To really see that the source is isotropic, i.e. the particle flow is equally distributed throughout the source volume. Everything is already transparent. Thanks for your answer, I'll try it.Alex A said:How rigorous does the check need to be?
You could make everything else transparent, put a sphere round your source, segment it like an orange and then section the orange in half. Every surface would then have equal area and you could do tallies.
To verify isotropy, you can simulate the source and tally the particle flux or current in different directions using F2 or F4 tallies. Compare the results to ensure uniform distribution. Additionally, visualizing the source distribution with tools like MCNP's plotter or external visualization software can help confirm isotropy.
Use F2 (surface flux) or F4 (cell flux) tallies to measure the particle distribution in various directions. By placing these tallies symmetrically around the source, you can compare the flux values to check for uniformity, indicating isotropy.
In MCNP, you can define an isotropic source using the SDEF card with appropriate parameters. For example, setting the distribution of angles (DIR) uniformly over 4π steradians ensures that particles are emitted equally in all directions. The syntax might look like: SDEF POS=0 0 0 ERG=1 PAR=1 VEC=0 0 1 DIR=d1 SI1 -1 1 SP1 0 1.
Common mistakes include incorrect specification of the source direction (DIR) or vector (VEC) parameters, not defining the angular distribution correctly, or using improper tally placement. Ensuring that the SDEF card parameters are set to produce a uniform distribution and verifying the setup with visual and tally checks can help avoid these issues.
Yes, visualization tools can be very helpful. MCNP's built-in plotter can show the spatial distribution of particles, while external tools like VisIt or ParaView can provide more detailed visualizations. By examining the particle distribution visually, you can confirm whether the source is emitting particles isotropically.