I finally wrote my first stand alone code that does real physics.  I've written a lot of code, but it was always based on code that someone else wrote, or just scripts to deal with the output of a big program. But a week ago I wrote a  program that calculates the energies of recoil protons from a ⁴⁰Ca beam smashing onto a plastic (CH₂) target.  The relativisitic energies are calculated for a range of recoil angles and I've included inelastic scattering for those excited Ca nuclei.  This may sound trivial, and perhaps it is, but it was a worthwhile experience and I was very happy when my results were the same as what LISE gives.  That's right, there's another program that offers the same calculation, but it only allows 1024 steps over 90 degrees in the lab frame, and I wanted 4000+ steps.  Why? Because I'm using it for calibrating our CsI crystals.  

If you know the lab angle of the recoil proton, then you know what energy it should have when it enters the crystal.  We can know the angle to less than a tenth of a degree because we have a 32x32 grid of silicon in front of the crystals.  All we have to do it figure out which pixel the proton went through, assign it an angle, and thus an energy, and then equate that energy with the channel number read out by the electronics for the crystal.

We were lucky enough to be able to see not only elastically scattered protons,  but also those from the 1st excited state of ⁴⁰Ca.  Then you just have to plot energy(MeV) vs channel to get a function to calibrate your crystals.

They don't look all that pretty yet... but they will.   The proton loses energy going through a variety of foils and only 1st order losses are used for the plot above.  Of course, the data will never be as tight as the line fitting it because of the energy resolution of the crystal itself.  The crystal emits light when a charged particle goes through, and that light is converted into a signal that goes into the electronics and eventually comes out as a channel number.    It's amazing how accurate this process is, but there will always be a small width to our distribution of data.  

On a completely different note, this last batch of graduate recruits were awesome and I hope to see all of them here in the fall.