You are required to have a valid MCNPX license in order to use the code. If you are publishing results based on it, someone from the author list must have a valid license ("preferably" the one that made the calculations). Try to get info from RSICC.
MCNPX is a general purpose Monte Carlo radiation transport code designed to track many particle types over broad ranges of energies. It is the next generation in the series of Monte Carlo transport codes that began at Los Alamos National Laboratory nearly sixty years ago. MCNPX 2.6.0 is the latest Radiation Safety Information Computational Center (RSICC) release of the code, following the 2005 release of MCNPX 2.5.0 The MCNPX program began in 1994 as an extension of MCNP4B and LAHET 2.8 in support of the Accelerator Production of Tritium Project (APT). The work envisioned a formal extension of MCNP to all particles and all energies; improvement of physics simulation models; extension of neutron, proton, and photonuclear libraries to 150 MeV; and the formulation of new variance-reduction and data-analysis techniques. The program also included cross-section measurements, benchmark experiments, deterministic code development, and improvements in transmutation code and library tools through the CINDER90 project.
Since the initial release of MCNPX, version 2.1, on October 23, 1997, an extensive beta-test team has been formed to test the code versions prior to official release.
Approximately 1750 users in approximately 400 institutions worldwide have had an opportunity to try the improvements leading to version 2.6.0 and to provide feedback to the developers. This process is invaluable, and we express our deepest appreciation to the participants in the beta-test program. Applications for the code among the beta-test team are quite broad and constantly developing. Examples include the following:
• Design of accelerator spallation targets, particularly for neutron scattering
Facilities
• Investigations for accelerator isotope production and destruction programs,
including the transmutation of nuclear waste
• Research into accelerator-driven energy sources
• Nuclear safeguards
• Nuclear criticality safety
• Nuclear material detection
• Design of neutrino experiments
• Accelerator based imaging technology such as neutron and proton radiography
• Detection technology using charged particles via active interrogation
• Design of shielding in accelerator facilities
• High-energy dosimetry and neutron detection
• Medical physics, especially proton and neutron therapy
• Investigations of cosmic-ray radiation backgrounds and shielding for high altitude
aircraft and spacecraft
• Single-event upset in semiconductors from cosmic rays in spacecraft or from the