Enhanced low-level LSC performance for carbon-14 dating using a bismuth germanate (Bi{sub 4}Ge{sub 3}O{sub 12}) quasi-active guard
- Scottish Universities Research and Reactor Centre, East Kilibride (United Kingdom)
The Packard 2770TR/SL is a novel low-level liquid scintillation spectrometer which employs bismuth germanate (BGO - Bi{sub 4}Ge{sub 3}O{sub 12}) as a quasi-active guard to reduce background count rates and improve limits of detection. The results of this study indicate that this system shows tremendous potential for radiocarbon dating. Its great advantage is that it can give exceptional performance using standard low {sup 40}K borosilicate glass vials costing only a few cents each. For example, in an optimized counting window, 4.6-mL {sup 14}C benzene contained in a standard 7-mL glass vial produced a background count rate of 0.49 cpm and an efficiency of 70.3%, yielding a figure of merit (E{sup 2}V{sup 2}/B) value of 213,000 {+-}9,000 (where B = background count rate in counts per minute [cpm], E = percentage efficiency, and V = volume of benzene). This performance is comparable to published data for low-level instruments which employ active coincidence guard detectors and standard glass vials. When the same vials were recounted in vial holders, specially fabricated from BGO, the corresponding optimum values for background, efficiency and figure of merit, respectively, were 0.24 cpm, 61.0% and 328,000 {+-} 19,000. This performance is comparable to that of other low-level counting instruments when they are used in combination with specialized Teflon and silica vials. The BGO vial holders were also used in previous generations of Packard instruments which employ time resolved liquid scintillation counting (TR-LSC) for electronic background reduction and this resulted in significant improvements in performance.
- OSTI ID:
- 401760
- Journal Information:
- Radioactivity and Radiochemistry, Vol. 6, Issue 4; Other Information: PBD: 1995
- Country of Publication:
- United States
- Language:
- English
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