A bad crystal but still nice to look at.

[luuk]

Hello guys,
The growing process of scintillation crystals is very complicated and sometimes it goes wrong, in this case with a 80x80mm NaI(Tl) crystal.
The effect can be interesting although the crystal is not usable, but I thought that you would like to see this.
I have seen a few times but this one is exceptional nice and bright.
We used a few 80x80mm NaI(Tl) crystals and we made it into a well detectors.
At the pre-test one of the crystals seems to have a second peak in the Cs-137 spectrum that should not be there.
So the crystal was taken out of the can and viewed while irradiated with uv light to see if there were any errors in it and there was one, I took a view pictures from it for you to look at.
The result is spectacular there is a bright illuminated line in the detector caused by a very high local Thallium concentration.
So not a usable crystal but still nice to look at.
Any questions? feel free to ask me.
Luuk

[GigaBecquerel]

This is very interesting to see!
How does an uneven doping like that happen?
If you cut that line out would the rest of the crystal still be usable, or is there too little Tl in there?

Lukas

[luuk]

Hello Lukas,
Growing a good crystal is tricky, small errors can have big consequents.
Maybe there went something wrong in the heating or cooling down process, not sure.
I have seen it before it simply happens now and then but with the proffecional growers not too often.
Just made some pictures from it because this one was so strong and good to see I had to show it to you guys because in hobby use you have almost no chance to see it.
I expect that the remaining part is still working but maybe with a little less light output, as you can see in the pictures the crystal part just below the high Thallium concentration is not as bright as the rest so there is for sure less Thallium in it.
Luuk