Welcome to the home of the MCNPX code!

MCNPX is a general-purpose Monte Carlo radiation transport code for modeling the interaction of radiation with everything. MCNPX stands for Monte Carlo N-Particle eXtended. It extends the capabilities of MCNP4C3 to nearly all particles, nearly all energies, and to nearly all applications without an additional computational time penalty. MCNPX is fully three-dimensional and time dependent. It utilizes the latest nuclear cross section libraries and uses physics models for particle types and energies where tabular data are not available. Applications range from outer space (the discovery of water on Mars) to deep underground (where radiation is used to search for oil.) MCNPX is used for nuclear medicine, nuclear safeguards, accelerator applications, nuclear criticality, and much more.

MCNPX is written in Fortran 90, runs on PC Windows, Linux, and unix platforms, and is fully parallel (PVM and MPI). As a superset of MCNP4C3, MCNPX does everything MCNP4C3 does and much more: see the 1-page MCNPX Features Summary: Features.pdf, Features.doc.

MCNPX Beta Release

MCNPX (source code, executables, data) is available from this WWW site to "beta testers" who have access to intermediate code versions. Beta versions of MCNPX are available from "The Code" tab on the left. Beta Testers are sponsors, collaborators, and those who take MCNPX workshops (see "Classes tab on right.) For further information on the Beta Test program, contact mcnpx@lanl.gov.

The latest beta test version is MCNPX 26F (March 24, 2008). The principal new capabilities added since the latest RSICC release (MCNPX 2.5.0, April 2005) are:

* = new or significantly enhanced capabilities in MCNPX26F added since MCNPX26E (November 17, 2007).

These new MCNPX 26F features are described in: "MCNPX V26F Extensions" LA-UR-08-1808.pdf, LA-UR-08-1808.doc (March 24, 2008) (73 pages).

MCNPX RSICC International Release

MCNPX is available (source code, executables, data) to nearly everyone (subject to export controls on sensitive countries) from the Radiation Safety Information Computational Center (RSICC) in Oak Ridge, TN. MCNPX is packaged with MCNP5 and the nuclear data common to both codes. Be sure to specify that you want the whole package, MCNPX, MCNP5, and data.

The last RSICC release is version of MCNPX 2.5.0 (April 2005). The principal new capabilities added since MCNP4C3 (2000) and MCNPX 2.3.0 are:

Many of these features are described in more detail in an 80-page document, "MCNPX Extensions, Version 2.5.0" LA-UR-05-2675.pdf (.6 MB), LA-UR-05-2675.doc (1.0 MB).

Downlolading Caution

Note that certain builds of Netscape, Internet Explorer, etc., do not properly display embedded pdf or doc files. Instead they give garbage, a blank screen, or error messages like, "Error reading xref entry." You may need to destroy temporary copies and then save rather than view them in the browser.

Cash Awards

We are so confident in the quality of MCNPX that we pay cash awards to the first person identifying any bug or error in the code. See the list of cash awards (4 pages): Cash.pdf, Cash.doc. Considering all the new MCNPX capabilities relatively few bugs have been identified. It is far easier to find an error in the predecessor codes to MCNPX than in the new capabilities added.

Last modified: March 24, 2008
To report errors on the web page, or make other comments, contact Gregg W. McKinney / 505-665-8367