Radioactive Decay and Penetration Depth – Why Should There Be an e?

When students are first introduced to the idea of radioactive decay, a large conceptual hurdle must be overcome. The thought that an object's age has no bearing on the chance it will “die” (decay in this case) on a particular day is completely at odds with biological notions of life and death. Through the use of a simple spreadsheet, students are shown that something analogous to coin flips will yield the exponential curve describing decay. A similar spreadsheet is then used to show that the exponential curve associated with the penetration depth of radiation is produced through the use of the same kind of random process applied to slices of matter rather than slices of time. The spreadsheets model two common introductory laboratory experiments but avoid the need for Geiger counters, radioactive sources, and sheets of absorbing material.