Direct Measurement of Hexacontatetrapole, E6 γ Decay from

The only proposed observation of a discrete, hexacontatetrapole (E6) transition in nature occurs from the T_{1/2}=2.54(2)-min decay of ^{53m}Fe. However, there are conflicting claims concerning its γ-decay branching ratio, and a rigorous interrogation of γ-ray sum contributions is lacking. Experiments performed at the Australian Heavy Ion Accelerator Facility were used to study the decay of ^{53m}Fe. For the first time, sum-coincidence contributions to the weak E6 and M5 decay branches have been firmly quantified using complementary experimental and computational methods. Agreement across the different approaches confirms the existence of the real E6 transition; the M5 branching ratio and transition rate have also been revised. Shell model calculations performed in the full fp model space suggest that the effective proton charge for high-multipole, E4 and E6, transitions is quenched to approximately two-thirds of the collective E2 value. Correlations between nucleons may offer an explanation of this unexpected phenomenon, which is in stark contrast to the collective nature of lower-multipole, electric transitions observed in atomic nuclei.

Electric Monopole Transition from the Superdeformed Band in

The electric monopole (E0) transition strength ρ^{2} for the transition connecting the third 0^{+} level, a "superdeformed" band head, to the "spherical" 0^{+} ground state in doubly magic ^{40}Ca is determined via e^{+}e^{-} pair-conversion spectroscopy. The measured value ρ^{2}(E0;0_{3}^{+}→0_{1}^{+})=2.3(5)×10^{-3} is the smallest ρ^{2}(E0;0^{+}→0^{+}) found in A<50 nuclei. In contrast, the E0 transition strength to the ground state observed from the second 0^{+} state, a band head of "normal" deformation, is an order of magnitude larger ρ^{2}(E0;0_{2}^{+}→0_{1}^{+})=25.9(16)×10^{-3}, which shows significant mixing between these two states. Large-scale shell-model (LSSM) calculations are performed to understand the microscopic structure of the excited states and the configuration mixing between them; experimental ρ^{2} values in ^{40}Ca and neighboring isotopes are well reproduced by the LSSM calculations. The unusually small ρ^{2}(E0;0_{3}^{+}→0_{1}^{+}) value is due to destructive interference in the mixing of shape-coexisting structures, which are based on several different multiparticle-multihole excitations. This observation goes beyond the usual treatment of E0 strengths, where two-state shape mixing cannot result in destructive interference.

Properties of

Mass-separated ^{187}Ta_{114} in a high-spin isomeric state has been produced for the first time by multinucleon transfer reactions, employing an argon gas-stopping cell and laser ionization. Internal γ rays revealed a T_{1/2}=7.3±0.9 s isomer at 1778±1 keV, which decays through a rotational band with perturbations associated with the approach to a prolate-oblate shape transition. Model calculations show less influence from triaxiality compared to heavier elements in the same mass region. The isomer-decay reduced E2 hindrance factor f_{ν}=27±1 supports the interpretation that axial symmetry is approximately conserved.

Proton Shell Evolution below

The ß-delayed γ-ray spectroscopy of neutron-rich ^{123,125}Ag isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN, and the long-predicted 1/2^{-} ß-emitting isomers in ^{123,125}Ag are identified for the first time. With the new experimental results, the systematic trend of energy spacing between the lowest 9/2^{+} and 1/2^{-} levels is extended in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. Shell-model calculations with the state-of-the-art V_{MU} plus M3Y spin-orbit interaction give a satisfactory description of the low-lying states in ^{123,125}Ag. The tensor force is found to play a crucial role in the evolution of the size of the Z=40 subshell gap. The observed inversion of the single-particle levels around ^{123}Ag can be well interpreted in terms of the monopole shift of the π1g_{9/2} orbitals mainly caused by the increasing occupation of ν1h_{11/2} orbitals.

In prenatally diagnosed CPAM, does the affected lobe influence the timing of symptom onset?

PURPOSE: We investigated the relationship between the affected lobe and symptom onset in prenatally diagnosed congenital pulmonary airway malformation (CPAM). METHODS: 53 CPAM patients diagnosed prenatally were reviewed retrospectively by creating 2 groups according to symptom onset. Group Sneo: (symptomatic during the neonatal period; n = 13) and group S > neo: (symptomatic after the neonatal period; n = 40) were compared for type of CPAM, affected lobes, types of symptoms/infections, treatment, duration of follow-up, and histopathology. Requirement for surgery (Sx) was then used to create three subgroups: Sneo + Sx, S > neo + Sx, and Sx-. RESULTS: Some cases had multiple affected lobes. In Sneo, symptoms developed in 55.6%, 50.0%, 0%, 0%, and 36.8% of right upper lobes (RUL), right middle lobes (RML), right lower lobes (RLL), left upper lobes (LUL), and left lower lobes (LLL) diagnosed with CPAM, prenatally. In S > neo, symptoms developed in 0%, 0%, 6.3%, 55.6%, and 33.3% of RUL, RML, RLL, LUL, and LLL diagnosed with CPAM, prenatally. CONCLUSION: In prenatally diagnosed CPAM, RUL and RML lesions are more likely to become symptomatic in neonates, and LUL lesions in infants. Surgery is recommended before the onset of respiratory infections after 1 year of age.

Isomer depletion as experimental evidence of nuclear excitation by electron capture.

The atomic nucleus and its electrons are often thought of as independent systems that are held together in the atom by their mutual attraction. Their interaction, however, leads to other important effects, such as providing an additional decay mode for excited nuclear states, whereby the nucleus releases energy by ejecting an atomic electron instead of by emitting a γ-ray. This 'internal conversion' has been known for about a hundred years and can be used to study nuclei and their interaction with their electrons. In the inverse process-nuclear excitation by electron capture (NEEC)-a free electron is captured into an atomic vacancy and can excite the nucleus to a higher-energy state, provided that the kinetic energy of the free electron plus the magnitude of its binding energy once captured matches the nuclear energy difference between the two states. NEEC was predicted in 1976 and has not hitherto been observed. Here we report evidence of NEEC in molybdenum-93 and determine the probability and cross-section for the process in a beam-based experimental scenario. Our results provide a standard for the assessment of theoretical models relevant to NEEC, which predict cross-sections that span many orders of magnitude. The greatest practical effect of the NEEC process may be on the survival of nuclei in stellar environments, in which it could excite isomers (that is, long-lived nuclear states) to shorter-lived states. Such excitations may reduce the abundance of the isotope after its production. This is an example of 'isomer depletion', which has been investigated previously through other reactions, but is used here to obtain evidence for NEEC.

ß-Decay Half-Lives of 110 Neutron-Rich Nuclei across the N=82 Shell Gap: Implications for the Mechanism and Universality of the Astrophysical r Process.

The ß-decay half-lives of 110 neutron-rich isotopes of the elements from _{37}Rb to _{50}Sn were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A≈130) and the rare-earth-element (A≈160) abundance peaks may result from the freeze-out of an (n,γ)⇄(γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events.

Monopole-driven shell evolution below the doubly magic nucleus 132Sn explored with the long-lived isomer in 126Pd.

A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in (126)Pd and is proposed to have a spin and parity of 10(+) with a maximally aligned configuration comprising two neutron holes in the 1h(11/2) orbit. In addition to an internal-decay branch through a hindered electric octupole transition, ß decay from the long-lived isomer was observed to populate excited states at high spins in (126)Ag. The smaller energy difference between the 10(+) and 7(-) isomers in (126)Pd than in the heavier N=80 isotones can be interpreted as being ascribed to the monopole shift of the 1h(11/2) neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below (132)Sn are discussed in terms of the central and tensor forces.

1p3/2 proton-hole state in 132Sn and the shell structure along N = 82.

A low-lying state in 131In82, the one-proton hole nucleus with respect to double magic 132Sn, was observed by its γ decay to the Iπ=1/2- ß-emitting isomer. We identify the new state at an excitation energy of Ex=1353 keV, which was populated both in the ß decay of 131Cd83 and after ß-delayed neutron emission from 132Cd84, as the previously unknown πp3/2 single-hole state with respect to the 132Sn core. Exploiting this crucial new experimental information, shell-model calculations were performed to study the structure of experimentally inaccessible N=82 isotones below 132Sn. The results evidence a surprising absence of proton subshell closures along the chain of N=82 isotones. The consequences of this finding for the evolution of the N=82 shell gap along the r-process path are discussed.

Role of laparoscopy during surgery at the porta hepatis.

Minimally invasive surgery in children has evolved to the extent that complex procedures can be performed with safety, with comparable outcomes to open surgery and with the advantages of minimal scarring and less pain. In this article, we describe the latest laparoscopic techniques used at Juntendo University Hospital in Japan, for treating conditions affecting the porta hepatis, focusing on biliary atresia and choledochal cysts. We also summarise our postoperative management protocols and discuss preliminary outcomes.

Role of laparoscopy during surgery at the porta hepatis.

Minimally invasive surgery in children has evolved to the extent that complex procedures can be performed with safety, with comparable outcomes to open surgery and with the advantages of minimal scarring and less pain. In this article, we describe the latest laparoscopic techniques used at Juntendo University Hospital in Japan, for treating conditions affecting the porta hepatis, focusing on biliary atresia and choledochal cysts. We also summarise our postoperative management protocols and discuss preliminary outcomes.

Isomers in 128Pd and 126Pd: evidence for a robust shell closure at the neutron magic number 82 in exotic palladium isotopes.

The level structures of the very neutron-rich nuclei 128Pd and 126Pd have been investigated for the first time. In the r-process waiting-point nucleus 128Pd, a new isomer with a half-life of 5.8(8) µs is proposed to have a spin and parity of 8(+) and is associated with a maximally aligned configuration arising from the g(9/2) proton subshell with seniority υ=2. For 126Pd, two new isomers have been identified with half-lives of 0.33(4) and 0.44(3) µs. The yrast 2(+) energy is much higher in 128Pd than in 126Pd, while the level sequence below the 8(+) isomer in 128Pd is similar to that in the N=82 isotone 130Cd. The electric quadrupole transition that depopulates the 8(+) isomer in 128Pd is more hindered than the corresponding transition in 130Cd, as expected in the seniority scheme for a semimagic, spherical nucleus. These experimental findings indicate that the shell closure at the neutron number N=82 is fairly robust in the neutron-rich Pd isotopes.

Anomalous isomeric decays in 174Lu as a probe of K mixing and interactions in deformed nuclei.

A K(pi)=13+, 280 ns four-quasiparticle isomer in the odd-odd nucleus 174Lu has been identified and characterized. The isomer decays to both K(pi)=7(+) and K(pi)=0(+) rotational bands obtained from the parallel and antiparallel coupling of the proton 7/2+[404] and neutron 7/2+[633] orbitals. K mixing caused by particle-rotation coupling explains the anomalously fast transition rates to the 7+ band but those to the 0+ band are caused by a chance degeneracy between the isomer and a collective state, allowing the mixing matrix element for a large K difference to be deduced.

Excitation energies of superdeformed States in 196Pb: towards a systematic study of the second well in Pb isotopes.

The excitation energy of the lowest-energy superdeformed band in 196Pb is established using the techniques of time-correlated gamma-ray spectroscopy. Together with previous measurements on 192Pb and 194Pb, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a "superdeformed shell gap."

Multiphonon vibrations at high angular momentum in 182 Os.

Evidence is presented for multiphonon excitations based on a high-spin (25 Planck) intrinsic state in the deformed nucleus 182 Os. Angular momentum generation by this mode competes with collective rotation. The experimental data are compared with tilted-axis cranking calculations, supporting the vibrational interpretation. However, the lower experimental energies provide evidence that more complex interactions of states are playing a role.

Evidence for a new type of shears mechanism in 106Cd.

Lifetimes of states in the lowest lying positive parity band in 106Cd have been measured using the Doppler shift attenuation method. The deduced B(E2) transition rates show a marked decrease with increasing spin. Cranking and semiclassical model calculations suggest that the structure has the character of a shears-type band resulting from the coupling of g(9/2) proton holes to aligned pairs of h(11/2) and g(7/2) neutron particles. This is the first clear evidence for the phenomenon of "antimagnetic" rotation in nuclei.

Direct decays from superdeformed states in 192Pb observed using time-correlated gamma-ray spectroscopy.

Correlations of decays above and below isomeric states in the normally deformed minimum of 192Pb have been used to identify discrete transitions in the decay of the superdeformed (SD) band. The data establish the absolute excitation energy of the lowest observed SD level as 4.425 MeV. Extrapolation to the bandhead indicates that the excitation energy of the superdeformed well in 192Pb is 0.5 MeV lower than in the heavier isotope 194Pb. The results confirm the trend to decreasing excitation energy with decreasing neutron number predicted by both a macroscopic Strutinsky method approach and microscopic mean field calculations.

Effective charge of the (pi)h(11/2) orbital and the electric field gradient of Hg from the Yrast structure of 206Hg.

The gamma-ray decay of excited states of the two-proton hole nucleus, 206Hg, has been identified using Gammasphere and 208Pb+238U collisions. The yrast states found include a T(1/2) = 92(8) ns 10(+) isomer located above the known 5(-) isomer. The B(E2;10(+)-->8(+)) strength is used to derive the quadrupole polarization charge induced by the h(11/2) proton hole. Also, the implied quadrupole moment has been used to provide an absolute scale for the electric field gradient of Hg in Hg metal.

Empirical investigation of extreme single-particle behavior of nuclear quadrupole moments in highly collective A approximately 150 superdeformed bands.

The intrinsic quadrupole moment Q(0) of superdeformed rotational bands in A approximately 150 nuclei depends on the associated single-particle configuration. We have derived an empirical formula based on the additivity of effective quadrupole moments of single-particle orbitals that describes existing measurements from (142)Sm to (152)Dy. To further test the formula, the predicted Q(0) moments for two superdeformed bands in (146)Gd of 14.05 eb were confronted with a new measurement yielding 13.9+/-0.4 eb and 13.9+/-0.3 eb, respectively. This excellent agreement provides empirical evidence of extreme single-particle behavior in highly deformed, collective systems.