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Results of a comprehensive test of the first commercial TDCR device presented


The Triple-to-Double-Coincidence Ratio (TDCR) method allows activity determinations of radioactive solutions which are inserted in a liquid scintillator to be carried out. The flashes generated by the radioactive decays are counted with three photomultiplier tubes. The detection probability is determined by means of a free-parameter model from the ratio of triple or double coincidences [1] so that, finally, the activity can be determined.

In view of the great success and the large number of radionuclides which can meanwhile be measured with the TDCR method, an increasingly large number of laboratories apply this technique. Up to now, the users can mainly be found in national metrology institutes. This is - not least - surely due to the fact that the construction of TDCR apparatuses requires some knowledge and - in particular - that the construction of the respective coincidence electronics is quite demanding.

For some years now, the Finnish company Hidex Oy has been selling a commercial liquid scintillation counter with three photomultipliers. Within the scope of a joint project, such a device has been made available to PTB (in the so-called "METRO version") in order to be subjected to a comprehensive test and to possibly find approaches for improvements.

The results of these tests were presented on the occasion of the ICRM Conference 2011 in Tsukuba, Japan, and have now been published in a scientific article [2]. At the beginning of the test, linearity investigations with 241Am sources were carried out. These showed, at first, weak points of the system, as the expected proportionality of the net count rate and the activity was not given. Thereupon, the manufacturer of the devices made great efforts to improve the electronics and finally succeeded in achieving a satisfactory linearity in a large range of count rates. The further investigations at PTB included the influence of the threshold adjustment and the coincidence resolving time. Later, activity determinations of a great number of radionuclides were realized with small uncertainties. The wide variety of the radionuclides covers several beta-ray-emitting radionuclides, electron capturing nuclides and some nuclides with a complex decay scheme. A TDCR apparatus developed at PTB served as a reference [3]. The results clearly show that the Hidex device tested at PTB allows activity measurements with an acceptable uncertainty to be realized. A bilateral comparison with 89Sr sources, carried out between the Italian institute ENEA and PTB at a later date, showed that the Hidex devices of the two institutes furnish almost identical results with small uncertainty. A publication of the results of the bilateral comparison is planned.

In addition, the Hidex TDCR device was used to test high-energy beta-ray-emitting nuclides in aqueous solutions. A new analytical TDCR-Čerenkov procedure developed at PTB [4] allows activities of aqueous radioactive solutions to be directly determined. A mixture with the organic liquid scintillator is not necessary so that in particular mixed radioactive waste is avoided. The TDCR-Čerenkov method thus helps to reduce costs and to protect the environment.


  1. Broda, R., Cassette, P., Kossert, K.:
    Radionuclide Metrology using Liquid Scintillation Counting.
    Metrologia 44 (2007) S36-S52 (Special issue on radionuclide metrology).
  2. Wanke, C., Kossert, K., Nähle, O. J.:
    Absolute activity measurements with the HIDEX 300 SL TDCR system.
    Applied Radiation and Isotopes 70 (2012) 2176-2183.
  3. Nähle, O. J., Kossert, K., Cassette, P.:
    Activity standardization of 3H with the new TDCR system at PTB.
    Applied Radiation and Isotopes 68 (2010) 1534-1536.
  4. Kossert, K.:
    Activity standardization by means of a new TDCR-Čerenkov counting technique.
    Applied Radiation and Isotopes 68 (2010) 1116-1120.