Analyzing Radiation Introduction Radiation has always been a natural part of our environment. Radiation on earth comes from many natural sources; the origin of all types of naturally occurring radiation can be classified into three groups, terrestrial, internal, or cosmic. Depending on their location and daily activities, a person can be exposed to different levels of Naturally Occurring Radioactive Material (NORM). Man-made sources of radiation can be classified as processes that produce radioactive materials. Some industries will technologically enhance NORM, causing the resulting materials to have higher levels of radiation due to industrial processes. Materials with higher concentrations of radioactivity as a result of these industrial processes are called Technologically Enhanced Naturally Occurring Radioactive Material (TENORM). For example, the production of phosphate fertilizers uses mined phosphate rock, which also contains, uranium and radium. In order to produce the fertilizer, the phosphate rock is dissolved in an acid solution, in order to remove the phosphorus. This process leaves behind a waste product that contains a higher than normal concentration of uranium and radium. When dealing with radiation, it is important for scientists to know where it exists, and how much is present. In this investigation sources of ionizing radiation will be examined using a radiation monitor. This monitor consists of a Geiger-Mueller tube that detects when ionizing radiation is present, and tells us how much is present by electronically counting the number of interactions with the counter. In general, the following kinds of radiation are monitored for purposes of radiation protection: alpha particles, beta particles, gamma rays, x- rays and neutrons. In this investigation sources of alpha (, beta (, and gamma ( radiation will be analyzed to determine their respective properties. Read the article from the American Nuclear Society, as you read, complete the table below. The first five rows can be completed from reading the introduction and the article. The last two rows will be completed after experimental data has been collected and analyzed. Pre-Lab Exercise Type of Radiation Alpha Particle Beta Particle Gamma Ray Symbol Mass (amu) 4 1/2000 0 Charge Speed Ionizing Ability Penetrating Power Stopped By Page 1 of 6
Essential Questions How can the properties of alpha, beta, and gamma radiation be used to determine what type of radiation is being emitted from matter? What arguments can be made for and against nuclear power generation, compared to other types of power generation? Materials LabQuest 2 Radiation Monitor Forceps Ruler Sealed sources (alpha, beta, and gamma) Ring Stand 3-finger clamp Calibrated Absorber Set Safety Considerations The radioactive materials used in this lab are exempt quantities and present no unusual safety hazards; however, forceps should be used to handle radioactive materials. Pre-Lab Questions 1. More massive particles generally travel more slowly than light particles. Based on your knowledge of the properties of alpha, beta, and gamma radiation which type of radiation would you expect to interact most strongly with matter? Explain your reasoning. Keep in mind that, if the interaction with matter is stronger, the more likely the radiation will be absorbed by the matter. 2. Which type of radiation do you predict would generally, interact least strongly with matter, and be less absorbed than others? Explain your reasoning. 3. Which radiation type do you predict would have an intermediate level of interaction with matter? Why? Page 2 of 6
Procedure PART I: Background Count 1. Connect the Radiation Monitor to DIG 1 of LabQuest. Choose New from the File menu. If you have an older sensor that does not auto-id, manually set it up: a. Choose Sensor Setup from the Sensors menu. b. Select Radiation Monitor from the DIG 1 sensor list. c. Select OK. 2. Set up the data-collection mode. a. On the Meter screen, tap Mode. b. Change the data-collection mode to Selected Events, change count interval to 30 seconds, and select OK. 3. Set up the monitor. To use a Radiation Monitor, place the source with label facing down on the base of the ring stand. When you test an absorber (paper or aluminum), place the absorber between the source and the screen. 4. Determine the background count rate. a. Move all sources at least 40 cm away from the monitor. b. Start data collection to prepare the system for data collection. c. Tap Keep. Counts are taken for 30 seconds. d. Stop data collection. Open the table tab to view counts. Record the background count on the student data table. This count is to be subtracted from all other counts. PART II: Time 1. Place the Beta sealed source on the ring stand directly under the Radiation Monitor with the label facing downward. The Radiation Monitor should be 2 cm from the bottom of the ring stand and the time counter interval is 30 seconds. 2. Test the beta source for 30 second time interval. a. Start data collection to prepare the system for data collection. Tap Keep. Counts are taken for 30 seconds. b. Stop data collection. Correct the count by subtracting the background count from the count for 30 seconds and record on data table. 3. Test the beta source for 60 second time interval. a. Repeat step 2 of PART I, but set the count interval at 60 seconds. b. Start data collection to prepare the system for data collection. c. Tap Keep. Counts are taken for 60 seconds. d. Stop data collection. Correct this count by subtracting TWICE the background reading. (You must double the background reading since you doubled the time limit exposed.) 4. Test the beta source for 90 second time interval. a. Repeat step 2 of PART I, but set the count interval at 90 seconds. b. Start data collection to prepare the system for data collection. c. Tap Keep. Counts are taken for 90 seconds. d. Stop data collection. Correct this count by subtracting TRIPLE the background reading. (You must triple the background reading since you tripled the time exposed.) Page 3 of 6
PART III: Distance 1. Set up the data-collection mode. a. On the Meter screen, tap Mode. b. Change the data-collection mode to Selected Events, change count interval to 30 seconds, and select OK. 2. Place a sealed source on the ring stand directly under the Radiation Monitor with the label facing downward. The Radiation Monitor should be 5 cm from the bottom of the ring stand. 3. Test the beta source at a distance of 5 cm. a. Start data collection to prepare the system for data collection. b. Tap Keep. Counts are taken for 30 seconds. c. Stop data collection. Correct the count by subtracting the background count from the count for 30 seconds and record on data table. 4. Repeat this step three more times by moving the Radiation Monitor 10 cm from the bottom of the ring stand then 15 cm and 20 cm in any order. Be sure to subtract the background from each reading. 5. Repeat this procedure (Step 12) the other two sealed sources. The order does not matter. PART IV: Shielding 1. Set up the data-collection mode. a. On the Meter screen, tap Mode. b. Change the data-collection mode to Selected Events, change count interval to 30 seconds, and select OK. 2. Place the sealed source on the ring stand directly under the Radiation Monitor with the label facing downward. The Radiation Monitor should be 5 cm from the bottom of the ring stand. It will remain at this height for the rest of the experiment. 3. Test the source with shielding by air. a. Start data collection to prepare the system for data collection. b. Tap Keep. Counts are taken for 30 seconds. c. Stop data collection. Correct the count by subtracting the background count from the count for 30 seconds and record on data table. 4. Repeat for the other indicated shielding materials. There are several thicknesses of Al and Pb available. You may use whatever thickness you would like, just be sure that you use the same thickness for all three sealed sources (alpha, beta, and gamma) so that the results will be comparable. Repeat this procedure (Step 16) for the other two sealed sources. The order does not matter. Page 4 of 6
Data Table PART I: Background Count (for 30 seconds): PART II: Student Name: Time Effects Time Counts Background Corrected Count 30 seconds 60 seconds (x2) 90 seconds (x3) PART III: Distance Effects Alpha Source Distance 5 cm Beta Source Gamma Source 10 cm 15 cm 20 cm PART IV: Shielding Effects Alpha Source Shielding Material Air Paper Al (thickness= ) Pb (thickness= ) Other ( ) Beta Source Gamma Source Page 5 of 6
Analysis Questions 1. What is the purpose for determining the background count? 2. What were the three independent variables whose effects were studied in this experiment? 3. Describe the effect of time exposure to radiation that you found in Part II. 4. Describe the effect of distance from the radiation source that you found in Part III. 5. What differences did you discover between the different sealed sources in Part III? What does this tell you about the ability of different types of radiation to travel through air? 6. What occurred when the distance between the source and the detector doubled? What mathematical relationship can be established from the data? 7. How would you determine if a shielding material has completely stopped a particular type of radiation? 8. What differences did you discover between the different sealed sources in Part IV? What does this tell you about the ability of different types of radiation to travel through various materials? 9. Based on the data collected from your experiment, what material should be used to create a safe area that would prevent alpha, beta and gamma radiation from entering? What other precautions would you provide for persons who may be exposed to radiation? Page 6 of 6