Excited-State Half-Lives in

The known I^{π}=8_{1}^{+}, E_{x}=2129-keV isomer in the semimagic nucleus ^{130}Cd_{82} was populated in the projectile fission of a ^{238}U beam at the Radioactive Isotope Beam Factory at RIKEN. The high counting statistics of the accumulated data allowed us to determine the excitation energy, E_{x}=2001.2(7) keV, and half-life, T_{1/2}=57(3) ns, of the I^{π}=6_{1}^{+} state based on γγ coincidence information. Furthermore, the half-life of the 8_{1}^{+} state, T_{1/2}=224(4) ns, was remeasured with high precision. The new experimental information, combined with available data for ^{134}Sn and large-scale shell model calculations, allowed us to extract proton and neutron effective charges for ^{132}Sn, a doubly magic nucleus far-off stability. A comparison to analogous information for ^{100}Sn provides first reliable information regarding the isospin dependence of the isoscalar and isovector effective charges in heavy nuclei.

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.

Dominance of Tensor Correlations in High-Momentum Nucleon Pairs Studied by (p,pd) Reaction.

The isospin character of p-n pairs at large relative momentum has been observed for the first time in the ^{16}O ground state. A strong population of the J,T=1,0 state and a very weak population of the J,T=0,1 state were observed in the neutron pickup domain of ^{16}O(p,pd) at 392 MeV. This strong isospin dependence at large momentum transfer is not reproduced by the distorted-wave impulse approximation calculations with known spectroscopic amplitudes. The results indicate the presence of high-momentum protons and neutrons induced by the tensor interactions in the ground state of ^{16}O.

Shell Evolution towards

The level structure of the neutron-rich ^{77}Cu nucleus is investigated through ß-delayed γ-ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of ^{77}Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in ^{77}Cu are identified for the first time by correlating γ rays with the ß decay of ^{77}Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near ^{78}Ni and suggests a single-particle nature for both the 5/2_{1}^{-} and 3/2_{1}^{-} states in ^{77}Cu, leading to doubly magic ^{78}Ni.

94 ß-Decay Half-Lives of Neutron-Rich _{55}Cs to _{67}Ho: Experimental Feedback and Evaluation of the r-Process Rare-Earth Peak Formation.

The ß-decay half-lives of 94 neutron-rich nuclei ^{144-151}Cs, ^{146-154}Ba, ^{148-156}La, ^{150-158}Ce, ^{153-160}Pr, ^{156-162}Nd, ^{159-163}Pm, ^{160-166}Sm, ^{161-168}Eu, ^{165-170}Gd, ^{166-172}Tb, ^{169-173}Dy, ^{172-175}Ho, and two isomeric states ^{174m}Er, ^{172m}Dy were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of ß-decay half-lives are observed at neutron-number N=97 for _{58}Ce, _{59}Pr, _{60}Nd, and _{62}Sm, and N=105 for _{63}Eu, _{64}Gd, _{65}Tb, and _{66}Dy. Features in the data mirror the interplay between pairing effects and microscopic structure. r-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system.

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.

ß-Decay half-lives of 76,77Co, 79,80Ni, and 81Cu: experimental indication of a doubly magic 78Ni.

The half-lives of 20 neutron-rich nuclei with Z=27-30 have been measured at the RIBF, including five new half-lives of (76)Co(21.7(-4.9)(+6.5) ms), (77)Co(13.0(-4.3)(+7.2) ms), (79)Ni(43.0(-7.5)(+8.6) ms), (80)Ni(23.9(-17.2)(+26.0) ms), and (81)Cu(73.2 ± 6.8 ms). In addition, the half-lives of (73-75)Co, (74-78)Ni, (78-80)Cu, and (80-82)Zn were determined with higher precision than previous works. Based on these new results, a systematic study of the ß-decay half-lives has been carried out, which suggests a sizable magicity for both the proton number Z = 28 and the neutron number N=50 in (78)Ni.

Yrast 6⁺ seniority isomers of (136,138)Sn.

Delayed γ-ray cascades, originating from the decay of (6⁺) isomeric states, in the very neutron-rich, semimagic isotopes (136,138)Sn have been observed following the projectile fission of a ²³8U beam at RIBF, RIKEN. The wave functions of these isomeric states are proposed to be predominantly a fully aligned pair of f(7/2) neutrons. Shell-model calculations, performed using a realistic effective interaction, reproduce well the energies of the excited states of these nuclei and the measured transition rates, with the exception of the B(E2;6⁺→4⁺) rate of ¹³6Sn, which deviates from a simple seniority scheme. Empirically reducing the νf(7/2)(2) orbit matrix elements produces a 41⁺ state with almost equal seniority 2 and 4 components, correctly reproducing the experimental B(E2;6⁺→4⁺) rate of ¹³6Sn. These data provide a key benchmark for shell-model interactions far from stability.

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.

Isomer decay spectroscopy of 164Sm and 166Gd: midshell collectivity around N=100.

Excited states in the N=102 isotones 166Gd and 164Sm have been observed following isomeric decay for the first time at RIBF, RIKEN. The half-lives of the isomeric states have been measured to be 950(60) and 600(140) ns for 166Gd and 164Sm, respectively. Based on the decay patterns and potential energy surface calculations, including ß6 deformation, a spin and parity of 6- has been assigned to the isomeric states in both nuclei. Collective observables are discussed in light of the systematics of the region, giving insight into nuclear shape evolution. The decrease in the ground-band energies of 166Gd and 164Sm (N=102) compared to 164Gd and 162Sm (N=100), respectively, presents evidence for the predicted deformed shell closure at N=100.

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.

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.

Human hormone production in vitro.

A new in vitro hormone-synthesizing cell system, line BeWO, derived from human gestational choriocarcinoma, has been permanently established; a high degree of synthesis of functional hormone has been maintained for 18 months in tissue culture. Predominantly glycolytic metabolism, dependent on the level of glucose in the medium, has been observed. Many facets of placental and tumor-cell metabolism, growth, and differentiation are found in this unique multipotential cell.

Changes in vitamin and mineral intakes and serum concentrations among free-living men on cholesterol-lowering diets: the Dietary Alternatives Study.

Nutritional adequacy of diets with 18-30% of calories from fat was investigated in men with elevated serum cholesterol (n = 396) at the end of diet classes and 1 and 2 y later. On 4-d food records, intakes of vitamin A, beta-carotene, folate, vitamin C, magnesium, vitamin B-6, iron, thiamin, and riboflavin increased from baseline whereas niacin, selenium, vitamin E, and zinc decreased. Median zinc intake, 80% of the recommended dietary allowance (RDA) at baseline, decreased to approximately 75% of the RDA, most markedly when intakes of meat, fish, and poultry were limited to 85 g/d. Nutrient densities generally increased. Of the serum nutrients measured, median beta-carotene and vitamin C increased, whereas vitamin B-6, iron, and zinc were unchanged. Below-normal values were fewer for vitamin C and magnesium. Diets similar to the National Cholesterol Education Program Step-Two Diet [less than 7% saturated fatty acids, less than 200 mg cholesterol/d] appeared to provide increased levels of most micronutrients both short and long term to men receiving comprehensive dietary counseling.