[mcstas-users] Fwd: split neutron into component

[Santiago Gómez]

Hello Kim, thank you for the answer.

Yes, in the case of a complex instrument with several components, an 
important source of statistical error is the lost of neutron into the 
relevant monitors.

In the case of my component, its a monochromator and there are two kind 
of statistical errors. One is related to the effective neutron which are 
impacting on the component (similar of that you mention). Other one is 
the necessary correlation between the direction and the energy inside 
the thickness of the monochromator for the Bragg diffraction.

For a given incoming direction, my component can link the source 
component to implement a variance reduction in energy, so it selects 
only the suitable energy range where bragg diffraction is possible 
(satisfying the energy-direction correlation), so I think an split in 
that point of the coding will be very effective, there are a lot of 
calculation to know the energies intervals for one incoming direction, 
and if I can do an split there, it is not necessary to do this part 
again.

Surely, an special care must be taken to split the neutron with the 
correct weights, but may be it can be done automatically by some macro 
function.. but I don't know how difficult will be to implement it if 
it's not already coded.

Regards
Santiago



> On Fri, May 12, 2017 at 1:53 PM, Kim Lefmann <lefmann at nbi.ku.dk> wrote:
> Hi Santiago,
> 
> The short answer is that SPLIT is meant to function at the instrument 
> level, e.g. for users that will not need to worry about programming 
> components themselves.
> 
> To make a SPLIT inside a component, much more bookkeeping is needed, in 
> particular for the fractional rays that would emerge in the middle of a 
> component, and this has only been imagined and never implemented (Peter 
> may correct me here if some test fragments exist?).
> 
> However, most of the computational work done by the simulation at 
> (almost) any given point in the instrument lies in all the rays that 
> were lost earlier in the simulation, e.g. in the guide system, the 
> slits, the monochromator, and so on. Therefore, in most cases not much 
> actual running time would be gained by an in-component SPLIT compared 
> to the existing instrument-level SPLIT. This analysis is roughly what 
> lies behind the fact that the in-component SPLIT has never been 
> implemented.
> 
> best, Kim
> 
> On 05/12/2017 06:31 PM, Santiago Gómez wrote:
> Hello
> 
> I would like to split a neutron inside component.
> 
> As far I see it is possible to split a neutron that reaches a specific 
> component using the SPLIT macro before the component declaration in the 
> instrument file, but it cannot be used inside de component.
> 
> I would prefer to split the neutron inside my component because if I do 
> the SPLIT outside, a series of calculations already done be my 
> components will be redundant (I would say more than 50% of all the 
> calculation of the component).
> 
> The idea of the split is to do a variance reduction which optimizes the 
> time, so for my component will be much more better to do that inside 
> the component code.
> 
> Is it possible to performs it? I think that a similar issue is the 
> possibility to have more than one source component in a single 
> instrument file.
> 
> Best regards
> 
> _______________________________________________
> mcstas-users mailing list
> mcstas-users at mcstas.org
> http://mailman.mcstas.org/cgi-bin/mailman/listinfo/mcstas-users [1]

--

Santiago Miguel Gómez

Si queremos un mundo de paz y de justicia hay que poner decididamente la 
inteligencia al servicio del amor. Antoine de Saint-Exupery

-- 

Santiago Miguel Gómez

Si queremos un mundo de paz y de justicia hay que poner decididamente la 
inteligencia al servicio del amor. Antoine de Saint-Exupery

-- 
Santiago Miguel Gómez
Departamento de Física de Reactores y Radiaciones
Centro Atómico Bariloche
Int.: 5971

"Si queremos un mundo de paz y de justicia hay que poner decididamente 
la inteligencia al servicio del amor." Antoine de Saint-Exupery


Links:
------
[1] http://mailman.mcstas.org/cgi-bin/mailman/listinfo/mcstas-users