Mirion PDS 100G, Spectrometric Personal Radiation Detector

Scintillation crystals, PMTs, voltage dividers etc...
Stratal83
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Re: Mirion PDS 100G, Spectrometric Personal Radiation Detector

Post by Stratal83 » 14 Mar 2020, 07:44

Thank you Tom,

The GS-USB-PRO paired with one of your Scionix Holland Gamma Scintillation Detector NaI(Tl) would perfectly match my budget. I'll get in touch with you once I've made my mind.
Alain, France

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

Post by iRad » 14 Mar 2020, 11:40

Sure thing Alain. Please send me a message at iradinc at att dot net when you are ready to do something, or if you have any further questions. And PLEASE be safe. Cheers, Tom
Cheers, Tom Hall / IRAD INC / Stuart, FL USA
Please check out my eBay Store: http://stores.ebay.com/The-Rad-Lab

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

Post by gravelmonkey » 08 Apr 2020, 21:40

Hi All,

Finally got things up and running, I've actually had the PDS100G since 2017, it must have been one of the first of the surplus sold on ebay?

Below is a short (138 second) acquisition spectra of Am-241 - the only source I currently have to hand.

Image

The peak is recorded as 55.8keV.

Am I correct this should be 59.6keV? Though I'm aware Am-241 is only a low-energy source, and the general quality of that acquisition is poor, I'm worried that the calibration is way out. Here is spectra of an unknown isotope-

Image
Linear scale on the Y axis.

I don't know whether my inability to identify the isotopes recorded is due to incorrect calibration or my lack of experience!

The PDS calculated dose rate was c.1μSv/hr. This spectra was recorded un-shielded next to a person who'd just had some kind of nuclear medicine to identify a tumor. I thought it would be Tc-99m but the peaks do not match!?
Will

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

Post by Svilen » 11 Apr 2020, 00:21

You are correct that it should be 59.6 KeV, but don't expect this detector to be that precise. And even if it is, at the range where the Am241 peak is, it very likely won't show you 1460.8 KeV for K40. The scintillation detectors are not linear through the whole range. If you want to check the callibration of this PDS unit, don't look to just the extrema you took. To get more peaks, and some of them in the higher range, take a Th232-containing gas lantern mantle for example, since it is easy to find and buy.
This below doesn't look like Tc99.

Greetings,
Svilen
Svilen

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

Post by Go-Figure » 19 Jun 2020, 18:47

gravelmonkey wrote:
08 Apr 2020, 21:40
Hi All,

Finally got things up and running, I've actually had the PDS100G since 2017, it must have been one of the first of the surplus sold on ebay?

Below is a short (138 second) acquisition spectra of Am-241 - the only source I currently have to hand.

Image

The peak is recorded as 55.8keV.

Am I correct this should be 59.6keV? Though I'm aware Am-241 is only a low-energy source, and the general quality of that acquisition is poor, I'm worried that the calibration is way out. Here is spectra of an unknown isotope-

Image
Linear scale on the Y axis.

I don't know whether my inability to identify the isotopes recorded is due to incorrect calibration or my lack of experience!

The PDS calculated dose rate was c.1μSv/hr. This spectra was recorded un-shielded next to a person who'd just had some kind of nuclear medicine to identify a tumor. I thought it would be Tc-99m but the peaks do not match!?


Hello there,
To my the last spectrum looks like Th232, with calibration off by roughly 8-9%. (a factor 1.085 more or less).
This is the spectrum a classic thorium mantle
Thorium Mantle - ID - 4 Hours - BG Subtraction - Counts x Bin - No Shield - 0.045 Clean - 19-05-19.png
What made me think about Th232 is the long peak in the 800-900 keV region which could be Actinium 228 at 911 and 969 keV.
As said above calibration looks a bit off, underestimating the energy of the peaks, you can adjust that using gain and offset.

My first spectrum was off by a factor 1.3 across the board so I just increased the gain parameter by the same factor. Essentially "gain" is a proportionality factor between energy and channels, while offset moves the whole spectrum right or left, adding or subtracting a constant.
Do you know the equation of a straight line? y = mx + b. It's just like that.
y is the energy in keV.
x is the channel.
m is the gain.
b is the offset.

For most people the "normal" gain value seems to be close to 2 (some are a bit below, some a bit above), I currently use 2.09, my first setting was 2.04. Some people I know have slighly lower values.
My offset is currently set at 6.
Once you have found the "gain" setting that puts the peaks close to where they need to be you may realise they are still a few keV higher or lower than where they are supposed to be and this is where "offset" comes into play. For instance if I am very off at high energy I correct with gain because it has a bigger impact as the channel number increases, and then I use offset to adjust the lower energies (adding or subtracting a constant has a percentually bigger impact at lower values).
But in the end it's just ad adjusting process, there are many way to do it.
It's never going to be exactly perfect at all energies but you can get pretty close.

When I want to check my calibration I record a spectrum with a Thorium source and see if I am good or not.
The detector holds its calibration very well as far as I can tell, after the first big calibration change I only had to do adjustments due to temperature change, because calibration changes with temperature, and then calibration needs to be checked and adjusted.

Hope this helps.

Best.

Massimo

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