Previous measurements of the half-life of [sup 32]Si, which is produced by cosmic-ray spallation of [sup 40]Ar and of interest for geophysical dating, display large discrepancies. We present a new method for half-life measurements of this and other isotopes. Two samples containing 6.7[times]10[sup 8] and 7.4[times]10[sup 8] 2Si nuclei, respectively, were prepared by implantation of separated projectile fragments. The half-life of [sup 32]Si was calculated from the two independent measurements of the specific activity to be 132[plus minus]13 yr.