MCNP cone source definition

[MadGander]

TL;DR Summary

Need help defining a cone collimated source in MCNP

Hi folks,

I'm attempting to define an SDEF cone source but am getting tripped up in the SI/SP/SB distributions. I need all particles to be generated at angles within the cone, with all angles in the cone having equal probability. I feel like this should be relatively simple to define since the probability is 1 inside the cone and 0 outside. Any help is appreciated.

 

[Alex A]

This document is helpful. The plot doesn't make it look like a cone section of an isotropic source, it looks flat, but that is because it is showing a log plot.

SDEF X=0 Y=0 Z=0 ERG=14.0 VEC= 1 0 0 DIR=D1
SI1 -1 0.90 1
SP1 0 0.0 1

That is with a half angle of 25.8 degrees (the cosine of which is 0.90, in the SI card). It's a clever use of the histogram up to a value feature, sampling the range of cosine values between 0.9 and 1 to make the cone. I don't know why there is a -1 0 pairing, this doesn't seem to be needed. It's probably worth sticking with the full example anyway.