Gamma Spectrometry Forum

Hi everyone,

I'm planning to build a LaBr3:Ce probe this year and would like to have your opinion.

LaBr3 having a really good resolution.. and being expensive, I will naturally privilege SBA or UBA PMT.
I saw that there is a Q.E difference near 8% between these (see attachment) but SBA are often mentionned as enough.

My first question will be, is there a difference in the final resolution that would justify using a UBA?

About the crystal now, I also saw the shape was important to obtain the best resolution.
So for these crystals, a cubic or cylindrical shape is recommended ?

Thanks.

Yvan.

Hi Yvan,

Building your own LaBr3 detector that is a real interesting project.
A pmt with sba Cathode will give a great resolution, and is I think the best choice for a LaBr3 detector.
I(we) use only pmt’s with sba Cathode and but excellent results with CeBr3 and LaBr3 detectors.
With a good LaBr3 crystal and a pmt with a sba Cathode the expected resolution will be 2.6 to 3.0% @ 662 KeV that is if the pmt is directly coupled with the crystal.
So keep in mind that if you are building your own detector and I expect that you buy a canned LaBr3 crystal, than the resolution will be a little worse because of the glass window between the crystal and the pmt it may cost you between 0.1 to 0.2% that is not so much but still significant if your average resolution is 2.8%.
I don’t know exactly the price difference between the sba and uba Cathode but a sba is a good choice and will not only be cheaper but also more types are available.
Best is to use a bigger pmt than the size of the crystal e.g. with a 1”x1”crystal a 2”pmt is the best choice!
If the crystal is cylindrical or square will not make a very big difference but a cylindrical crystal is the best choice, if the length and diameter are the same you may expect the best resolution.

Luuk

Luuk - What is the expected resolution for a good CeBr3 scintillator crystal these days? I know it used to be higher than LaBr3, but a better choice where the inherent background of LaBr3 can get in the way of low level measurements. Has there has been some improvement in CeBr3 resolution from >4.0 to closer that of LaBr3 crystal?

Hi Tom,
The resolution for CeBr3 is still around 4% @662KeV, I have seen 3.7% but that as low as it's get.
Yes, the low background is the main reason to buy a CeBr3.
Luuk

Hi Luuk and Tom,

I indeed planned to use this recommendation about the pmt size since I read the possibibility that the photocathode wouldn't be homogenous.
So SBA PMT is definitely enough for these crystals.

Anyway, I planned to make this scintillator full homemade with detailed building steps (choice of PMT/crystals, coupling, HV power supply, signal conditioning, ...) and post it when finished. I hope it will help in the future for others.

Thanks for your replies!

Yvan.