[mcstas-users] Fwd: Neutron Beam tracking - MCSTAS

[Britt Rosendahl Hansen]

Hi Maria

I think you could use the premonitor_nd and monitor_nd components to get the answer you need. I suggest looking at these components in the component manual.

Feel free to write me again if you cannot get it to work.

Regards,
Britt


Sent from my iPhone

> On 05 Feb 2014, at 09:50, "María Freiría López" <m.freiria87 at gmail.com> wrote:
> 
> 
> Hello everybody,
> 
> my name is María Freiría, Master Student in Nuclear Engineering at the Technische Universität München. Right now I am working at my Master Thesis at the research reactor FRM II, studying the viability of a future fuel conversion.
> 
> The fact is that we did some experiments at the reactor in order to measure the cold neutron spectrum for different reactor power levels.
> 
> Here is a brief description of the reactor:
> 
> <Beam_tubes.jpg>
> Several beam tubes supply various experimental stations with neutrons from different parts of the reactor. In our experiment we considered the tube SR-1 (connected to the cold source), which is subdivided into 6 smaller tubes as shown in the figure above.
> 
> One of these 6 tubes (NL-4) is again divided into 2 tubes (named NL-4a and NL-4b) which lead to the 2 stations (SANS-1 and PGAA) where the measures were taken:
> 
> <Experiment_Scheme_1.jpg>
> 
> 
> 
> The obtained results concerning neutron spectrum at the 2 stations differ from each other. Eventhough the neutrons in both tubes come from the cold source, based on the results, we think that the neutrons have a different nature, due to the heterogeneous properties along the cold source. A point to be taken into account is the fill level  of the cold source (D2 - liquid deuterium aprox. 25K). Some experts suggest that the major part of the neutron flux analyzed at SANS-1 comes from the lower part of the cold source and in the case of PGAA the neutrons have their origin in the upper part of the tank (near the fill level). This would explain the different results at the 2 stations:
> 
> <Experiment_Scheme_2.jpg>
> 
> In order to proof this theory, we started to work with MCSTAS. 
> 
> I got the instruments and components defined in MCSTAS which describe the geometry of the tube structure. But, as a beginner, I need to ask for some help:
> 
> I need to know the origin of the neutrons which enter the tubes NL-4a and b. In other words: from which part of the cold source do most of the neutrons come in each case (NL-4a and NL-4b):
> 
> <Experiment_Scheme_3.jpg>
> 
> Is it true that the neutron spectrum is different at the 2 experimental stations because the beam has its origin in different parts (the lower and the upper part) of the cold source? Or is the distribution almost homogeneous so that the beam properties in both tubes should be the same? 
> 
> In order to answer these questions, the suggestion made is to implement a kind of "marker" at the beginning of SR-1 divided in "n" cells. This would make it possible to know which of these neutrons "make their way" to SANS-1 and which others to PGAA.
> 
> Is it viable to create such a "marker"? Or do you have any other suggestions for solving this problem?
> 
> As I said, as a beginner I am not conscious of the possibilities that MCSTAS offers, that is why I was directed to you by Peter Link, Neutron Optics department at the FRM II.
> 
> I hope I could explain my problem in a more or less understandable way :)
> 
> I would be really greatfull for your help!
> 
> Kind regards,
> 
> María
> 
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