Multichannel Analyzer:

As we mentioned above, the charge produced in the diode is proportional to the energy of the alpha.  After the amplifier, this is converted into a voltage pulse whose amplitude is related to the original particle energy.  A multi-channel analyzer (MCA) is typically used to measure these pulses, recording the pulse height for each pulse and building histograms for counting.  Again, we have designed a flexible instrument that is cheap and can be applied to other purposes.  We have purchased several STEMlab instruments \cite{pitaya}. These are single-board Linux-based instruments that include a re-programmable FPGA and 14-bit analog outputs and inputs sampled at 125 MS/second.  The STEMlab is open source, about $500 (depending on options), can be controlled remotely through Python, LabVIEW and other languages, but also has built-in applications including an oscilloscope, function generator, logic analyzer and others.  The FPGA can be reprogrammed, and several interesting applications have been built, including a MCA with source code available \cite{demin}.  We created a web application for this back-end, allowing any web browser to access and control the MCA - with source code and documentation available here \cite{thompson}.