Interesting He3 Tube Result
Posted: Thu Jan 02, 2020 7:59 pm
I was running a short experiment today which gave suggestive but rather unbelievable results.
I'd like to run it by the forum for wiser (or at least more experienced) people to comment.
The goal of this experiment was to try and learn about the SNM-18 proportional tube.
For the bias I am using an old HV DC power supply and the classic bias/measurement circuit
using a 100Mohm bias and a 2pF series cap. The output of the cap is connected to a Rigol
DS1054Z scope.
When the SNM-18 tube is biased up to about 1300V I can see an occasional 0.25 to 1 volt downward
pulse. The pulse width is about 1usec at FWHM. The rate (an average of 24 events) is about one every
17 seconds. A typical pulse is shown below.
So far this does not seem totally crazy. The rate is higher than the background rates I have seen on
this forum. But not by a lot.
All this is with the tube in open air. When I put it into my wax moderator (8" dia by 19" high) the
counts go up dramatically. It is more difficult to count them because sometimes they come too fast but
after 15 minutes trying I got a count rate that is almost double, about one count every 9 seconds.
This seems crazy. But the only variable I am changing is the addition of the wax moderator.
Are there really that many fast neutrons ready to be moderated at sea level?
Any comments?
Cheers.
I'd like to run it by the forum for wiser (or at least more experienced) people to comment.
The goal of this experiment was to try and learn about the SNM-18 proportional tube.
For the bias I am using an old HV DC power supply and the classic bias/measurement circuit
using a 100Mohm bias and a 2pF series cap. The output of the cap is connected to a Rigol
DS1054Z scope.
When the SNM-18 tube is biased up to about 1300V I can see an occasional 0.25 to 1 volt downward
pulse. The pulse width is about 1usec at FWHM. The rate (an average of 24 events) is about one every
17 seconds. A typical pulse is shown below.
So far this does not seem totally crazy. The rate is higher than the background rates I have seen on
this forum. But not by a lot.
All this is with the tube in open air. When I put it into my wax moderator (8" dia by 19" high) the
counts go up dramatically. It is more difficult to count them because sometimes they come too fast but
after 15 minutes trying I got a count rate that is almost double, about one count every 9 seconds.
This seems crazy. But the only variable I am changing is the addition of the wax moderator.
Are there really that many fast neutrons ready to be moderated at sea level?
Any comments?
Cheers.