High spin level schemes of 118,119 Ag are established for the first time by analyzing the high statistics γ-γ-γ and γ-γ-γ-γ coincidence data from the spontaneous fission of
Masses of 52g,52m Co were measured for the first time with an accuracy of ∼ 10 keV, an unprecedented precision reached for short-lived nuclei in the isochronous mass spectrometry. Combining our results with the previous β -γ measurements of 52 Ni, the T = 2, J π = 0 + isobaric analog state (IAS) in 52 Co was newly assigned, questioning the conventional identification of IASs from the β -delayed proton emissions. Using our energy of the IAS in 52 Co, the masses of the T = 2 multiplet fit well into the Isobaric Multiplet Mass Equation.We find that the IAS in 52 Co decays predominantly via γ transitions while the proton emission is negligibly small. According to our large-scale shell model calculations, this phenomenon has been interpreted to be due to very low isospin mixing in the IAS.PACS numbers: 21.10. Dr, 27.40.+z, 29.20.db The concept of isospin was introduced by Heisenberg [1] and developed by Wigner [2] to describe the charge independence of nuclear forces. This concept is being widely used in particle and nuclear physics [3, 4]. Within the isospin formalism, a nucleus composed of Z protons and N neutrons has a fixed isospin projection of T z = (N − Z)/2, while all states in the nucleus can have different total isospins T ≥ |T z |. In other words, states of a given T can occur in a set of isobaric nuclei with T z = T, T − 1, ..., −T . These states with the same T and J π are called the isobaric analog states (IAS). The states with T = |T z | are the ground states of the corresponding nuclei and the ones with T > |T z | are excited states, except for some oddodd N = Z nuclei [5,6]. A set of IASs with fixed A and T are believed to have very similar structure and properties and to be energetically degenerated in the framework of isospin symmetry. This energy degeneracy is mainly altered due to the Coulomb interaction, the proton-neutron mass difference, and the charge-dependent forces of nuclear origin [7]. In an isobaric multiplet, the masses of the IASs of a given T can be described in first order approximation by the famous quadratic * Corresponding author.
The neutron rich 107 Mo has been reinvestigated by analyzing the large statistics γ-γ-γ and γγ-γ-γ coincidence data from the spontaneous fission of 252 Cf at the Gammasphere detector array. Two new bands have been identified. The potential energy surface calculations of this nucleus have been performed. The calculations show evidence for the 5/2 + [413] configuration of the ground state band and 7/2 − [523] for the 348 keV excited band, as assigned in previous work. The two bands newly established are proposed to be one and two phonon γ vibrational bands built on the 7/2 − [523] Nilsson orbital, respectively, in the current work. Triaxial projected shell model (TPSM) calculations have been performed to explain the level structure and are found in fair agreement with experimental data. In particular, TPSM study confirms the γ-and γγ-vibrational structure for the two observed excited band structures. Systematics of the one and two phonon γ vibrational bands in the A ∼ 100 Mo series is also discussed.
β-decay spectroscopy of 173,174 Ho (Z = 67, N = 106,107) was conducted at Radioactive Isotope Beam Factory at RIKEN by using in-flight fission of a 345-MeV/u 238 U primary beam. A previously unreported isomeric state at 405 keV with half-life of 3.7(12) μs and a spin and parity of (3/2 + ) is identified in 173 Ho. Moreover, a new state with a spin and parity of 9 − was discovered in 174 Er. The experimental log ft values of 5.84(20) and 5.25( 18) suggest an allowed-hindered β decay from the ground state of 174 Ho to the K π = 8 − isomeric state in 174 Er. Configuration-constrained potential energy surface (PES) calculations were performed and the predictions are in reasonable agreement with the experimental results.
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