I use Dired mode in Emacs which I guess also counts as one of those. I find it very convenient because it's integrated into Emacs. Also, I wouldn't like to use the mouse for file management.
None of the depicted particles is radioactive. They are just the product of radioactive decay. And btw, neutrinos are also the product of radioactive decay, they just interact so little with anything that we can't effectively measure them from radioactive substances. (We can measure them from the sun though.)
Let's do the math. Let's name the points A B C D, where A and D are separated by 6 feef, and all other point pairs by 6 feet. There fore, ABC and BCD are equilateral triangles of side length 6 feet. This leaves two possibilities for the distance between A and D: either they are the same point, or their distance is twice the height of an equilateral triangle with 6 feet side. Since A and D are clearly distinct, we'll go with the latter. That makes the distance AD to be equal to 6 feet times the square root of three, giving a value of sqrt(3) feet for one feef.
In French "machine" is feminine like in the other languages.