Probing the nature of the conjectured low-spin wobbling bands in atomic nuclei

The precession of an atomic nucleus can be approximately described as wobbling motion, arising from the coupling of a rotation and a harmonic vibration. Recently, a number of wobbling bands were reported at low spin, which violate the wobbling approximation that can be valid only at high spin. In the present work, we explore the nature of the reported low-spin wobbling bands. Via a new experiment including both angular correlation and linear polarization measurements, we demonstrate that one such band in 187Au is generated by dominant single-particle excitation rather than by the excitation of a wobbling phonon. Assessing the experimental proofs and discussions to assign the reported low-spin wobbling bands, we further point out that the imperfect research paradigm used previously would lead to unreliable identification of low-spin wobbling bands

Fine structure in the α decay of 223U

Fine structure in the α decay of 223U was observed in the fusion-evaporation reaction 187Re(40Ar, p3n) by using fast digital pulse processing technique. Two α-decay branches of 223U feeding the ground state and 244 keV excited state of 219Th were identified by establishing the decay chain 223U →α1 219Th →α2 215Ra →α3 211Rn. The α-particle energy for the ground-state to ground-state transition of 223U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62−10+14 μs. Evolution of nuclear structure for N = 131 even-Z isotones from Po to U was discussed in the frameworks of nuclear mass and reduced α-decay width, a weakening octupole deformation in the ground state of 223U relative to its lighter isotones 219Ra and 221Th was suggested

Decay of the very neutron-deficient isotope 131^{131}Pm

The decay of $^{131}$Pm has been investigated by means of $\gamma$-ray spectroscopy. The $^{131}$Pm nuclei were produced by fusion-evaporation reaction of $^{106}$Cd($^{32}$S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and $\gamma$ rays measurement. Two $\gamma$ rays of 185.0 and 220.0 keV were unambiguously identified to follow the $\beta ^{+}$ decay of $^{131}$Pm by results of X-$\gamma$ and $\gamma$-$\gamma$ coincidence. A growth-decay feature of the decay curve for 87.8 keV $\gamma$-ray of $^{131}$Nd confirmed the production of $^{131}$Pm nuclei. The half-life of $^{131}$Pm was measured to be 6.3$\pm$0.8 s. A partial decay scheme of $^{131}$Pm is proposed on the basis of X-$\gamma$ and $\gamma$ - $\gamma$ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus $^{131}$Nd

A new alpha-particle-emitting isotope 259Db\mathsf{^{259}Db}

An isotope of the element 105 with mass number 259 has been produced via the reaction $^{241}$Am($^{22}$Ne, 4n)$^{259}$Db at $E_{lab} =118$ MeV. The reaction products were transported and collected using the helium-jet technique and the rotating wheel apparatus. The $\alpha$-decays of the products and their daughter nuclides were detected by a set of Si(Au) detectors arranged ingeniously. The $Z$ and $A$ of the nuclide have been unambiguously identified by the genetic relationship between the new activity and the known nuclide $^{255}$Lr established by $\alpha$-recoiled milking measurement. The new nuclide $^{259}$Db has a half-life of $0.51\pm 0.16$ s and decays by alpha-particle emission of $E_\alpha =9.47$ MeV. Furthermore, the nuclide $^{258}$Db and its daughter $^{254}$Lr have also been clearly observed using the same projectile-target combination. Their half-lives and $\alpha$-particle energies determined in this work are in agreement with previous known data, thus also proving the reliability of our assignment of $^{259}$Db

New yrast excited states of the \mth{N=84} nucleus \chem{^{142}Ce} observed in deep inelastic reactions

Excited states of $^{142}$Ce, populated in deep inelastic reactions of $^{82}$Se projectiles bombarding $^{139}$La target, have been studied up to medium spins using in-beam $\gamma$ spectroscopy techniques. Three new levels have been identified at 2625, 2995, 3834 keV, and assigned as 8$^{+}$ , 9$^{(-)}$ and 11$^{(-)}$, respectively. These new yrast states follow closely the level systematics of the even mass $N=84$ isotones. Their strctures have been discussed with the help of empirical shell model calculations