Last night, I wrote a short script to simulate the random decay of radiocative particles.  While this code would be horrible for simulating more than a few hundred atoms, it is perfect for classroom exercises where the students need to count the decays.  Surprisingly, students could only keep pace with 3x3 grids if the half-life was as short as 70 seconds.   To handle any more, they needed to work in groups and parallel process the events.