  Using spectra obtained with the VLT/FORS2 and Gemini-S/GMOS instruments we
have investigated carbon, nitrogen and sodium abundances in a sample of red
giants in the Small Magellanic Cloud cluster Kron 3. The metallicity and
luminosity of this cluster are comparable to those of Galactic globular
clusters although with a notably younger age of $\sim$ 6.5 Gyr. Specifically we
have investigated the strengths of the CH ($\lambda$ 4300 A) and CN ($\lambda$
3800, $\lambda$ 4215) molecular bands finding a bimodality of CN band-strengths
and a CH/CN anti-correlation. Application of spectrum synthesis techniques
reveals a large spread ($\sim$1.2 dex) in nitrogen abundance and a spread in
[C/Fe] of $\sim$0.3 dex after applying corrections for evolutionary mixing. We
have also estimated sodium abundances from the strengths of the Na D lines
finding a range of $\sim$0.8 dex in [Na/Fe] that correlates positively with the
N abundances. This is the first star-by-star spectroscopic demonstration of
correlated Na, N abundance variations in an intermediate-age star cluster,
adding to existing photometric and spectroscopic indications of the presence of
multiple populations in such clusters with masses in excess of $\sim 10^5$
solar masses. Our results confirm that the mechanism(s) responsible for the
multiple populations observed in globular clusters cannot be an early
cosmological effect applying only in old clusters, and provide a key additional
factor in the quest to understand the origin of the abundance anomalies.
