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. So we recommend that you contact Lello, 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. Luca CAMPANA says:

    Thanks for the exhaustive clarifications.

    I will keep you informed of any developments



  2. Paul says:

    Hello, I’m trying to re-activate a Theremino PMT Adapter V3.3, which I bought some years ago.
    If I insert the modified USB stick into my computer it shows constant LED and after a while is starts blinking.
    But whatever I do on the PMT adapter box I don’t see any “microphone” input level. I hear the transverter sound in the box. Maybe the PMT connected to the box is broken?
    How can I check if the microphone input is OK? Removing the PMT adapter box and touching the contacts of the connection cable between USB and the box does not show any microphone signal.
    Please give me some help!
    Many thanks, Paul

    • Livio says:

      Please do a right mouse button and translate in your language.

      Difficult to understand from a distance. You would need an electronics expert who, with the diagrams and some tools can understand what happened.
      I try to give you some advice…
      If Windows sees the MIC input that is added when you connect the adapter then at least the USB part works.
      When you plug the adapter into the USB Windows makes the right sound?
      Perhaps the jack is not fully inserted?
      Maybe something happened to the photomultiplier?
      Maybe he took a hit and broke the glass?

      If you really can't, you will have to send it back to one of us and we will fix it for you for free (provided there are no expensive components to buy back)

  3. Anonymous says:

    Hello Livio,

    thanks for the quick reply. By checking various PMT probes I found out that the problem is not with the PMT adapter but with one of the PMT probes. So everything should work fine from the USB adapter side.
    Regards, Paul

  4. Kai says:


    Your “compensation” feature seems to do an excellent job of improving gamma spectra. Can you point me to a description of what this is actually doing?

    In in the description of v4.2 it is called “Resolution compensation”. In on pg 35 it is called “broadening compensation”. In it is called “Software compensation”.

    Are these the same thing? What is it actually doing?


  5. Eugene Sigal says:


    I am trying to modify the 3D sound card adapter, however, they don’t make them exactly like the one in the instructions. Does anyone have the updated instructions on how to modify the audio sound card (perhaps some schematics as well).

    thank you!

    • Livio says:

      If the sound card is different no one can help without reverse engineering your card.

      My best advice is to follow the MIC signal all the way to the chip and then figure out where to cut and where to put the components.

      I’m sorry but only you (or some of your friends who are experts in electronics) can do it.

  6. Jay Cast says:

    Hello Livio, a have a theremino master DIL-V5.

    How can I make the Theremino MCA recongnise the signals from USB port of my computer ?

    The Theremino MCA only recongnise sinals of the microphone.

    Or how can I do to get a analogic sinal on pin 1 and transmit a digital sinal from pin 2.

    • Livio says:

      The Theremino-MCA application only recongnize the microphone signals.

      If you do not have the modified sound card, you could use any sound-card with a MIC input, also without modifications.
      The noise at the low energies will be more than normal but it will work.

      • Jay Cast says:

        How can I do to receave an analogic signal on the Theremino Master DIL-V5 and transmit to the sound card with a MIC imput ?

        thanks for answering me

        • Livio says:

          The Master can not receive audio signals.
          You can not use the master for the Gamma Spectrometry.

          You MUST use a NaiTl Christal and a PMT tube and then connected the PMT to a PMT-Adapter and then connect the PMT-Adapter output to an audio card MIC input.

          A better alternative is to use a PMT_AudioAdapter directly connected to the USB

          Call to Lello if you can not build these components.
          Lello =
          Lello seller on eBay = maxtheremino

  7. Anonymous says:

    Hello Livio,

    I am working on making a portable version of Gamma spectrometer. Where can I get an MCA system for Apple (iPhone and iPad)? The one listed on Apple store is just a Geiger counter (Geiger bot) and doesn’t have a spectrometry function.

    Thank you,

    • Livio says:

      Sorry, we know windows systems only and so we can not help about this.
      To make working our projects on systems other than Windows is very difficult and requires a deep knowledge about programming those systems.

  8. Anonymous says:

    I am talking about the same system by Theremino you guys mentioned on the same webpage where we are right now. Just scroll up a few:

    “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.”

    • Livio says:

      Sorry, I was thinking about our MCA software, but if you need the hardware only maybe it is possible.
      Now I explore this old project (about 5 or 10 years ago) and then I write another message explaining how to obtain this hardware module or build it (if possible).

    • Livio says:

      I looked at Alessio’s section. Now a small tablet with Windows would cost even less than 100 Euros and the resulting spectrums would be significantly better.

      But if you really want to do it with Apple you will need:
      1) The Geiger Bot app :
      2) A PMT Adapter that you can build yourself or have it built by Lello as explained here:
      3) Power the PMT Adapter with a 5 volt you can find it everywhere but be careful that it must not be noisy. A power bank would do very well while a 220V power adapter would not do.
      4) Add a resistive divider or a trimmer to the PMT Adapter output.
      5) Connect the PMT Adapter output to a Jack suitable to the Apple input (probably it will take a 4-pole jack and the signal should be the tip)

      If you have Lello do it, I’ll explain to him how to divide and which Jack to use. But in this case you will also have to tell exactly which Apple you have to connect it to and if possible tell us how the Jack for the microphone input must be made.

      To contact Lello write your mail in the message data (we will not publish it),
      or write to Lello at:

  9. Anonymous says:

    Ok thank you!

  10. etc says:

    Hello Livio,
    I’ve been using the MCA for a good while now for XRF above 10 keV, the lowest possible with my sensor NaI PMT set up, and with good results. Thank you for providing this application.

    However, for the energy ranges below that I plan to use a X100-7 diode sensor for which I have a Micod amplifier and shaper board as described by Lodovico in the article ‘Si-PIN Photodiode with Micod CSA-SA’. He mentions in the article that the pulse width of the output is 15 uS and not very compatible with the MCA. Is there a way to improve the the MCA’s response to the signal perhaps by tweaking settings?
    Also, I have not been successful in adding adding new entries to the Isotope list. How does that work?
    Kind regards

    • Livio says:

      Hi ECC

      I advise against photodiodes, we have never managed to make them go well, too noisy (compared to the right PMT and in the best working conditions as we have indicated). However you can experiment with the application controls (especially the Baseline test and Params panels) and if you can’t get it right we won’t know what to do or what to change.

      The Edit Sample Rows File button is only used to select some commonly used isotopes, you can add or remove some. But it is only used to select the square boxes.

      The long table is stored at the end of the INI file next to the application executable. You can edit the isotopes and also add new ones as explained on page 5 of the instructions.


  11. etc says:

    Hi Livio,

    Thanks for your advice concerning photo diodes, I hear you there. Seeing that I have all the parts already – including some Am241 buttons – and can’t afford buying a another better, low energy PMT just for XRF below the 10 keV range – I may give it a try anyway.
    What I did already plan for improving the diode noise situation – other than using batteries as power supplies – is cooling the detector diode’s small mounting board (amplifier board as well?) with a Peltier element.
    Starting with an existing fan cooled set up which can pull down a leaky and uninsulated small box to -7 C should provide some initial data.
    If a measurement chamber was evacuated to say 500 mBar – what would be the effects? Would that help to increase the energy reaching the sample from the Am241 buttons and in turn the detector?
    As for the Am241 buttons illuminating the sample – what would their most effective and practical angle and distance relative to the detector?
    Following instructions I successfully added an Isotope. Thank you.

    Kind regards

    • Livio says:

      The isotope list is at the end of the “Theremino_MCA_INI.txt” file. You could edit this file also with Notepad (when the MCA app is not running).

      You could also find in the folder “Extra” the following lists and other useful files:
      – Isotopes_Energy.txt
      – Isotopes_Energy-with-medicals.txt
      – LibraryNaI.txt
      – XRFTable.txt

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