Understanding IMP:N in MCNP5 for Beginners

[Lastsniper]

TL;DR Summary

I find a solve to my problem

I knew MCNP at 3 month ago but I do not know Why followed IMP:N (or IMP:P)
IMP:N 1 2 2M or IMP:N 1 3 2M. I do not understand Why 2 (or 3) behind 1. Please, Someone indicate an answer physic, thank

 

[Aaron Barnard]

The notation IMP:N 1 2 2M or IMP:N 1 3 2M is used in MCNP to define an importance-weighted neutron source weight window. The first number (in this case, 1) specifies the importance level of the source, while the second and third numbers (2 and 2M, or 3 and 2M) specify the lower and upper bounds of the weight window respectively.

The importance weighting scheme allows MCNP to accurately simulate the transport of particles while still using a limited number of histories. It does this by giving different weights to different particles according to their importance in the simulation. The importance level (1 in this case) indicates the relative importance of the source in comparison to other sources in the problem. The weight window (2 and 2M) defines the range of importance weights that will be assigned to particles from the source. Particles with an importance weight outside of this range will not be simulated.

 

[raining Pete]

you

Hi there,

It's great that you have been learning MCNP for the past 3 months! From what I understand, IMP:N is a command in MCNP that specifies the importance of a neutron in a simulation. The number after the command (in this case, 1, 2, or 3) represents the neutron importance level. This is important because it allows you to control the accuracy and speed of your simulation by assigning different levels of importance to different neutrons.

As for the 2M after the importance level, that stands for 2 million. This means that the neutron importance level will be calculated for every 2 million neutrons in the simulation. This helps to reduce the computational time and resources needed for the simulation.

I hope this helps to answer your question about the numbers behind the IMP:N command. If you need further clarification, I would recommend checking the MCNP user manual or reaching out to the MCNP community for more information. Keep up the good work with your learning!