Moritz Pascal Reiter
Dr M P Reiter
I am interested in studies of the nuclear structure far from stability – in particular precision measurements of very exotic isotopes. My research in this filed aims to understand the evolution of nuclear shells, formation of new sub shells and quenching of existing canonical shells. In addition I am interested in applying new findings in nuclear physics to astrophysical processes – in particular the rapid neutron capture process, believed to be responsible for the creation of half of the stable isotopes beyond iron, is in need of more and high quality nuclear physics inputs.
General Introduction & Overview
High-precision mass measurements and spectroscopy give an insight into the variation of the nuclear structure and stability across the nuclear chart. Systematic measurements along isotopic chains and the observed shell structure of nuclei, reflected by increased binding energies at the so-called magic neutron and proton numbers, led to the development of the current shell model. From precise mass values, important differential quantities, such as the proton and neutron separation energies can be calculated, which highlight different nuclear structure effects.
Approaching the limits of nuclear binding, the structure and properties of nuclei is of great interest and attracts large attention, theoretically and experimentally. It has become evident that the nuclear shell structure can change towards the drip-line. New effects such as shell quenching, weakening or disappearance of shells around the classical magic numbers and appearance of new magic numbers have been theoretically predicted and observed in experiments. One of the best studied examples are the N=20 and N=28 "island of inversion" where the normal level population according to a spherical mean field model is overcome and as a result the traditional N=20 and N=28 shell closures completely disappear.
Mass measurements for the evolution of nuclear shells
In recent work we investigated the evolution of the N=32 neutron shell closure, that forms in neutron-rich Sc, Ca and K isotopes. Here we performed mass measurements of neutron-rich Ti and V isotopes at TITAN, TRIUMF, Vancouver, with a new multiple-reflection time-of-flight mass-spectrometer (MR-TOF-MS) in combination with the established TITAN Penning Trap system. The new MR-TOF technology has shown to be particular suitable for low count rate measurements of short lived isotopes with relative uncertainties on the ~ 10-7 scale, sufficient for nuclear structure and nuclear astrophysics investigations.
Our direct measurements, together with new state-of-the-art ab-initio shell model calculations, showed the transitional character of Ti, right between “no shell effects” and “strong shell effects”. The results challenge modern ab-initio theories and serve as an excellent testing ground for new shell model calculations. We plan to exploit the new experimental capabilities and push towards an investigation of the N=34 neutron shell closure, currently under discussion in Ti. Further we aim to expand our studies across the mid-shell region between the proton shell closures at Z=20 and 28 along the neutron-rich side of the nuclear chart, as well as investigate the evolution of the N=82 neutron shells on the neutron-deficient side.
Mass measurements towards the proton drip line
Mass measurements of these very neutron-deficient Tm and Lu isotopes allow a determination of the proton drip-line, where the one proton separation energy becomes negative and isotopes further away from stability only exist as resonances, making them particular short lived. Using fast mass spectrometry techniques, we plan to measure these short lived ( ~ few ms half-life) isotopes beyond or close to the proton drip line. Yield estimates and half-life considerations show, that measurements of very neutron-deficient lanthanides (even beyond the drip line) are reasonable. The results will allow a direct determination of the proton drip-line in this region.
Mass measurements for nuclear astrophysics
Since the discovery of the gravitational waves of a binary neutron star merger by the Ligo-Virgo Collaboration in 2017 in combination with the gamma-ray burst and subsequent kilonova emission, direct evidence has been established, that heavy isotopes are formed by the rapid neutron capture process (r-process) in such an event. This increased the need for accurate nuclear physics properties of isotopes involved in the r-process even further. Measurements of these isotopes are particular challenging, due to their short half-life and low production yields at current facilities.
New and upcoming radioactive beam facilities, FAIR-GSI, ARIEL-TRIUMF and FRIB-MSU will drastically enhance the production of isotopes around the 2nd and 3rd r-process abundance peak. Here we work closely with the FRS-Ion Catcher experiment at GSI aiming to study neutron-rich isotopes along the N=128 neutron shell closure below Pb-208, which are responsible for the formation of the 3rd r-process abundance peak.
Moritz Pascal currently offers the following PhD project opportunities:
- Investigating nuclear structure near N=32 and N=34: Precision mass measurements of neutron-rich Ca, Ti, and V isotopes DOI, Physical Review C, 106, 2, p. 1-7
- Summit of the N=40 Island of Inversion: precision mass measurements and ab initio calculations of neutron-rich chromium isotopes DOI, Physics Letters B, 833, p. 1-7
- Physical Review C, 105, 4, p. 1-8
- Commissioning and performance of TITAN’s Multiple-Reflection Time-of-Flight Mass-Spectrometer and isobar separator DOI, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1018, p. 1-14