Regarding Weight Window Generation Iteration in MCNP

[LeoKong]

TL;DR

Hello everyone. I would like to ask about the specific steps involved in the Weight Window iteration method within MCNP's variance reduction techniques. As I am a beginner with limited understanding, I have been attempting this for several days without success.

The code content is as shown above. Running this file generates a `wwout` file; I then copy and paste the contents of this `wwout` file into a backup file. Next, I run the program again to generate a *new* `wwout` file, use the new weights to overwrite the original weights, and then run the program once more. Is this the correct procedure for performing the iteration?

 

[LeoKong]

Apologies—the densities shown in the figure should be 2.3 and 1.5.

 

[Alex A]

(I don't know)
Where did you get this idea? It sounds very strange and this isn't in the manual, but if the run actually uses the supplied weights it might speed up converging to the new weights. It's a very different calculation to the regular run and I have no idea if the code does this.

 

[PSRB191921]

You can use this very powerful protocol to converge a case. It is described in the book "Radiation Problems: From Analytical to Monte Carlo Solutions".
In the first run, enter the line "WWG (tally number) (cell source) j j j j 0". In your case, wwg 5 21 j j j j 0 (not 5 1). Run for 5 minutes (ctme 5 and not NPS). The seven lines of the WWOUT file created have to be include within de 3rd block of the initial input file.

This operation must be reiterate until the number of particles transported in each of slab cells is substantially equivalent (this number of particles is found in the "population" column of the output file.