A Simple, Extremely Stable Single-Tube Liquid Scintillation System for Radiocarbon Dating

Abstract

ABSTRACT. This paper describes a simple and compact liquid scintillation radiocarbon dating system, ICELS, and demonstrates its long-term stability and reproducibility to a precision level rarely presented before, better than 0.04% (3 14 C yr). Inexpensive systems of this kind may, in the future, help to meet increasing demand for high precision (±16 to ±20 14 C yr) and strict quality control. ICELS comprises a compact detector unit, where a 3-mL dome-shaped vial, with an optimal light reflector, sits on the top of a vertical 30-mm photomultiplier tube. Sample changing is manual. The high voltage is set at the balance point for each sample, securing maximal counting stability. The quench correction method used (spectrum restoration) corrects with 0.04% precision for all parameters that can normally shift the 14 C spectrum. For 3 mL of benzene at 71% 14 C counting efficiency (recent carbon 23 cpm), the background is 1.72 cpm behind a 5-cm-thick shield of lead (27 kg) and 1.53 cpm behind 10 cm of lead. The background count rate corrected for atmospheric pressure variations was completely stable over 47-and 57-d testing periods for the 2 systems.

Background Components of a Liquid Scintillation Counter in the 14C Window

“…ICELS comprises a detector unit, a dedicated electronic unit, and a laptop computer (Theodorsson 2005). A multichannel analyzer (MCA) is added in the present study.…”

The Application of ICELS Systems for Radiocarbon Dating

“…The stability of ICELS systems was presented previously (Theodórsson 2005) but not directly for 14 C dating. Some tests of 14 C dating stability and reproducibility were performed in our laboratory using ICELS 2.…”

“…Kojola et al 1984;Theodórsson 2005). Thus, only a brief description is needed here, with an emphasis on the systems' differences.…”

“…The vials are wrapped, except for the bottom, with polytetrafluoroethylene (PTFE) tape. A drop of glycerol is added between the PMT and the vial for high-photon transmission (Theodórsson and Gudjónsson 2009). …”

“…The ICELS system was designed a few years ago specifically for 14 C dating with an emphasis on simplicity. It has been thoroughly tested using elevated 14 C-activity samples, and its high stability has been verified (Theodórsson 2005). Here, results of measurements using the Quantulus 1220 and the ICELS systems are compared in order to test the ICELS as an alternative counting system that could be used by an established 14 C dating laboratory to increase its dating capacity.…”