EXOTRAP · Pushing the limits of online mass spectrometry

Pushing the limits of online mass spectrometry

The mass of the nucleus, through its binding energy, reflects the net effect of all aspects of the underlying fundamental forces and is of capital importance for many branches of physics, from pure nuclear physics via production of nuclei in stellar environment, to tests of the Standard Model. The physics questions which can be answered with mass measurements depend strongly on the experimental technique which determines the nuclei which can be addressed and the precision which can be achieved. Penning traps have turned out to be ideal tools for high-precision mass measurements for both stable and unstable nuclei. Up to now in the case of radio-nuclides, their masses could be measured with a relative uncertainty better than one part in 100 million, a resolving power approaching 10 million, production rates as low as 1 ion/s, half-lives as low as 10 ms, and for singly or maximum doubly ionized ions. However, these impressive performances in accuracy, resolving power, sensitivity and applicability have not be achieved simultaneously for one specific species. The EXOTRAP project aims at pushing the present limits of mass spectrometry on radio-nuclides, thus allowing studies of nuclides and physics questions inaccessible before. It consist of two objectives: improving the resolving power and sensitivity of online Penning trap mass spectrometers, thus giving access to radionuclides which could not be addressed before, as well as increasing the precision of the online mass studies, while maintaining the high resolving power and sensitivity, because in many cases the achievable precision still does not allow addressing some interesting topics. The above project had several multidisciplinary aspects. It employed experimental techniques used in both atomic and nuclear physics and it addressed various physics topics concerning atomic physics, nuclear physics, and fundamental studies. Within the project 8-month period the preparatory part of the work was completed. It included a series of experiments investigating the effects connected to the presence of multiple ions in an ion trap and the start-up of corresponding simulations performed with state-of-the-art parallel computing with graphics cards, like the ones used for 3D computer games and movies. Another test concerned the implementation of a new electrostatic trap which allowed purifying the ion beam much faster than before. Finally, new mass measurements included very precise determination of the energy released in a postulated double electron-capture exotic decay of cadmium-106 into palladium-106 with no emission of a neutrino particle, which will help searching for evidence of this extremely rare event. Also, for the first time the detection of beta particles and gamma rays from radioactive decay was used to assist mass measurements which were taking place almost in parallel. The final goals of the project include improving the selectivity of the method by implementing simulation results, as well as understanding the main sources of systematic uncertainties in mass determination and investigating ways of minimizing them. The project allowed transferring the knowledge and experience gathered at the CERN laboratory in Geneva to the MPIK in Heidelberg. It is relevant for the whole field of mass spectrometry, also the one using stable ions, molecules, and more complicated compounds which are relevant for applications in chemistry, biology, or medicine.

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