We report on a measurement of the 44 Ti half-life aimed at lowering existing systematic uncertainties in this value, which is important to astrophysics. The half-life was measured by following the decay of 44 Ti relative to 60 Co for about 5 yr and the measurements were performed independently in three laboratories-Argonne, Jerusalem, and Torino. We suggest to combine our result, 59.0 6 0.6 yr, with the one from the accompanying Letter by Görres et al., 60.3 6 1.3 yr, to obtain a current "best value" for the half-life of 44 Ti of 59.2 6 0.6 yr (1s error). [S0031-9007(98)05567-7] PACS numbers: 21.10. Tg, 26.30. + k, 26.40. + r, 27.40. + z The half-life of 44 Ti plays an important role in determining the amount of 44 Ti produced by cosmic rays in meteorites [1], and in supernova explosions [2][3][4]. 44 Ti production is currently determined via the 1157 keV g line of the 44 Sc daughter in secular equilibrium (see Fig. 1). In order to determine the original 44 Ti production, the half-life value of 44 Ti enters twice: (i) in calculating the number of 44 Ti nuclei from the activity measurement, and (ii) in the correction for decay between production and measurement. Meteoritic 44 Ti measurements are usually performed for falls only, for which a date is known by direct observation of the fiery entry to Earth. Owing to the value of its half-life, 44 Ti produced in meteorites provides an important monitor of the galactic cosmic ray flux in the last few hundred years and its modulation by solar activity [1]. The first observation of the 1157 keV g-ray flux from the Cassiopeia A supernova remnant, made by the space-borne g-ray instruments COMPTEL [2,3] and OSSE [4], emphasized the necessity to solve the question of the uncertain 44 Ti half-life. Although further searches with COMPTEL on board of the Compton Gamma Ray Observatory did not reveal definite 44 Ti g-ray signals from other supernova remnants [3], such signals may well be found with the increased sensitivity of future g-ray observatories [e.g., the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) to be launched [5] in 2001]. In calculating the total 44 Ti yield of a supernova from the 44 Ti activity observed in a space-borne instrument, uncertainties of four quantities (g-ray flux, distance, explosion date, half-life) contribute to the overall precision of the 44 Ti yield result. Among these uncertainties, that of the halflife is still surprisingly large, despite the fact that it has been measured several times in the past (Table I). It can be seen in Table I that these half-life measurements for 44 Ti give discordant results. This situation, not uncommon for long half-life measurements, most likely results from the difficulty to reliably estimate systematic errors.This was the case, for example, for the important half-life of 14 C. Only after a reasonable understanding of systematic effects, a recommended half-life of 5730 6 40 yr was finally accepted [12].In view of the significance of the 44 Ti half-life, several attempts to remeasure it have been ...