Elementary Question on using an Oscilloscope with a Neutron detector

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Post Reply
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Elementary Question on using an Oscilloscope with a Neutron detector

Post by Dennis P Brown »

I noticed that a number of members show neutron pulses from a detector/pre-amp system using an oscilloscope. I would like to try this but the voltage output is far too high for an oscilloscope - is a high voltage probe required? I know a coupling cap is essential. But isn't the pulse height of the neutron signal in the milli-voltage range? I'd think that the high voltage would swamp this signal after the reduction via the HV probe? Coupling via a coaxial splitter for the cables and building a box with proper connectors containing a 1 or 100 M-ohm resister is straight forward so if a HV reduction is the proper method - if so, I'd guess that is the way to go.

As someone who has never used a scope except a handful of times and that was only with signal generators just to see its function, this process is rather new and neither the FAQ's here (after some searches; likely I'm not being specific enough) nor the web (they just say use the HV probe) really answers such a simple but for this application, a rather involved issue.
Last edited by Dennis P Brown on Wed Apr 13, 2022 10:52 am, edited 1 time in total.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Elementary Question on using an Oscilloscope with a Neutron detector

Post by Richard Hull »

If you are taking your O'scope reading from the OUTPUT of a proper preamp, there is no high voltage present. You might expect pulse amplitudes of between 0.1 volt and 1.0 volt, depending on the preamp. The High voltage DC bias never even makes it into the preamp at all due to the input blocking capacitor with a typical 3kv or higher rating. The capacitor only passes the AC component pulse into the preamp.

There is the forever admonition that when powering up the preamp HV bias input, that it should be brought up slowly and not just snapped on from zero to full HV bias. Likewise when powering down the bias, the high voltage needs to be slowly backed down to 0 volts before turning off the HV supply. This is just a precaution to protect the input FET from turn-on spike or a turn-off spike. This is all part of "best practice" in powering up and down the preamp bias.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Post Reply

Return to “Neutrons, Radiation, and Detection (& FAQs)”