Lifetime measurements using RDDS method in the vicinity of 78 Ni

Reduced quadrupole transition probabilities for low-lying transitions in neutron-rich N = 52 isotones 88 Kr and 86 Se were investigated with a recoil distance Doppler shift (RDDS) experiment. The experiment was performed at GANIL (Caen, France) using the Orsay Universal Plunger System (OUPS) for the RDDS technique and the AGATA array for the \u3b3-ray detection coupled to the VAMOS++ magnetic spectrometer for an event-by-event particle identification. In 88 Kr, the lifetimes of seven levels were determined and in 86 Se, the lifetimes of five levels were determined. The deduced B(E2; 2 +1 \u2192 0 +1 ) are compared with mean-field and shell-model calculations

Search for 22^{22}Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of $^{26}$Al and $^{22}$Na. While γ rays from the decay of the former radioisotope have been observed through-out the Galaxy, $^{22}$Na remains untraceable. The half-life of $^{22}$Na (2.6 yr) would allow the observation of its 1.275 MeV γ-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus. The $^{22}$Na(p, γ)$^{23}$Mg reaction remains the only source of large uncertainty about the amount of $^{22}$Na ejected. Its rate is dominated by a single reso- nance on the short-lived state at 7785.0(7) keV in $^{23}$Mg. In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the $^{23}$Mg states, combining magnetic and highly-segmented tracking γ -ray spectrometers, places strong limits on the amount of $^{22}$Na produced in novae, explains its non-observation to date in γ rays (flux < 2.5×10$^{-4}$ ph.cm$^{-2}$ s$^{-1}$), and constrains its detectability with future space-borne observatories

Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni-78 Region : A Hint from Lifetime Measurements

Lifetime measurements of excited states of the light N = 52 isotones Kr-88, Se-86, and Ge-84 have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2; 2(+)-&gt; 0(+)) and B(E2; 4(+)-&gt; 2(+)) were obtained for the first time for the hard-to-reach 84Ge. While the B(E2; 2(+)-&gt; 0(+) ) values of Kr-88, Se-86 saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g(7/2), 1h(11/2)) space of an inert Ni-78 core, the value obtained for Ge-84 largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N less than or similar to 49, extend beyond N = 50. The onset of collectivity at Z = 32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector rho field in shell-structure evolution