Konzeption eines kryogenen Penningfallenaufbaus für SHIPTRAP und Massenbestimmung von Radionukliden um den Z=82–Schalenabschluss an ISOLTRAP

Conceptual Design of a Cryogenic Penning Trap Set–Up for SHIPTRAP and Mass Determination of Radionuclides around the Z = 82 – Shell Closure with ISOLTRAP: The Penning trap mass spectrometers SHIPTRAP/GSI and ISOLTRAP/CERN enable precise mass determination of unstable, exotic nuclei. The following detection methods are presented: the destructive time–of–flight method (TOF–ICR) and the non–destructive Fourier Transform–Ion Cyclotron Resonance method (FT–ICR). Planned experiments with SHIPTRAP focus on transuranium elements whose low production limit their experimental investigation. The sensitive FT–ICR– detection allows the identification of stored ions as well as their mass determination. Within this thesis, a cryogenic Penning trap set–up has been designed and constructed, in order to detect and to observe the cyclotron frequency of a single singly-charged heavy ion. It consists of a vacuum system at liquid nitrogen temperature in the bore of a superconducting magnet housing a double trap set–up, a purification trap and a measurement trap. A superconducting inductance in a liquid-helium Dewar provides extreme sensitivity for detection of the cyclotron frequency. At ISOLTRAP the resonant excitation at the cyclotron frequency is detected by the time– of–flight method. Atomic masses of the radionuclides $^{145,147}\!$Cs , $^{181,183,186m,187x,196m,205}$Tl , $^{187,187m,197,208}$Pb , $^{190−197,209,215,216}$Bi , $^{203,205,229}$Fr and $\,^{214,229,230}$Ra were determined experimentally with a relative mass uncertainty of typically some 10$^{−8}$. The results were included into the atomic mass evaluation and a mass adjustment was conducted. Resulting separation energies show the expected global trend, whereas thallium and mercury isotopes reveal a deviation from this linear behaviour. This could point to unexpected nuclear structure effects as observed in nuclear and laser spectroscopic experiments.