An algebraic model with three-body boson interactions is proposed to incorporate the different quadrupole modes in nuclear collectivity. It is shown that the recently observed anomalous collective structure characterized by B-4/2 = B(E2;4(1 )-> 2(1))/B(E2;2(1 )-> 0(1)) < 1.0 and R-4/2 = E(4(1))/E(2(1)) >= 2.0, which cannot yet be explained by any other microscopic nuclear models, naturally emerges in the present model due to the inclusion of triaxial rotor modes. This description is further extended to describe odd-A nuclei by including the coupling to the Fermion degree of freedom. This allows us to give a unified explanation of the anomalous B(E2)strengths in both even-even and even-odd systems, which indicate different behaviors. As examples, the model is applied to describe the spectroscopy and E2 transition properties of Os-168,Os-169,Os-170,Os-171. All recent measurements of these isotopes can be well reproduced on the same footing, which suggests that the anomalous collectivity persists even in odd-A systems.

Novel collective modes characterized by a B4/2 ratio (≡B(E2;41+→21+)/B(E2;21+→01+)) less than 1.0 that were observed recently have been identified within the proton-neutron interacting boson model (IBM-2) using the consistent-Q Hamiltonian. These modes are shown to give rise to triaxial spectral features, including significant band mixing. The results provide a compelling explanation for the deeply suppressed B4/2 ratio observed in 166W, 168,170Os, and 172Pt, offering new insights into the B(E2) anomaly phenomenon in neutron-deficient nuclei.

The mean lifetimes of the low-lying positive-parity yrast states up to Jπ = 6+ in 116Te were measured using the recoil distance Doppler shift method, and the corresponding B(E2) values were determined. By combining our values for 116Te with the most recent measured transition strengths for other isotopes in this region, we show that the B(E2) values, particularly those of the 2+ → 0+ transition, display a smooth evolution of quadrupole collectivity, with only minor asymmetric behavior across the middle of the shell, unlike the asymmetry observed in Sn isotopes. The transition strengths of even-even Te isotopes are then compared with systematic theoretical calculations within the shell model using realistic pairing plus multipole terms with monopole interaction, and with the large-scale shell-model configuration-interaction approach using a realistic interaction, while the projected shell model is applied to calculate only the structure of 116Te. The latter model provides a very good description of the individual B(E2) values in 116Te, whereas the first two models predict stronger asymmetric behavior across the middle of the shell than observed experimentally.

Millisecond isomers were recently observed in ^213,215Tl. These two isomers can be interpreted by the π0h_11/2 single-proton-hole states. The 11/2^- states in Tl isotopes decrease in energy when neutrons are added to the v0g_9/2 orbital, as driven by the protonneutron monopole interaction. Based on the mechanism, this work investigates the isomerism in the southeastern vicinity of ²⁰⁸Pb with an optimized shell-model effective Hamiltonian. The 11/2^- isomeric γ-decay half-lives are predicted to be longer in more neutron-rich nuclei, potentially exceeding the β-decay half-lives. In this way, β decay may predominantly occur in the 11/2^- states, which are crucial for understanding the N = 126 waiting points and the A = 195 peak.

With the recent lifetime measurements of the 2 + states in Te 116 and Te 118 , the evolution of the collectivity in the midshell region of the Te isotopic chain is starting to reveal itself. However, more information on the structure of the ground-state bands and the nature of the collectivity can be gathered from studying the odd-mass systems, in which lifetimes have not been extensively studied.

The purpose of the present work is to investigate the structure of low-lying excited states of the ν h 11 / 2 band in the odd-mass systems Te 117 and Te 119 , that correspond to the ground-state band in even-even Te.

Lifetimes of low-lying states in the ν h 11 / 2 band of Te 117 are measured for the first time and remeasured in Te 119 , using the recoil distance Doppler shift technique, and analyzed with the differential decay curve method in coincidence mode.

The lifetimes and B (E2) values of the first two transitions, 15 / 2 − → 11 / 2 − and 19 / 2 − → 15 / 2 − , in the ν h 11 / 2 band, are determined in both Te 117 and Te 119 . From the lifetimes, the B (E2) values and corresponding B 4 / 2 ratios are determined. The results are compared to systematics in both even- A and odd- A Te isotopes, as well as with theoretical results from the large-scale shell model and interacting boson model calculations.

While the energy levels of Te 117 and Te 119 , similarly to Te 118 , exhibit textbook vibrational behavior, the unexpectedly small B 4 / 2 ratios of these odd-mass nuclei point to a puzzling discrepancy and question the vibrational nature of these states.

This study determined the lifetime of the first excited state (5/21+) in 139La via β–γ time-difference measurement using a LaBr3 + plastic scintillator array. This state is populated following the decay of 139Ba produced in the 138Ba(n,γ) reaction. Compared with previous experiments using only stilbene/plastic crystals, this experiment separates the background contribution in the γ-ray spectrum owing to the high energy resolution of LaBr3. The L-forbidden M1 transition strength, B(M1, 5/21+→7/21+), in 139La was measured and compared with detailed large-scale shell model calculations, with a special focus on the core-excitation effect. The results showed the importance of both proton and neutron core-excitations in explaining the M1 transition strength. Meanwhile, the effective g-factor for the tensor term of the M1 operator was smaller than the previously reported value in this region or around 208Pb.

Solving the Dirac equation has played an important role in many areas of fundamental physics. In this work, we present the Dirac equation solver DiracSVT, which solves the Dirac equation with scalar, vector, and tensor nuclear potentials in spherical coordinate space. The shooting method was used with a Runge–Kutta 4 integration scheme. The potentials are parameterized in a Woods–Saxon form, which reproduce well the known single-particle states around all doubly magic nuclei and can be applied to study the shell evolution of exotic nuclei. The code can be easily extended to the study of other systems, including atomic, hadron, and molecular physics.

We study the recently measured β decay of 70Kr into 70Br within the framework of the large-scale shell model. The enhancement in the Gamow-Teller (GT) transition strength in Br70 compared to the β decay of the lighter Ge62 was suggested as an indication for increased neutron-proton (np) pairing correlation. To explore the np correlations in nuclei, we systematically examined the β-decay properties of the even-even nuclei A=58,62,66, and 70 into N=Z odd-odd nuclei. By employing an interaction involving solely J=1,T=0 and J=0,T=1 pairing matrix elements, we observe that the pairing does not necessarily lead to an enhancement in the GT strength for the same coupling strength. But with the inclusion of the g9/2 orbital, the GT strength can be increased with increasing np pairing in connection with the enhanced contribution from the g9/2 orbital. We further compare those results with realistic calculations in the fp and f5/2pg9/2 model space to gauge the contribution from f7/2 and g9/2 orbitals in the GT strengths. With the JUN45 interaction, there is an increment for the yrast 1+ state for the decay of Kr70 as compared to the decay of Ge62 due to increased g9/2 contribution. Additionally, we probe the effect of np pairing on BGT by modifying the single-particle energies and the T=0 matrix elements of the interaction responsible for the decay transition strength. In calculations with realistic interaction, we find that the accumulated transition strength can increase with enhanced np pairing.

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (fair) Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian.

Excited states in the neutron-deficient nuclide Hf155 have been investigated in experiments performed at the Accelerator Laboratory of the University of Jyväskylä. The Hf155 nuclei were produced in fusion-evaporation reactions induced by beams of 295 and 315 MeV Ni58 ions bombarding an isotopically enriched Pd102 target and separated using the recoil mass separator MARA. An isomeric state having a half-life of 510(30) ns was discovered and is interpreted as a seniority υ=3, (πh11/22 - νf7/2)27/2- configuration. The γ-ray transitions emitted in the deexcitation of the isomeric state to the ground state were identified and a level scheme was constructed, from which the excitation energy of the isomer was determined to be 2581.5(10) keV. A B(E2) value of 0.45(3) W.u. was deduced for the 105.4 keV transition depopulating the isomeric state. The deduced level scheme and B(E2) value are compared with systematics and shell-model calculations.