|MadSci Network: Physics|
My guess based on the limited information is that the alpha particles, because they are so large (atomically) and have a +2 charge love to interact with whatever is in their path. Your source contains a parent nuclide which must eject the alpha out of the nucleus of the atom and from their everything it interacts with will degrade it's original energy level. Thus the spectrum will be a distribution of energies from zero to the maximum energy of the alpha particle, in theory. Hope this helps. [Moderator note: Ideally, an alpha particle source that provides a sharp energy peak should be very thin, so that the emitted alpha doesn't lose much energy exiting the source. ]
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