Neutron activation of natural materials in a PWR spectrum feedback on $^{116m}$In relative $\gamma$ emission intensities and half-life

International audienceDuring the MAESTRO program, carried out between 2011 and 2014 in MINERVE zero power reactor, common Gen-II and Gen-III light water reactor materials were irradiated. For some of these materials, the decay of their activation products was also measured by gamma spectrometry. Initially devoted to the measurement of the integral capture cross section by activation and reactivity-oscillation method, these results can also provide useful information on decay data of various radionuclides. This led to a common roadmap shared by the Experimental Physics Section and the Henri Becquerel National Laboratory to improve decay data in nuclear data libraries.Results discussed in this paper concern the relative emission intensities of the main gamma rays of $^{116m}$In. Six irradiations of samples with various physical forms of natIn were carried out. Measurements were analyzed using decay data from several evaluations and it is shown that gamma ray activities are not consistent. Analyses were carried out to provide new relative gamma emission intensities from these measurements. The $^{116m}$In half-life has also been measured and shows a good agreement with existing values (< 0.1 percent discrepancy).Finally, an overview of the foreseen results on additional decay data from the MAESTRO program is given