LabNet Geiger-Müller Interface

Transcription

1 Instruction Manual and Experiment Guide for the PASCO scientific Model SE A 7/94 LabNet Geiger-Müller Interface for use with the Mac 65 Computer Interface ADAPTER CABLE CI-6522 PLASTIC G-M DETECTO R SE-7981 SE-7985 SE by LabNet SOURCE STORACE LEAD 1994 PASCO scientific $7.50

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3 A LabNet G-M Interface Table of Contents Section Page Copyright, Warranty and Equipment Return... ii Introduction... 1 Warranty Check... 2 Using the Science Workshop Program... 3 Selecting Data Displays:... 4 Recording Data in an Experiment:... 5 Experiment 1: Introductory Activity... 7 Experiment 2: Random Events Experiment 3: Half-Life Experiment Experiment 4: Radiation Shielding Experiment 5: Inverse Square Law Appendix: Nuclear Safety Technical Data i

4 LabNet G-M Interface Copyright, Warranty and Equipment Return Please Feel free to duplicate this manual subject to the copyright restrictions below. Copyright Notice The PASCO scientific Model SE-7997 Geiger-Müller Interface manual is copyrighted and all rights reserved. However, permission is granted to non-profit educational institutions for reproduction of any part of this manual providing the reproductions are used only for their laboratories and are not sold for profit. Reproduction under any other circumstances, without the written consent of PASCO scientific, is prohibited. Limited Warranty PASCO scientific warrants this product to be free from defects in materials and workmanship for a period of one year from the date of shipment to the customer. PASCO will repair or replace, at its option, any part of the product which is deemed to be defective in material or workmanship. This warranty does not cover damage to the product caused by abuse or improper use. Determination of whether a product failure is the result of a manufacturing defect or improper use by the customer shall be made solely by PASCO scientific. Responsibility for the return of equipment for warranty repair belongs to the customer. Equipment must be properly packed to prevent damage and shipped postage or freight prepaid. (Damage caused by improper packing of the equipment for return shipment will not be covered by the warranty.) Shipping costs for returning the equipment, after repair, will be paid by PASCO scientific. Equipment Return Should the product have to be returned to PASCO scientific for any reason, notify PASCO scientific by letter, phone, or fax BEFORE returning the product. Upon notification, the return authorization and shipping instructions will be promptly issued. ä NOTE: NO EQUIPMENT WILL BE ACCEPTED FOR RETURN WITHOUT AN AUTHORIZATION FROM PASCO. When returning equipment for repair, the units must be packed properly. Carriers will not accept responsibility for damage caused by improper packing. To be certain the unit will not be damaged in shipment, observe the following rules: ➀ The packing carton must be strong enough for the item shipped. ➁ Make certain there are at least two inches of packing material between any point on the apparatus and the inside walls of the carton. ➂ Make certain that the packing material cannot shift in the box or become compressed, allowing the instrument come in contact with the packing carton. Address: PASCO scientific Foothills Blvd. Roseville, CA Credits This manual authored by: Dave Griffith Phone: (916) FAX: (916) techsupp@pasco.com web: ii

5 A LabNet G-M Interface Introduction About This Manual These instructions describe the hardware that makes up the PASCO SE-7997 Nuclear Sensor for Mac65 (CI-6550). This manual also includes a brief section about the Science Workshop program that is included with the Mac65 interface, and an experiments section that contains suggested experiments. What s Included The PASCO SE-7997 Nuclear Sensor comes in a storage box. In contains the LabNet Geiger-Müller Interface (LGI), a clamp for holding the G-M tube, a small container for storing radioactive sources (sources not included), a small container with pieces of 1 square lead, a small container with pieces of 1 square plastic, an adapter cable (Model CI-6522) for connecting the G-M tube to the Mac65 interface, and this instruction manual. LEAD ADAPTER CABLE CI-6522 PLASTIC SOURCE STORACE Additional Recommended Equipment G-M DETECTO R SE-7981 SE-7985 SE radioactive sources right angle clamp isogenerator kit (for half-life experiment) base and support rod meter stick or metric ruler Please see the PASCO catalog for more information. by LabNet Description The LabNet G-M Interface (LGI) has a sturdy acrylic housing and a built-in power supply. A neon light inside the housing indicates when the power is on. A light emitting diode (LED) inside the housing flashes when the sensor detects an event. The delicate mica window of the G-M tube allows detection of alpha, beta, and gamma radiation. The housing has two cords. One is the power cord and the other is the signal cable. The modular phone plug at the end of the signal cable connects to the CI-6522 adapter cable (included). The stereo phone plug on the end of the adapter cable goes into a digital channel on the Mac65 interface box. Plug for G-M tube Digital channels Adapter cable Figure 1 Connecting to Interface Computer Interface A Word about the LabNet Geiger-Müller Interface (LGI) The SE-7997 Nuclear Sensor for the Mac65 includes an adapter cable for connecting the G-M tube to the Mac65 interface box. With the proper adapter plugs (not included), the LabNet G-M Interface can be connected externally to the fifteen pin game port of an IBM or IBM compatible computer, or the game port of an Apple II+, IIe, IIc, or IIGS computer. An IBM adapter package (including software), and an Apple II adapter package (including software), are available from LabNet, Inc. LabNet, Inc Trailridge Road Omaha, NE phone: (402) LabNet, Inc., specializes in education-oriented computer applications. The LabNet staff has a combined total of over fifty years of experience in science and electronics education, and twenty years of experience with computers. 1

6 LabNet G-M Interface A Warranty Check The LabNet Geiger-Müller Interface (LGI) detector was designed and built with safety and ruggedness in mind; however like many Geiger-Müeller tubes, the detection end of the tube is a fragile sheet of mica so thin that the entire end window has a thickness of only about.01 inch. With reasonable care, the tube will last for many years. Tube failure can be caused by puncture or by microscopic cracking of the mica window. In either case, the mixture of gases in the tube becomes contaminated by air and the tube will no longer function. The LGI unit is permanently sealed when manufactured. There are no user-serviceable parts. Voltages above 450 volts DC are required for normal operation of the tube, and therefore, any opening of the unit represents a serious hazard and voids the warranty. LabNet will replace defective units subject to the warranty policy. Every LGI unit is operationally tested before it is shipped, however... NOTE: It is very important to protect your investment by completing the user warranty verification test as soon as possible after the LGI arrives. Here is the warranty verification test: Connect the Mac65 interface to the computer, turn on the interface, and then turn on the computer. ➀ Carefully remove the plastic protective cap from the end of the LGI unit. Using the clamp supplied, mount the LGI unit on a base and support rod (not included) with a right angle clamp (not included). ➁ Position a known, active, beta or gamma source directly under the detector and adjust the height of the detector so that it is 1 to 2 cm above the radiation source. ➂ Plug the power cord from the unit into a 120 volt outlet. The small neon power light at the rear of the circuit board should light up. ➃ Connect the signal cable from the LGI into the CI-6522 adapter cable. Attach the stereo phone plug of the adapter cable to digital channel 1 of the Mac65 (CI-6550) interface. The signal cable is no more dangerous to handle than a typical telephone cord. The order of steps 3 and 4 is not critical. ➄ Begin the Science Workshop program. The counts LED light that is located on the LGI circuit board near the Geiger-Müeller tube should be flashing faintly and randomly. 2 ➅ In the Experiment Setup window, click-and-drag the digital sensor plug icon to the digital channel 1 icon. Select Geiger Counter from the list of sensors. Click-and-drag a Digits data display icon to the sensor icon. Select Counts per Time Period from the list of calculations to display. Click on MON or press Command-M on the keyboard to begin monitoring the data. The Digits data display should begin showing the counts per second. (Click on STOP or press Command-(period) to end.) Figure 2 Experiment Setup window and Digits data display If the unit does not seem to operate, refer to the Troubleshooting section below. Troubleshooting The LGI unit is very reliable. Most apparent failures can be easily corrected by the user. Please read the suggested solutions below. Neon power light not ON Check the wall outlet with some other appliance. Neon light may be defective. If the neon light is the only problem, the unit will still operate. Contact PASCO about repairs. Green LED counts light does not flash when near a known active beta or gamma source. LED may be defective. If the LED is the only problem, the unit will still operate. Contact PASCO about repairs. The G-M tube may be defective. To test further, tune a small transistor radio to a quiet spot on the dial and place the radio next to the LGI. You should be able to hear the transistor radio speaker clicking when a known active beta or gamma source is near the detector tube. Contact PASCO about repairs.

7 A LabNet G-M Interface Using the Science Workshop Program User s Guide and Balloon Help The Mac65 (CI-6550) computer interface User s Guide gives a complete description of the Science Workshop program. Please refer to it for more information. The Science Workshop program also has over a hundred Balloon Help messages (available under System 7) covering every feature. To use Balloon Help, select Show Balloons from the Help menu (indicated by the question mark icon in the upper right corner of the screen). Experiment Setup Window: Part of the Experiment Setup window looks like the front of the Mac65 interface box. There are icons to represent the four digital and three analog channels. The control section of the Experiment Setup window has REC (record), MON (monitor), and STOP buttons as well is information about recorded data sets and buttons for REC OPT (recording options), the Science Workshop signal generator, and the Notes window. Signal generator button Setting Up an Experiment Notes window button NOTE: Some of the suggested activities in the experiments section may be included as Science Workshop documents on the Experiment Guide diskette that comes with the Mac65 interface. Check the listing in the User s Guide. If the experiment is included on the Experiment Guide diskette, doubleclick on the icon or name of the experiment to begin. Starting Science Workshop Double click on the icon of the Science Workshop program to open the application. After the opening title screen appears, an untitled document opens with an Experiment Setup window. Two of the icons found below the interface box on the Experiment Setup window represent the plug on the end of a sensor s cable. One icon represents the stereo phone plug on a digital sensor, or the plug on the end of the CI Adapter Cable used with the LabNet G-M tube. The other icon represents the DIN plug on an analog sensor such as a temperature sensor. Digital sensor plug icon Analog sensor plug icon Record button Monitor button Stop button Mac65 interface front panel Analog Output Signal icon (1) Between the sensor plug icons are six icons representing the different types of data displays in Science Workshop. They are the Digits display, Meter display, Scope display, FFT display, Table of data, and Graph. (2) (3) (4) (1) Data Sets list Digital sensor plug icon (2) Recording (3) Signal Generator Options button Window button Data display icons (4) Notes Window button Voltage Sensor icon Analog sensor plug icon 3

8 LabNet G-M Interface A Sensors Click-and-drag the digital sensor plug icon to the digital channel 1 icon (just as if you were plugging the sensor into the interface box). Select Geiger Counter from the list of digital sensors. Click OK to return to the Experiment Setup window. You will see the sensor icon in the area below digital channel 1 with an arrow pointing at the channel. Selecting Data Displays To select a data display, click-and-drag the icon of the data display you want to use to the sensor icon. Because the Science Workshop program can modify the recorded data from the Geiger Counter sensor, a list of calculations will appear. Select the calculation or calculations that you want, and then click Display. List of digital sensors Double-click on the sensor icon to open the Sensor Setup dialog box. The data display will open with the name of the calculation you selected in the title bar, and icons to indicate the sensor and the channel. If you selected a Digits display or a Meter, for example, one display or meter will open for each calculation you picked. If you selected a Table or Graph, the table will have one column for each calculation you picked, or the graph will have one plot for each calculation you picked. Sensor Setup dialog box One second (1.000 sec) is the default setting for the Count Time Period. To change the Count Time Period, highlight the default value, type in the new value and then click on OK. 4

9 A LabNet G-M Interface Recording Data in an Experiment Setup the equipment for the experiment as described in the experiment section or the Notes window in the Science Workshop document. When you are ready to record data, do one of the following: Click on REC button Press Command-R on the keyboard Select Record from the Experiment menu If you want to monitor data instead of record it, do one of the following: Click on MON button Press Command-M on the keyboard Select Monitor from the Experiment menu When you are ready to end data recording, do one of the following: Click on STOP button Press Command-(period) on the keyboard Select Stop from the Experiment menu See the Science Workshop User s Guide for more information about monitoring and recording data, setting up Start and Stop conditions for recording data, recording multiple sets of data, using different data displays, and other details about data collection and analysis. Deleting Data To delete data, click on the run of data in the data sets list in the Experiment Setup window. Press delete on the keyboard. An alert dialog box will prompt you to either cancel the process, or continue. You can select more than one set of data at a time using the shift key or command key. See the User s Guide for details on deleting data sets. Select the location where you want the document to be stored, and enter a filename for the document. Quitting Science Workshop To end an experiment, select Quit from the File menu or press Command-Q on the keyboard. If you recorded data or modified the Experiment Setup window, you will be prompted to either quit without saving the data and/or changes, cancel the Quit, or save the data and/or changes. Saving an Experiment When you are finished with an experiment, you can save the Science Workshop document you created, and the data you recorded. To save an untitled experiment, select Save from the File menu. To save the changes you have made to a previously saved experiment, select Save As from the File menu. 5

10 LabNet G-M Interface A Copy-Ready Experiments The following experiments are written in worksheet form. Fell free to photocopy them for use in your lab. The experiments are not written to be performed in any particular order, although it is recommended that the introductory activity be done first. NOTE: The first paragraph in each experiment lists all the equipment needed to perform the experiment. Be sure to read this equipment list first, as the requirements vary with each experiment. 6

11 A LabNet G-M Interface Experiment 1: Introductory Activity Purpose Theory Setup: EQUIPMENT NEEDED - Macintosh computer - LGI and CI-6522 Adapter Cable - Mac65 Interface (CI-6550) - Base and support rod (ME-9355) - Science Workshop program - Right angle clamp (SE-9444) - Printer (optional) - Radioactive sources (alpha, beta, gamma)* (* The PASCO SN-8110 Radioactive Sources (set of 3) are mounted in 2.5 cm diameter sealed plastic disks. No licensing is required. They consist of Polonium-210 (alpha, gamma), Strontium-90 (beta), and Cobalt-60 (beta, gamma).) The LabNet Geiger-Müller Interface (LGI) provides simple, flexible, ways for you to explore the characteristics of radioactive materials. You can collect real time data for radioactive substances and display the data in several ways. Any collected data can be saved and recalled later. Try the suggested activities listed below to become familiar with the nuclear sensor. Refer to the Technical Data Appendix for information about the operation of a Geiger-Müller tube and typical tube characteristics. ➀ Connect the Mac65 interface to the computer, turn on the interface, and turn on the computer. ➁ Carefully remove the plastic protective cap from the end of the LGI. Clamp the LGI unit vertically about 1 or 2 cm above a beta source. Plug the LGI power cord into a wall outlet. Connect the modular phone plug on the end of the signal cord into the CI-6522 Adapter Cable. Plug the adapter cable into digital channel 1. ➂ Prepare the computer to record data. Find the Science Workshop document titled Nuclear Sensor in the Sensor Files folder on the Experiment Guide diskette. Double click on the icon or name of the document. Follow the instructions in the Notes window. The document will open with a Digits display for Counts per Second and a Graph display of Counts per Second versus Time. (Note: To bring the Digits or Graph display to the top, click on its window or select the name of the display from the list at the end of the Display menu.) The Graph is set to display counts per second for 100 seconds. Data Recording: Reminder: You can start recording data by doing the following: click on the REC button, press Command-R on the keyboard, select Record from the Experiment menu. To end data recording, click on the STOP button, press Command-(period) on the keyboard, select Stop from the Experiment menu. 7

12 LabNet G-M Interface A ➃ Begin recording data. Data should appear in the Digits display and also on the Graph. After data recording stops, Run #1 will appear in the list of data sets in the Experiment Setup window. ➄ Replace the beta source with an active alpha source and repeat the data recording. The new data will be plotted on top of the data from Run #1 in the Graph. (Note: The scale for the beta source may be too high for the data from the alpha source. If you can t see the data, click on the Zoom Out tool in the vertical scroll bar to rescale the vertical axis.) After data recording stops, the Run #2 data will be the only data visible in the Graph. ➅ ➆ Replace the alpha source with an active gamma source and repeat the data recording. Finally, remove all sources and repeat the data recording to find the background count (the count of naturally occurring radiation). Analyzing the Data ➀ Select New Table from the Display menu. The Table will display the data for the last run the measurement of the background count. Click on the Digits button in the top area of the Table and change the number of digits to zero. Digits button Then click on the Statistics button in the upper left area of the Table to view the minimum, maximum, and mean of the background counts. Record the mean in Data Table 1 at the end of this section. ➁ Use the Data popup menu to select Run #3 (the data for the gamma source). Record the mean for the gamma source in Data Table 1. Use the popup menu again to select Run #2 (the data for the alpha source). Record the mean for the alpha source in Data Table 1. Select Run #1 (beta) and record the mean for the beta source in Data Table 1. ➂ Click on the Graph or select it from the list at the end of the Display menu to make it active. Use the Data popup menu in the left part of the plot to view each data run (background, gamma, alpha, and beta). For each data run, use the Smart Cursor tool (second from left, top row, lower left corner of the Graph) to find the bucket in the histogram with the highest count. Record the Bucket Max and Bucket Min for each type of radiation in Data Table 2. Optional If a printer is available, print the graph of each data run. Select Print Active Display from the File menu, or press Command-P on the keyboard. 8

13 A LabNet G-M Interface Data Table 1.1 Type of Radiation Beta Alpha Gamma Background Mean of counts per second after 100 sec. Data Table 1.2 Type of Radiation Bucket Max. Bucket Min. Beta Alpha Gamma Background Questions ➀ In the Graph, what is the general shape of the histogram for each active source? ➁ Which source has the most activity? Which source has the least activity? ➂ For each type of radiation, how does the mean of counts per second compare to the Bucket Max and Bucket Min? 9

14 LabNet G-M Interface A Notes: 10

15 A LabNet G-M Interface Experiment 2: Random Events Purpose Theory Setup: EQUIPMENT NEEDED - Macintosh computer - LGI and CI-6522 Adapter Cable - Mac65 Interface - Base and support rod (ME-9355) - Science Workshop program - Right angle clamp (SE-9444) - printer (optional) - Radioactive sources (alpha, beta, gamma)* - 1 lead square (included with SE-7997) (* The PASCO SN-8110 Radioactive Sources (set of 3) are mounted in 2.5 cm diameter sealed plastic disks. No licensing is required. They consist of Polonium-210 (alpha, gamma), Strontium-90 (beta), and Cobalt-60 (beta, gamma).) In this experiment you will explore the behavior of random radioactive events over a period of time. Radioactive decay is strange and mysterious for several reasons. Besides the obvious fact that none of our senses can detect individual decay events, the nuclear decay process seems at the same time to be random yet predictable. How can a random event be predictable? This analogy may be helpful. Think about making popcorn. As you heat the kernels of corn, it would be very difficult to say exactly which kernel is going to explode next, yet it is fairly easy simply by listening to say how many kernels pop per second. In the same way, it is impossible to say which nucleus will become unstable enough to decay next, however it is fairly easy to use a Geiger counter to count the number of nuclei which do decay per second at all the locations in the radioactive sample. If you listened to the nuclear decay of a radioactive sample with a good Geiger counter, and plotted counts per second over a period of time, what would the results look like? ➀ Connect the Mac65 interface to the computer, turn on the interface, and turn on the computer. ➁ Carefully remove the plastic protective cap from the end of the LGI. Clamp the LGI unit vertically about 1 or 2 cm above a beta source. Plug the LGI power cord into a wall outlet. Connect the modular phone plug on the end of the signal cord into the CI-6522 Adapter Cable. Plug the adapter cable into digital channel 1. ➂ Prepare the computer to record data. Find the Science Workshop document titled Random Events (Nuclear Sensor) in the Physics Experiments folder on the Experiment Guide diskette. Double click on the icon or name of the document. Follow the instructions in the Notes window. The document will open with a Table display for Counts per Second and a Graph display of Counts per Second versus Time. (Note: To bring the display to the top, click on its window or select the name of the display from the list at the end of the Display menu.) The displays are set to show counts per second for 120 seconds. 11

16 LabNet G-M Interface A Data Recording: ➃ Reminder: You can start recording data by doing the following: click on the REC button, press Command-R on the keyboard, select Record from the Experiment menu. To end data recording, click on the STOP button, press Command-(period) on the keyboard, select Stop from the Experiment menu. Begin recording. Data should appear in the Table display and also on the Graph. After 120 seconds, data recording stops and Run #1 will appear in the list of data sets in the Experiment Setup window. Record the value of the Mean in Data Table 1. ➄ Repeat data recording four more times. At the end of each data run, record the value of the Mean in Data Table 1. ➅ ➆ Repeat data recording again, but use a 1 lead square to block the path of radiation for approximately 5 seconds near the midpoint of the 120 second recording period. Record the value of the Mean in Data Table 2. Repeat data recording again, but use a 1 lead square to block the path of radiation for approximately 10 seconds near the midpoint of the 120 second recording period. Record the value of the Mean in Data Table 2. Analyzing the Data ➀ From Data Table 1, determine the overall average for the first five data runs. ➁ Switch to the Graph display. Use the Stats popup menu in the right hand area of the plot to select Histogram, 50 Divisions. Use the Data popup menu in the area to the left of the vertical axis to select Run #1. Click on the Autoscale button (top row, right hand button, lower left corner of the Graph) to resize the graph to fit the data. Study the overall shape of the histogram for Run #1. If a printer is available, print the active display. 12

17 A LabNet G-M Interface ➂ Use the Data popup menu to select Run #2. Autoscale the graph, study the overall shape of the histogram, and print the active display if possible. Repeat this process for the remaining data runs. Data Table 2.1 Trial Run #1 Run #2 Run #3 Run #4 Run #5 Average Value of the Mean Data Table 2.2 Trial Run #6 (5 second block) Run #7 (10 second block) Value of the Mean 13

18 LabNet G-M Interface A Questions ➀ How much effect did momentarily blocking the path for five seconds have on the value of the mean? How much effect did blocking the path for ten seconds have on the value of the mean? ➁ Describe in words the shape of the histogram for data runs 1 through 5. What else has a distribution of values that looks like the histogram for these data runs? ➂ Describe the shape of the histogram for data runs 6 and 7. Optional Questions ➀ Is there any way to change the average count rate for a radioactive substance? ➁ Does the average count rate remain the same until all the radioactivity stops? ➂ How has the radioactive material changed when all the radioactivity stops? 14

19 A LabNet G-M Interface Experiment 3: Half-Life Experiment Purpose Theory EQUIPMENT NEEDED - Macintosh computer - LGI and CI-6522 Adapter Cable - Mac65 Interface - Base and support rod (ME-9355) - Science Workshop program - Right angle clamp (SE-9444) - Printer (optional) - Radioactive isotope with short half-life* - Watch glass (or similar shallow dish) (* The PASCO SN-7995 Isogenerator Kit provides short-lived nuclides for half-life experiments. A solution is passed through a column containing Cesium-137 to produce Barium-137m, which has a half-life of 2.6 minutes, and emits 662 kev gamma radiation. If properly cared for, the generator can be used hundreds of times. No licensing is required.) The time required for the counts per time period of a radioactive sample to fall to half of its previous value is called the half-life of the radioactive isotope. In this experiment you will determine the half-life of a radioactive isotope. The number of counts per second (c/s) produced by a radioactive source gradually becomes smaller and smaller as time goes on. If that didn t happen, then the radioactive waste we are so concerned about these days would never become less dangerous. We know that all radioactive substances have count rates which change toward zero counts per second. Eventually, even the most dangerous radioactive waste becomes safe. This might take only minutes, but could take thousand or even millions of years, depending on the kind of nucleus involved. A simple analogy involving popcorn might help you understand how the number of counts per second can become smaller. The number of kernels per second which pop is fairly constant as the corn starts popping vigorously, but eventually the rate trails off until just a few kernels explode per second. Actually there is something about the popping corn which does not change. For popcorn it is nearly true that in each equal time interval, the same fraction of remaining unpopped kernels do in fact pop. For example, let s say that one half of the remaining unpopped kernels pop each minute. If you start with 100 kernels, then 50 pop and 50 remain kernels at the end of one minute. In the next minute half of the remaining 50 pop, so there are 25 kernels left. One more minute and half of the remaining 25 kernels pop leaving 12 or 13 kernels, and so it goes. Fewer and fewer kernels per second actually pop but the same fraction of unpopped kernels pop each minute. This is approximately how corn pops, but it is exactly the way that radioactive nuclei decay. In each unit of time, the same fraction of unchanged nuclei decay into different elements. The time required for the counts per second of a radioactive sample to fall to half of its previous value is called the half-life of the radioactive isotope. The half-life value is a property of the nucleus itself and does not depend on temperature, pressure or any other measurable property. This is a clock which can t be changed without changing the nucleus itself. What do you think a graph of counts per second would look like as time goes on for a type of nucleus which decays rapidly? 15

20 LabNet G-M Interface A Setup: ➀ Connect the Mac65 interface to the computer, turn on the interface, and turn on the computer. ➁ Carefully remove the plastic protective cap from the end of the LabNet Geiger-Müller Interface (LGI). Clamp the LGI unit vertically so it will be 1 or 2 cm above the watch glass that will hold the liquid containing the radioactive isotope. Plug the LGI power cord into a wall outlet. Connect the modular phone plug on the end of the signal cord into the CI-6522 Adapter Cable. Plug the adapter cable into digital channel 1. ➂ CAREFULLY read and follow all the instructions for preparing, using, and storing the short halflife radioactive source. Also read and follow the instructions about disposing of the liquid containing the radioactive isotope. ➃ Prepare the computer to record data. Find the Science Workshop document titled Half-Life (Nuclear Sensor) in the Physics Experiments folder on the Experiment Guide diskette. Double click on the icon or name of the document. Follow the instructions in the Notes window. The document will open with a Graph display of Counts per Time Period versus Time. Each time period is 5 seconds. NOTE: To bring the display to the top, click on its window or select the name of the display from the list at the end of the Display menu. The display is set to show counts per second for 10 minutes. ➄ Drain about 10 drops of liquid through the radioisotope cow into the watch glass. Place the watch glass under the G-M tube of the LGI. Data Recording: Reminder: You can start recording data by doing the following: click on the REC button, press Command-R on the keyboard, select Record from the Experiment menu. To end data recording, click on the STOP button, press Command-(period) on the keyboard, select Stop from the Experiment menu. ➅ Autoscale icon Begin recording. Data should appear in the Graph. After 10 minutes, data recording stops and Run #1 will appear in the list of data sets in the Experiment Setup window. Click on the Autoscale button to resize the graph to better fit the data. ➆ Dispose of the liquid containing the radioactive isotope as directed by your instructor. 16

21 A LabNet G-M Interface Analyzing the Data ➀ Use the Smart Cursor tool to find the initial count rate (counts per five seconds). Convert this value to counts per second. Record the value in the Data Table. Smart Cursor icon ➁ Use the Smart Cursor tool to find the time at which the count rate is one-half the initial count rate. Record the time in the Data Table. Convert the count rate to counts per second and record the value in the table. ➂ If a printer is available, select New Table from the Display menu, and print the Table of data. Graph the data on a piece of semi-log graph paper. (Alternative: If you have an analysis program like Graphical Analysis from Vernier Software, export the Table of data as a TEXT file, open the data in the analysis program, and use the program to create a semi-log graph of the data.) Data Table 3.1 Initial Value (c/s) Time at half-max. (half-life) Value at half-max. (c/s) Questions ➀ How long will it take for Ba-137m to decay to 1/8th of the original counts/second? ➁ From your data, what is the calculated half-life of Barium-137m? How does this compare to a handbook value? ➂ What advantage does using semi-log graph paper have compared to conventional graph paper? Optional Questions ➀ Is there any way to reduce the time it takes for Barium-137m to decay to 1% of its original activity? ➁ Does the time it takes to decay 1% of its original activity depend on how much radioactive material there is to start with? ➂ How are the Barium-137m nuclei different after they decay? What element does Barium-137m change into when it decays? 17

22 LabNet G-M Interface A Notes: 18

23 A LabNet G-M Interface Experiment 4: Radiation Shielding EQUIPMENT NEEDED - Macintosh computer - LGI and CI-6522 Adapter Cable - Mac65 Interface - Base and support rod (ME-9355) - Science Workshop program - Right angle clamp (SE-9444) - printer (optional) - Radioactive sources (alpha, beta, gamma)* - 1 lead squares ** - 1 plastic squares ** - 1 paper squares (* The PASCO SN-8110 Radioactive Sources (set of 3) are mounted in 2.5 cm diameter sealed plastic disks. No licensing is required. They consist of Polonium-210 (alpha, gamma), Strontium-90 (beta), and Cobalt-60 (beta, gamma).) (** Included with the SE-7997 LabNet Gieger Müller Interface.) Purpose The purpose of this experiment is to investigate the penetrating ability of three common types of nuclear radiation and the ability of different materials to absorb the energy associated with nuclear radiation. Theory Setup: Because in many ways nuclear radiation behaves as though the radiation were tiny bullets, it makes sense that different materials absorb the energy of nuclear radiation in different ways. The nature of the material through which nuclear radiation moves does influence how much energy is absorbed. ➀ Connect the Mac65 interface to the computer, turn on the interface, and turn on the computer. ➁ Carefully remove the plastic protective cap from the end of the LabNet Geiger-Müller Interface (LGI). Clamp the LGI unit vertically. Plug the LGI power cord into a wall outlet. Connect the modular phone plug on the end of the signal cord into the CI-6522 Adapter Cable. Plug the adapter cable into digital channel 1. ➂ Prepare the computer to record data. Find the Science Workshop document titled Shielding (Nuclear Sensor) in the Physics Experiments folder on the Experiment Guide diskette. Double click on the icon or name of the document. Follow the instructions in the Notes window. The document will open with a Table display of Counts per Time Period. Each time period is 15 seconds. Each run of data recording will last 60 seconds. The Statistics for the Table are on. (Note: To bring the display to the top, click on its window or select the name of the display from the list at the end of the Display menu.) 19

24 LabNet G-M Interface A Data Recording: Reminder: You can start recording data by doing the following: click on the REC button, press Command-R on the keyboard, select Record from the Experiment menu. To end data recording, click on the STOP button, press Command-(period) on the keyboard, select Stop from the Experiment menu. ➃ Prepare to measure the average background radiation count. Move all radiation sources at least 10 feet from the Geiger counter. Click on REC to begin recording data. The recording will automatically stop after 60 seconds. Record the Mean as the average background radiation count (per 15 second interval) in Table 1. After you record the Mean, delete the run of data by selecting it in the data sets list and pressing Delete on the keyboard. (An alert box will open to make sure you want to delete the data run.) ➄ Measure the radiation counts from an unshielded alpha source. Position the sealed alpha source 1 or 2 cm directly under the Geiger-Müller tube. Click on REC to record counts for 60 seconds. Record the Mean as the unshielded alpha source radiation count in Table 1. 20

25 A LabNet G-M Interface ➅ Now measure the radiation counts from a shielded alpha source. Click-and-hold on the Add-a- Column popup menu to add another column to the Table. Add-a-Column popup menu Select Counts Per Time Period from the popup menu. Place one small square of paper on top of the sealed alpha source, and record the counts for 60 seconds. Record the Mean as the One Layer shielded alpha source radiation count. ➆ Click-and-hold on the Add-a-Column popup menu to add another column to the Table. Select Counts Per Time Period from the popup menu. Place another small square of paper on top of the alpha source. Record the counts for 60 seconds. Record the Mean as the Two Layer shielded alpha source radiation count. ➇ Repeat the steps until you have a total of five small squares of paper on top of the alpha source. Determine and record the radiation counts for each trial. When you are done with the alpha source, delete the data runs. ➈ Replace the sealed alpha source with a sealed beta source. Repeat the steps, recording counts for the unshielded beta source and then for the source with zero through five thicknesses of paper on top. Determine and record the radiation counts per minute for each trial. When you are done with the beta source, delete the data runs. ➉ Replace the sealed beta source with a sealed gamma source and repeat the data recording process again. Determine and record the radiation counts per minute for each trial. When you are done with the gamma source, delete the data runs. Record data for all three radiation sources for two more shielding materials, thin plastic and thin lead. Follow the same procedure used in recording data for the paper shielding material. If you find that the activity falls as low as the background radiation count, then you can assume that all the energy of that particular radiation is absorbed by the shield, and additional shielding is not necessary

26 LabNet G-M Interface A Analyzing the Data Average background counts = Data Table 4.1 Radiation Counts per Fifteen Second Intervals PAPER: Layers of Shielding Material Source zero one two three four five alpha beta gamma PLASTIC: Layers of Shielding Material Source zero one two three four five alpha beta gamma LEAD: Layers of Shielding Material Source zero one two three four five alpha beta gamma Questions ➀ Which type of radiation is the most penetrating? ➁ Which type of radiation is the least penetrating? ➂ What generalization can you make about the effect of the thickness of the shielding material on the count rate? ➃ What generalization can you make about the effect of the density of the shielding material on the count rate? Optional Questions: ➀ Since the energy of the radiation is absorbed by the shield, what effect does the absorbed energy have on the shield? ➁ Why is there a difference in the penetrating ability of the three basic radiation types? ➂ How effective are other shielding materials such as air or water in stopping radiation? ➃ What material is the most effective in absorbing the energy of nuclear radiation? 22

27 A LabNet G-M Interface Experiment 5: Inverse Square Law Purpose Theory Setup EQUIPMENT NEEDED - Macintosh computer - LGI and CI-6522 Adapter Cable - Mac65 Interface - Base and support rod (ME-9355) - Science Workshop program - Right angle clamp SE-9444) - Printer (optional) - Radioactive sources (alpha, beta, gamma)* - Metric ruler (* The PASCO SN-8110 Radioactive Sources (set of 3) are mounted in 2.5 cm diameter sealed plastic disks. No licensing is required. They consist of Polonium-210 (alpha, gamma), Strontium-90 (beta), and Cobalt-60 (beta, gamma).) The purpose of this experiment is to investigate the relationship between the distance to a radioactive source and the measured activity from the source. One of the most common natural laws is the inverse square law. As one famous scientist put it, the inverse square law is characteristic of anything which starts out from a point source and travels in straight lines without getting lost. Light and sound intensity both behave according to an inverse square law when they spread out from a point source. Your intuition says that as you move away from a point source of light like a light bulb, the light intensity becomes smaller as the distance from the bulb becomes larger. The same is true for sound intensity as you move away from a small radio speaker. What may not be as obvious is that if you move twice as far from either of these sources, the intensity becomes one fourth as great, not half as great. In a similar way, if you are at the back of an auditorium listening to music and you decide to move three times closer, the sound intensity becomes nine times greater. This is why the law is called the inverse square law. Does nuclear radiation behave this way as well? If you measure the counts per second at a distance of 1 centimeter, what will the counts per second be at 2 centimeters or at 4 centimeters? ➀ Connect the Mac65 interface to the computer, turn on the interface, and turn on the computer. ➁ Carefully remove the plastic protective cap from the end of the LabNet Geiger-Müller Interface (LGI). Clamp the LGI unit vertically about 1 or 2 cm above an active beta source. Plug the LGI power cord into a wall outlet. Connect the modular phone plug on the end of the signal cord into the CI-6522 Adapter Cable. Plug the adapter cable into digital channel 1. ➂ Prepare the computer to record data. Find the Science Workshop document titled Inverse Square (Nuclear Sensor) in the Physics Experiments folder on the Experiment Guide diskette. Double click on the icon or name of the document. Follow the instructions in the Notes window. The document will open with a Table display of Counts per Time Period. Each time period is 40 seconds. Each run of data recording will last 120 seconds. The Statistics for the Table are on. (Note: To bring the display to the top, click on its window or select the name of the display from the list at the end of the Display menu.) 23

28 LabNet G-M Interface A ➃ Carefully measure the distance from the top of the active source to the A calibration mark found on the printed circuit board inside the acrylic housing of the LGI near the detector tube (see the figure). Record the distance in the Data Table as the initial distance. COU A B C D E F G H Acrylic housing Calibration letters Detector tube Data Recording: LabNet Geiger-Müller Interface Reminder: You can start recording data by doing the following: click on the REC button, press Command-R on the keyboard, select Record from the Experiment menu. To end data recording, click on the STOP button, press Command-(period) on the keyboard, select Stop from the Experiment menu. ➄ Prepare to measure the radiation count. Click on REC to begin recording data. The recording will automatically stop after 120 seconds. Record the Mean as the average radiation count for the initial distance in the Data Table. 24

29 A LabNet G-M Interface ➅ Move the LGI unit 2 cm farther from the source. Carefully measure the distance and record it in the Data Table. Click on REC to begin recording data. The recording will automatically stop after 120 seconds. Record the Mean as the average radiation count for the second distance.. ➆ Repeat the previous steps until you have recorded data at five to seven different distances. (Optional: If possible, repeat the procedure using an alpha source and then repeat the procedure using a gamma source.) Analyzing the Data ➀ Calculate the square of the distances and also the inverse square of the distances in the third and fourth columns of the Data Table. Data Table 5.1: (Beta Source) Data Distance Distance 1/Distance Mean of the Product Point (D) Squared Squared Radiation (Mean) x (D^2) (1/D^2) Counts (D^2) ➁ Using standard graph paper make a graph of the mean of the radiation counts versus distance from the source. ➂ Using standard graph paper make a graph of the mean of the radiation counts versus the inverse square of the distance from the source. ➃ Using log-log paper make a graph of the mean of the radiation counts versus distance from the source. Questions ➀ Does nuclear radiation follow the inverse square law? Justify your answer. ➁ Is the product of the mean of the radiation counts and the square of distance from the source a fairly constant value? ➂ What first action would be important to protect yourself from the radiation released from a broken container of radioactive material? Optional Questions: ➀ Does alpha and gamma radiation have the same relationship to distance from the source as beta radiation? ➁ How would the risk of exposure to radioactive substances be different if nuclear radiation followed an inverse cube law? ➂ If radiation does follow an inverse square law, is it possible to reduce the counts per second to zero? 25

30 LabNet G-M Interface A Appendix Nuclear Safety Most radioactive sources available to educators are very low level isotopes referred to as license free sources. This does not mean, however, that these materials represent no hazard to students. The Nucleus, P.O. Box R, Oak Ridge, Tennessee, 37830, has provided the following guidelines for use of low-level radioactive materials in classroom environments: ➀ Eating, drinking, and the application of cosmetics in the laboratory are not permitted. ➁ Pipetting by mouth is never permitted. Use suction devices such as pipette fillers. ➂ Gloves and lab coats should be worn when working with all liquid radioisotopes. ➃ Before leaving the lab, wash your hands thoroughly then check for possible contamination with a survey instrument. ➄ All radioactive liquid wastes are to be poured into the liquid waste container, NEVER into a sink. ➅ Report ALL spills, wounds, or other emergencies to your instructor. ➆ Maintain good housekeeping at all times in the lab. ➇ Store radioactive materials only in the designated storage area. Do not remove sources from the lab. Typical Geiger-Müeller Tube Characteristics Sensitivity alpha, beta, gamma Window thickness 1 to 2 mg/sq. cm. Gas filling Neon + Halogen Starting voltage 400 V DC Operating voltage 450 V DC to 550 V DC Dead time 100 microseconds Background from unit 10 counts per minute max. Capacitance 4 picofarads Operating temp. range -40 to +75 degrees C. Tube life 10 billion counts Geiger-Müller Tube Technical Data Background Simple Geiger-Müller tubes similar to the type used in the LGI are referred to as mica end window tubes. The stainless steel tube is hermetically capped with a thin sheet of mica only.001 to.002 grams in mass. The interior of the sealed tube has an anode rod running the length of the long axis of the tube, and the tube contains neon gas spiked with a halogen contaminant. When an incoming alpha, beta or gamma causes a neon atom to lose an electron, the ejected electron finds itself pushed very strongly toward the anode rod while the neon ion is pushed strongly toward the steel case of the tube. Along the way, collisions with these charged particles cause other neon atoms to lose their electrons. From a singular disintegration, an avalanche builds in a few microseconds, as momentary conduction through the neon gas occurs, driven by the 450 to 500 volt potential between anode rod and case. As neon ions acquire electrons from the case, the neon atoms return to an excited metastable state. This means that the neon atoms, although now neutral, still have energy to give up before they return to their ground state. This energy would keep the tube continuously discharging. The halogen gas contaminant is designed to quench this continuous discharge by absorbing the energy released by the neon as it falls from its neutral metastable excited state to the ground state. Typically, it takes 100 microseconds for the avalanche of neon ions to be neutralized to their ground state. 26

31 Technical Support Feedback If you have any comments about the product or manual, please let us know. If you have any suggestions on alternate experiments or find a problem in the manual, please tell us. PASCO appreciates any customer feedback. Your input helps us evaluate and improve our product. To Reach PASCO For technical support, call us at (toll-free within the U.S.) or (916) fax: (916) techsupp@pasco.com web: Contacting Technical Support Before you call the PASCO Technical Support staff, it would be helpful to prepare the following information: If your problem is computer/software related, note: - Title and revision date of software; - Type of computer (make, model, speed); - Type of external cables/peripherals. If your problem is with the PASCO apparatus, note: - Title and model number (usually listed on the label); - Approximate age of apparatus; - A detailed description of the problem/sequence of events. (In case you can t call PASCO right away, you won t lose valuable data.); - If possible, have the apparatus within reach when calling to facilitate description of individual parts. If your problem relates to the instruction manual, note: - Part number and revision (listed by month and year on the front cover); - Have the manual at hand to discuss your questions.