MASS MEASUREMENTS OF VERY HIGH-ACCURACY BY TIME-OF-FLIGHT ION-CYCLOTRON RESONANCE OF IONS INJECTED INTO A PENNING TRAP

The possibility of absolute mass measurements using time-of-flight detection of ion cyclotron resonance on ions injected into a Penning trap has been demonstrated. Resolving powers of 2 million have been achieved, with accuracies of about 0.5 ppm. Absolute accuracy is obtained by direct observation of the sum frequency of the cyclotron and the magnetron motions through the use of an azimuthal quadrupole r.f. field to transform initial magnetron motion into cyclotron motion. Imperfections of the Penning trap leading to systematic errors are discussed. The system has been designed specifically to measure the masses of radionuclides produced at the on-line isotope separator ISOLDE. With further developments this system will provide mass measurements of 0.1 ppm accuracy on nuclei which are available in quantities such that on average one will survive nuclear decay for the duration of the measurement cycle. © 1990.