NOTE: Users will also need to request the respective Source or EXE only versions of MCNP6.1 (C810MNYCP00 or 01) to access the included data files.

1.         NAME AND TITLE

MCNPX-PoliMi v2.0 : Monte Carlo N-Particle Transport Code System To Simulate Time-Analysis Quantities.


MPPost  v2.1:  MCNPX-PoliMi Post-Processor

2.         CONTRIBUTOR

Polytechnic of Milan, Milano, Italy and the University of Michigan, Ann Arbor, MI, USA.


Fortran 90; Shell Scripts (C00791MNYCP00).


The Monte Carlo simulation of correlation measurements that rely on the detection of fast neutrons and photons from fission requires that particle emissions and interactions following a fission event be described as close to reality as possible. The -PoliMi extension to MCNP and to MCNPX was developed to simulate correlated-particle and the subsequent interactions as close as possible to the physical behavior.

Initially, MCNP-PoliMi, a modification of MCNP4C, was developed. The first version was developed in 2001-2002 and released in early 2004 to the Radiation Safety Information Computational Center (RSICC). It was developed for research purposes, to simulate correlated counts in organic scintillation detectors, sensitive to fast neutrons and gamma rays. Originally, the field of application was nuclear safeguards; however subsequent improvements have enhanced the ability to model measurements in other research fields as well.

During 2010-2011 the -PoliMi modification was ported into MCNPX-2.7.0, leading to the development of MCNPX-PoliMi. Now the -PoliMi v2.0 modifications are distributed as a patch to MCNPX-2.7.0 which currently is distributed in the RSICC PACKAGE CCC-810 MCNP6.1/MCNP5/MCNPX. 

Also included in the package is MPPost, a versatile code that provides simulated detector response. By taking advantage of the modifications in MCNPX-PoliMi, MPPost can provide an accurate simulation of the detector response for a variety of detection scenarios.


MCNPX treats an arbitrary three-dimensional configuration of materials in geometric cells bounded by first- and second-degree surfaces and some special fourth-degree surfaces. For neutrons, all reactions in a particular cross-section evaluation are accounted for. Both free gas and S(α, β) thermal treatments are used. Criticality sources as well as fixed and surface sources are available. For photons, the code takes account of incoherent and coherent scattering with and without electron binding effects, the possibility of fluorescent emission following photoelectric absorption, and absorption in pair production with local emission of annihilation radiation. A very general source and tally structure is available. The tallies have extensive statistical analysis of convergence. Rapid convergence is enabled by a wide variety of variance reduction methods. Energy ranges are 0-60 MeV for neutrons (data generally only available up to 20 MeV) and 1 keV - 1 GeV for photons and electrons.

The -PoliMi extension to MCNP and to MCNPX was developed to simulate fission events and the subsequent interactions as close as possible to the physical behavior. In particular, neutron and photon fission multiplicity distributions have been implemented, and neutron interaction and photon production are made correlated. At each collision, relevant information on neutron and gamma collisions is recorded, for example reaction type, target nucleus, energy deposited, time and position. A post-processing code (MPPost) has also been developed and can be tailored to model specific detector characteristics. These features make the -PoliMi extension to MCNP and to MCNPX a versatile tool to simulate particle interactions and detection processes.

The leading principle in the MCNPX-PoliMi photon-production routine is the conservation of energy at each neutron-nucleus interaction. Secondary photon production is performed after determining the neutron reaction type. This information is crucial in deciding how many photons are born, and in assigning their energy and outgoing direction. At each collision, the possible neutron-nucleus interactions are:


·         Capture

·         Inelastic scattering

·         Elastic scattering

·         Fission

·         (n, Xn) reactions (X > 1)

·         Charged particle production reactions (i.e. (n,α), (n,p), (n,d), etc.)

·         Neutron and charged particle production reactions (i.e. (n,nα), (n,np), etc.)


New Capabilities in MCNPX-PoliMi ver. 2.0 (new compared to MCNP-PoliMi ver. 1.0)


·         New built-in fission and other sources

o   New source 238Pu (spontaneous fission).

o   Improved photon emission in AmBe and AmLi (α,n) sources.

o   Definition of D-T and D-D sources.

o   Definition of PuO2,n) sources.

o   It is now possible to select a larger mix of sources present at the same time (both interrogating and self-sources) and multiple isotropic sources.

o   The user can define a neutron source with spectra depending on multiplicity

·         Improved modeling of the physics of fission

o   Physics of fission upgraded with nuclear models for fission neutron anisotropy; neutron energy spectra dependent on multiplicity.

o   The neutron direction of emission can be specified as both isotropic and anisotropic with respect to the direction of the light fission fragment.

·         Physics of detection: write to file a detailed list of all collisions occurring in detector cells.

o   Collision output file has been expanded to include the energy of the incident particle. It is possible to write it as unformatted binary file.

o   Nucleus recoil can be accounted for.

·         New output files are available; among them:

o   A file listing the T0 of each history (TOF for distributed source).

o   A file listing the sampled fission multiplicities and generations.

·         Photonuclear physics capability

o   Fission neutron and gamma multiplicity data are applied to photofission.

o   Photonuclear reaction information can be written as a source file for subsequent use as the input source for future runs.

·         The collision output file now supports repeated lattice structure cell numbers

·         Implemented the photon emission following neutron capture by cadmium

·         All MCNPX ver 2.7.0 capabilities

·         Still under testing: radioactive isotope emission specification by a code.


This package also contains MPPost, a program developed to simulate the response for several detector types based on the particle transport and collision information provided by MCNPX-PoliMi. This code can simulate the detector response for organic scintillators, inorganic scintillators, and 3He detectors. In addition, several options for advanced data processing are available, such as time-of-flight and cross-correlation.


MCNPX-PoliMi requires analog Monte Carlo. The secondary gamma generation performed by MCNPX-PoliMi is in general limited by the information present in the MCNP/MCNPX cross section nuclear data libraries.  Do not use multigroup cross sections.  Delayed neutrons should be used with care (as defined in the manual for photonuclear physics).


Running time varies greatly depending on problem parameters. The program will execute the included example problems in few minutes on a 2.67 GHz XEON processor.


MCNPX-PoliMi is operable on Windows, Linux, and MacOS systems, generally on systems compatible to MCNPX.


The included Windows executable was created and tested under WINDOWS XP and 7 on an Intel Xeon processor. MCNPX-PoliMi was tested using Intel 12.0.8 FORTRAN and C compilers in a cluster environment under RedHat Enterprise Linux.  It was also tested using Intel 12.0.4 FORTRAN and C compilers on a MacOS 10.7.2 operating system. Note: FORTRAN and C compilers are required for Linux and MacOS users (executables are not included).  

Linux and MacOs users require the MCNP_DATA files and the MCNPX source files from the MCNP6.1/MCNP5/MCNPX (C00810MNYCP00) package. Windows users require the MCNP_DATA files from the MCNP6.1/MCNP5/MCNPX-EXE (C00810MNYCP01) package.

10.       REFERENCES

Adobe Acrobat Reader freeware is available from to read and print the electronic documentation.

a. included documentation in electronic format on the CD in v2.0.0 - Release\Docs:


Enrico Padovani, Sara A. Pozzi, Shaun D. Clarke, Eric C. Miller, “MCNPX-PoliMi User’s Manual.”

Enrico Padovani, Sara A. Pozzi, Shaun D. Clarke, Eric C. Miller, “A Brief Description of –PoliMi Modifications to MCNPX”.


b. included documentation in electronic format on the CD in v2.0.0 -Release\References:


S.A. Pozzi, S.D. Clarke, M. Flaska, P. Peerani, “Pulse-Height Distributions of Neutron and Gamma Rays from Plutonium-Oxide Samples,” Nuclear Instruments and Methods in Physics Research (Section A), Volume 608, pages 310-315, 2009.

S.D. Clarke, S.A. Pozzi, M. Flaska, T.J. Downar, “Monte Carlos Study of Photoneutron Production in U-235 Following Perturbations in Cross-Section Data,” Annals of Nuclear Energy, Volume 36, pages 393-398, 2009.

S.A. Pozzi, Y. Xu, T. Zak, S.D. Clarke, M. Bourne, M. Flaska, T.J. Downar, P. Peerani, V. Protopopescu, “Fast Neutron Spectrum Unfolding for Nuclear Nonproliferation and Safegaurds Applications,” Societa Italiana di Fisica, Volume 33, 2010.

Sara A. Pozzi, Marek Flaska, Andreas Enqvist, Imre Pazsit, “Monte Carlo and Analytical Models of Neutron Detection with Organic Scintillation Detectors,” Nuclear Instruments and Methods in Physics Research (Section A), Volume 582, pages 629-637, 2007.

S.D. Clarke, M. Flaska, S.A. Pozzi, P. Peerani, “Neutron and Gamma-Ray Cross-Correlation Measurements of Plutonium Oxide Powder,” Nuclear Instruments and Methods in Physics Research (Section A), Volume 604. pages 618-623, 2009.

S.D. Clarke, S.A Pozzi, E. Padovani, T.J. Downar, “Sensitivity of Photoneutron Production to Perturbations is Cross-Section Data,” Nuclear Science and Engineering, 160(3), 370 – 377, 2008.

E.C. Miller, B. Dennis, S.D. Clarke, S.A. Pozzi, J.K. Mattingly, “Simulations of Polyethylene-Moderated Plutonium Neutron Multiplicity Measurements,” Nuclear Instruments and Methods in Physics Research (Section A), Volume 652, pages 540-543, 2011.


c. included MPPost documentation in electronic format on the CD in MPPost\ Release\docs:


      Eric C. Miller, Alexis Poitrasson-Riviere, Andreas Enqvist, Jennifer L. Dolan, Shikha Prasad, Mark M. Bourne, Kyle Weinfurther, Shaun D. Clarke, Marek Flaska, Sara A. Pozzi, Enrico Padovani, John K. Mattingly, “MCNPX-PoliMi Post-Processor (MPPost) Manual.

Eric C. Miller, Shaun D. Clarke, Marek Flaska,  Shikha Prasad, Sara A. Pozzi, and Enrico Padovani; “MCNPX-PoliMi Post-Processing Algorithm for Detector Response Simulations,” Journal of Nuclear Materials Management, Volume XL, Number 2, 2012.


d. background information not included in the package:


S. A. Pozzi, E. Padovani, and M. Marseguerra, “MCNP-PoliMi: a Monte Carlo code for correlation measurements,” Nuclear Instruments and Methods in Physics Research (Section A), Volume 513, Issue 3, pages 550-558 (November 2003).

M. Marseguerra, E. Padovani, S. A.Pozzi, M. Da Ros, “Phenomenological simulation of detector response for safeguards experiments,” Nuclear Instruments and Methods in Physics Research, (Section B), Volume 213 pages 289-293 (January 2004).

S. A. Pozzi, E. Padovani, J.K. Mattingly, and J.T. Mihalczo, “MCNP-PoliMi Evaluation of Time Dependent Coincidence between Detectors for Fissile Metal Vs. Oxide Determination,” Institute of Nuclear Materials Management 43rd annual meeting, Orlando, Florida (June 23-27, 2002).

S. A. Pozzi, J.K. Mattingly, J.T. Mihalczo and E. Padovani “Validation of the MCNP-PoliMi code for the simulation of nuclear safeguards experiments on uranium and plutonium metal,” Nuclear Mathematical and Computational Sciences M&C2003, April 6-11, 2003, Gatlinburg, Tennessee, USA.

S. A. Pozzi and J.T. Mihalczo, “Monte Carlo Evaluation of the Improvements in Nuclear Materials Identification System (NMIS) resulting from a DT Neutron Generator,” Institute of Nuclear Materials Management 43rd annual meeting, June 23-27, 2002, Orlando, Florida, USA.

S. Prasad, S. D. Clarke, S. A. Pozzi, and E. W. Larsen, “Response Matrix Method as a Variance Reduction Tool for Simulating Neutron Pulse Height Distributions,” Accepted to Nuclear Science and Engineering, in press. (2012)



Included are the referenced electronic documents listed in sections 10.a.b.c, Windows executables, and test problems transmitted on CD ROM in zip format.


January 2004, June 2011, April 2012.