A study of proportional counter optimization for long-term counting

Developments in Radiocarbon Technologies: From the Libby Counter to Compound-Specific AMS Analyses

“…It was recognized from the beginning that CO 2 requires special cleaning from impurities such as water vapors, nitrogen and sulfur oxides, and halogen compounds (de Vries and Barendsen 1953;Rafter and Fergusson 1957;Nydal 1962). Later, it was documented that this is due to CO 2 sensitivity to electronegative impurities present in CO 2 ( Figure 5), which dramatically decrease the transit time of electrons from a place of their origin to the anode (Povinec 1979). The great advantage of CO 2 filling was also the fact that the same CO 2 sample was transferred to a mass spectrometer for measuring 13 C/ 12 C ratio without possible instrumentation change in the isotope ratio.…”

14C Gas Counting: Is There Still a Future?

“…After a thorough investigation of the characteristics of proportional counters, I have developed (Povinec 1980) a new type of detector for low-level 14C counting, the multi-element proportional chamber (MEPC). The main aim of this detector is to achieve high-precision 14C measurements of atmospheric CO2 and tree rings with an accuracy of ca.…”

“…The electron transit time increases or decreases with increasing p 1, caused by typical dependencies of electron drift velocities on p"1 (Povinec 1979). The electron transit time depends also on the anode and cathode radii.…”

“…For a quantitative characterization of the processes in the counter, one must know the transit time of electrons from near the cathode to the anode. I have shown (Povinec 1979) that the electron transit time depends strongly on the type of gas filling and on counter geometry. Gas fillings used for proportional counters can be divided into three groups: 1) "very fast" gas filling, such as methane; 2) "medium fast" fillings (other hydrocarbon gases); 3) "very slow" gases, such as carbon dioxide.…”

“…However, this is not the case in large volume counters with diameters of a few centimeters, where small impurities of electronegative gases are always present. Large diameters of the proportional counters are inimical to primary electrons because they can be captured more easily by electronegative atoms on their path from near the cathode to the anode (Povinec 1979).…”