Lab: Radioactivity and Radiation Dry Lab
Overview (pgs. 311-312)
Read the Purpose, Background, Materials, and Safety First sections of Experiment 52 in the Prentice Hall Chemistry: Laboratory Manual.
Pre-Lab Questions
Complete the pre-lab questions for this lab and submit them to your instructor or online instructor.
Procedure (pgs. 312-313)
Read the procedures for Geiger counter measurements.
Observations (pgs. 314-315)
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Data Table 1: Effect of Distance on Radiation Intensity
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Distance from Source (cm)
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Radiation Intensity (cpm)
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4
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228
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2
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883
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1
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3321
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Transfer these measurements to the data sheet.
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Data Table 2: Effect of Shielding on Radiation Intensity
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Shielding Material
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Radiation Intensity (cpm)
Source: 14C
Radiation type: β
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Radiation Intensity (cpm)
Source: 137Cs
Radiation type: β, γ
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none
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1284
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1462
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paper
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1140
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1458
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wood
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862
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1410
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aluminum
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412
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1326
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glass
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363
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1302
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lead
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24
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1265
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cotton fabric
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1054
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1445
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plastic
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1162
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1452
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Data Table 3: Effect of Time on Radiation Exposure (Source: 137Cs)
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Time (min)
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Total Counts
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1
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1368
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5
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6840
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30
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40800
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60
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81600
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Analyses and Conclusions (pg. 316)
Answer questions 1 - 5 and "Going Further" in the lab manual using the data and observations provided above.
#1. A Geiger counter is used for the detection and measurement of all types of radiation: alpha, beta andgamma radiation. It consists of a pair of electrodes surrounded by a gas.
#3. Lead was the best shielding material.
4. When you double the distance from a radioactive source, the energy at that distance decreases by a factor of four. So the counts per minute should also decrease by a factor of four.
5. To a significant extent, yes. Radiation is not like poison, in that you can "consume" some and it can do damage to you later, at leisure. For the most part, radiation does its damage immediately (although the effects may only be felt over time), and it begins when you begin exposure, and then goes on until you stop. The longer you're exposed, the more damage. It's just like the fact that you get wetter the longer you stand in the rain. Generally, the harm radiation does harm you, if it is harmful at all, it's proportional to the total energy you absorb, and that is equal to the intensity of the radiation multiplied by the length of time to which you are exposed to it.
Develop a Hypothesis:
Based on the results of this lab, develop a hypothesis to explain why the radiation from the 14C source could be shielded more effectively than the radiation from the 137Cs source. What do your results suggest about the decay mode of each radioactive isotope?