COMPENSATED ION CHAMBER
Radiation Detectors
The ionization chamber compensation
Figure 21 Typical Compensation Curve
curve, Figure 21, is a plot of the percent
compensation
versus
compensating
voltage. This compensation curve must
be plotted prior to using a compensated
ion chamber.
In ideal situations, compensated ion
chambers operate at 100% compensation,
and indicated current is due to neutrons.
Small changes in compensating voltage
change the percent compensation.
The consequences of operating with an
overcompensated or undercompensated
chamber are important. The purpose of
nuclear instrumentation is to detect and
measure neutron level, which is the direct
measure of core power.
If the
compensating voltage is set too high, or
overcompensated, some neutron current,
as well as all of the gamma current, is
blocked, and indicated power is lower
than actual core power. If compensating
voltage is set too low, or undercompensated, not all of the gamma current is blocked, and
indicated power is higher than actual core power. At high power, gamma flux is relatively small
compared to neutron flux, and the effects of improper compensation may not be noticed. It is
extremely important, however, that the chamber be properly compensated during reactor startup
and shutdown.
IC-06
Page 38
Rev. 0
