The second test was to determine what effect long-term temperature exposure might have on the neutron pulse height spectrum. For this test the detector and about 5 feet of the attached in-core cable were heated to about 700°F for approximately 300 hours. Curves of the chamber’s neutron pulse height spectrum were recorded at ambient and 700°F at the start and finish of the 300-hour test. These curves are shown in Figures 4-6, 4-7, 4-8, and 4-9. It can be noted that there is no visibly significant difference between the curves taken at the start of the tempera­ture run and those taken at the end.

This test brought to light another temperature effect. By comparing Figures 4-6, 4-8, and 4-10 it can be seen that the pulse height spectrum taken at 710°F and a polarizing potential of 250 volts (Figure 4-8) lies between the pulse height spectrum taken at 75°F and polarizing potentials of 300 (Figure 4-10) and 400 volts (Figure 4-6). This increase in pulse height with increased temperature is probably caused by either an increase in electron mobility or a decrease in recombination rate, or both.

Although the change appears to be of no great significance, the increase of pulse height from the chamber might well compensate for the increase in cable attenuation as the temperature is raised.