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The 12C/13C isotope ratio in the interstellar medium (ISM), and its evolutionwith time, is an important tracer of stellar yields. Spatial variations of thisratio can be used to study mixing in the ISM. We want to determine this ratioand its spatial variations in the local ISM from CH+ absorption lines in theoptical towards early-type stars. The aim is to determine the average value forthe local ISM and study possible spatial variations. We observed a large numberof early-type stars with Feros to extend the sample of suitable target starsfor CH+ isotope studies. The best suited targets were observed with Uves withhigher signal-to-noise ratio and spectral resolution to determine the isotoperatio from the interstellar CH+ lines. This study significantly expands thenumber of 13CH+ detections. We find an average ratio of <R> = 76.27 +- 1.94 or,for f = 1/R, <f> = (120.46 +- 3.02) 10^{-4}. The scatter in f is 6.3sigma(<f>). This findings strengthens the case for chemical inhomogeneity inthe local ISM, with important implications for the mixing in the ISM. Given thelarge scatter, the present-day value in the ISM is not significantly largerthan the solar value, which corresponds to the local value 4.5 Gyr ago.

Interstellar 12C/13C from CH+ absorption lines: Results from an extended survey