Solve MCNP Error: Low Sampling Efficiency with Lattice Source

[Mahboubeh]

Hi, I have a sphere that it contains many sub-spheres. I want to define these small spheres as volumetric source. But when I run MCNP, it doesn't work. MCNP error: the sampeling effeiciency is too low
Maybe someone can help me.

100 0 10
200 1 -1 -10 fill=2
300 1 -1 -2 3 -4 5 -6 7 u=2 lat=1
fill=-8:8 -8:8 -8:8 3 4912r
400 1 -1 30 u=3
500 1 -1 -30 40 u=3
600 1 -1 -40 50 u=3
700 1 -1 -50 u=3

c *************** Surfaces**********************
10 so 5
2 px 0.31
3 px -0.31
4 py 0.31
5 py -0.31
6 pz 0.31
7 pz -0.31
30 so 0.3
40 so 0.29
50 so 0.2

c Water (rho=1)
M1 1001 0.333
8016 0.667
imp:e 0 1 1 1 1 1 1
mode e
sdef pos=0 0 0 rad=d1 cell=d2
si1 0 0.3
sp1 -21 2
si2 L (700<300<200)
sp2 1
nps 1000

Thank you
with best regards

 

[Achy47]

,

Thank you for sharing your issue with us. I would like to offer some suggestions that may help you solve your problem.

Firstly, it is important to make sure that your input file for MCNP is correct and complete. This includes defining all necessary materials, surfaces, and cells, as well as specifying the desired physics options and parameters. You may want to check the MCNP manual or consult with an experienced user to ensure that your input is accurate and appropriate for your problem.

Secondly, the error message you received indicates that the sampling efficiency is too low. This could be due to a number of reasons, such as inefficient geometry or physics settings, or an incorrect definition of the source. I would recommend checking your source definition and adjusting it if necessary. You may also want to try running a smaller number of particles and gradually increasing it until you reach the desired number.

Lastly, it is always helpful to compare your results with those from previous studies or experiments to verify the accuracy of your simulation. If you are still experiencing difficulties, I would recommend reaching out to a knowledgeable colleague or seeking assistance from the MCNP user community.

I hope these suggestions are helpful to you. Best of luck with your simulation!