My Master's Thesis is "due" tomorrow, and today I was just finishing up my MCNPX simulations. And while I should have done this about a month ago, the results are still pretty nifty. The following figure shows the effect of moderating a Cf-252 source with a 0.5 cm of lead and 2.5 cm of HDPE. What is neat is that the 2.5 cm of HDPE (lead won't moderate neutrons much because of a neutron cannot impart much recoil energy to the a lead nucleus) is that the spectra is essentially thermalized - the peak is around 0.025 eV, which if you recall is the kinetic energy of room temperature particles predicted by the Boltzmann Distribution.
The detector assembly is composed of a bunch of layers of thin (less than 100 microns) films each separated by acrylic. The following two plots show the effects of the different layers. The first layer see's the most neutrons, but doesn't have the largest contribution to the reactions because it only sees them from the front - there isn't much effect of the reflector. As you go farther into the detecor the number of neutrons crossing a film decrease (it is not because the films absorbs them, only about 20 neutrons are absorbed in all 120 of the films) but rather neutron's escape and scatter out of the detector.
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| This is probably my favorite plot of my thesis |
I looks like I will graduate with a Masters either in May or Summer, and then hopefully (finger's crossed) I can get out of here by May 2013. Have to do work.
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