FAQ - neutron background

[Richard Hull]

You certainly can't calibrate any neutron detector based on background levels. What you can do is determine whether your combined applied tube bias, electronic windowing and discrimination is whacked out into another galaxy using recorded background levels.

There is a critical setup, demanded before any neutron counting assembly morphs into a good, reliable, neutron counting system. It is a delicate setting of applied voltage to the detector, be it a BF3 tube, a 3He tube, a boron lined tube or one of the Russian Corona tubes that warrents stable operation. Once a proper voltage is applied, we are confronted with electronic massaging of the tube's output signal. This will involve preamplification and electronic pulse height discrimination settings to rule out detection of x-rays, gamma rays, etc. (dealt with in other FAQs here)

I attach a small graph and explanation.

Assuming you have a real neutron counting scenario setup with a proper tube in same, and in a suitable moderator, you can automatically assume that a background above 30 cpm is wrong and that a deep fractional count per minute is also wrong unless you are using a counting detection method that is extremely or grossly inefficient.

Richard Hull