  The phenomenon of multiple populations in globular clusters is still far from
understood, with several proposed mechanisms to explain the observed behaviour.
The study of elemental and isotopic abundance patterns are crucial for
investigating the differences among candidate pollution mechanisms. We derive
magnesium isotopic ratios for 13 stars in the globular cluster 47 Tucanae (NGC
104) to provide new, detailed information about the nucleosynthesis that has
occurred within the cluster. For the first time, the impact of 3D model stellar
atmospheres on the derived Mg isotopic ratios is investigated. Using both
tailored 1D atmospheric models and 3D hydrodynamical models, we derive
magnesium isotopic ratios from four features of MgH near 5135{\AA} in 13 giants
near the tip of the RGB, using high signal-to-noise, high-resolution spectra.
We derive the magnesium isotopic ratios for all stars and find no significant
offset of the isotopic distribution between the pristine and the polluted
populations. Furthermore, we do not detect any statistically significant
differences in the spread in the Mg isotopes in either population. No trends
were found between the Mg isotopes and [Al/Fe]. The inclusion of 3D atmospheres
has a significant impact on the derived 25Mg/24Mg ratio, increasing it by a
factor of up to 2.5, compared to 1D. The 26Mg/24Mg ratio, on the other hand,
essentially remains unchanged. We confirm the results seen from other globular
clusters, where no strong variation in the isotopic ratios is observed between
stellar populations, for observed ranges in [Al/Fe]. We see no evidence for any
significant activation of the Mg-Al burning chain. The use of 3D atmospheres
causes an increase of a factor of up to 2.5 in the fraction of 25Mg, resolving
part of the discrepancy between the observed isotopic fraction and the
predictions from pollution models.
