MCNP and capabilities at UofC

Grayson C. Rich Enrico Fermi Institute and Kavli Institute for Cosmological Physics

University of Chicago

DAMIC-M kickoff meeting Paris

2018 Jun 12

Monte Carlo N-Particle transport code• Developed by Los Alamos National Lab

- These folks need to know how neutrons move

- Development dates back 50+ years

• Export controlled - distribution is restricted by US government, users must apply for license

• Some people consider it the unassailable standard for simulation of low-energy neutron transport

• Can use MPI to take advantage of many-core architectures (i.e., supercomputers or university clusters)

- Mildly complicated by export control

• Features “variance reduction” techniques intended to speed up simulation (weighting of particles, roulette, biasing of sources)

2G.C. Rich - DAMIC-M kickoff - 2018 Jun 12 [1] D.Z. Freedman, Phys Rev D 9 (1974) [2] A. Drukier, L. Stodolsky, Phys Rev D 30 (1984)

Example inputc CsI crystal 99 99 -4.51 -1 -2 3 IMP:N=1 IMP:P=1 $ central scatterer (CsI) c PTFE reflector around crystal 700 21 -2.25 (1 -711 700 -2) : (2 -710 -711 ) IMP:N=1 IMP:P=1 c Al housing around crystal 701 20 -2.7 (700 -701 711 -704):(701 -702 711 -705): & (702 -710 711 -704):(710 -703 -704) IMP:N=1 IMP:P=1 c borosilicate glass window 702 22 -2.23 700 -3 -1 IMP:N=1 IMP:P=1 c Deuterium gas cell 100 2 -0.0005 -100 101 -102 IMP:N=1 IMP:P=1 $ D cell … c CSI ASSEMBLY c Target Detector 1 1 cx 0.95 $ cylinder bounding sides of scatterer 2 px 2.55 $ plane bounding top of scatterer 3 px -2.55 $ plane bounding bottom of scatterer c surfaces related to outer (aluminum) boundary 700 px -2.7 $ bottom of assembly 701 px -2.5 $ lip near bottom 702 px 1.71 $ top lip 703 px 2.8 $ top of assembly 704 1 cx 1.27 $ outer of Al assembly, thickest parts, 1inch dia. 705 1 cx 1.17 $ out of Al assembly, axial midsection, 23.4mm dia. c interior surfaces of assembly 710 px 2.7 $ bdry of top layer of Al with reflector, Al 1mm thick 711 1 cx 1.09 $ outer edge of PTFE reflector, 1.4mm thickness … c tally counting neutrons entering/exiting CsI f91:n 1 2 3 *c91 90 0 fq91 d f c fc91 Neutron current across boundaries of CsI crystal. Neutrons entering in 90-180 bin of surf 1 and 3, 0-90 surf 2

3G.C. Rich - DAMIC-M kickoff - 2018 Jun 12

Simulation geometries• Complicated geometries are realizable (see image of CCD

test chamber geometry, made in part by Karthik Ramanathan, UofC grad student)

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Np

Np Np Am

Cs Ka1 esc. I Ka1 esc.

Cs Ka2 esc.

I Ka2 esc.

I Kb1 esc.

Cs Kb1 esc.

10 20 30 40 50 60

E [KeV]

100

101

102

103

104

Count

241AMMCNP

Neutral- and charged-particle transport possible• Can simulate not only neutral particles (neutrons, photons), but can also transport charged particles

• Can track recoiling ions, electrons generated by interactions

- Tracking of electrons can add lots of computation time

- Has techniques for efficiently approximating net result of photon interaction without tracking resulting electrons

5G.C. Rich - DAMIC-M kickoff - 2018 Jun 12

Particle-tracking output: MCNPX-PoliMi• By default, MCNP does not produce step information (e.g., can’t see if particle X scattered off of

nucleus of type Y at time Z)

• Default outputs are in the form of tallies

- Tallies are flexible but time coincidences can be especially difficult if not impossible

• PoliMi is an official “hack” of MCNP’s internal tracking information

- Also accessible via “PTRAC” output built into MCNP

- Learning curve for PTRAC use is much more steep, however…

• Utilities for PTRAC use also exist

- Can allow certain explorations that PoliMi makes difficult

- Flexibility generally makes this the way you would want to approach tracking

- Opens up use of MCNP6, the newest version of the code which brings all the features of parallel versions 5 and X plus some new low-energy electron improvements (among other things)

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Quick comparisons with GEANT4• Input

- Do not have to define a physics list

- “Variance reduction” techniques can be turned off, reverting to “analog transport” (necessary for tracking)

• Output

7G.C. Rich - DAMIC-M kickoff - 2018 Jun 12 [1] S.D. Monk et al., Nucl. Instrum. Meth. B 399 (2017) [2] C. Guardiola et al., J. Inst. 6 (2011)

- Some studies have found serious discrepancies (e.g., figure from [1])

- Exact source is not clear

‣ Possibly related to interpolation of cross sections [2]

‣ Possibly related to simplified treatment of materials by GEANT4 [2]

- You can also find studies that show very good agreement, or good agreement in certain situations

Expertise at UofC• Experience using MCNPX/5/6 in myriad use cases

- In-beam neutron scattering experiments (quenching factor measurements)

‣ These involve time coincidences, quenching in liquid scintillator detectors, energy cuts, location-dependent beam-neutron production, etc…

- Neutron source experiments (e.g., 252Cf, AmBe), including photo-neutron source QF measurements

- Various gamma-focused simulations (e.g., 241Am, 137Cs, 55Fe) including Compton calibration

- Background simulations (cosmic-induced neutrons, neutrons from U/Th in surroundings)

• Familiarity with tally-based output as well as tracking

- Utilization of both PoliMi and PTRAC (allowing use of MCNP6)

8G.C. Rich - DAMIC-M kickoff - 2018 Jun 12