Hello
I'm carrying on making experiments on the different components of my pmt setup in order to understand how things work.
So I tried to play with the load resistance value.
- PMTconnection résistance de charge.jpg (69.65 KiB) Viewed 2680 times
The Pdf document about Theremino suggests 1M although many profesionnal doc advocate 50 Ohm. I understood that it influences the lengh of the pulses through the coupling capacitor if we want to process the signals with a standard sound card. But it works only if a pulse shaper is used. I use the shaper from the Pmt adapter from THermino :
- crude shaper fromt PMT adapter.jpg (94.66 KiB) Viewed 2680 times
Here is the effect of the use of the shaper on the pulse lengh and precision of the spectrum.
So I used a 3M load resistance as it gives the pulse around 150-180uS lengh. The spectrum shows the peaks with better precision.
Here is Radium 226 spectrum.
Also I noticed that the nature of the material on with I put the sample On as a big influence on the spectrum. If I use lead the peaks shows more energy on some parts. If I used just my table the spectrum was a bit different. I suspect some Xrays produced by fluorescence but the general aspect seems better with lead than wood.
