EXPERIMENT #8:
RADIATION MAKES HOUSE CALLS

Introduction

     Radioactivity is found in the home. The news media has reported on the problem of radon, Rn, buildup in our homes. However, the news reports failed to mention that Rn is a naturally occurring nuclear decay product. It is a daughter element of uranium and thorium.
     All around us natural deposits of uranium, 235U (0.7% abundance) and 238U (99.3% abundance) and thorium, 232Th are decaying and producing many progeny. We ourselves are radioactive. Our intake of food will sometimes have traces of radioactive elements. Potassium-40 is found in many foods such as bananas and salt substitutes.


This smoke detector uses the radioactive isotope Americium as a detection device.

Objective

     To demonstrate to the student that some household items are radioactive.

Materials

Procedure

  1. Turn on the Geiger counter with the scale set to x1 and allow it to warm up for a few minutes.
  2. Take background activity measurements.
  3. Place the different materials in front of the Geiger counter.
  4. Record the reading in Table 8.1.
  5. Applying usage of the "Chart of Nuclides," recorded data in Table 8.1 and 8.2, fill in the question marks in Table 8.2 for crystal glass.

Data

Table 8.1: RADIATION IN HOME

Background __________ cpm
Sable=x1     time=60 s
Materials Counts Per Minute
Lantern mantle  
Pottery glaze  
Smoke detector  
Watch  
Glass crystal  

Table 8.2: RADIATION DECAY
Radioactive source Isotopes Radiation(s) Gamma ray energy Notes
Lantern mantle 232Th alpha rays & beta & gamma rays 0.240 MeV natural
Pottery glaze 235U, 238U alpha rays & beta & gamma rays 0.063 MeV natural
Smoke detector 241Am alpha rays & beta & gamma rays 0.059 MeV man-made
Painted watch 226Ra alpha rays & beta & gamma rays 0.0510 MeV natural
Glass crystal ?Pb ? ? MeV ?

Questions

  1. Which of the household materials had the greatest radiation intensity? The least radiation intensity?
  2. What radioactive element is present in a Coleman Mantle? In a smoke detector? In a painted watch?
  3. What unit is used to describe the magnitude of radioactive decay energies?
  4. An isotope of the element calcium has a half life of 12 years, how long will it take for 1/4 of the calcium to decay?
    a. 5 years     b. 8 years     c. 12 years     d. 16 years     e. 24 years

This document was produced by the Nuclear Science Division of the Lawrence Berkeley National Laboratory.