Bonn Radiocarbon Measurements I

Abstract

The laboratory started dating in 1966 using liquid scintillation techniques. Considerable effort has been expended on improvements in both sample preparation and detection (Pietig and Scharpenseel, 1964 and 1966). Yields now approach 100% and 4 to 6 samples are completed each week. A solution of 3 cc synthesized benzene and 1 cc “dead” commercial toluene is employed for ordinary measurements. Toluene contains PPO and POPOP scintillators that give final concentrations of 0.4% and 0.01%, respectively, when diluted with sample benzene. The counting arrangement with normal shielding gives a net modern count rate of 25.6 cpm (78% efficiency) with a background of 9.7 cpm. A special counter equipped with 5 cm mercury and 10 cm lead shielding as well as an anti-coincidence “umbrella” of polystilbeneplastic scintillator has considerably better characteristics. In addition to reduced background, samples as large as 100 cc can be accommodated. The exceptional performance obtained here is presently reserved for natural radioactivity measurements, such as T-3 and C1–36.