Visual Editor Banner
About Us Training Software Support
Main Page Visual Editor Training The Visual Editor Get the Visual Editor
Company Info Penelope/PenGUIn Workshops Nucwiz Help, Support, Known Bugs
Email Randy Schwarz MCNP6 Intermed. Workshops Penelope/PenGUIn Free Downloads
Vised Gallery Onsite Training Other Software C++ Tips and Tricks
Vised Video Demos. Consulting Gamma Spectroscopy Tools  

Don't Do That BannerCell Rejection with Source Biasing Gives Wrong Answer.

Anomaly: When cell rejection is used with source biasing, MCNP may return a wrong answer.
History: Submitted by user.
Versions affected: MCNP5, MCNPX, MCNP6
Impact: Potential Wrong Answer
Work Around: Don't use cell rejection with source biasing.  Note warning: "biased source position rejection sampling is dangerous" when running.

 

Steps required to reproduce this anomaly:

 

Note:  Run this example in the RSICC release of each of these codes.

 

About the Input file:

This input file contains a truncated cone.

 

cell rejection source biasing image

 

cell rejection source biasing input file

 

Click here to download the input file, iddt7 (2 kb).

 

 

Run the input file in MCNP5 and/or MCNPX and/or MCNP6 verify the result.

 

Work around:

Do not use cell rejection with source biasing.  Note that MCNP gives the following warning:

 

warning. biased source position rejection sampling is dangerous.

 

Modify the input file to remove the source biasing by commenting out the sb2 line.

 

Click here to download the modified input file, iddt7a (2 kb).

 

Results obtained from our test:

MCNP6 runs with warnings.

cell rejection source biasing fail_run

 

Open the .o file and view the results.  The source weight should be 1 and it is 1.24

source weight

 

The tally value should be 1 and it is 1.24.

 

tally weight