LaBr3(Ce) 1 x 1" Build

[Sesselmann]

Some of you might be interested in the latest order I have finished. It's a 1x1" LaBr3 detector. I have made at least 3-4 or these over the years and it's always a bit of fun to run a few spectra with such resolution.

As most of you are aware LaBr3 crystals have some Lanthanum 138 and Actinium 227 trapped inside the crystal and this does result in some annoying background counts.

The gamma from La 138 is not that significant in these small crystals, a little peak at 788 keV and another at 1435 which for the most part overlaps K40, but the Alpha noise from Ac 227 does mess up the region from around 1600 keV to around 2400 keV.

These issues are easily overcome using background subtraction, so i't's not such a big deal.

LaBr3-Background

In the background spectrum from this 1" crystal we can hardly see the gamma from La 138, but the counts from Ac 227 are quite noticable.

GS-1010-LABR

Here I used a 1 hour background recording for subtraction during the recording of a Cs137 spectrum, and got a pleasing 3.1% resolution.

Cs-137 Spectrum (LaBr3)

I always enjoy making these and feel just a little bit sad 😢 when I have to let them go ...

Steven

[RobertD]

Very impressive results, Steven. Thanks for sharing.

[iRad]

Steven - Not only is the LaBr3(Ce) build impressive, but so is the Spectrum displayed in your very nicely designed Impulse MCA software. Nice job on both counts! (counts... get it...lol)

[jasonzb]

Hi Steven

Amazing!!

Which model of PMT is in your detector?

Thank you

[Sesselmann]

Which model of PMT is in your detector?

Jason,

This build used a Hamamatsu R980 PMT and had the 1" crystal centred on the 1.5" pmt with a 3D printed collet.

Steven

[Marco75]

Amazing! You always do a fantastic job with your works
I need to find the time to finally test the Impulse because I love it!

Marco

[tim.hbn]

Hi Steven

Which voltage divider did you use for this?

What voltage do you set the GS-USB-PRO to for this?

Thank you very much.

Kind regards

Tim

[Sesselmann]

Tim,

I make my own dividers for the R980 PMT's, but it's just a standard K-2R-R-R-R... divider with 1M resistors, nothing fancy.

Voltage for the R980 can vary between 680 and 720 Volts.

Steven

[tim.hbn]

Hi Steven

Thank you very much for your reply.

What would be the effect if the 1M resistors were replaced with 2M resistors?

I am asking this because I want to gain a bit of understanding about voltage dividers.

Thank you very much.

Kind regards

Tim

[Sesselmann]

Tim,

Not much effect, some portable detectors have much higher resistors like 10M for keeping battery consumption low and dividers can also be made with lower value resistors to reduce thermal noise. It is honestly not that critical. We usually add some capacitors to improve linearity. There are other methods of designing a divider such as active dividers, which use a combination of resistors and transistors.

Steven