Gamma Spectrometry Forum

Hi!
I want to report about one of my favorite hobby projects that I did in the last time.
A while ago I was very lucky because a friend gave an old HPGe detector to me that was not in use for several years and stored in a basement of a company. From the datasheet the detector is from 1995. It was the complete equipment with the detector, the dewar for liquid nitrogen and the electronics. But no one did know if even the detector is working. Everything was not touched for years and one day they cleaned up the basement and my friend could get these things for me.
So this is already more than 1,5 years ago. When I had everything at home I switched on the NIM crate and the first thing that happened was a big noise and smoke came out of it…
So I started to fix this problem and found out that one resistor was burned and replaced it. That was easy because I could see that this one was burned. Not so easy was to find out that the resistor was burned because of a broken capacitor because that was not visible from the outside of this capacitor, but with some patience I found that one and replaced it.

After this was repaired, there was a lot of more things to do:
- Check with liquid nitrogen if the vacuum of the dewar and of the detector is still good
- get manuals for all the NIM modules, preamp and how to put everything together
- replace and find another NIM modul because one of them had also broken parts inside
- get the software
- find out how to connect all the cables, there is one SHV cable, but some BNC cables and the name on the connectors was not possible to read anymore on some of them
- communicate with the software and electronics (now I have a separate Windows XP computer for it)
- find out what settings need to be made (high voltage, polarity, type of preamp...)
- build a wagon (for some practical reasons) where the detector with the dewar can stand inside and a sample container can be put on the detector
- build the lead shielding
- find out the settings in the software (gain, channels, preamp settings, there are many possibilities to adjust...)
- and at last the calibration, that I did with a piece of uranium ore

So over the last months I could manage step by step and in the end it came out that the detector is working really nice!
I’m very thankful to the friend who gave this detector to me, without him I would never have this possibility, I also got some very friendly help from Canberra people who I contacted. I really appreciate because they knew that it was for a hobby project and still they were very helpful. And also I got a big Thanks to my boyfriend who helped me with software communication, setup of windows computer and network things and he gave me also the material to build the wagon :-)

As it is a bit more complicated to use a germanium detector because it must be cooled with liquid nitrogen I don’t have it always in operation, but once it is cooled I can use it about two weeks until the liquid nitrogen is empty.
So I recorded a lot of spectra already. On the photos the first is the background in my living room and the second one is a spectrum of a piece uranium ore without background subtraction.
I marked the peaks with the information I got from the software in the nuclide database, but also in the internet to compare the peaks I should find. As I’m not a master spectrometry expert, I would really appreciate comments, hints of mistakes in my marks and any other comments.
Thank you! More spectra will follow!

Hi Janni,
That is a nice old detector, looks like it is still working great!
Do you know the efficiency and resolution of this detector?
Luuk

Janni,

That's a lucky scoop, and well done on fixing and restoring the electronics.

The spectra are spectacular, I wish one day a room temperature detector will come close to this resolution.

Steven

Lovely post! I wish I had one of those too.. Very exact! Curious, what are you using to capture the spectrum in terms of A/D?

Janni,

These spectrums are beautiful. The best I have seen. They explain some of the weird composite photopeak shapes I get with Uranium and a NaI detector.
I have always wondered about some of these.

Could you do a U spectrum focused on the low end, say below 610 keV? Are you sure that the peaks around 60 and 90 are Th227? I am thinking Th234 (U238 chain).

Mike Loughlin

I have heard something that companys like Canberra and Ortec are working on such detectors for room temperature or maybe something with a different cooling system that does not need liquid nitrogen, sorry I don't know more about that and how that works...

What is really amazing for me is that until now I never had to make a new energy calibration. I calibrated it some months ago and in the mean time it was not cooled for weeks. Then I cooled it again and the calibration was still perfect and completely linear :-)

The resolution is 1,8keV (FWHM) at 1,33MeV
0,85keV (FWHM) at 122keV
0,68keV (FWTM) at 5,9keV
and rel. efficiency 24%

This I have from the datasheet.

Does anyone here know from the photo what material the window is? It can be beryllium or carbon, I think it looks like carbon, but I'm not sure because beryllium looks not so different for me. In the datasheet it is not written...

Regarding the electronics for capture the spectrum there are these four modules that communicate over a bus system and the first one is the module that communicates then with the computer. Another module makes the high voltage, then one module for the amplifier and one for the ADC that gives the signal to the modul that communicates over a network connection with the computer. So you need the original software because in the software all the settings for bus adresses of the modules must be made.
Self programming is maybe also possible, but not so easy because you need to know this data protocol. I'm a little hobby programmer, but for me this is too complicated... :-)

Hi Janni,
Thanks for the info, yes it is a nice HpGe for sure!
Looking at the picture it is not 100% to see but it looks to me like a beryllium window.
Beryllium has a colour that looks a little bit like (new)lead.
Good luck with your detector.
Luuk

Hi luuk,
thanks for your answer!
Here is another spectrum with this detector from a thorium mantle.

Good job and great luck to get this detector, Janni! So nice looking spectra, but well, HPGE is another story. Thanks for sharing this.

Very nice detector, and extremly fortunate for you that the detector still works without any work. I'm wishing for a HPGE for a long time, but i was advised by Carl Willis (maybe some of you know his blog) that HPGe's can in very bad condtion, even if they are sold at a high price. Most sellers know jack about these, they just find out that these were expensive professional devices. So most of the used detectors sell for like 1.5-4k$. Most used HPGe's have either blown preamps (due "lets power up and see what happens") or/and vacuum leaks, which require professional repair or some home repairs.

Also i would like to ask how you are dealing with the nitrogen, i've read that nitrogen will be constantly evaporated out of the tank, expanding into gas, which is toxic.. do you have ventilation system or so? Or is it not that much of a deal?

@Steven, nowadays most HPGe users (pros) have usually a electric coolant unit, so you dont need liquid nitogen. Its not exactly "room temperature" ;) but its way easier than dealing with ln2. Check out Ortec X-Cooler on the web. I've even seen a portable HPGE unit with electric cooler at a german rescue exhibition.