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In the out-of-core system, the chamber is one in which the U is coated on a base metal. The differential and integral spectra for out-of-core detector No. 6 are shown in Figures 6-4 and 6-5, respectively.

6. 4 THE EFFECT OF IN-CORE CABLE ON THE NEUTRON SPECTRA

As described previously, the in-core cable attenuates the magnitude of the signal available at the chamber. The theoretical attenuation varies as the inverse exponential of the attenuation factor and the length of cable, and is given by Equation (5-7):

a

resistivity of conductor material, in ohmmeters, frequency in cycles per second, relative dielectric constant of insulation, inner radius of outer conductor, in feet, outer radius of inner conductor, in feet, . length of cable, in feet, magnitude of voltage at sending end, and magnitude of voltage at receiving end.

05

I

As a result of this attenuation, there is a reduction in the pulse amplitudes and an increase

in the pulse rise time. The differential and integral pulse height spectra for the chamber with

in-core cable attached (referred to as "detector assembly No. 2") are shown in Figures 6-6 and

6-7, respectively. (It should be noted that these spectra were obtained with a 40-foot length of

cable. Since the attenuation is also a function of cable length, additional in-core cable length will

result in additional signal attenuation.) The peak on the differential pulse height distribution has

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moved toward the noise portion of the spectrum, and is positioned at approximately 13 x 10

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coulombs equivalent charge. Without the in-core cable, it was positioned at 16. 6 x 10 coulombs equivalent charge. .

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The electronic subsystem has a sensitivity of 6. 5 x 10 coulombs at a discriminator setting of 2. 6, and therefore is counting the major portion of the pulses in the peak distribution in both cases. Figures 6-8 and 6-9 are integral pulse height spectra for detector assemblies No. 2 and No. 1, respectively, with the complete subsystem in place. Figure 6-10 is a plot which relates equivalent charge input required to trigger to discriminator dial setting.

In the out-of-core subsystem, regular coaxial cables are used. These cables typically have 3 dB frequency attenuations at several hundreds of megacycles. The out-of-core information pulse is therefore essentially unchanged in its frequency content by the out-of-core interconnecting cable. Integral bias curves for out-of-core chambers No. 6 and No. 7 are shown in Figures 6-11 and 6-12, respectively. As before, Figure 6-10 provides the relationships of discriminator dial setting to equivalent input charge. .