopes, have additional uses• They can be used to find leaks or weak spots in metal pipes and to

study wear on surfaces that rub together• They can also be used to follow an element through an organism, or

through an industrial process• Such radioactive elements are called tracers• The tracer iodine-131 can be used to study the function of the

thyroid gland• Radioactivity is also used to destroy unhealthy cells, such as those that

cause cancer• Finally, radioisotopes can be used to kill bacteria that cause food to

spoil

http://www.summitradiology.com/nuclear-medicine.php

DANGERS OF RADIATION

• The same radiation used to treat disease can also cause it • Radiation has the potential to damage DNA• Large doses of radiation can cause reddening of the skin, a

drop in white blood cell count, nausea, fatigue, and loss of hair

• Metals and other structural materials can also be weakened by intense radiation

• Today people who work with radioactive materials wear radiation-sensitive badges that serve as a warning of unsafe levels of radiation

http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/radiation_safety_equipment/film_badges.htm