[neutron-mc] McStas Polarisation details

[Klaus Lieutenant]

Dear Robert,

why should the neutron spin be decoupled from the ROTATED command ? This 
command takes care that all parameters (velocity, ...) of the neutron 
are transformed to the local co-ordinate system of the component. This 
is also necessary for the spin.
Imagine you have polarised a beam into a certain direction and you like 
to analyse the polarisation direction afterwards with a component that 
is rotated relative to the polariser. For this analyser, you need to 
know the polarisation direction in its co-ordinate system, i.e. a 
rotation of the spin co-ordinates is necessary.

Best regards,

   Klaus




Dalgliesh, RM (Robert) wrote:

>Peter,
>I suppose that's what I was trying to get to but wrote a totally garbled e-mail. If the field/polarisation direction is defined locally within the component then I guess we have got back to applying the ROT_A_CURRENT_COMP transform locally, as you first suggested. As far as I can see the ROT_A_CURRENT_COMP is a cumulative transform so this shouldn't be a problem but the neutron spin does then need to be decoupled from the ROTATED command.
> 
>Regards
> 
>Rob
>  
>