GSWG Exercises and Publications – Laboratoire National Henri Becquerel

Past exercises and publications

Verification of gamma-ray spectrometry analysis software for the computation of characteristic limits according to ISO 11929

Coordination: Milton van Rooy

Metrologically sound analyses of radioactivity of samples requires that the measurement method is fit for purpose and validated. One of the parameters to consider in the validation, especially when dealing with low-level radioactivity analysis, is the detection limit of the method or for a specific measurement condition of the method. In 2010, with an upgrade in 2016, the concepts of the computation of detection limits and characteristic limits for nuclear measurement methods have been published in the ISO 11292 norm. Since most laboratories rely on commercial software to make gamma-ray spectrometry analyses, verification of this software with respect to the computation of detection limits may be required to obtain the prove of compatibility with the ISO norm. To examine in more details the problem of characteristic limits in gamma-ray spectrometry, well defined gamma-ray spectra together with specific instructions fixing key parameters in the computation of detection limits were send to several laboratories for analysis, evaluation and reporting. The results obtained by different participating laboratories were then compared and were also verified by manual computation. The results of the exercise will be presented during the next ICRM conference in Bucharest.

Simple exercise on self-consistency of the methods applied for the evaluation of coincidence summing corrections in the case of volume sources

Coordination: Octavian Sima

An action to test the internal self-consistency of the methods applied to evaluate coincidence-summing corrections for extended sources is proposed. While internal consistency does not guarantee the correctness of the method, if it is not satisfied, it points out that the method has some shortcomings and its validity has specific limitations. The proposed self-consistency test is based on exact relations that should be fulfilled in the case of specific ideal measurement configurations. More precisely, the results obtained using any computation method for one such configuration should be related by exact equations to the results given by the same method for other configurations. Thus, this test does not require experimental data (avoiding the problem of experimental uncertainties) or comparisons of a method with other methods (avoiding the debate concerning the selection of a particular reference method). Specifically, the participants in this exercise are asked to evaluate the coincidence-summing correction factors for several peaks of Co-60, Cs-134, Ba-133 and Eu-152 for one detector and 3 volume source geometries.

Further information is available here.

Coincidence summing correction

There are several ways of computing the coincidence summing corrections and each method has advantages and drawbacks (accuracy, easiness, speed, etc.) that were compared during this action.
In a first step, the comparison was restricted to point sources and to two radionuclides (¹³⁴Cs and ¹⁵²Eu). The same decay scheme and photon emission intensities were used by all the participants (NUCLEIDE database) to avoid bias linked to data discrepancies. The results were expressed as the coincidence summing correction factors for the multi-energetic nuclides for several energies and several source-to-detector distances.
In a second step, the exercise focussed on the case of volume sources using the same experimental setup as in the first part of the comparison, for the same two radionuclides (¹³⁴Cs and ¹⁵²Eu), but with different geometrical conditions: three volumes were considered, whose container diameter was smaller, equal or larger than the detector diameter. These containers were measured in three geometrical conditions: without absorber and with a Plexiglas or copper screen to examine the influence of X-rays. Experimental corrections were determined using the ratio between the activity derived from the processing of individual peaks (without correction) and the true activity of the source.

Exercise coordinator: Marie-Christine Lépy (LNE/LNHB, France)

Publications
– Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry, by M.-C. Lépy and all the participants of the intercomparison, Applied Radiation and Isotopes 68 (2010) 1407-1412.

– Intercomparison of methods for coincidence summing corrections in gamma-ray spectrometry—part II (volume sources), M.-C. Lépy, T. Altzitzoglou, M.J. Anagnostakis, M. Capogni, A. Ceccatelli, P. De Felice, M. Djurasevicf, P. Dryak, A. Fazio, L. Ferreux, A. Giampaoli, J.B. Han, S. Hurtado,A. Kandic, G. Kanisch, K.L. Karfopoulos, S. Klemola, P. Kovar, M. Laubenstein, J.H. Lee, J.M. Lee, K.B. Lee, S. Pierre, G. Carvalhal, O. Sima, Chau Van Tao, Tran Thien Thanh, T. Vidmar, I. Vukanac, M.J. Yang, Applied Radiation and Isotopes 70 (2012) 2112-2117.

Efficiency transfer

Four general Monte Carlo codes (GEANT3, PENELOPE, MCNP and EGS4) and five dedicated packages for efficiency determination in gamma-ray spectrometry (ANGLE, DETEFF, GESPECOR, ETNA and EFFTRAN) were checked for equivalence by applying them to the calculation of efficiency transfer (ET) factors for a set of well-defined sample parameters, detector parameters and energies typically encountered in environmental radioactivity measurements. The differences between the results of the different codes never exceeded a few percent and were lower than 2% in the majority of cases.

Exercise coordinator: Tim Vidmar (Jozef Stefan Institute, Ljubljana, Slovenia)

Publications
– Testing efficiency transfer codes for equivalence, T. Vidmar, N. Çelik, N. Cornejo Díaz, A. Dlabac, I.O.B. Ewa, J.A. Carrazana González, M. Hult, S. Jovanovic, M.-C. Lépy, N. Mihaljevic, O. Sima, F. Tzika, M. Jurado Vargas, T. Vasilopoulou and G. Vidmar, Applied Radiation and Isotopes 68 (2010) 355-359

Monte Carlo codes intercomparison exercise

The aim of the exercise was to test the possible differences between Monte Carlo codes in order to assess the intrinsic uncertainties of such calculations, due to the different approaches to particle tracking and the nuclear and material data used for it. In accordance with its objective the exercise did not involve any reference to the experimental data and simply confronted the codes one with another, as they were applied to the calculation of full energy peak and total efficiencies for a precisely defined and very schematic model of a HPGe detector and the sample. Since there was no experimental data to compare the results of the codes against, this exercise only tested their mutual compatibility and not their absolute performance. The results of the exercise provided useful information for future intercomparisons involving the application of Monte Carlo codes to efficiency transfer and coincidence summing correction calculations.