The construction of TRIGA-TRAP and direct high-precision Penning trap mass measurements on rare-earth elements and americium

Nuclear masses are an important quantity to study nuclear structure since they reflect the sum of all nucleonic interactions. Many experimental possibilities exist to precisely measure masses, out of which the Penning trap is the tool to reach the highest precision. Moreover, absolute mass measurements can be performed using carbon, the atomic-mass standard, as a reference. The new double-Penning trap mass spectrometer TRIGA-TRAP has been installed and commissioned within this thesis work, which is the very first experimental setup of this kind located at a nuclear reactor. New technical developments have been carried out such as a reliable non-resonant laser ablation ion source for the production of carbon cluster ions and are still continued, like a non-destructive ion detection technique for single-ion measurements. Neutron-rich fission products will be available by the reactor that are important for nuclear astrophysics, especially the r-process. Prior to the on-line coupling to the reactor, TRIGA-TRAP already performed off-line mass measurements on stable and long-lived isotopes and will continue this program. The main focus within this thesis was on certain rare-earth nuclides in the well-established region of deformation around N~90. Another field of interest are mass measurements on actinoids to test mass models and to provide direct links to the mass standard. Within this thesis, the mass of 241-Am could be measured directly for the first time.

Nearrings and a construction of triply factorized groups

In this thesis a connection between triply factorised groups and nearrings is investigated. A group G is called triply factorised by its subgroups A, B, and M, if G = AM = BM = AB, where M is normal in G and the intersection of A and B with M is trivial. There is a well-known connection between triply factorised groups and radical rings. If the adjoint group of a radical ring operates on its additive group, the semidirect product of those two groups is triply factorised. On the other hand, if G = AM = BM = AB is a triply factorised group with abelian subgroups A, B, and M, G can be constructed from a suitable radical ring, if the intersection of A and B is trivial. In these triply factorised groups the normal subgroup M is always abelian. In this thesis the construction of triply factorised groups is generalised using nearrings instead of radical rings. Nearrings are a generalisation of rings in the sense that their additive groups need not be abelian and only one distributive law holds. Furthermore, it is shown that every triply factorised group G = AM = BM = AB can be constructed from a nearring if A and B intersect trivially. Moreover, the structure of nearrings is investigated in detail. Especially local nearrings are investigated, since they are important for the construction of triply factorised groups. Given an arbitrary p-group N, a method to construct a local nearring is presented, such that the triply factorised group constructed from this nearring contains N as a subgroup of the normal subgroup M. Finally all local nearrings with dihedral groups of units are classified. It turns out that these nearrings are always finite and their order does not exceed 16.

High mobility rates during the period of the "Celtic migrations"? - 87 Sr, 86 Sr and delta 18 O evidence from Early La Tène Europe

Although the period of the historic “Celtic migrations” is archaeologically extensively studied, the long-lasting question whether mass migration or increased individual mobility caused the expansion of the La Tène culture throughout continental Europe persist. Strontium (Sr) and in part oxygen (O) isotope analysis of human remains from the early La Tène cemeteries of Nebringen (Germany), Münsingen-Rain (Switzerland), Monte Bibele (Italy) and the Czech cemeteries of Radovesice I, Radovesice II and Kutná Hora was, therefore, carried out to investigate the importance of residential changes during this time period. These isotope analyses showed that most analysed individuals either came from the area they were buried in or from the surrounding area of the cemetery. An exception was formed by the Czech cemeteries, where almost a quarter of the studied individuals appeared non-local. Together with Nebringen, these cemeteries also had the most varied Sr isotope ratios, which suggest highly mobile communities in which individuals regularly changed their residency. The isotopic ratios of the cemeteries of Münsingen-Rain and Monte Bibele appeared far less varied. In part, these differences might be explained by the community structures of these cemeteries. Morphological kinship analysis in Münsingen-Rain demonstrated biological relatedness among most of the analysed individuals. These related individuals also shared similar isotope signatures, which suggest an origin from the surrounding Aar Valley. In the vicinity of the cemetery of Monte Bibele, an associated settlement site was discovered. The deceased presumably not only shared this settlement, but also cultivated the same land plots. Dispersed settlement structures were suggested for Nebringen, Radovesice and Kutná Hora, as these agriculturally favourable landscapes were densely populated during prehistoric times. Connected to these community structures are the prevailing geological conditions in these areas. Both Münsingen-Rain and Monte Bibele are located in a region where homogeneous geological conditions prevail, whereas the landscapes of Nebringen, Radovesice and Kutná Hora are characterised by complex heterogeneous geological conditions. As the majority of individuals in Nebringen and the Czech cemeteries correspond to the expected isotope values for the studied areas, regularly changing land plots might have contributed to the observed variation. Although mass migration as depicted by the historical sources was not observed individual mobility of a small part of these studied communities certainly played a role. Males appeared, thereby, to have slightly more often a non-local birthplace or moved during childhood. Male mobility was, however, not always associated with burial as a warrior. Females, on the other hand, originated more often from the region. Patrilocal residential patterns, with the exception of the Czech cemeteries, were nevertheless not observed. Objects and ideas also seem to have been exchanged freely, as there are no indications that individuals with particular grave goods came from specific areas. It rather appears that the individuals buried with them were either local or had different places of origin. This can be explained by the fact that the exact origin of grave goods is difficult to establish and the occurrence of similar 87Sr/86Sr values in different areas. This study provided important new insights on the period of the “Celtic migrations” and the way of life of these prehistoric people.