[en] The Auger-electrons emitted by "9"9"mTc have been recently associated with the induction of thyroid stunning in in vivo experiments in mice, making the dosimetry at the sub-cellular level of "9"9"mTc a pertinent and pressing subject. The S-values for "9"9"mTc were calculated using MCNP6, which was first validated for studies at the sub-cellular scale and for low energies electrons. The calculation was then performed for "9"9"mTc within different cellular compartments in a single mouse thyroid follicle model, considering the radiative and non-radiative transitions of the "9"9"mTc radiation spectrum. It was shown that the contribution of the "9"9"mTc Auger and low energy electrons to the absorbed dose to the follicular cells' nucleus is important, being at least of the same order of magnitude compared to the emitted photons' contribution and cannot be neglected. The results suggest that Auger-electrons emitted by "9"9"mTc play a significant role in the occurrence of the thyroid stunning effect in mice. - Highlights: • MCNP6 was validated for dosimetric studies at the sub-cellular scale. • Radionuclides used in the validation studies: 67Ga, 99mTc 111In, 123I, 125I, 201Tl. • 99mTc S-values calculated for a mouse single thyroid follicle model. • Contribution of the 99mTc Auger-electrons to the absorbed dose cannot be neglected. • Results suggest low energy electrons play a significant role in occurrence of observed effect.