### Working group actions

Starting with the ICRM 2005 conference, the GSWG members participated in a series of exercises to compare codes as applied to detector calibration. The exercises addressed problems such as direct computation of efficiency, application of Monte Carlo codes to efficiency transfer, computation of coincidence summing corrections in various cases. The results of the most recent exercises (self-consistency of the methods applied for the evaluation of coincidence summing corrections and benchmark for Monte Carlo simulation) were presented during the ICRM 2019 conference in Salamanca.

### On-going actions

#### 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.

#### Self-attenuation corrective factors in the low-energy range: an experimental study on ^{210}Pb

Coordination: Marie-Christine Lépy

Quantitative analysis of environmental samples generally involves volume source with low radioactivity and an unknown composition of the sample matrix. Unless an efficiency calibration with the same geometry and matrix is available, it is necessary to correct the raw counting rates for self-attenuation effects in order to obtain the correct sample activity. This can be achieved either experimentally or by means of calculation based on mass attenuation coefficients that can be directly measured or taken from tabulated absorption data. The self-attenuation effect is more pronounced when the energy of the emitted photons is low. This is the case with ^{210}Pb, which is a low-energy gamma emitting radionuclide (46.54 keV) suffering strong absorption in the sample matrix and whose concentration in the environment must be regularly monitored according to public health regulations.

Within the framework of the GSWG, twelve laboratories agreed to carry out measurements with matrices containing ^{210}Pb and to compare their approaches to the determination of self-attenuation correction factors in order to draft practical recommendations for users. With this aim, the Laboratoire National Henri Becquerel (LNHB) prepared two different sets of three samples, each packed in cylindrical containers with known activities of ^{210}Pb and ^{137}Cs. One sample was considered as a standard source by the participants and could be used for the efficiency calibration of the detectors. The goal of the exercise was to determine the activity of the two radionuclides included in the other two samples, with unknown matrices. This required the participants to establish the self-attenuation correction factors between the calibration and the measurement matrices. The different approaches and results obtained by the participants will presented during the next ICRM conference in Bucharest and general recommendations will be proposed.

#### 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.

#### Action to facilitate the use of Monte Carlo simulation software

Coordination: Marie-Christine Lépy

To facilitate the use of generalist Monte Carlo (MC) simulation software (GEANT, MCNP, PENELOPE, etc.), it is proposed to prepare geometrical files for a selection of detectors (HPGe) and measurement conditions including volume samples and external shielding. The participants will contribute to prepare benchmark files specific to the different MC codes. Two cases must be considered since GEANT code, which is object-oriented and run under UNIX, must be compiled including the geometry while the other codes are written in FORTRAN and run with an external geometry file. To test the feasibility of the action, the action will start on study-case models with simple cylindrical detectors. It should be easy to prepare a first set of input data for these simple cases and come to an agreement between the participants on a common structure. It will be necessary to define a file structure that could be easily modified by an external user or by a dedicated user-friendly code.

Further information is available here.