Spring 2019

Carolyn Hasselkus

Ricochet

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-Today’s Slide-

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02/07/2019

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After talking with Jonathan, I spent a lot of time trying to figure out what could be the difference between how I am simulating to match the Edelweiss plots and the results they get in their plots.

• Most time put into trying to match units to the Edelweiss plots

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Borated Polyethylene: Continued (still)

• Edelweiss plot is measuring Flux as neutrons/(keV s cm^2)
• Dividing by time and/or surface area would both be constant coefficients so for now, I’ll leave them out to just get the trends correct, but the dividing by keV shouldn’t be ignored
• If I do this correctly, the 20cm lead line on the Edelweiss plot should be identical to my plot of flux of neutrons after 0cm of borated poly, since I am taking the 20cm lead as the starting spectrum

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Borated Polyethylene: Continued (still)

I am going about this as follows:

1. Digitize the line from the edelweiss plot into a set of points to define the spectrum by
2. Multiply the digitized flux values by the corresponding energy to get raw counts to use for the spectrum magnitude at that energy
3. Run simulation
4. Take number of neutrons captured at each thickness interval and divide by energy to get back to the flux unit (barring s and cm^2)

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Borated Polyethylene: Continued (still)

Borated Polyethylene: Continued (still)

My flux after 0cm of borated poly

Edelweiss 20cm lead line

Borated Polyethylene: Continued (still)

My flux after 0cm of borated poly

Edelweiss 20cm lead line

So I’m clearly missing something and I’m feeling silly that I can’t find what I’m missing.

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Is the /keV just a convention after all?

Even so, if I don’t account for energy at all (either for incoming spectrum or my counts), the plots still don’t match up.

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Definitely confused.

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Borated Polyethylene: Continued (still)

Borated Polyethylene

• At long last, I have resolved my simulated data with the results produced by the Borated Polyethylene background neutron simulations performed by Edelweiss
• After adjusting my starting spectrum magnitudes and carefully reviewing my code (and finding no obvious errors . . . ) my plots (finally) match Edelweiss’

Borated Poly:

Neutron Capture Studies

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03 14 19

Quick Process Review:

• Digitized the Edelweiss plot of neutron flux through layers of borated polyethylene shielding
• Take the 20cm lead line to be the starting energy spectrum for my simulation
• Using a cube made up of of 10cm thick 2mx2m slabs of borated polyethylene simulate:
• 500,000 neutrons
• Straight down into cube
• Starting energy spectrum defined as 20cm lead line (linear interpolation of digitization)

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Borated Polyethylene: Continued (for the last time ?)

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Data Processing: Plot neutrons as they enter each slab (10cm through 50cm of borated polyethlene)

• If the track is a neutron track
• for each step in the track
• update the current energy
• get the current process
• get the current volume
• get the current slab --> cur slab = (int) (2000 - curPos.Z())/100) + 1
• If the neutron is just entering this slab for the first time:
• if step == 0
• add this neutron (curKE) to numNeutronsVSnrg0cm
• if curSlab == 2 and hasn't already gone through this slab
• add this neutron (prevKE) to numNeutronsVSnrg10cm
• if curSlab == 3 and hasn't already gone through this slab
• add this neutron (prevKE) to numNeutronsVSnrg20cm
• .....
• That's it. Pretty simple.
• This is unchanged from my first iterations

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Borated Polyethylene: Continued (for the last time ?)

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Borated Polyethylene: Continued (for the last time ?)

Edelweiss

My Simulation

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Changes:

• Using the correct energy spectrum
• Not dividing by energy (regardless of the confusing units on the original plot)
• I have tried this combination before, but I must have missed a bug in my code that I fixed since the last time I ran this combination

Borated Polyethylene: Continued (for the last time ?)

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