Excited states in the neutron-rich N=38,36 nuclei uc{60}{Ti} and uc{58}{Ti} were populated in nucleon-removal reactions from uc{61}{V} projectiles at 90~MeV/nucleon. The gamma-ray transitions from such states in these Ti isotopes were detected wit
h the advanced gamma-ray tracking array GRETINA and were corrected event-by-event for large Doppler shifts (v/c sim 0.4) using the gamma-ray interaction points deduced from online signal decomposition. The new data indicate that a steep decrease in quadrupole collectivity occurs when moving from neutron-rich N=36,38 Fe and Cr toward the Ti and Ca isotones. In fact, uc{58,60}{Ti} provide some of the most neutron-rich benchmarks accessible today for calculations attempting to determine the structure of the potentially doubly-magic nucleus uc{60}{Ca}.
We report on the experimental study of quadrupole collectivity in the neutron-deficient nucleus uc{104}{Sn} using intermediate-energy Coulomb excitation. The $B(E2; 0^+_1 rightarrow 2^+_1)$ value for the excitation of the first $2^+$ state in uc{10
4}{Sn} has been measured to be $0.180(37)~e^2$b$^2$ relative to the well-known $B(E2)$ value of uc{102}{Cd}. This result disagrees by more than one sigma with a recently published measurement cite{Gua13}. Our result indicates that the most modern many-body calculations remain unable to describe the enhanced collectivity below mid-shell in Sn approaching $N=Z=50$. We attribute the enhanced collectivity to proton particle-hole configurations beyond the necessarily limited shell-model spaces and suggest the asymmetry of the $B(E2)$-value trend around mid-shell to originate from enhanced proton excitations across $Z=50$ as $N=Z$ is approached.
We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei uc{47,48}{Ar} using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly-magic Ca to collective S and Si isot
opes, a critical region of shell evolution and structural change. The deduced $B(E2)$ transition strengths are confronted with large-scale shell-model calculations in the $sdpf$ shell using the state-of-the-art SDPF-U and EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
Excited states in the very neutron-rich nuclei 35Mg and 33Na were populated in the fragmentation of a 38Si projectile beam on a Be target at 83 MeV/u beam energy. We report on the first observation of gamma-ray transitions in 35Mg, the odd-N neighbor
of 34Mg and 36Mg, which are known to be part of the Island of Inversion around N = 20. The results are discussed in the framework of large- scale shell-model calculations. For the A = 3Z nucleus 33Na, a new gamma-ray transition was observed that is suggested to complete the gamma-ray cascade 7/2+ --> 5/2+ --> 3/2+ gs connecting three neutron 2p-2h intruder states that are predicted to form a close-to-ideal K = 3/2 rotational band in the strong-coupling limit.
The neutron-rich N=50 isotones 82Ge and 84Se were investigated using intermediate-energy Coulomb excitation on a 197Au target and inelastic scattering on 9Be. As typical for intermediate-energy Coulomb excitation with projectile energies exceeding 70
MeV/nucleon, only the first 2^+ states were excited in 82Ge and 84Se. However, in the inelastic scattering on a 9Be target, a strong population of the first 4^+ state was observed for 84Se, while there is no indication of a similarly strong excitation of the corresponding state in the neighboring even-even isotone 82Ge. The results are discussed in the framework of systematics and shell-model calculations using three different effective interactions.
We report on the first in-beam gamma-ray spectroscopy study of the very neutron-rich nucleus 46S. The N=30 isotones 46S and 48Ar were produced in a novel way in two steps that both necessarily involve nucleon exchange and neutron pickup reactions, 9B
e(48Ca,48K)X followed by 9Be(48K,48Ar+gamma)X at 85.7 MeV/u mid-target energy and 9Be(48Ca,46Cl)X followed by 9Be(46Cl,46S+gamma)X at 87.0 MeV/u mid-target energy, respectively. The results are compared to large-scale shell-model calculations in the sdpf shell using the SDPF-NR effective interaction and Z-dependent modifications.
We report on the first in-beam $gamma$-ray spectroscopy of uc{23}{Al} using two different reactions at intermediate beam energies: inelastic scattering off uc{9}{Be} and heavy-ion induced one-proton pickup, uc{9}{Be}( uc{22}{Mg}, uc{23}{Al}$+gamma
$)X, at 75.1 MeV/nucleon. A $gamma$-ray transition at 1616(8) keV -- exceeding the proton separation energy by 1494 keV -- was observed in both reactions. From shell model and proton decay calculations we argue that this $gamma$-ray decay proceeds from the core-excited $7/2^+$ state to the $5/2^+$ ground state of uc{23}{Al}. The proposed nature of this state, $[ uc{22}{Mg}(2^+_1) otimes pi d_{5/2}]_{7/2+}$, is consistent with the presence of a gamma-branch and with the population of this state in the two reactions.
