Spectrométrie avec une carte son

Bonjour à tous,
excusez-moi pour mon Français terrible ...

Je participe à l'équipe qui développe Theremino open source et matérielle ouverte pour que chacun puisse améliorer les applications de l'électronique ou la construction de leur propre.

Nous avons développé un PMT_Adapter très stables et pas bruyant pour obtenir le meilleur de tout "Spectrométrie de carte son" sw comme PRA, FitzPeak, Bekumon (maintenant traduit en anglais) et Theremino_MCA.

Ce kit est un beau morceau de l'électronique, car toute l'équipe est très exigeant.
Ce kit présente les caractéristiques suivantes:
1) Le pouvoir est dérivé de l'USB avec une consommation vraiment minuscule, ultra stable avec une ondulation minuscule. L'étage de préamplification présente un bruit de crête à crête 70microVolt seulement.
2) La valeur de la haute tension doit être réglée de façon à avoir un bon signal audio (visible avec l'oscilloscope intégré sw) entre les valeurs minimales et maximales acceptées par le PMT (le gain est une fonction linéaire de la haute tension et doit être réglé pour avoir un bon signal audio sans saturation de la carte son, le gain de correction pourrait être obtenu par le logiciel).
3) En utilisant notre USB carte son externe (dongle) modifié, vous aurez tous les paramètres MCA indépendants du système principal multimédia du PC, de sorte que les niveaux de volume, le réglage automatique de gain désactivé et ainsi de suite pourrait être fixé pour le dongle USB seulement, sans interférer avec de la musique, Skype, etc
4) Les deux logiciels PRA et Theremino_MCA fonctionnent sur Windows, Linux par Wine, CrossOver Mac OSX par, Parallels, VirtualBox, etc

Ciao,
Roberto
www.theremino.com

Hello Roberto,

Thank you for your message. What's the price for the PMT_Adapter kit ? Is it assembled/soldered or not ? It seems that your electronics scheme is much butter than the Gamma Spectacular from BeeResearch.

Have you tried to use semi-conductor detectors ? (like CdZnTe or HP-Ge ? )
Thank you for your answers.

http://www.theremino.com/blog/gamma-spectrometry
http://www.gammaspectacular.com/

Hi northstar,
first of all thank you of your interest in the Theremino System.

We tested the PMT_Adapter with NAI(Tl) and BGO scintillation crystals only.
The crystals are optically coupled with a Photomultiplier Tube so every time a particle strikes the scintillation media a photon is emitted and the PMT converts it into an electric pulse which amplitude is proportional to the energy of the striking ray.
The obtained pulse is then conditioned and equalized to be correctly classified into a bin of the Multi Channel Analyzer.
I don't know which is the shape of a CdZnTe or HP-Ge generated pulse. However the hw and sw are open source and could be tailored to manage these pulses.
I'm going to ask to Alessio Giusti that is our radiation expert and to Livio Cicala that is the electronic engineer. Stay tuned!
The Theremino Team is a research and no profit organization and whoever wants either to build or modify our modules could do so. The schematics are on http://www.theremino.com/technical/schematics and the firmware and the software are freely downloadable from the Theremino web site.
Some of moduled of ours are built and sold by "ideegeniali" and by Alessio. Look at http://www.theremino.com/contacts/price-list .
The PMT_Adapter has a price of about 110 Euro (I don't know if the shielded case is provided or not). Please contact Alessio@Meteolink .
We are going to engineer some semi-conductor radiation detectors but in the short time we are studying an Impulsive Ionizing Chamber to measure the Radon concentration in the air.

I'll write here about the CdZnTe or HP-Ge compatibility ASAP.

à bientôt,
Roberto

Hello northstar,
I asked to Alessio Giusti and to Livio Cicala about the semiconductor detectors.

HPGe detectors are really expensive and need to be refrigerated to work well, so we didn't investigate this issue.

Instead the CZT CdZnTe detectors work well at ambient temperature and could be connected to the Theremino PMT_Adapter being powered by an High Voltage.

As you can see in the http://www.theremino.com/technical/schematics web page, the PMT_Adapter powers the detector with a stable and continuous High Voltage.
The connection to detect the pulses is "AC coupled" as discussed in the page http://cremat.com/CZT_detectors.htm?gclid=CLPMptP-x7UCFQLwzAodBEcA1g .

To connect a CZT sensor, please follow these rules:
- Before connecting the sensor to the PMT_Adapter, trim the value of the High Power to the value specified into the sensor datasheet. These sensors could be damaged by a too high voltage, even if the power supply of the PMT_adapter delivers only a little current.
- Pay attention to connect the positive high power to the proper wire of the sensor and the gnd to the negative wire of the sensor. An inverse polarization could damage the sensor.
- The pulses of a CZT are really narrow, a few nanoseconds, but the preamplification and conditioning circuit should be able to enlarge them to some microseconds.
- In the gamma spectrum, the peaks should be very narrow, the FWHM should be about 1% . Look at http://www.amptek.com/cdte.html .
- To have the best results, the Theremino_MCA software should have to implement the 'Rise Time Discriminator' (RTD). Computing this function in software should lead to better results than doing it by hardware.
- To develop this RTD filter, we need either a CdTe or a CdZnTe sensor that don't know how to buy.

Please contact the Theremino Team on the Blog http://www.theremino.com/blog/gamma-spectrometry to discuss these items.

Ciao,
BoB :-)

Looking for some CZT sensors and detectors to buy, we found images and schematics of the CdZnTe probes of the URSA-II gamma spectrometer.

EV CZT CdZnTe modules - These probes could sometimes be bought on eBay.

Look at the picture and the schematics: http://groups.yahoo.com/group/GammaSpectrometry/attachments/folder/1224057931/item/1517826320/view?picmode=original&mode=tn&order=ordinal&start=1&dir=asc .

A lot of times the sensor is Ok but the electronics is failed. However we only need the sensor because the HV and the preamp/conditioner is already into the #theremino PMT_Adapter.


However I read that:

- The electronics is usually broken:

> If anyone's module isn't working, my first guess is that the FET is kaputt.


- The HV has to be very carefully set:

The bias voltage should be increased from zero very slowly in order to avoid a sudden HV transient input on the FET gate due to capacitive feed through via the CZT element. This goes for all preamps (FET and bipolar), using all sensors (PMT included) when there are no protection diodes on the input. I am not so sure I would take the bias voltage past 500 VDC, but I am not really certain of that. The easiest (and perhaps the safest) way to determine an unknown bias voltage is to start low and slowly increase the HV until noise begins to dominate the signal, then back off to a lower voltage.


- The handling of the sensor is problematic:

If you open it up and look inside there is a superfine gold wire from the top of the semiconductor to the board, and if this wire is damaged the unit has had it.
It worked for me with a 60V bias. If you look at the cables, you can see that it is not designed for 1000V, the cable insulation just isn't rated for this kind of voltage. Unlike a PMT the signal does not become stronger with higher bias voltage.
Faster sampling is the way to go, I was using an E-MU sampling at 192 Khz


- This sensor is sensible to the low energy Gamma and X-rays, maybe it is useful to do XRF - X Ray Fluorescence:
Remember these are not going to pick up high energy gamma, but they have a great resolution in the X-Ray region. I think they would make a good XRF.

Thank you very Much Roberto. I will think to buy a PMT_Adapater kit, I'll let you know.
For the CZT, I know EVProducts but my favored supplyer is RITEC from Latvia (from 5mm3 to 1500mm3).

http://www.ritec.lv

Dear northstar,
I'm writing you to underline that you should be very careful to power supply your expensive CZT probe.

In past emails I wrote:

To connect a CZT sensor, please follow these rules:
- Before connecting the sensor to the PMT_Adapter, trim the value of the High Power to the value specified into the sensor datasheet. These sensors could be damaged by a too high voltage, even if the power supply of the PMT_adapter delivers only a little current.
- Pay attention to connect the positive high power to the proper wire of the sensor and the gnd to the negative wire of the sensor. An inverse polarization could damage the sensor.

Please note that to correctly measure the High Voltage you need to use a very high impedance voltmeter plus a resistor divider made with resistors of tenth of megaohms.
Being the Theremino power supply a weak one, measuring with a too little impedance would give you little HV values but when you only connect the CZT probe the voltage will be higher than measured!
Be careful to connect your probe!

Ciao,
Roberto