Browsing Radiocarbon, Volume 28 (1986) by Subjects
Now showing items 1-2 of 2
Optimization of Liquid Scintillation Counting for 14C DatingThe effects of different measurement conditions and sample preparation in liquid scintillation counting of benzene for 14C dating were tested. The goal of this work was to find the highest figure of merit through the variation of scintillation cocktail to benzene ratio, and measurement windows. Measurements were performed on 5m1 of benzene plus increasing quantities of scintillation cocktail (7g of PPO and 0.5g of Me2POPOP in IL of scintillation-grade toluene). Spectra of both background and standard were obtained and the counting windows selected for the highest figure of merit (Q). The best condition was 5m1 of benzene plus 0.75ml of scintillation cocktail. This spectrum is compared with that of I) pure toluene-14C plus cocktail, and 2) pure benzene-14C in which the equivalent amount of PPO and Me2POPOP present in 0.75ml of cocktail was dissolved. A correlation between the increase of the aniount of cocktail and the broadening of the spectrum was observed. The effect of wrapping the upper part of the counting vial with aluminum foil to reduce background was also tested. A drastic background increment was observed in the low energy range, for unwrapped vials; the standard spectrum showed a broadening and a lower counting efficiency which reduced the figure of merit.
The Potential of the London Underground for Liquid Scintillation CountingA portable gamma spectrometer has been used to survey three locations that are part of the London Underground Transport System (the "tube"). Up to an order of magnitude reduction in the cosmic ray flux was observed relative to the laboratory level. The likely reduction in background count rate achievable by underground siting of currently used Packard and LKB liquid scintillation counters is considered. It is noted that in the present, surface usage for radiocarbon dating, the background count rate of low-potassium glass vials in the LKB is not substanially higher than that of PTFE vials.