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Published online by Cambridge University Press: 18 July 2016
Most of the measurements reported here have beenobtained with the 4.5-L CO2 counterpreviously described (Kiel I; Erlenkeuser, 1965). Afew samples have been dated with a 3-L proportionalcounter. The copper counter is surrounded by 28 GMcounters in the form of a double ring. The totalassembly is shielded by 10 cm of old lead. Neitheran inner lead shield between counter andanticoincidence ring nor screening of sensitivevolume by a quartz tube-as in the 4.5-L counter-hasbeen used. Background of the small counter is 17.20cpm or The 0.95x NBS value is 9.5 cpm at 400 torr. Withinstatistical error background does not depend onatmospheric pressure. The 3-L counter is placedunder a concrete wall, 2.5 m in length and 9.4 m inheight.