Do you know what that piece of plastic is?
A: It's a linear accelerator test target and judging by its size, a powerful one.
In college, I worked as a machinist in a shop that made various parts for a company that made small medical linear accelerators (I personally drilled four water cooling holes in each of about a thousand cavity blanks). The finished accelerator was about a meter in length. I have a similar target that's only about an inch in diameter and an inch long that was produced by our customer (with a itty-bitty tree to match).
At the SLAC Visitors Center, they had one that was about six inches in diameter and nine inches long, with a tree to match. The SLAC linear accelerator is two miles long! That's why I judge yours came from a powerful one.