Gamma Spectrometry Forum

This is PART 1 my review of the Mirion PDS 100G, Spectrometric Personal Radiation Detector.
I’ve been using this detector for three weeks now and I am really happy with that.
This device is as portable as it can be, just 12x7x4 cm, so it’s smaller than my Geiger counter, but contains both a neutron and gamma detector, it only weights 300 grams. Not only it gives you the dose rate with a good degree of accuracy but it’s also a multichannel spectrum analyser (1024 channels).

The gamma detector is a 9 cc CsI(Tl) crystal (approximately 22mm diameter by 25 mm), the energy range for gamma is 35-1600 keV, but it actually goes a little bit higher than 2000 keV

You only have two buttons, but they are enough to access and browse the menu, so you never feel limited by that. It can work in two modes, “search” and “detect”.
In “search” mode the detector gives you CPS using a short integration time allowing a faster response, although, as the manual points out, that is at the expense of a larger statistical fluctuation.
In “detect” mode you have both CPS and dose rate in µSv/h, in this mode you can access the MCA feature. Spectra can be acquired in 512 or 1024 channels. You can set a limit of the data acquisition both in seconds (up to 999 seconds) and counts (up to 999 million counts). This might sound like a problem, 999 seconds are less than 17 minutes, but once any of the two limits is reached you can simply press “resume” and the data acquisition will continue. I don’t know what the real limit is, I recorded spectra almost 3 hour long.

The device will store in its memory up to 50 spectra with 1024 channels or 100 spectra with 512 channels. To good thing is that you can transfer data to a PC or a mobile device.

For this review I tested my good old Radium Clock. Well, I actually owned it for less than three months, but it’s old nevertheless. As soon as you start the spectrum acquisition the screen shows you the total data acquisition time, the total number of counts and the average dose in µSv/h during the acquisition time. The data are updated every second. For this particular measure I stopped the acquisition after 1998 seconds. When the acquisition is over you can save the spectrum in the detector’s memory. Once the data are saved you can transfer them using Bluetooth or IRDA. Part 2 is on the way.

PART 2.

I got myself a transformer 10’’ Tablet/PC with Windows OS so the PDS software can run on it. I wanted something as portable as it could be in order to be able to record data and analyse them while in travel. Just a few seconds and you can see your spectrum on the screen, both in Logarithmic and Linear view. You can also see real time data from the detector (graph and reading). Here’s a better view of the spectrum in Lin and Log view. Calibration looks pretty good. You cannot subtract the background, so what you have is "background + sample". If you access the software as administrator (which you can do by logging in using username and password which are in the manual) you can recalibrate the detector if necessary. I had to do that as soon as I started to use it, about three weeks ago, because in the first spectrum I recorded calibration was off by 30% across the board. I only had to slightly adjust calibration once since then. You can see the spectrum screen the average equivalent dose rate is showed.
Whatever the actual acquisition time was the software screen will never show an acquisition time longer than 999 seconds. So if you want to remember what the average CPS was you have to save the duration of the test separately (like for instance taking a photo of the detector display once the acquisition is over).

Here you can see the spectrum analysis of the test I did on the Radium Clock with my GS 2’’x2’’ NaI(Tl) last May (viewtopic.php?f=5&t=512).
You can see in terms of exposure (and equivalent dose) the result of my calculation based on the spectrum and that from the PDS are in good agreement. It's worth mentioning that the background was not exactly the same, although difference is small, and that the distance between the sample and the crystal cannot be exactly the same for both measurements. You can in theory also have isotope identification adding another software component.
The device is really amazing and I already have a list of places, both in Italy and abroad, where I want to take some measure with it.


But I also have some small “complaints”.

1 – the average equivalent dose on the detector display shows three decimals, but once you transfer the data to the software the third decimal place is lost. So 0.217 µSv/h becomes 0.21 µSv/h.

2 – The spectra can be saved in the computer or tablet memory, so they can be erased from the detector’s memory. Once in the computer files are surprisingly small, just a few Kbs. Nothing wrong with it, only problem is if you load the spectra from the computer instead from the detector the average equivalent dose rate isn’t there (there’s just a zero there), so this is another data you have to save separately, unless there’s another way I still didn’t find out about.

3 – The detector runs on two AA batteries, which can be alkaline or rechargeable (the charger is included). Every time you turn on the device it will ask you to set the kind of batteries currently on use. That’s perfectly ok, but the charge level indicator at times seems to go up and down a bit erratically. As soon as you exit the Bluetooth mode it looks pretty down, then it goes up again, so it’s not easy to exactly know how much battery is left.
When the battery is really down the detector will automatically exit the Bluetooth mode after just a few seconds. so that’s the best indication you have.

A part from these few things, that’s one of the best “toys” I have ever had.

[broken link removed - Steven]

Hi Massimo,
That is a great looking toy you got there, small and still with a lot of options to measure, very nice!
I am not going to ask you the price because I know they are really expensive but it still a great buy , I know you will have have lots of fun with it.
Luuk

luuk wrote: ↑

11 Aug 2019, 17:52

Hi Massimo,
That is a great looking toy you got there, small and still with a lot of options to measure, very nice!
I am not going to ask you the price because I know they are really expensive but it still a great buy , I know you will have have lots of fun with it.
Luuk

Hi Luuk!
In order to find out what the price actually was I had to send half a dozen emails, it looks like these companies are not very used to deal with single private costumers.
In the end they told me it's in the region of 3500 Euros, which is more or less the same of the alternatives I was considering.

But then I found out there was a stock of (barely) used ones on sale on ebay for less than 20% of the price of the new ones!
[broken link removed - Steven]
That of course gave this option a clear edge on the opposition. There are still some available by the way...

Apparently this detector was used by the security personnel of the 2012 London Olympics (which can be checked here https://erncip-project.jrc.ec.europa.eu ... _James.pdf) and now they are selling them little by little.

I have to say the detector looks as new as it can be, there are no scratch at all on the display, I am not sure it's actually been used at all before it got here, and the fact it was not even calibrated is another indication of that.

Only "problem" is the software, they are going to give you an "unofficial" copy stating clearly they don't guarantee it will work, so I took a small chance there, but in the end it all worked just fine and I had some "help" for the registration.

Yeah, I expect to have plenty of fun with it, and I have to thank Pilgrim for making me aware this detector existed.

Hi Massimo,
That is a good deal still not cheat but a real nice detector!
Did you know that we make all the detectors used inside your dosimeter ? so they are good for sure :-)
Luuk

luuk wrote: ↑

11 Aug 2019, 19:01

Did you know that we make all the detectors used inside your dosimeter ? so they are good for sure :-)
Luuk

Tell me more about it!

Hi and thank you very much for recommending this very nice device for a really good price!

I bought it very spontanously on Monday because it looked so interesting to me and it arrived already yesterday :-)

I played with it a little bit and I'm impressed about the sensitivity and good handling. I could not try the spectrometry function because they did not send me the software, and I did also not ask explicitly for it. But I probably have the possiblilty to get it from a friend, I will know tomorrow. Otherwise I will contact the seller again. Maybe even you could send me a copy...? But I first wait for the friend's answer.

However it is so small and portable and nice detector, when I (hopefully) soon have this software I will take it to Ukraine Chernobyl holiday trip in September and make nice spectra with it :-)

Janni wrote: ↑

15 Aug 2019, 19:06

Hi and thank you very much for recommending this very nice device for a really good price!

I bought it very spontanously on Monday because it looked so interesting to me and it arrived already yesterday :-)

I played with it a little bit and I'm impressed about the sensitivity and good handling. I could not try the spectrometry function because they did not send me the software, and I did also not ask explicitly for it. But I probably have the possiblilty to get it from a friend, I will know tomorrow. Otherwise I will contact the seller again. Maybe even you could send me a copy...? But I first wait for the friend's answer.

However it is so small and portable and nice detector, when I (hopefully) soon have this software I will take it to Ukraine Chernobyl holiday trip in September and make nice spectra with it :-)

You are welcome Janni.
Mine will come with me to Fukushima this coming November.
Let me know if you need anything, I am happy to help.
If you have a friend who has the software try to find out if he also has the additional software for isotope identification. i personally prefer identifying them myself, and I think a software can easily get it wrong when it comes to that, but it'd be still nice to have it.

As for the charger: I bought an external battery charger and it works much better, I had confirmation that charging batteries inside the detector you will get an indication of "full charge" when battery are not fully charged yet, which can be confusing.

Hi Go-Figure,

thank you for offering your help! I still do not have information from my friend, but I will know soon and will also ask for this nuclid identification module. From tomorrow I will be on holiday for two weeks, so maybe it can take some more days. If I do not get the software from my friend, I would be very happy if you could give me a copy :-)

I also tried to charge my batteries, but then I found out that nothing happened because no voltage comes out of the charger. I will examine that later, but first put normal batteries inside, so it is not the most important for first. I also found out that dose rate is not completely correct. I have some uranium minerals and all of my other radiation detectors show higher dose rate. Anyway the reaction time of the PDS-100 is really amazing! Maybe dose rate can be calibrated with the software, do you know?

I have also visited Fukushima this year in June. But I did not have spectrometry equipment there, only normal geiger counter. But I took some soil sample of the area to analyze at home. But shame on me, I did not do it until now because all the weeks I was too busy with other things...
But after some more holiday I will analyze and put in the forum. I even have a germanium detector and brought to working condition in the last months, that is really phantastic device! But because of beeing too busy I did not operate it for several weeks because I first need to bring liquid nitrogen and that is little bit complicated logistic task. ;-)

Janni wrote: ↑

17 Aug 2019, 06:49

I also found out that dose rate is not completely correct. I have some uranium minerals and all of my other radiation detectors show higher dose rate. Anyway the reaction time of the PDS-100 is really amazing! Maybe dose rate can be calibrated with the software, do you know?

Consider this device has a neutron detector above the gamma detector, so even if you put the sample at contact there are at least a few millimetres between the sample and the crystal. That has an impact on the dose you read. At small distances few millimeters can make a measurable difference.
Besides the distance, in my experience it's easy to have a 10-20% difference measuring a hot sample if the relative position of sample and detector is not exactly the same, same angle, same everything, there's always a spot slighthly more radioactive than the others. That's true in particular for ores and rocks which have a pretty irregular surface.

Where did you go exactly near Fukushima? and what kind of read did you get from the geiger counter?