Testing if particle is looking away from camera

[V737]

Hello everyone!

I'm have some particles that wrap around an object (currently a sphere) they continuously adjust their rotation to align to the object's normal, I'm trying to make a test to isolate the particles when they move so that the angel between their rotation (or normal vector) and the camera (or an object/surface in the same location as the camera) is greater than a set value, basically check when this particle moved so that it's looking away form the camera, or a fresnel effect basically.
I tried using a surface test with a falloff texture, but for some reason tyflow doesn't register falloff, even when rendering.
Any suggestions or ideas are welcome!
Thanks!

[tyFlow]

You can't sample falloff maps with a particle system.

You can use a Script operator to calculate the dot product between a surface normal and the camera direction, outputting particles if the dot product surpasses your desired threshold value.

[V737]

You can't sample falloff maps with a particle system.

You can use a Script operator to calculate the dot product between a surface normal and the camera direction, outputting particles if the dot product surpasses your desired threshold value.

Thank you for the reply, I didn't try using a script in Tyflow before, just looked at the operator, it seems it will do what I want, just have to figure out the code. 
thanks!