Instrumental background

Counter system for high-precision 14C dating + pre-treatment unit




The gas proportional counting system was developed for high precision radiocarbon dating and consists of nine electrolytic copper proportional counters of identical diameters with sensitive volumes of 0.35-0.73 dm3 and filled with CO2 at 1115 mbar and 2 bar. The inner counters are surrounded by an anticoincidence shield consisting of five multiwire proportional flat counters filled with propane. The pulses of the detectors are handled by integrated amplifiers, discriminators and anticoincidence units interfaced to a microprocessor-controlled data evaluation unit. Software is written in BASIC using ASSEMBLER sub-routines. The overall precision of the system for modern carbon samples is better than 4 ‰ after a counting period of seven days.


  Counters
System parameters 1 2 3 4 5 6 8 9
Total active volume (dm3) 0.7 0.7 0.7 0.7 0.5 0.35 0.35 0.7
Standard counting rate (S) (cpm) 4.9256 8.7715 4.8603 4.7992 6.5739 4.6498 4.7617 4.8602
Background (B) (cpm) 0.4945 0.6074 0.5084 0.5373 0.5328 0.4498 0.4566 0.5828
Figure of merit (S/ÖB) 7.00 11.25 6.82 6.55 9.00 6.93 7.05 6.34
Max. measurable age (2 days) (yr) 33705 37516 33530 33171 35724 33624 33762 32909