Applying the pulsed ion chamber methodology to full range reactor ...
J 1:1 hj v.! ia ra r,? a
J 1:1 hj v.! ia ra r,? a h! U M — t'i W fa t* I 5 J 1 4 *'] «| ^ -! *"-•• ; n r 7* 55 i'4 Hi ! : Pi r> 14 $ s j ; '^ Ij! i •,! y ;! i |4 y u P U U U T fM T
as stated earlier, for a given exposure rote, theionization rates in both chambers are not equal, due tothe effect of the uranium wall coat- ing in the neutron sensitive chamber. Examining figure 4-4, one can see the presence of the linear and second order response regions of v(t ,) versus R/hr as predicted by thetheory given earlier. However, the presence of transition regions and their characteristics should be noted. In the fissionchamber curve, 4 5 this region, extends from approximately 10 to at least b x 10 R/hr. The gamma chamber appears to have a much more defined transition region: from b 6 10 to 10 R/hr. fhese effects are observed in figure 4-5 as well. The broad exposure range covered by the transition region, coupled with the fact that this region of response does not coincide between chambers, makes gamma compensation difficult. The gamma chamber signal cannot be simply multiplied by a constant and subtracted from the fissionchamberto give full compensation over thefullrange of exposure rates, because, as seen, due tothe increased gamma sensitivity of the fissionchamber, the two chamber responses are not linearly related.. T hus, to accomplish gamma compensation, using thechamber selected, more than simple differ- 7 ential gain controlled inputs, as were used by Cooper and suggested by 9 Ellis, were required. To compensate using nonlinear electronics would have been complicated. On the ether hand, compensating through computer methods appeared relatively simple and straight forward. Computer based compensation was accomplished as follows. The cham- ber responses shown in figure 4-4 were curve fitted to eighth order poly- nomials, using Chebyshev Pclynominals. A description of the code is contained in the Appendix. The resulting equations were;