Corrected SBT11A dead time calculation

  • Sonarflash
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4 years 6 months ago #3743 by Sonarflash
:woohoo: Four months ago, I posted on this topic. Here is an update with pleasantly surprising results. I ran the procedure to calculate dead time once again, but this time I used tape and fixed the americium buttons along with the SBT11A. Had the tube mounted in a metal box with Aware Electronics HV/discriminator PCB. Running AW-RADW software.
First, I did both buttons for over 8 minutes, then lifted the tape and flipped off one button for several more minutes (thanks to a phone call). Finally, I resecured the button and flipped off the other for 10 minutes. I eliminated readings for the one minute interval after making each change.

I took an 8 minute average for each reading. Button A, button B and buttons A+B. Just copied the text numbers into Excell and used a formula in A2, B2 and C2, =average(d1:d2) etc.

This time, I put the =abs() function into Bryan's formula.

Averages for the 241Am buttons were as follows:

Buttons A+B = 68,660 CPM
Button A = 41,983 CPM
Button B = 28,275 CPM

The combined A+B average formula goes in C2
The average formula for button A goes in A2
The average formula for button B goes in B2

Deadtime in Microseconds uses the formula:
=abs((((A2*B2)-SQRT((A2*B2)*(C2-A2)*(C2-B2)))/(A2*B2*C2))*60000000)

The result was a surprising 41 microseconds, far better than my previous result, and a pleasant surprise. 440 microseconds is the dead time for a 900 volt LND7313-1 pancake. The LND7317 is given as 80 microseconds, as is my Aware Electronics RM-80 using the 500 volt LND7313-3 GM tube.

So, not only is the SBT11A inexpensive and tiny, it is very efficient.
My window sill background readings with an SBT11A are averaging 15 to 16 CPM, while the larger LND7313-3 is averaging 30 CPM.

Regards, Brian, VA7BDG
The following user(s) said Thank You: mw0uzo

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