Observation of the X17 anomaly in the decay of the Giant Dipole Resonance of 8^8Be

Angular correlation spectra of $e^+e^-$ pairs produced in the $^{7}$Li($p$,$\gamma$)$^{8}$Be nuclear reaction were studied at a proton beam energy of $E_p$~=~4.0~MeV, which corresponds to the excitation energy of the Giant Dipole Resonance (GDR) in $^8$Be. The spectra measured show a peak like anomaly at 120$^\circ$ and a broader anomaly also above 140$^\circ$. Both anomalies could consistently be described by assuming that the same hypothetical X17 particle was created both in the ground-state transition and in the transition going to the broad ($\Gamma$=1.5~MeV), first excited state in $^8$Be. The invariant mass of the particle, which was derived to be $m_Xc^2 = 16.95 \pm 0.48$(stat.)~MeV, agrees well with our previously published values.Comment: 5 pages, 7 figures. arXiv admin note: text overlap with arXiv:2209.1079

First observation of excited states in 120La and its impact on the shape evolution in the A ≈ 120 mass region

Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus 57120La63. The observed γ rays have been assigned based on coincidences with lanthanum X rays measured with the JUROGAM 3 array and with A=120 fusion-evaporation residues measured with the MARA separator. The observed γ rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity 4+ to the ground state and a πh11/2⊗νh11/2 configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the np interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of E2 transitions, giving credit to the np interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei

Multiple chiral doublet bands in 104Rh

Two new negative-parity bands have been identified in the odd-odd 104Rh nucleus. According to their experimentally observed properties, they have the same π(1g9/2)−1⊗ν(1h11/2)1 high-j configuration as the previously known negative-parity chiral doublet bands. This observation raises the possibility of the existence of multiple chiral doublet bands, MχD, in this nucleus. Comparing the properties of the observed bands with results of detailed theoretical calculations, one can conclude that the lower energy parts of bands 1 and 2 are chiral partner bands with the π(1g9/2)−1⊗ν(1h11/2)1 two-quasiparticle configuration, while bands 3 and 4 are chiral partner bands with the π(1g9/2)−1⊗ν(1g7/2)−2(1h11/2)1 four-quasiparticle configuration. Thus, MχD based on different configurations is observed in 104Rh