A known fault site at Decorah, Iowa, was surveyed for indicative variations in surface radioactivity. A portable ionization chamber revealed significant increases in gamma ray intensity at several locations. At one point the radiation level was 70% greater than the background intensity. Measurements repeated one year later verified this pattern. Radiation contours were plotted over an extensive area in the city of Decorah. This map, with other items of supporting evidence, indicated a possible fault strike of approximately N 55° W.
Proceedings of the Iowa Academy of Science
©1961 Iowa Academy of Science, Inc.
Lorenz, Philip J.; Rodenberg, Orville C.; Shadle, Larry G.; Antes, Alan C.; and Hess, William D.
"Background Radioactivity in the Decorah Fault Region,"
Proceedings of the Iowa Academy of Science, 68(1), 397-403.
Available at: https://scholarworks.uni.edu/pias/vol68/iss1/56