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Lecture 2-Experimental Design Define the scientific method Learn how to design a scientific experiment calculate exposure times limit experimental error collect data analyze data present results write a technical report
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Experimental Design
Chapter 3
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Objectives
Define the scientific method Learn how to
design a scientific experiment calculate exposure times limit experimental error collect data analyze data present results write a technical report
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The Scientific Method
The process by which scientists, over time, attempt to build an accurate representation of the world.
Who we are and what we believe can influence our perceptions and our interpretations of the world around us.
As a result, scientists use standard procedures and criteria to minimize those influences (biases) when developing a theory.
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The Four Steps Observe and describe a phenomenon or
group of phenomena Formulate an hypothesis to explain the
phenomena Use the hypothesis to
Predict the existence of other phenomena, or
To predict quantitatively the results of new observations
Test the predictions by several independent experimenters and properly performed experiments
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Creating and Testing a Hypothesis Example: Radiation
What do you/we know about radiation exposure?
Create a hypothesis about radiation dose:
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Designing a Scientific Experiment How would you test your
hypothesis? What end result would you look
for? How might you bias your
experiment? How would you minimize it?
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Testing a Hypothesis
How would you know if you have proven or disproven your hypothesis?
How would you compare everyone’s results?
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Reporting Results
How would you report your results? Would you construct a table or a
graph? How would you label it/them?
How would you present your results?
Where do you go to find instructions?
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An Experiment: Radiation Effects on Pinto Beans
The experiment you are starting today will do four things: Demonstrate the use of one of our
irradiation facilities; Make you familiar with the unit of
absorbed dose (the gray or rad); Promote a class discussion on
experimental design; And, Allow you to see the effects of
radiation on plant growth.
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Irradiated Pinto Beans
Irradiated in the OSU Radiation Center 60Co gamma cell.
Each group of seeds was irradiated to different doses.
Neither the students nor the instructor knows the dose given to any of the groups.
The groups have been named: Marvin, Rhonda, Walter, Shiela, Betty, and Fred
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Radiation Doses
Absorbed Dose, rads
0 (control)
5,000
10,000
15,000
30,000
80,000
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GammaCell 220 60Co
A device for providing uniform radiation doses throughout a large volume
Approximately 8” h by 6” wide
Several small sources surround the irradiation chamber
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Exposure MapWithin the
Gammacell 220
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Planting Directions
Plant 5 beans (of the same dose group) in each Styrofoam cup
Label each cup with the name of the student group and the bean seed treatment (dose) group
Punch drainage hole(s) in each cup Fill cup approximately 3/4 full with dry
potting soil Using a pencil or stick, make holes in the
soil to a uniform depth (e.g., five bean seeds, five planting holes)
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Planting Directions, cont’d Lightly pat soil over beans Place styrofoam cups in the aluminum
baking pans.. Place baking pans on window sill Fill baking pans with water Periodically
water the plants in the same way. Do not let the soil dry out completely Do not over-water
observe the behavior and growth of the seeds.
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Science – It’s Great Stuff
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Summary
Design a scientific experiment Calculate exposure times Limit experimental error Collect data Analyze data Present results Write a technical report