These variations are called isotopes of that element.
While the number of neutrons varies, every atom of any element always has the same number of protons and electrons.
So, after only half an hour, half the sand should be in the top bowl, and the other half should be in the bottom bowl.
Suppose that a person did not observe when the hourglass was turned over.
These parent radioisotopes change into daughter lead-206, lead-207, argon-40, strontium-87, and neodymium-143 isotopes, respectively.