COMPENSATED ION CHAMBERRadiation DetectorsThe ionization chamber compensationFigure 21 Typical Compensation Curvecurve, Figure 21, is a plot of the percentcompensation versus compensatingvoltage. This compensation curve mustbe plotted prior to using a compensatedion chamber.In ideal situations, compensated ionchambers operate at 100% compensation,and indicated current is due to neutrons.Small changes in compensating voltagechange the percent compensation.The consequences of operating with anovercompensated or undercompensatedchamber are important. The purpose ofnuclear instrumentation is to detect andmeasure neutron level, which is the directmeasure of core power. If thecompensating voltage is set too high, orovercompensated, some neutron current,as well as all of the gamma current, isblocked, and indicated power is lowerthan actual core power. If compensatingvoltage is set too low, or undercompensated, not all of the gamma current is blocked, andindicated power is higher than actual core power. At high power, gamma flux is relatively smallcompared to neutron flux, and the effects of improper compensation may not be noticed. It isextremely important, however, that the chamber be properly compensated during reactor startupand shutdown.IC-06 Page 38 Rev. 0
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