McStas 2018 Survey Feedback 5

[willend]

More intuitive use of multi processor / grid computing. New feature: allow neutrons to go back to previous components

[mads-bertelsen]

Allowing neutrons to go back to previous components would require changes in many components that simply assume the neutrons are originating upstream. If your requirements are related to samples or sample environment, the Union components may be able to help. Here one can have for example co aligned samples and sample environment where the ray can go back and forth between these components until it naturally leaves.

[willend]

Agreed @mads-bertelsen, Union is a way forward here.

Another way that has been applied in the past is the use of:

• Instrument variables
• WHEN statements
• JUMP

But this is typically very involved and requires lots of thinking and experimentation.

( Another semi- relevant note is that we in fact are considering to go through all components to ensure that they work both in a "forward" and "backward" application, which would allow the same type of "reverse transport" that SIMRES uses, i.e.:

• Start the neutrons at the sample position with unit weight
• Transport them backwards to the source to establish weight etc.
• Teleport back to the sample position to scatter off sample and become detected in detector(s) )