Lifetime of the isomeric intruder state in 105 Ru

We propose to measure half-lives of several excited states in Ru by using C-induced neutron transfer reaction. In this nucleus, at low excitation energies, single-particle and seniority isomers emerge and compete with collective degrees of freedom. In order to study the interplay between these modes we propose to measure lifetimes of the low-lying excited states by using the hybrid RoSphere. Of particular interest is the lifetime of the intruder state at 209 keV. Preliminary results, had shown that the lifetime of this particular states is by ≈ 10 orders of magnitude shorter than previously expected. The results from the present proposal are thus expected to have an impact on our understanding of the interplay between the single-particle and collective degrees of freedom in this mass region. 1 Motivation On the Segré chart, Ru is located between its heaviest stable isotope Ru [1, 2] and the most exotic Ru nuclei, produced in relativistic fission [3, 4, 5]. Being just on the edge of the line of β-stability, only few experimental methods can be used to populate its excited states. So far, the nucleus was studied in the Tc β-decay [6], Ru(d,p) reaction [8, 7] and n-capture on Ru [10, 9]. More recently, Ru was studied from (d, pγ) at IFIN-HH. It should be noted, however, that these reaction mechanisms are highly selective and populate only low-spin states. In the 1990s the high-resolution high-granularity multidetector γ-ray arrays become available, which have enabled the use of induced fission reactions for γ-ray spectroscopy, providing the opportunity to fill in the gap of transitional nuclei situated between the line of beta stability and the most exotic neutron-rich nuclei produced in fission. This type of reactions also provide the opportunity to obtain some of the higher-spin states in these ”transitional” nuclei. Thus, by using induced fission reaction, the intruder negative-parity band in Ru was observed for the first time and extended up to (31/2−) [11]. There, the spin and parity assignment of J = 11/2−, made to the band head, was based on systematics and theoretical assumptions. This assignment was then extrapolated towards the most exotic neutron-rich ruthenium nuclei.