Interesting Freeware: Part II
x4FFF; (Part I, Geochemical freeware, was published in GN139).
Rad Decay This periodic table is distinguished by its plots of nuclide decay paths. The accompanying text lists the particles, x-rays, and energy emitted at each decay step. Shown here is the decay of 239Pu to 207Pb. Fast breeder reactors contain a core of 239Pu surrounded by a shell of 238U. Neutrons1 from decaying 239Pu strike the 238U, which changes into 239Pu by two beta decays. The reactions stop when the 238U shell is used up. This is a valuable and intelligent program.
Statistics is a dangerous discipline2. Computer programs can make any statistical test you want, but naïve users may misinterpret the results. We include ourselves in this group, so we stick to simple tests. Our favorite statistical routines are Excel add-ins because they work in a familiar spreadsheet format. Many add-ins and stand-alone statistics programs are listed at Free Statistics. The add-in used in the example is XL-Toolbox v. 2.57.
The example shows the results of a one-way ANOVA test of pH values of lakes in Maine. The sample set includes 2080 pH measurements from 42 lakes.
Our hypothesis is that average pH values differ among the lakes. The null hypothesis is that the average pH values are not different. The numbers of measurements per lake are variable so the test is not valid. The example illustrates the utility of this Excel add-in; it does not prove any scientific point.
The ANOVA find a 95% probability that the pH values do differ among the lakes. Now we have to figure out why. That can be done with additional water chemistry in the database of Maine limnology.