Sensor types/ranges? How to detect a pea-sized sample of some material, hidden behind a thin piece of wood, up to 2 feet away, hidden behind a thin piece of wood?

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Electronics amateur but anxious to learn using Fritzing and lots of coffee.
For my first post, this question immediately came to mind:

How could I detect a pea-sized sample of some material, up to two feet away, which is hidden behind a thin piece of wood?

Obviously, line-of-sight sensors are out of the question. Can any sensors out there do this?
Which material should be used for best detection?

Can this be done? (Remember, I'm an absolute electronics newb, but I am a scientist in his forties.)

Thanks for Fritzing!
Have a great day,
Miguel3d