Abstract: DETERMINATION OF THE ISOTOPIC ABUNDANCE OF IRON AND NICKEL WITH TWO-STEP LASER TIME-OF-FLIGHT MASS SPECTROMETRYZhou Mingfei;Qin Qizong(Laser Chemistry Institute，Fudan University，Shanghai 200433)Abstract:Two-step laser time-of-flight mass spectrometry is established to measure the isotopic abun dance of iron and nickel．A pulsed Nd：YAG laser(532nm) is used to evaporate iron and nickel atoms from a meral alloy sample，These atoms are ionized by a Nd：YAG pumped pulsed dye laser ar 300. 7nm and 303．4nm via resonance ionization and subsequently detected by time-of-flight mass spectrometry. Arrival time distributions are obtained by varying the time delay between e vaporarion laser and ionization laser，Overlap of the pulsed atomic beam and the ionization laser beam is excellent with about 1％effective duty cycle，then the sensitivity of isotopic detection will be increased substantially using resonance ionization time-of-flight mass spectrometry，A one color two-photon(1＋1)ionization scheme is employed for Fe and Ni atoms，Our results show that all the measured isotopic abundances of Fe and Ni are in agreement with values published in the lit erature.Keywords: Two-step laser mass spectrometry Resonance ionization Iron Nickel