Today I have been having fun building and testing a small 1" x 1" LaBr3 detector. After seeing the 3.1% resolution I'm not sure if I will ever be happy with NaI(Tl) again :)
While running the background spectrum I didn't see much of the internal radiation from this crystal, but that might be because it's relatively small.
This one is for a client, so unfortunately I won't be able to hold on to it.
The basic construction is;
1" x 1" LaBr3 Crystal
Single SHV connection
Gold anodised aluminium housing with black cap.
Resolution came in at a pleasing 3.1% and linearity was good, but I had to run it at 400V, lower than normal voltage.
The price of these crystals (especially the bigger ones) puts them out of reach for most amateur scientists, but if anyone is interested I can supply LaBr3 at competitive prices.
PS: Note on Linearity
I found this quote in a paper by Saint Gobain, this is consistent with my findings today.
LaBr3:Ce scintillator has 1.6 times the light output and is more than 10 times faster than NaI(Tl). This can produce
non-linear effects in the pmt. A simple calculation shows that the instantaneous charge pulse is about 25 times that
of NaI(Tl). This is based on the ph ratio of 1.6 and multiplied by the faster time factor of 250ns/16ns specifically:
25X = 1.6X(250/16).
The non-linearity manifests itself in two ways. First, the FWHM of a peak is better than expected at that energy and
second, the position of higher energy peaks will be at lesser pulse height than expected from a linear extrapolation.
It is possible to verify that this is occurring by decreasing the HV by about 100V and observing an improvement in
linearity and a correspondingly a slight decrease in FWHM. In order to keep these undesirable effects to a minimum,
Saint-Gobain Crystals is selecting pmts that have superior linearity properties. Often these are 8-stage pmts.