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Register a new user10He low-lying states structure uncovered by correlations
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The 0+ ground state of the 10He nucleus produced in the 3H(8He,p)10He reaction was found at about $2.1pm0.2$ MeV (Gamma ~ 2 MeV) above the three-body 8He+n+n breakup threshold. Angular correlations observed for 10He decay products show prominent interference patterns allowing to draw conclusions about the structure of low-energy excited states. We interpret the observed correlations as a coherent superposition of the broad 1- state having a maximum at energy 4-6 MeV and the 2+ state above 6 MeV, setting both on top of the 0+ state tail. This anomalous level ordering indicates that the breakdown of the N=8 shell known in 12Be thus extends also to the 10He system.
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The electromagnetic structure of $^{140}$Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The $2^+$ and $4^+$ states of the ground-state band and a second $2^+$ state were populated by multi-step excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the $2_1^+$ state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that $^{140}$Sm shows considerable $gamma$ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region.
Excitation functions of elastic and inelastic 7Be+p scattering were measured in the energy range between 1.6 and 2.8 MeV in the c.m. An R-matrix analysis of the excitation functions provides strong evidence for new positive parity states in 8B. A new 2+ state at an excitation energy of 2.55 MeV was observed and a new 0+ state at 1.9 MeV is tentatively suggested. The R-matrix and Time Dependent Continuum Shell Model were used in the analysis of the excitation functions. The new results are compared to the calculations of contemporary theoretical models.
The electromagnetic transitions to various low-lying excited states of 16O, 48Ca and 208Pb are calculated within a model which considers the short-range correlations. In general the effects of the correlations are small and do not explain the required quenching to describe the data.
The properties of the low-lying 2^+ states in the even-even nuclei around 132Sn are studied within the quasiparticle random phase approximation. Starting from a Skyrme interaction in the particle-hole channel and a density-dependent zero-range interaction in the particle-particle channel, we use the finite rank separable approach in our investigation. It is found that the fourth 2^+ state in 132Te could be a good candidate for a mixed-symmetry state.
The evolution of nuclear magic numbers at extremes of isospin is a topic at the forefront of contemporary nuclear physics. $N=50$ is a prime example, with increasing experimental data coming to light on potentially doubly-magic $^{100}$Sn and $^{78}$Ni at the proton-rich and proton-deficient extremes, respectively. Experimental discrepancies exist in the data for less exotic systems. In $^{86}$Kr the $B(E2;2^+_1rightarrow0^+_1)$ value - a key indicator of shell evolution - has been experimentally determined by two different methodologies, with the results deviating by $3sigma$. Here, we report on a new high-precision measurement of this value, as well as the first measured lifetimes and hence transition strengths for the $2^+_2$ and $3^-_{(2)}$ states in the nucleus. The Doppler-shift attenuation method was implemented using the TIGRESS gamma-ray spectrometer and TIGRESS integrated plunger (TIP) device. High-statistics Monte-Carlo simulations were utilized to extract lifetimes in accordance with state-of-the-art methodologies. Lifetimes of $tau(2^+_1)=336pm4text{(stat.)}pm20text{(sys.)}$ fs, $tau(2^+_2)=263pm9text{(stat.)}pm19text{(sys.)}$ fs and $tau(3^-_{(2)})=73pm6text{(stat.)}pm32text{(sys.)}$ fs were extracted. This yields a transition strength for the first-excited state of $B(E2;2^+_1rightarrow0^+)=259pm3text{(stat.)}pm16text{(sys.)}$ e$^2$fm$^4$. The measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than $3sigma$, while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted $B(E2;2^+_1rightarrow0^+_1)$ value indicates a more sudden reduction in collectivity in the $N=50$ isotones approaching $Z=40$.
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