INTRODUCTION

Nuclear radiation is energy in the form of particles or electromagnetic (EM) waves. This form of energy can be produced in a number of ways, including nuclear reactions (e.g. fission or fusion), spontaneous nuclear decay, or by various other particle interactions. There are four main types of nuclear radiation that we will discuss: gamma, alpha, beta, and neutron. Gamma radiation is electromagnetic waves of very short wavelength, high energy, and high penetrating ability. Alpha radiation consists of charged particles that have 2 protons and 2 neutrons. Alpha's relatively large size and charge give it a very low penetrating ability. Beta radiation is fast moving electrons or positrons whose small size and charge combine to give it a penetrating ability greater than alpha but less than gamma. And finally, neutron radiation consists of fast moving neutrons with penetrating ability and damaging effects dependent upon the neutron's energy.

Since radiation cannot be detected directly by our senses, we must use some observable detection method that utilizes the interaction of the radiation with matter. There are several methods, but the most common is the Geiger tube. In a Geiger tube, the particles or photons from a radiation producing event will ionize gas molecules inside the tube, yielding electrical pulses that can be amplified and counted. The entire instrument is referred to as a Geiger counter.

Several skills and concepts relating to work in the field of radiation must be mastered in order to perform any meaningful investigations of the characteristics of radioactive materials. A familiarity with the operation of measuring devices, such as the Geiger counter, is necessary, as well as a basic knowledge of certain important concepts. The significance of and some causes of background radiation, for example, are important factors that must be taken into account when any study of radiation is undertaken. We will explore these concepts as well as look at some materials that are common in our everyday lives to see that radioactive substances are not as rare as one may think.
 

INSTRUMENTS AND MATERIALS

1. INSTRUMENTS:

1. Radioactivity measuring devices
2. Stopwatches
3. Metric rulers or vernier calipers

1. Salt-substitute containing potassium chloride (e.g. No-Saltâ brand)
2. Test sources (1.0 m Ci is sufficient)

Radiation is present everywhere to some extent and it must be taken into consideration in any radiation measurement. This is called background radiation and it is a result of cosmic rays and environmental radiation. Some specific sources of environmental background radiation are nuclear fallout from bomb testing, nuclear power plants, building materials, and nuclear medicine, just to name a few. Background radiation is measured with no source present. This background rate is then deducted from all measurements made with the source present.
 

PROCEDURE

1. Instruct students on the basic operation of the radiation counting device.

1. Group 1: Background radiation reading *
2. Group 2: No-Saltâ
3. Group 3: Test source at a small distance
4. If more counters are available, assign each remaining group to duplicate one of the tasks specified above.
5. Note: Separate groups as far from one another as possible to reduce erroneous readings caused by other groups' sources.

1. With no source under the counter, take a reading for at least 15 minutes, but for no longer than 30 minutes.
2. Record the total counts and the duration of the measurement.

1. Carefully pour about 1.0 g. of salt substitute onto a piece of paper or the platform to be placed under the counter. Record this mass.
2. Slide the paper or platform under the counter so that the salt substitute is directly under the detector. Select the level closest to the detector (about 1.0 cm. away). Record this distance.
3. Take a reading for at least 20 minutes, but for no longer than 30 minutes.
4. Record the total counts and the duration of the measurement.
5. Properly dispose of the salt substitute used in the experiment.

1. Obtain a test source and record its activity, calibration date, half-life, and source type.
2. Place the test source onto the stage to b placed under the counter.
3. Slide the stage into the counter so that the source is directly under the detector. Select a level that is approximately 2.0 cm. from the detector.
4. Take a reading for at least 20 minutes, but for no longer than 30 minutes.
5. While you are waiting, measure the distance between the detector and the source. Record this measurement.
6. Record the total counts and the duration of the measurement.
7. Return the test source to your instructor.

1. Have one representative from each group write their data, in table form, on the board. Data from corresponding groups can then be averaged together. (E.g. If two groups took independent background radiation readings, the average of these two should be calculated.)
2. Have all students record data from each part of the experiment on their own data sheet.

1. Determine the net counts above background for the No-Salt^®and the test source.
2. Determine the net counts per minute and counts per second for each source.
3. Using ratios, calculate the activity of the No-Salt^®.
4. What is the importance of taking a background radiation reading?
5. List several sources of background radiation.

BACKGROUND READING – Group 1
 

Total Counts	Duration (s)	CPM

 

SALT SUBSTITUTE – Group 2
 

Mass (kg)	Distance (m)	Total Counts	Duration (s)	CPM

 

TEST SOURCE – Group 3

Source Type: ________________________

Activity: ________________________

Half-life: ________________________

Calibration: ________________________
 

Distance (m)	Total Counts	Duration (s)	CPM

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