Techniques for the precise measurement of the P–T melting curves of gases at pressures up to about 12 kbar have been developed. In the method used, a pressure vessel is maintained at a temperature constant to within ± 0.002°K. The pressure in the system is adjusted by manipulation of the pressure generating intensifier until solid–fluid coexistence is obtained within the vessel. The melting temperature is then measured with a platinum resistance thermometer mounted on the vessel, while the corresponding melting pressure is measured with a high-precision manganin resistance pressure gauge, which is connected to the pressure system. This method has been employed in making extensive P–T melting curve measurements in argon at pressures ranging from 0.58–11.41 kbar and temperatures from 97.8–272.9°K. The estimated precision in the results is ± 0.4 bar in pressure and ± 0.002°K in temperature. The absolute accuracy of the measurements, especially pressure, may be somewhat less due to uncertainty in the defining scales. The data show systematic deviations of as much as 10 bar from a Simon melting equation of the form Pm = ATmc + B. These deviations can be substantially reduced by use of a melting equation of the form Pm = A(Tm + D)c + B.

The growth of color centers during irradiation, and the decay after irradiation, has been studied in two glasses using recently developed equipment for making optical absorption and luminescence measurements during and after electron irradiation. The glasses studied were NBS 710, a soda-lime silicate glass and NBS 711, a lead silicate glass. Both glasses exhibit similar coloring characteristics. The radiation induced absorption spectra consists of a weak gaussian shaped band in the visible, a stronger gaussian band in the ultra violet and a band edge "shift" which may be accurately approximated by a third gaussian band. For all absorption bands the color center v.s. dose (or irradiation time) curves can be accurately resolved into two saturating exponential and one linear component. The decay curves obtained after the irradiation is terminated can be accurately expressed by three exponential components. Coloring and decay curves made at different dose rates indicate that the processes responsible for decay after irradiation and electron hole recombination during irradiation play important roles in determining the rate and extent of coloring. The results are qualitatively in agreement with some very simple kinetic treatments for color center formation. In some, but not all, respects the quantitative agreement is also good. Lastly, the results appear to provide strong evidence to conclude that it is necessary to make measurements during irradiation to establish Che formation kinetics of color centers that are unstable at the bombardment temperature.

A dual channel constant fraction timing discriminator incorporating multiple energy windows and coincidence logic has been developed. Incorporation of energy discrimination and fast coincidence logic into Che timing channel has distinct advantages in terns of system simplicity, stability and data rates. A prototype applying Che F 2 approach has been constructed and tested. The system gives a Co 60 FWHM of i 210 psec at a singles rate of > 7.5 x tO 5 sec* 1

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