Substitution of Equation (3-51) into Equation (3-14) yields the following expression for the expected value of the signal:

If both neutrons and gamma photons are being detected, this expression becomes

Note that the total signal is the sum of one part due to neutrons and one due to photons.

A measure of the gamma-discrimination ability of a system is the ratio of the flux of gammas to the flux of neutrons when both are producing the same output. This ratio can be obtained by equating the two terms in the right-hand side of Equation (3-53):

Ф

Ф

POWER SPECTRUM OF CURRENT FROM ION CHAMBER

SQUARE OF ABSOLUTE VALUE OF TRANSFER FUNCTION OF LINEAR PART OF SYSTEM

1010

102

ANGULAR FREQ, (radians/sec.)

GO • ‘

I

-J. Figure 3-2. Frequency Considerations