Gamma Spectrometry

The Theremino_MCA while being completely Freeware and OpenSource is a true multi-channel-laboratory Analyzer.

More information:
– Electrical schematics and Assembly plans:
– Software:
– Hardware, DIY and kits:
– Images and videos:
– Article about Open Source Electronics: crafts-to-gamma-spectrometry-signal conditioning-of-


Hardware for the Gamma spectrometry

The Theremino_PmtAdapter contains a feedback loop that can keeps the tension stable even in the presence of strong temperature fluctuations. In this way the calibration remains accurate over time and rows of isotopes do not move and do not expand.

ATTENTION: For optimal performance use pipes PMT wired as shown in the file PmtAdapters.pdf – PMT for low impedance tubes (with resistors 1 Mega or even from 560k) cannot operate with these adapters. To use them you should replace their resistors, as indicated.

This adapter can be used with the well known freeware software PRA (We thank Marek Dolleiser for having paved the way for this kind of analysis, its software PRA is a reference for many years and helped a lot) but only with the Theremino_MCA you can do filtering and deleting useful background to get maximum information within a reasonable time.

This file includes the design of PCB, le immagini e le simulazioni SPICE: PMT_Adapter_V3.1
This is version 3.2 con molti piccoli miglioramenti: PMT_Adapter_V3.2
This is version 3.3 con ulteriori miglioramenti: PMT_Adapter_V 3.3

Most salient features:
– Compact only 50 X 70 mm
– No initial thermal drift due to the feedback loop.
– Adjustable voltage from 500 to 1500 V
– Very low power consumption only 10 mA @ 5 V
– Very low ripple only 100 UV
– Protected against short circuit
– Maximum power output 100 MW
– Preamp circuit and pulse enlargement (from 3/5 uS to 100 uS to be read by a PC sound card)

Caratteristiche tecniche:
– Compact only 50 X 70 mm
– No initial thermal drift thanks to the feedback circuit.
– Adjustable voltage from 500 to 1500 V
– Very low consumption at 5 v only 10 mA
– Ultra-low ripple only 100 UV
– Protected against short circuit
– Max power output 100 MW
– Preamp circuit and widening of built-in impulses (carries impulses from 3-5 us to 100 us to be read by a PC sound card)

The simple and neat reduces manufacturing defects and makes them readily apparent.

In the following pictures you see the PMT in rehearsal.

The circuit diagram and an impulse to sample that shows the noise level of ’ power supply, Note that this is a low-energy pulse.

In the latest versions of PmtAdapter noise is less than 100uV. Practically the only noise due to sampling in 16 bit soundcard, as shown in the two following images.

The first picture shows only noise sound card, the second noise with a separate connected.


The complete system


The Pmt Adapter is not in production, You can build it but contains a number of special components, hard to find and expensive. Why you should turn to Alexei, who knows how to find a cheap components and also print a number of PCB for friends:

The theremino team only deals with research and does not sell hardware. The system is completely "Freeware", "Open Source", "Not for Profit" and "DIY", but there are manufacturers who can provide modules assembled and tested at a great price. One could hardly self-build them spending less. For a list of the producers read this page:

A hoof to the Hamamatsu PMT R6095 (and the like)

In this ZIP file the complete project Eagle and the GCode for the cutter: PMT_Socket

These pictures show how to adapt the connectors to printed and how is the plinth ended (click on images to enlarge them)

The capacitor might also be welded across (with two insulating sleeves on leads) and, to avoid short circuits with the outer aluminum tube, It is good to wrap the whole area from PMT to printed circuit board, with a sheet of plastic sheet..

An MCA system for Apple (iPhone and iPad)

By popular demand Alessio has designed a special version of PmtAdapter, usable with software available on iPhone and iPad. The software is called Geiger bot, ed è un riferimento per la comunità Apple.

Theremino system - iPhone_MCA

The circuit diagram is very similar to PmtAdapter for PC, but I added a battery (There is the ’ USB powered). The signal amplitude is reduced considerably, You can send all ’ mic input, that otherwise would saturate and would distort the pulse shape.

Theremino system - iPhone_MCA Am241 Theremino system - iPhone_MCA - Cs137

Here you can see the spectra obtained with Americium and cesium. Thanks to the wonderful display resolution “retina”, the words are so small, that do not disturb the vision of the beautiful black background.

We are light years away from a true MCA, line width “FWHM” (that is the most important parameter for an MCA) is overwhelming. Minor details of the spectrum are completely invisible. Here's the same Spectra produced by Theremino MCA:

Theremino MCA - Am241 spectrum Theremino MCA - Cs137 spectrum

With a Tablet 12 inches by 180 Euro (with Windows 10 and shipping included in price), you would have a portable instrument much more convenient and accurate. But the satisfaction of using an Apple system, It costs an exaggeration, is priceless!

Calibration and temperature

The Pmt Adapter and the photomultiplier consume only a few tens of milli Watts, that are insufficient to cause significant temperature variations. So you don't have to wait for a “warm up time” between the ignition and the measures. And there ’ is not even a progressive warming during very long measurements.

Though the crystals change with ambient temperature performance scintillators, as you can see in the image below:

Scintillation chrystals temperature response graph

Note that the response to temperature is not linear and that changes even slope from positive to negative, right in the area of normal temperature. Whereby an automatic correction would be inaccurate. It would take a correction table to be calibrated for each Crystal and this would be very complicated and ultimately unreliable. Much better make an adjustment with two markers before each measurement.

Check with the marker before each measurement is quick, accurate and very reliable. It is recommended to keep in place two small samples (for example, Caesium and Americium) at appropriate distances, so you always have two small rows of reference. Caesium is weaker and you hold it close enough to the probe while l ’ Americium hold about ten centimeters, or is enclosed in a capsule, to decrease its activity and keep him close to the probe.

The two lines should be the same height and small enough not to disturb the measurements. If you do not have to measure precisely the cesium and l ’ Americium, then the two markers can always stay in position. See their lines on the final chart (possibly commented) from the security that the chart is perfectly calibrated.

Build a well in lead

To use to measure the level of radioactivity and radioactive substances, natural background.


The measure consists of a base plate, plus some concentric cylinders, of various sizes and thicknesses. Among the components leaves something’ of slack, in order to facilitate the Assembly ’.

The material is actually brass lead, to distinguish it from the ’ probe grey aluminium, While the piece of inner cylinder (barely visible) is the unique ’ of plastic, with concentric ring in lead.

All the lead parts were made from sheet metal 1,5 mm thick, cut with a common Bill-sheet and shaped by hand, wrap around cylinders of aluminium/steel/plastic I had available (used only as “DIME”).

The base plate is made by folding several times a strip of sheet metal of equal width, getting a decent thickness.

Sheet bends easily around the straight edge of a table and flattens with hammer taps. The lead is very malleable.

All the pieces were wrapped with paper wide enough, so handle them does not come into direct contact with lead, that tends to get your hands dirty. Also why is good to calculate a little’ of slack between the various diameters of pieces, so then that paper coating doesn't break any insertion/extraction of cylinders all ’ same, that partially must fit one inside ’ more (as for the cylinder and top shirt)

To measure you follow this pattern:

  1. First arises on a table the base plate and the cylinder base;
  2. You insert the sample to be tested in the base tube, so that it touches the inside (lower) Dell ’ ring of the measuring Chamber: You can tuck under to it appropriate spacers;
  3. You put the measuring Chamber (plastic cylinder and lead supportive ring) so the below sample is centered on the bottom of ’ ring;
  4. He slips his shirt more than basic ’ inside the cylinder: It will support the plastic pipe and concentric ring of ’ will lead to the hole to allow subsequent insertion of the probe;
  5. You insert the probe : in my case straight draw in ’ ring of lead measuring nursery.

From the tests I've done this setup reduces background noise for almost 20 CPS to 3,1 CPS

Marco Russiani

Download this project, complete with more information and pictures:
Theremino System - Theremino_Pozzetto_di_Misura_ITA.pdf
Theremino System - Theremino_G-Ray_Test_Chamber_ENG.pdf

  1. Martin Lundquist says:

    Currently using Dolleiser’s PRA (Pulse Recorder & Analyser version would very much like to try the MCA unit as described. Where do I obtain the hardware and software? This is a small research project for Dully Research Inc.
    Regards, Marty

  2. Martin Lundquist says:

    thank you for your prompt response, very much appreciated will follow your steps as outlined.

  3. Ron Sparks says:

    Sig Cicala,
    I really appreciate your paper “Tecniche di condizionamento del segnale per la Spettrometria Gamma”. Unfortunately I speak almost no Italian. So I used a few Linux programs and Google translate to convert your paper to English.
    It may not be of any use to you, but if you would like my English translation of your paper — I would be honored to email you a copy.
    My project will most certainly build off of your work and I have already credited you on my project blog.

  4. NIRvaScan says:

    Excellent and decent post, I found this much informative, as to what I was exactly searching for. Thanks for such post and please keep it up.

  5. Ian says:

    Thank you for your great work. We are using the Theremino MCA 7.1 software in our university research and we are very happy with it (in combination with a Gamma Spectacular driver and an X-ray probe).

    One problem we have is that the background spectrum (zero input, no sources) looks different when I connect to the computer that runs Theremino MCA 7.1 remotely via Teamviewer. In that case, we start to get much more counts/noise/pileup in the low KeV region. When I disconnect from Teamviewer and start a new run, then the counts in that region are down again.

    I suspect this has to do with the CPU load of the computer that runs Theremino MCA. Teamviewer adds about 20% CPU load when connected. I suspect similar issues may occur when the CPU load varies due to other reasons e.g. due to Windows Update, virus scan etc. This is a problem for us since we need to have a high reliability of baseline spectra, as long as no source is present. Have you encountered such an issue before i.e. that the spectra change depending on the CPU load even if the input signal remains the same (background with no source in our case)?

    • Livio says:

      Tested now with TeamViewer and no difference in noise observed.
      So I suggest to make further tests in the following areas:
      – The Audio-Recording panel properties (Maybe you selected stereo-mix instead of microphone? Maybe you are not using the modifyed audio card? Maybe some recording property changes when TeamViewer uses the audio?)
      – The TeamViewer audio preferences. Try to set properties to not use audio.
      – The power supply that comes from the USB and goes to the audiocard (maybe the 5 volt noise increases when using TeamViewer).

      • Ian says:

        Thank you very much for your quick response, Livio. I will carry out more tests here and will report back with more detailed information.

        • Ian says:

          Hi Livio, I observed this issue over time and I think the last suggestion that you made was the solution: once I switched from the computer’s USB 5V supply to a lab power supply with 5V DC, the problem stopped to show up.

  6. Ian says:

    We use the Gamma detector close to an ultrasound transducer. When we’re very close, we sometimes get pulses which are clearly not due to radiation but due to certain kinds of ultrasound-induced mechanical vibrations affecting the detector. Fortunately, in the pulse shape visualizer, I can easily identify those “fake” pulses because they don’t have a real peak and stay up for a long time. See the screenshot here: Unfortunately, Theremino MCA still recognizes them as valid pulses. Would it be difficult to change the Theremino MCA source code such that these type of fake pulses without real peaks are filtered out and treated as invalid? Thank you for any help or any advice!

    • Livio says:

      The pulse detection code has been stable for many years and works so well that we prefer not to risk generating defects. And anyway it would be just a patch.

      Since you see impulses, it should not be difficult to find a solution to eliminate them.

      Inside the probe there is a very delicate photomultiplier tube containing metal grids and thin links. Certainly the ultrasound generates resonances in some of these connections. It is also possible that some of these details of the PMT tube will break because of vibrations.

      I therefore suggest finding ways to mechanically isolate the probe.

      • Ian says:

        Thank you very much, Livio, for your advice. I tried my best to mechanically isolate the probe with all kinds of foam and damping materials. This helped a lot and reduced the occurrence of the fake peaks maybe by 95%. However, we still get some fake pulses and therefore unreliable results, so I decided to finally consider filtering the remaining ones out on the software side.

        I completely understand that changing the main branch of the Theremino MCA code is risky, given how well it works. Instead, I was thinking about making a few small adjustments to the source code on my computer (i.e. reject pulses that stay up) and recompiling locally.

        I have a lot of programming experience but not so much with VB, so it would help a lot if you could briefly point me at the file in the VB project where I have access to the data for every pulse that is visualized in the pulse shape visualizer and where it is determined whether a pulse is valid or not. Just pointing at the right file/place in the project code for me to look at, would be super helpful. Thanks a lot!

  7. Angel says:

    Hi I am layman in radioactivity and mass spectrometry, but for various reasons I needed to know if you can recommend a sensor similar to this one with similar characteristics i
    to use with theremino, I would add that the particularity is that it must be very sensitive and directors I mean I need to locate gamma sources although a few mm and very weak…Thank you

    • Livio says:

      With the theremino you could build something very similar and with the same performance.

      You need a photomultiplier, a Crystal NaiTl, a PMT adapter, the application Theremino MCA and a Tablet with Windows. Parts from the application Theremino MCA and you will find links to everything else:

      Unlike the device you specified does not have an LCD Panel and buttons but you'll need to use a Tablet with touch Screen (or a desktop for laboratory measurements).

      If you want help for building ask to Alexei, There's his email address here :

      – – – – – – – – – – – –
      The device that's already shown promise heaven and Earth but “forget” explain that the reality is much less pleasant than it looks to read its features. First of all these devices seem to measure towards the front but are not at all keys. More go next to the stream with the tip and more mark, all there. But if it turns sideways and go next to the stream with the tip mark equal. If the source is small enough that you go to a meter and do not score nearly nothing left. If it is large (for example all around you) then you turn around and you're still measure the same.

      Another aspect which does not appear to read what they wrote is that sensitivity to low radioactivity you pay with time. To measure low radioactivity, just above the bottom environment then we go around with beautiful handle that show in their image but the power is switched on and you leave it idle for an hour before having steps reasonably accurate.

      It would be different if you worked in a nuclear power plant and go around with the suit. In this case you could make rapid measurements, Let's say thirty seconds. But I don't think that's the case.

      Finally, it must also be said that the isotopes that normally can be found are four or five. The other hardly can find out from a central or by medical laboratories. And it also takes a lot of experience to understand something reliable by specters. So if you do it to learn it's fine, But if you plan on using it actually things change. Things to study for months or years and eventually measure more or less what there was to be expected. A little’ of caesium in environment, some sample testing and no more than useful.

  8. Angel says:

    Hello Livio, and thanks for the reply, about the aesthetics of the project doesn't interest me much but more than anything else the substance ... I go straight to the problem so you know what it is: I would like to locate nodes Hartmann.
    In his book "the health of the Habitat" nuclear physics professor Katie Lamkin (He taught at Harvard Univ. and La Sapienza of Rome), explains how he discovered the nodes hartmann,(what feasible so far only from psychics with chopsticks) with an infrared thermography or with a nuclear spectrometer probe in German (He also used the CERN in Geneva and of ENEA) or Geopotenziometro (I don't know ...).
    at those points found an ionizing gamma radiation, very weak one micron thickness of radio226. This radiation potratta for hours can create very serious diseases and geopatologie, and the only place where we're so many hours is the bedroom, so it would be good to revisit this area with this tool. Also if I remember correctly the potassium-40 influence much the thyroid and could see even with a thermal imaging to the hundredth of a degree that this radiation produced a hypothermia, Although very weak.
    The spectrometer reported to me with a link is one of that used by him,If I understand correctly, What I'm asking is if it's worth diving into this venture that fascinates me.
    I mean I could build with an undisclosed amount too much expensive (also a few hundred euros) a similar tool? (to Lamb costs over 30,000 and) or the detection could be an arduous task since the network with these nodes are spaced approximately 2 m and placed in an area of a few mm or even microns!?
    Thank you

    • Livio says:

      You can build it with less than 300 Euro. Ask to Alexei for greater precision.

      In my experience you'll measure not nothing significant, just noise and random events. But history is full of things thought impossible that then were true, so if you really care about it you should try it.

  9. Angel says:

    I'm sorry,but I can't find your email….on this site and wetteruseful there is

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