Alpha Spectroscopy Low Energy Error

[terryphi]

Hello,

I've taken a spectrum of a U238 sample, and I keep getting this hill of low energy values. Any ideas as to what could be causing them?

Sorry about the weird screenshot; it's the only one I had and my friend couldn't see the dots, so i had to go over them in paint.

 

[Astronuc]

What is the scale of the abscissa?

I would suggest comparing it to a standard alpha spectrum of U-238.