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ComputerLab2 - Geology 351 - Geomath Computer Lab - Problem...

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Geology 351 - Geomath Computer Lab - Problem 2-13 Basic Radioactive Decay/Age Relationships You received a pretty thorough introduction to Excel in the solution of problems 2.11 and 2.12. Some of the following may be a little redundant but will provide some basic review and opportunities to ask additional questions about Excel functionality. The lab discussion includes some old Excel version 2003 illustrations. The basic procedures remain similar. Take marginal notes as needed to clarify tasks as we go. GETTING INTO EXCEL At this point, you may have a shortcut button on your desktop to get into Excel 2007. If not, then in either version click on Start Programs to bring up a program list. You may find it in your Quick Start list or have to search it out within the Microsoft Office program list. Bring up Excel. You should have a view of an empty spreadsheet as before. Now consider problem 2.13 from Watlhtam’s text. Problem 2.13: Radioactive minerals become less radioactive with time according to the equation t a a λ = ln( ) ln( ) 0 Where a is the radioactivity (in counts per second), a 0 the initial radioactivity, t is the time and λ is a constant which depends upon the mineral. If a 0 = 1000 counts per second and λ = 10 -7 y -1 , draw up a table and plot a graph of ln(a) against t for times ranging from 0 to 100My. From your graph, estimate the age of a specimen which has decayed to a=100 counts per second. Spreadsheet Operations The direct computation of t in the above equation is fairly trivial algebra problem. As you can see from the equation above it is linear and we only need two points, so estimating the age could be done graphically without resorting to the computer. However, we’ll expand the nature of the problem to include analysis and plotting of the ln(a) relationship and also the radioactivity equation in its exponential form. We’ll make our computations of ln(a) from times t = 1 to 100 MYA at intervals of 1 MYA - i.e. for a total of 100 computations. Take some notes … 25
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Click, hold, & drag; the mouse tip shows the value that will be dropped in the current row. Remember that EXCEL will autofill values of t (our independent variable) from 1 to 100. All we need to do is give it the first two numbers in the series. The procedures for doing this are outlined in the window at right …. Type in the first number (1e6) in the series (1e6 stands for 10 6 or 1000000) Type in the second number in the series (2e6) Select those two cells Place the mouse arrow on the lower right corner of cell 2, click and hold left mouse button down and drag down to cell 100.
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ComputerLab2 - Geology 351 - Geomath Computer Lab - Problem...

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