## Using Monte Carlo Simulations

### Overview

Monte Carlo codes, in general, are used for many topics in the physical sciences and in other (less interesting, surely) disciplines including finance, biology, applied statistics, etc. In short, a random number is generated which is mapped to some probabilistic feature or event (for instance, the distance between photon interactions in a solid, or in finance, an investments sensitivity to unknown interest rates in the future). This process of generating random numbers and sampling probability distributions is repeated many times (upwards of 108 repetitions at times) until a statistically significant result is produced. In principle, any event with a probabilistic outcome can be studied using this method though there are limitations set by available codes and computational power.

## What Does OSU HEDP use Monte Carlo For?

MCNP (Monte Carlo N Particle) is a Monte Carlo code that the OSU HEDP research group uses to help characterize electron and photon transport in solids, neutron generation, and detector response.

### Electron and Photon Transport

MCNP includes a detailed physical treatment of the following transport physics:

- Photons:
- Compton scattering
- Thomson scattering
- Photoelectric effect
- Pair production
- Doppler broadening

- Electrons:
- Condensed history method for collisional transport
- Bremsstrahlung radiation production
- Impact ionization and radiation production
- Knock-on electrons
- Electron energy straggling

MCNP does not include fields so it is not used to do laser-plasma interactions and will not model the collective effects of large current densities. However, MCNP has been used extensively to study general transport effects like stopping distances, x-ray production, angular scattering effects, etc. It has also been used to benchmark various physics additions to the PIC code LSP that OSU HEDP also has expertise in.

## OSU HEDP Monte Carlo Resources

OSU HEDP has several expert graduate and undergraduate users of MCNP. Even though MCNP can be run on a user’s laptop, OSU HEDP has four dedicated hex-core and three quad-core machines, which can be used individually or in concert, as required.