ZAHN, GUILHERME S.GENEZINI, FREDERICO A.RIBEIRO JUNIOR, IBERE S.FAGIONATO, ESNEL A.2020-05-262020-05-26ZAHN, GUILHERME S.; GENEZINI, FREDERICO A.; RIBEIRO JUNIOR, IBERE S.; FAGIONATO, ESNEL A. On the use of gamma-gamma coincidence to detect very low activities. In: BRAZILIAN MEETING ON NUCLEAR PHYSICS, 40th, September 3-7, 2017, Campos do Jordão, SP. <b>Abstract...</b> São Paulo, SP: Sociedade Brasileira de Física, 2017. p. 1-1. Disponível em: http://repositorio.ipen.br/handle/123456789/31186.http://repositorio.ipen.br/handle/123456789/31186The detection of very low gamma ray activities is a delicate task, and very important in environmental radiation studies, for instance. It usually requires the use of low-background shielding, as the long counting times required usually make the background subtraction quite tricky, and often result in rather high experimental uncertainties. In this work a different approach is tested, where a two-detector gamma-gamma coincidence system is used to eliminate essentially all of the background continuum - at the cost of reduced overall efficiency and, more importantly, requiring that the radionuclide to be studied presents useful gamma-gamma coincidences. Two distinct methods of analysis are tested, either using an "open-window" coincidence where an event is registered whenever any event is registered in the other detector, or using a strict coincidence analysis, where a valid coincidence between two gamma-rays from the same decay are required; this allow for a discussion on the advantages and problems of each method, as well as for an experimental assessment of the performance of such a system.1-1openAccessResumo de eventos científicos0000-0002-6318-68050000-0003-3237-8588https://orcid.org/0000-0002-6318-6805https://orcid.org/0000-0003-3237-8588