# Litrani shapes

Hello.
I’m having troubles with putting together an object. The object is essentially a box that has 2 mirrors inside it. Mirrors should have 0 thickness and should go from the middle of one side to the corners of the side on the other end of a box. The juncture of the 2 mirrors in the middle of one side should be a thin line. My beam is coming from this side and is reflected sideways.
Thanks.

Hi,
It is not quite clear for me what shape have your mirrors. Could you explain a bit better your setup (or add a simple drawing) ?

Regards,

Yeah, sure. I’m not the artistic type, but here is how i would like my setup. A box, the yellow surface is aerogel, teal is reflecting part of upper mirror and blue is back side of second mirror. The red beam, comes from the left onto the mirror.

So far i’ve build the 2 mirrors with 2 TSPARA and made them just the right size and angle and 0 thickness and covered them with totally reflecting revetment. Since the thickness of the parallelepiped is 0 i don’t know if this is going to work.
Is there any way to add only walls?

Also is there a way to sketch incoming beam, like you draw the parts of the detector? I’m finding it hard to imagine where the beam will hit.

Hi,

Are you trying to use this in a sort of a simulation ? Why do you want to use 0 thickness for your mirrors - you can use few microns. What is TSPARA ??? Are you using TGeo to describe this setup ? If this is the case, I do not see any problem in describing this. Just that in TGeo you does not describe surfaces, but only bodies.

Yes, I’m simulating a pion detector for my diploma.
A beam of pions go into the aerogel where they emit light and I need to detect it.
There is a laser on the picture only to simplify things a little.

I guess few microns could do the trick.
TSPARA is a class in litrani that gives a shape of the parallelepiped.

Sorry I’m just learning Litrani and Root and I dont yet know what TGeo is for, so I guess I’m not using it.

Hello,
I’ve now looked into TGeo class and started to draw a detector with it, but I still can’t put in my mirrors. I wanted to use TGeoArb8 class for them, but seems like I can’t get a prism shape. Any ideas?
Thanx.

Hi,
Just define the mirrors as thin layers having box shape. Just position them (rotated) in a container aerogel box. You can use than TGeoManager raytracing functionality to propagate the light through the system.

Cheers,

Hi,
box shaped mirrors work wonderful. I have questions about wrappers.
When you put a wrapper around e.g. a box and you make a wrapper just a little bit larger to cover the box, does this wrapper have a thickness? Lets say you need your box in touch with another object, do you need to put it half length away of the object or half length + the thickness of the wrapper away? If I make wrapper just the same size as my box would that work? Also can you show me on a simple geometry how ray tracing works.
Thanx.

Hi,
If you make a wrapper “a bit larger”, its thickness will be that “bit”. It can be zero. Putting 2 volumes next to each other can make a 0-thick layer in between, that will not be seen in raytracing (this is allowed). Some example of navigating geometry is a recent one posted by a user here:
http://root.cern.ch/phpBB2/viewtopic.php?p=37144#37144

Cheers,

Hello,
I seem to lose all my generated photons before reaching the phototubes. And the ones that reach the wrapping of the phototube don’t get detected. Any ideas? Here is a macro for more accurate look. How do I get rid of wrapping between 2 mediums with the same wrapping? I’ve put them together, but I still lose photons in the wrapping when going from one medium to the other.
Is there any way to know where the illegal overlaps/extrusions occur?
Thanks.

Hi,
You completely confuse me… “Wrapping” seems to mean for you something else than a virtual volume embedding a real one, so I am lost. Then, looking to your macro seems that you use ROOT only for visualization and the tranport of photons is done with Litrani. Or, if you call TGeo navigation functionality from within Litranii I cannot know how you do it so I cannot help. Anyway, your macro is not so useful since I cannot execute it (not even the pure TGeo part because you have a custom TEuler class)

So the only question I can answer is that after CheckOverlaps() you may get a list of overlaps that you can draw and inspect from a TBrowser. If you want more help it would be useful to explain more (and send code) on how you do navigation.

Regards,

Hi,

sorry for the confusion. Indeed I have two kinds of wrappings. All around my detector there is a real wrapping of a diffusing material. But around phototubes and mirrors there is virtual total absorbing/reflecting wrapping, thus giving the objects properties upon contact with the photons. Yes I use SLitrani for simulation for the propagation of optical photons, and Slitrani uses ROOT objects for visualization.

Hi,
something still bothers me with putting together an object. If you want to have a volume inside another volume, do you first need to make a composite shape of the first volume and subtract the second volume, to form a gap, and then define the second volume and put it in the gap. Or, can you simply define one volume and put in another volume and you get a composite.

Thanks.

Hi,
The gap is automatic. Just put one volume inside another and the behavior is like you have first made a gap.

Hello

I’m trying to draw the tracks of my photons inside my object. But I don’t know anything about my photons. I don’t know the starting point or the direction they travel. They are born due to Cherenkov radiation and there is plenty of them. Is there any tutorial or example on how to get points for tracks for particles or photons?

thanx