I don´t like my background...

[ManuelDiaz]

Hi Folks!
So, still testing without shielding, and I feel like something must be wrong with my detector assembly. After my successfull Cs137 testing, I went to test the Thorium Mantles... and I was surprised to still find the 32kev peak, so I decided to check my background as well... and that peak is there again. And it seems to be there regardless of where I test, what I test or for how long I test (only with Cs137 it seems to be a bit bigger)



So... If I am correct, the background spectrum should look like an inverse logarithmic graph, right? What am I doing wrong? Could it be an issue with the voltage divider? I think it might be, but I´d rather not open it up again if anybody has suffered this before and has a better idea!


Thanks and kind regards,
Manuel.

[Sesselmann]

Manuel,

Strange, I wonder if your detector has an Am source built in??

Some detectors have a tiny source built in for the purpose of stabilising drift, the MCA can then lock onto this peak and keep the drift stable, Becqmoni has such a function.

Not suggesting this is the case with your detector, as there could be other explanations, but if you add a shield and still get a peak there, there might be something. Electronic noise is another possibility, try switching off any lamps and transformers you might have on your desk.

Steven

[ManuelDiaz]

Manuel,

Strange, I wonder if your detector has an Am source built in??

Some detectors have a tiny source built in for the purpose of stabilising drift, the MCA can then lock onto this peak and keep the drift stable, Becqmoni has such a function.

Not suggesting this is the case with your detector, as there could be other explanations, but if you add a shield and still get a peak there, there might be something. Electronic noise is another possibility, try switching off any lamps and transformers you might have on your desk.

Steven

It doesn´t have any source, I´ve built it myself with the help of Luuk. It consists only on the crystal, the PMT, the connector with the voltage divider and MUmetal grounded.

I strongly believe that this must be an issue with the voltage divider. Soldering everything in such a tight space was a challenge, and I´m afraid that something must be wrong. However I´ve opened it up this morning and checked every resistor with the multimeter and everything seems fine (my initial suspect was a resistor wrongly connected or in a wrong condition that might had been delivering a different voltage to one of the dynodes).

Now I am honestly a bit stuck... I don´t know what else to check! I might have to desolder the complete VD and re-do it I am afraid... It´s the only thing I suspect might be tricking me.


The funny thing is that this spectrum on the Theremino website looks exactly like mine haha

[Sesselmann]

Manuel,

It is unlikely that you voltage divider is causing a false peak at 32 kev. When you are confident there is no source, you look for electronic noise usually it is something with a regular frequency, you can do some analysis in PRA, using the advanced filter you can single out the pulse and find the mean interval etc..

It is a sharp peak, so it is something very consistent causing the pulse.

Steven

[ManuelDiaz]

Manuel,

It is unlikely that you voltage divider is causing a false peak at 32 kev. When you are confident there is no source, you look for electronic noise usually it is something with a regular frequency, you can do some analysis in PRA, using the advanced filter you can single out the pulse and find the mean interval etc..

It is a sharp peak, so it is something very consistent causing the pulse.

Steven

Hi Steven,
cause identified! It was my USB port. I switched to an external power source and the peak has dissapeared... amazing!

[ManuelDiaz]

And I answer to myself: Not everything is good in paradise. The Samsung USB charger starts delivering some additional noise when it heats up after some time running, so I need another adapter. This evening I will test with an external USB powerbank, and I have already ordered an USB plug that is supposed to be very stable (I hope it handles the noise good then) I'll post my results in case I can recommend it.

This is being more difficult than I expected!