Neutron Profiles

Some more flux profiles of the irridator.  I think the energy deposition is the coolest; you can see how much energy the cadmium (high neutron absorbance) adsorbs, compared to the air and the Li-6 glass.  You can also clearly see the reduction in the neutron flux as well. Still confused why the neutron flux over the two wells are equivalent when the alpha fluxes are not; the alpha's are produced in (n,alpha) reactions so I would expect there to be a one to one correspondence.

Gamma Flux Profile

You might think that the lead cylinder would attenuate photons more than the cadmium, but this is not so since the attenuation coeffients are about the same:

Source

The sudden changes in the spectrum are from the orbital levels of the electrons - they are label in the original data set.  (Pretty Nifty, huh?).  Note that gamma's follow an exponential decay $$I/I_0 = e^{-(\mu/\rho)x}$$, and I have already multiplied by the density, so it makes sense that there would be a large attenuation for low energy gammas.

Thesis Decision

I finally had to pick a thesis topic and I went with: "Scintillating Crystals in Scintillating and Non-scintillating Matrices".

The general idea is to embed crystals (micron sized, 6Li or 10B based (currently looking at LYB)) into polymers designed to support Pulse Shape Discrimination (the pulse can be molded by a double exponential, the first constant is PMT / electronic dependent and the second is the decay time of the material; crystals are usually 50 ns or so while polymers are in the 5 ns range).  Modeling will be done in Geant4 / MCNPX / MCNP6.

Kinda scared about having to actually pick a topic - and that I have been getting a lot of hints to stay on the project for a PhD, but I don't know how interested I am.  Staying on would provide a safe career choice and assure me of a well paid job afterwards, though . . .

I leave you with profiles of the neutron flux (a mesh tally) plotted over the geometry of the irridator.  Notice how much smaller the flux is in the Cadmium shielded well; that is because cadmium has a high absorbance cross section for thermal neutrons.

Finally, I think I would have more dating success if I went away from cheesy pick up lines. There so go though! What women could resist a man with a perchance for bad science puns?  None worth having, I tell you.