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The preparation of known amounts of Rn is a problem common to many fields of research dealing with Rn. Until now, known amounts of Rn were prepared by collecting Rn from a standard Ra source and determining the amounts based on the secular equilibrium between Ra and Rn. In order to collect accurate amounts of Rn by this method, it is indispensable to verify experimentally that all or a fixed fraction of Rn from a standard Ra source is removed and collected. In addition, the method requires a long waiting period (15−30 days) to grow Rn from the source. The need for a simple and reliable method for the preparation of known amounts of Rn has become apparent. In previous papers, the present authors determined several α-emitters including Rn by measuring the luminescence counts from excited nitrogen with a liquid scintillation spectrometer (LSS) and proposed a method for determining Rn using the air luminescence method (ALM). However, the reported counting efficiency of the ALM for Rn and its daughters (Po, Pb, Bi, and Po) was determined with a specially modified LSS which could not be universally utilized: the pulses from the sum circuit of the LSS (Model 6880, Tracor Analytic) were fed into an amplifier and then to a 1024-channel pulse-height analyser. Therefore, the counting efficiency of air luminescence due to Rn and its daughters was determined with LSSs by use of known amounts of Rn which were standardized by measuring γ-rays from Pb with a Ge well detector. Much attention was also given to Cherenkov counting efficiency due to β-particles from Pb and Bi and the counting efficiency for the short-lived daughters, some of which were assumed to be attached to the wall of the counting vial for LSS. In the present study, the counting efficiencies of air luminescence due to Rn and its daughters were determined for several LSSs. Based on the counting efficiencies obtained, we offer a simple, rapid and reliable method for preparing known amounts of Rn without elaborate instrumentation and technique. Some significant advantages of the proposed method are that the time required for the preparation of known amounts of Rn is only 3.5 h, and that the Ra source, from which Rn is collected, does not necessarily have to be a standardized one, because we do not determine Rn based on the secular equilibrium between Ra and Rn. We can obtain known amounts of Rn simply by measuring Rn that is actually transferred and stored in the counting vial. Therefore, we need not verify that all of the Rn from the Ra source was removed and collected. Disadvantages of the conventional method for preparing known amounts of Rn are also discussed in some detail. Exactly, the luminescence in this study should be termed “nitrogen luminescence”. However, “air luminescence” was employed in conformity with the expression used in the previous papers. 7

Counting Efficiency for Rapid Preparation of Known Amounts of 222Rn by the Air Luminescence Method