Mirion PDS 100G, Spectrometric Personal Radiation Detector

Scintillation crystals, PMTs, voltage dividers etc...
cicastol
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by cicastol » 21 Aug 2019, 05:50

Hi Luuk,
thanks for clarifying us the detector capabilities, it was too good to be true unfortunately !!
So the "neutron conversion" actually doesn't work …. :-((
Ciro

luuk
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by luuk » 21 Aug 2019, 06:27

Hi Ciro,
Yes it is a pity but the only way to detect neutrons can be done by replacing the standard detector by a CsI(Tl)/Lil(Eu) detector but that is expensive and
to get it to work properly it will need a new a factory callibration.
But still it is a nice detector as it is right now!
Luuk

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Go-Figure
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Go-Figure » 21 Aug 2019, 07:26

If luuk says so I would say case is closed.
I am not too disappointed I have to say, I didn't even consider detecting neutron as a factor while choosing this detector, but it would have been a nice bonus to have!

Still, I will get in touch with the Mirion man I had a conversation with a month or so ago, first of all to be 100% and also because I want to know where actually the crystal is. When I put a sample at contact with the detector I want to know what the actual distance between the sample and the crystal is.
If this position in different in the 100G than in the 100GN this could lead to the fact that the two detectors could give different readings putting the same sample at the same distance to the detector. That difference would of course become less and less significant as the distance increases.

Hope I can get these questions answered, the man is currently in holiday.
I will let you know.

Massimo

Janni
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Janni » 22 Aug 2019, 03:50

Hi, the problem imho is the source-detector geometry, i think you need to compare in a uniform radiation field , i did a check in a high radiation background near Uraninite mine
(2uSv/h field) and AD6 showed near identical results like PDS100.
I think, that's the point. I used a small uranium mineral, so just point source. I will compare in other conditions with more homogen radiation field and report.

Janni
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Janni » 22 Aug 2019, 03:54

Luuk, thanks for so precise information about the crystal! Would have been so nice to find neutrons with this device, but still I like it so much. :-)

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Go-Figure
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Go-Figure » 04 Sep 2019, 07:52

Hello there.
I have good news and bad news.

Bad news are no news actually, a man from Mirion confirmed me the neutron detector isn't there in the 100G. It's no news since luuk already told us so and we know he knows what's he's talking about.
I will still keep the neutron mode on in order to have additional information on high energy pulses, albeit I won't be able to discriminate actual neutron from cosmic rays.
It's a bit like having an high energy geiger counter built into it, you have a counts reading but you don't know what they really are. Still better than nothing.
Anyway, detecting neutrons wasn't my goal whan I bought this detector so I can live with that.

Now for the good news. According to the Mirion man the PDS calculates equivalent dose averaging counts in five, not three, energy windows, which are Am41, Cs137 and Co60 as we said earlier in this thread, but also Co57 and Ba133, which improves the "coverage" of the whole spectrum.

As usual, good news are shorter than bad ones.

Massimo

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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Janni » 06 Sep 2019, 01:43

Hi!

I'm back from holiday and have also some news. The first is that I got some software today, but I didn't try if I can even start it. I will try it in the evening or tomorrow.

The next news is, I openend the PDS device because I wanted to see myself how it looks like and took photos from the inside :-)

The third news is, I could make a compare measurement with a small piece of uranium ore because I got access to two more of these devices today, they are calibrated and I could exactly compare with my PDS which I reported the dose rate is not correct. I can now confirm that is is really not correct. My PDS shows the same cps, so sensitivity is ok. But dose rate in µSv/h is only about half of both the other devices. I don't know why, I think it can be calibrated maybe with the software... I have to find out and will report. Maybe if the energies are not calibrated and shifted the calculation of dose rate is not correct according to these five nuclid energies, that is what I think. Hopefully the software will give some awareness or maybe someone has an idea...

For the case someone is interested how the inside looks here are the photos. I also took photos of the compare measurement.
Attachments
Inside PDS-100G.png
Detector inside my PDS
PDS-100G von mir.PNG
measurement of uranium ore with my PDS
PDS-100G von Anne.PNG
measurement of same uranium ore in same distance with other calibrated device (cps is little bit higher but that is only because the point is not exactly the same, in general cps is more or less same, but dose rate not)

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Go-Figure
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Go-Figure » 08 Sep 2019, 17:51

Hi Janni,
First, thanks for the photos of the inside.

If two identical detectors give such different results testing the same sample one is clearly out of calibration.
The only menus where you can do something about it I can think of are the ones below, which both show the same values of cps per µSv/h for three energy windows. Incidentally the Co57 and Ba133 windows the Mirion man talked me about are not showed there and the manual never mentions them.
Factory Parameters.png
Factory Parameters.png (91.02 KiB) Viewed 694 times
Calibration.png
Calibration.png (67.35 KiB) Viewed 694 times
Here are the two pages of the software manual about it.
PDSMass Manual Page32-33.pdf
(470.49 KiB) Downloaded 42 times
I personally never touched most of those settings, only acted on the spectrum calibration parameters "gain" and "offset" which don't have any impact on the doserate. Incidentally I read a user of another forum has the gain set on a slightly different value than me (a little bit lower than 2, while I have 2.07, and sometimes 2.05) so maybe there can be slight differences between one device and the other, and they are still used ones (albeit mine looked like it was never been used), they are not coming out straight from the factory so in theory there's the chance someone "played" with the calibration in the past.

The problem is on the spectrum you can clearly tell and fine tune until the peaks are where they need to be, but for the doserate is more difficult to have a reference point, you would need to have a source giving off a known doserate at a given distance.

I was thinking, since now there are several people here owning this detector we might compare the calibration settings of our devices and see how much they differ (in case they do).
This might be helpful for all of us.

Massimo

cicastol
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by cicastol » 08 Sep 2019, 20:42

Hi,
this are my settings, mine was checked with several energy compensated GM dosimeters i own ( Canberra ADM300,Thermo Eberline ESM FH40F2,Automess 6150AD2) and give all pretty the same results in a uniform radiation field (high radiation background in an Uranium ore mine).
Attachments
parametri pds.jpg
Ciro

ipelupessy
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by ipelupessy » 08 Sep 2019, 20:49

I wouldn't worry too much; the way these detectors determine the dose rate has intrinsically limited precision (and dose itself is not a fundamental physical quantity, but derived and defined by regulation) , and if it turns out to be sensitive to the calibration parameters its all the more reason not to use it...

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