Temperature Dependent Seasonal Variation of the Background in Counters Used for Radiocarbon Dating

All background values measured in one of our 14C counters during 1977 were analyzed together with corresponding values for atmospheric pressure, outdoor temperature, and coincidence counting rate for investigation of the possibilities to separate the temperature dependency of the background from the better known atmospheric pressure dependency.The background values were normalized to a common atmospheric pressure and plotted in a time diagram. A seasonal trend with higher background values in winter than in summer shown by this diagram was confirmed by regression analysis.The regression line and the “Standard error of estimate” was calculated for the background values as a function of the atomspheric pressure, on the one hand and as a function of the coincidence counting rate, on the other hand. A comparison showed that the coincidence counting rate in this case was a better parameter than the atmospheric pressure for calculation of the actual background.The approximate consistency of the temperature effects on the background was checked for the years 1976 to 1978.

ANGULAR CORRELATION OF ANNIHILATION RADIATION FROM POSITRONS DECAYING IN SEVERAL SUBSTANCES

Using anthracene scintillation counters in coincidence, the angular correlation between annihilation quanta produced by the decay of positrons in the following materials has been measured: the pure elements Mg, S, Cu, Sn, Pt, and Hg, and the chemical compounds LiCl, KCl, CsCl, KF, and KI.Calculations were performed to determine the effect of the geometry on the shape of the angular correlation curves, and the effects of scattering were investigated.The curves for copper, platinum, and possibly mercury could be approximated to by the expression[Formula: see text], where C(θ) is the coincidence counting rate as a function of θ, the angular departure of the two quanta from collinearity, and K and θ0 are constants. The curves for the other materials are more complicated and suggest that there is a relation between the shape of the curves and the outer electronic structure of the atoms with which the positrons annihilate. In alkali halides the positrons appear to annihilate only against the outer electrons of the negatively charged halogen ions.