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A new method of extracting the g-ray intensities necessary to perform lifetime measurements using the differential decay curve method (DDCM) is presented in this work, the unresolved Doppler-shifted components method (UDCM). The UDCM allows for a DDCM analysis to be performed using a g-ray transition for which the fully Doppler-shifted and degraded components are unresolvable in energy and so are detected as a single peak. This technique was used to measure the known lifetime of the yrast 2+1 state in 50Mn with a depopulating transition that does not have resolvable fully Doppler-shifted and degraded components. The lifetime measured through applying the UDCM was consistent with the standard DDCM measurement of the 2+1 state. Use of the UDCM allows for DDCM lifetime measurements to be made using transitions of smaller g-ray energies, smaller recoil velocities and, in some cases, with a smaller uncertainty. In contrast to a standard DDCM analysis, a UDCM analysis is also independent of the widths of the fully Doppler-shifted and degraded components and as a result they do not need to be determined.

This work describes experimental studies that contribute to the understanding of the shell structure in the Ti-Cr-Fe region beyond N=28. For exotic nuclei, as examined in this thesis, significant changes in the shell structure may occur. Therefore, such nuclei offer the possibility to investigate the properties and validity of nuclear models under extreme conditions. From the experimental data available so far on the 2+ states in N=32 isotones, the occurrence of a phase transition from predominant collective structures in 58Fe to a neutron subshell closure is predicted, which evolves as the number of protons in the πf7/2 orbital reduces, i.e. of 56Cr-> 54Ti->52Ca, due to the weakening of the monopole interaction between the πf7/2 orbital of protons and the vf5/2 orbital of neutrons. However, modern shell-model calculations with different interactions, e.g. the GXPF1A, KB3G and FPD6 interactions, were not able to satisfactorily describe the observed staggering of the B(E2;2+ -> 0+) values in 50,52,54Ti, which probably results from neutron subshell closures. Therefore, in this work reduced transition probabilities of the lowest transitions of the respective ground-state bands in 46,50,52,53,54Ti were investigated experimentally by lifetime measurements, partly for the first time. The multinucleon-transfer reaction mechanism, which is a promising approach to the production of difficult to access and exotic atomic nuclei, was applied to study the evolution from nuclei in the valley of stability towards neutron-rich exotic Ti isotopes at the Grand Accélérateur National d'Ions Lourds (GANIL) in Caen, France: In the Cologne plunger for deep-inelastic reactions, a radioactive 238U beam with an energy of 6.76 MeV/u impinged on a stretched 50Ti target with nat Cu layer in front of the target, while a nat Mg degrader foil was used to decelerate the reaction products for measuring lifetimes using the Recoil Distance Doppler-shift (RDDS) technique. The reaction products of interest were identified with the magnetic spectrometer VAMOS++, while the gamma radiation was measured with the gamma tracking array AGATA. During this experiment beam-induced changes of the target occurred. These resulted in the fact that the distances between the target and degrader foil could not be extracted exactly, which are essential for an RDDS lifetime analysis. Therefore, another RDDS experiment was performed at the Cologne FN tandem accelerator using a fusion-evaporation reaction. The aim of this experiment was to determine the lifetimes of the 2+ and 4+ states of the ground-state band in the stable nucleus 46Ti with high precision, in order to subsequently determine the unknown distances between the target and degrader foil of the experiment performed at GANIL. This nucleus was chosen because it was populated with sufficient statistics in the multinucleon-transfer reaction at GANIL and the lifetimes of its low-lying states are in the sensitive range for the distances chosen in this experiment. The data from the experiment on 46Ti in Cologne were analyzed using the Differential Decay Curve method in gamma-gamma coincidences. The unknown distances from the GANIL experiment were then determined by comparing the experimental gamma-ray spectra with those generated by Monte-Carlo simulations using the chi-squared method. The lifetimes of the 2+, 4+, 6+ and 8+ in 52,54Ti and the (5/2-), 7/2-, 9/2-, 11/2- and 13/2- states in 53Ti were determined using both the DDCM and the minimum chi-squared method with the distances obtained in this way. Furthermore, a third RDDS measurement was carried out within this work, also at the Cologne FN tandem accelerator, with the aim of determining the lifetime values of the lowest-lying states of the ground-state band in 50Ti. Although this nucleus was also populated during the measurement at GANIL, the additional measurement provided a more precise determination of the lifetimes based on the knowledge of the exact relative distances between the target and degrader foil. The lifetimes were analyzed in a particle-gamma evaluation. The transition probabilities determined from the level lifetimes are interpreted based on shell-model predictions of different interactions in the f7/2, p3/2, f5/2, p1/2 valence space for protons and neutrons.

Lifetimes of the T = 1 isobaric analog Ip = 2+ states in 50Mn and 50Cr were measured simultaneously by employing the recoil distance Doppler-shift (RDDS) technique. The states were populated in a fusion-evaporation reaction with a ¹²C beam on a 40Ca target. An analysis of the data and the calculations from the present work, together with the available B(E2 : 2+ RT 0+) data of the isobaric analog states in 50Fe and 50Cr, were used to study isospin symmetry in the three A = 50 isobaric nuclei. Shell-model calculations reproduce the magnitudes as well as the increasing trend of the B(E2) data with increasing Z. To draw a firm conclusion on the level of isospin mixing in the triplet, a new precision measurement of the 2+ RT 0+ transition rate in 50Fe will be required.

The lifetime of the 21+ state of ²¹²Po was measured in the ²08Pb(¹²C,8Be)²¹²Po transfer reaction by g-ray spectroscopy employing the recoil distance Doppler shift (RDDS) method. The derived absolute B(E2) value of 2.6(3) W.u. indicates a low collectivity and contradicts previous claims of a-cluster components in the structure of the 21+ state. It is demonstrated that a consistent description of the properties of the 21+− 41+− 61+− 81+ sequence in ²¹²Po cannot be achieved in the framework of a single- j shell-model calculation, either. This puzzle is traced to the properties of the seniority-2 configurations in ²¹0Pb and ²¹0Po.