Measurement of liquid scintillation sources of (210)Pb obtained from (222)Rn decay.
Liquid scintillation samples were filled with (222)Rn and the activity was measured with good precision after reaching the secular equilibrium with the progeny (218)Po, (214)Pb, (214)Bi and (214)Po. After decay of most of (222)Rn activity, the samples contain (210)Pb and progeny. The activities of (210)Pb and progeny can be calculated as a function of time using the initial (222)Rn activity. The samples were measured in a TDCR counter and the experimentally determined counting efficiencies are in accordance with previously published results.
The 222Rn standard system established at IFIN-HH, Romania.
The paper presents the (222)Rn Standard System realized at the Radionuclide Metrology Laboratory from IFIN-HH, Romania. It contains a Pylon solid (226)Ra source, and a glass circuit for circulation and recovery of (222)Rn in glass ampoules, at the 77K temperature. The radon can be recovered both in ampoules with liquid scintillator (LS), for absolute standardization of (222)Rn by liquid scintillation counting (LSC) (Cassette et al., 2006), and in evacuated ampoules as gas, simultaneously or by the transfer of radon from gas into LS ampoules, in order to establish the traceability chain. The absolute standardization consists in the registration of the double coincidence counting rate in LS, due to the whole sequence of short life components of the (222)Rn chain, in equilibrium conditions. The main correction applied to the measurement results is due to the decay of (214)Po during the extendable dead time of the system. The following procedure was applied to take it into account. The value of the base duration of the dead time was precisely measured and used for the data corrections. The measurements of each source were repeated during a period of several days, and the decay curve parameters were calculated. If the dead time value and the correction formulae, presented throughout the paper, were adequate, then the re-determination of the (222)Rn half life, T(1/2)=(3.8232+/-0.0008) d, using the decay curve of the corrected counting rates should be correct. On the other hand, the effective dead time values obtained by parallel calculations were compared. The paper presents the results obtained in the standardization of several sources, by LSC, and the evaluation of the uncertainties associated to the method.
The IFIN-HH triple coincidence liquid scintillation counter.
The paper summarizes the IFIN-HH triple coincidence liquid scintillation counter used for the implementation of the TDCR method. The electronic unit was recently extended to record the three individual double coincidence ratios to take into account the differences in the quantum efficiencies of the three-photomultiplier tubes. Some details of the electronic system and the data processing are given. The critical point of a TDCR counter is to adjust correctly the discriminator levels on the three channels under the single electron peak. The paper describes the method of adjustment based on the evolution of the dark counting rate versus the discriminator level. Also indicated is the influence of the discrimination level on the activity results as measured at IFIN-HH using a 3H standard. The performances of the IFIN-HH TDCR counter was checked against the measurement results of the TDCR counters of CSIR NML (South Africa), RC (Poland) and LNHB (France). A set of ready-to-measure 63Ni sources in liquid scintillator, in sealed counting vials, was prepared and dispatched for measurement to all these laboratories. The paper describes designs of the TDCR counters used. An analysis and discussion of the measurement results is given.