Early Signal of Emerging Nuclear Collectivity in Neutron-Rich

Radioactive ^{129}Sb, which can be treated as a proton plus semimagic ^{128}Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, B(E2), for the 2^{+}⊗πg_{7/2} multiplet members and candidate πd_{5/2} state were measured. The results indicate that the total electric quadrupole strength of ^{129}Sb is a factor of 1.39(11) larger than the ^{128}Sn core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wave functions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure.

First Direct Measurements of Superheavy-Element Mass Numbers.

An experiment was performed at Lawrence Berkeley National Laboratory's 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two α-decay chains, produced via the ^{243}Am(^{48}Ca,xn)^{291-x}Mc reaction, that were separated by mass-to-charge ratio (A/q) and identified by the combined BGS+FIONA apparatus. One event occurred at A/q=284 and was assigned to ^{284}Nh (Z=113), the α-decay daughter of ^{288}Mc (Z=115), while the second occurred at A/q=288 and was assigned to ^{288}Mc. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) mass-number assignments.

Decays of the Three Top Contributors to the Reactor ν[over ¯]_{e} High-Energy Spectrum,

We report total absorption spectroscopy measurements of ^{92}Rb, ^{96gs}Y, and ^{142}Cs ß decays, which are the most important contributors to the high energy ν[over ¯]_{e} spectral shape in nuclear reactors. These three ß decays contribute 43% of the ν[over ¯]_{e} flux near 5.5 MeV emitted by nuclear reactors. This ν[over ¯]_{e} energy is particularly interesting due to spectral features recently observed in several experiments including the Daya Bay, Double Chooz, and RENO Collaborations. Measurements were conducted at Oak Ridge National Laboratory by means of proton-induced fission of ^{238}U with on-line mass separation of fission fragments and the Modular Total Absorption Spectrometer. We observe a ß-decay pattern that is similar to recent measurements of ^{92}Rb, with a ground-state to ground-state ß feeding of 91(3)%. We verify the ^{96gs}Y ground-state to ground-state ß feeding of 95.5(20)%. Our measurements substantially modify the ß-decay feedings of ^{142}Cs, reducing the ß feeding to ^{142}Ba states below 2 MeV by 32% when compared with the latest evaluations. Our results increase the discrepancy between the observed and the expected reactor ν[over ¯]_{e} flux between 5 and 7 MeV, the maximum excess increases from ∼10% to ∼12%.

Evidence for Gamow-Teller Decay of

The ß-delayed neutron emission of ^{83,84}Ga isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the ß decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed ß decay to ^{78}Ni core-excited states in ^{83,84}Ge favored by shell effects. We developed shell model calculations in the proton fpg_{9/2} and neutron extended fpg_{9/2}+d_{5/2} valence space using realistic interactions that were used to understand measured ß-decay lifetimes. We conclude that enhanced, concentrated ß-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense ß-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.

Double-magic nature of 132Sn and 208Pb through lifetime and cross-section measurements.

Single-neutron states in (133)Sn and (209)Pb, which are analogous to single-electron states outside of closed atomic shells in alkali metals, were populated by the ((9)Be, (8)Be) one-neutron transfer reaction in inverse kinematics using particle-γ coincidence spectroscopy. In addition, the s(1/2) single-neutron hole-state candidate in (131)Sn was populated by ((9)Be, (10)Be). Doubly closed-shell (132)Sn (radioactive) and (208)Pb (stable) beams were used at sub-Coulomb barrier energies of 3 MeV per nucleon. Level energies, γ-ray transitions, absolute cross sections, spectroscopic factors, asymptotic normalization coefficients, and excited-state lifetimes are reported and compared with shell-model expectations. The results include a new transition and precise level energy for the 3p(1/2) candidate in (133)Sn, new absolute cross sections for the 1h(9/2) candidate in (133)Sn and 3s(1/2) candidate in (131)Sn, and new lifetimes for excited states in (133)Sn and (209)Pb. This is the first report on excited-state lifetimes of (133)Sn, which allow for a unique test of the nuclear shell model and (132)Sn double-shell closure.

Large ß-delayed one and two neutron emission rates in the decay of 86Ga.

Beta decay of 86Ga was studied by means of ß-neutron-γ spectroscopy. An isotopically pure ^{86}Ga beam was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The decay of 86Ga revealed a half-life of 43(-15)(+21) ms and large ß-delayed one-neutron and two-neutron branching ratios of P1n=60(10)% and P2n=20(10)%. The ßγ decay of 86Ga populated a 527 keV transition that is interpreted as the deexcitation of the first 2+ state in the N=54 isotone 86Ge and suggests a quick onset of deformation in Ge isotopes beyond N=50.

New half-lives of r-process Zn and Ga isotopes measured with electromagnetic separation.

The ß decays of neutron-rich nuclei near the doubly magic (78)Ni were studied at the Holifield Radioactive Ion Beam Facility using an electromagnetic isobar separator. The half-lives of (82)Zn (228±10 ms), (83)Zn (117±20 ms), and (85)Ga (93±7 ms) were determined for the first time. These half-lives were found to be very different from the predictions of the global model used in astrophysical simulations. A new calculation was developed using the density functional model, which properly reproduced the new experimental values. The robustness of the new model in the (78)Ni region allowed us to extrapolate data for more neutron-rich isotopes. The revised analysis of the rapid neutron capture process in low entropy environments with our new set of measured and calculated half-lives shows a significant redistribution of predicted isobaric abundances strengthening the yield of A>140 nuclei.

Orbital dependent nucleonic pairing in the lightest known isotopes of tin.

By studying the (109)Xe→(105)Te→(101)Sn superallowed α-decay chain, we observe low-lying states in (101)Sn, the one-neutron system outside doubly magic (100)Sn. We find that the spins of the ground state (J=7/2) and first excited state (J=5/2) in (101)Sn are reversed with respect to the traditional level ordering postulated for (103)Sn and the heavier tin isotopes. Through simple arguments and state-of-the-art shell-model calculations we explain this unexpected switch in terms of a transition from the single-particle regime to the collective mode in which orbital-dependent pairing correlations dominate.

Large beta-delayed neutron emission probabilities in the 78Ni region.

The beta-delayed neutron branching ratios (P{betan}) for nuclei near doubly magic 78Ni have been directly measured using a new method combining high-resolution mass separation, reacceleration, and digital beta-gamma spectroscopy of 238U fission products. The P{betan} values for the very neutron-rich isotopes ;{76-78}Cu and 83Ga were found to be much higher than previously reported and predicted. Revised calculations of the betan process, accounting for new mass measurements and an inversion of the pi2p{3/2} and pi1f{5/2} orbitals, are in better agreement with these new experimental results.

Alpha decay of 109I and its implications for the proton decay of 105Sb and the astrophysical rapid proton-capture process.

An alpha-decay branch of (1.4+/-0.4) x 10(-4) has been discovered in the decay of 109I, which predominantly decays via proton emission. The measured Q(alpha) value of 3918+/-21 keV allows the indirect determination of the Q value for proton emission from 105Sb of 356+/-22 keV, which is approximately of 130 keV more bound than previously reported. This result is relevant for the astrophysical rapid proton-capture process, which would terminate in the 105Sn(p,gamma)106Sb(p,gamma)107Te(alpha decay)103Sn cycle at the densities expected in explosive hydrogen burning scenarios, unless unusually strong pairing effects result in a 103Sn(p,gamma)104Sb(p,gamma)105Te(alpha decay)101Sn) cycle.

Discovery of 109Xe and 105Te: superallowed alpha decay near doubly magic 100Sn.

Two new alpha emitters 109Xe and 105Te were identified through the observation of the 109Xe --> 105Te --> 101Sn alpha-decay chain. The 109Xe nuclei were produced in the fusion-evaporation reaction 54Fe(58Ni,3n)109Xe and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at Ealpha = 4062 +/- 7 keV and Ealpha = 3918 +/- 9 keV were interpreted as the l = 2 and l = 0 transitions from the 7/2+ ground state in 109Xe (T1/2 = 13 +/- 2 ms) to the 5/2+ ground state and a 7/2+ excited state, located at 150 +/- 13 keV in 105Te. The observation of the subsequent decay of 105Te marks the discovery of the lightest known alpha-decaying nucleus. The measured transition energy Ealpha = 4703 +/- 5 keV and half-life T1/2 = 620 +/- 70 ns were used to determine the reduced alpha-decay width delta2. The ratio delta105Te(2)/delta213Po(2) of approximately 3 indicates a superallowed character of the alpha emission from 105Te.

B(E2) upward arrow measurements for radioactive neutron-rich ge isotopes: reaching the N=50 closed shell.

The B(E2;0(+)(1)-->2(+)(1)) values for the radioactive neutron-rich germanium isotopes (78,80)Ge and the closed neutron shell nucleus 82Ge were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at N=40 and 50. The B(E2) behavior approaching N=50 is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the N=50 shell gap and a strong sensitivity of the B(E2) values to the effective interaction.

Fine structure in proton emission from 145Tm discovered with digital signal processing.

Fine structure in proton emission from the 3.1(3) mus activity of 145Tm was discovered by using a novel technique of digital processing of overlapping recoil implantation and decay signals. Proton transitions to the ground state of 144Er and to its first excited 2(+) state at 0.33(1) MeV with a branching ratio I(p)(2(+))=9.6+/-1.5% were observed. The structure of the 145Tm wave function and the emission process were analyzed by using particle-core vibration coupling models.

Strength of the 18F(p,alpha)15O resonance at Ec.m. = 330 keV.

Production of the radioisotope 18F in novae is severely constrained by the rate of the 18F(p,alpha)15O reaction. A resonance at E(c.m.)=330 keV may strongly enhance the 18F(p,alpha)15O reaction rate, but its strength has been very uncertain. We have determined the strength of this important resonance by measuring the 18F(p,alpha)15O cross section on and off resonance using a radioactive 18F beam at the ORNL Holifield Radioactive Ion Beam Facility. We find that its resonance strength is 1.48+/-0.46 eV, and that it dominates the 18F(p,alpha)15O reaction rate over a significant range of temperatures characteristic of ONeMg novae.

Plasticity of immune responses suppressing parasitemia during acute Plasmodium chabaudi malaria.

gammadelta T cells have a crucial role in cell-mediated immunity (CMI) against P. chabaudi malaria, but delta-chain knockout (KO) (deltao/o) mice and mice depleted of gammadelta T cells with mAb cure this infection. To address the question of why mice deficient in gammadelta T cells resolve P. chabaudi infections, we immunized deltao/o mice by infection with viable blood-stage parasites. Sera from infection-immunized mice were tested for their ability to protect JHo/o, deltao/o double KO mice passively against P. chabaudi challenge infection. The onset of parasitemia was significantly delayed in mice receiving immune sera, compared with saline or uninfected serum controls. Immune sera were then fractionated into Ig-rich and Ig-depleted fractions by HPLC on a protein G column. Double KO mice were passively immunized with either fraction and challenged with P. chabaudi. The onset of parasitemia was significantly delayed in recipients of the Ig-rich fraction compared with recipients of the Ig-poor fraction of immune sera. We conclude that deltao/o mice, which are unable to activate CMI against the parasite, suppress P. chabaudi infection by a redundant Ab-mediated process.

Gamma delta T-cell function in pathogenesis of cerebral malaria in mice infected with Plasmodium berghei ANKA.

Mice depleted of gammadelta T cells by monoclonal antibody treatment and infected with Plasmodium berghei ANKA did not develop cerebral malaria (CM). In striking contrast, delta0/0 mice infected with P. berghei developed CM despite their gammadelta T-cell deficiency. gammadelta T cells appear to be essential for the pathogenesis of CM in mice having experienced normal ontogeny but not in mice genetically deprived of gammadelta T cells from the beginning of life.

The time course of selected malarial infections in cytokine-deficient mice.

Murine malarial parasites have long been characterized by their requirement for either antibody-mediated immunity (AMI) or cell-mediated immunity (CMI) for suppression of acute parasitemia, with Plasmodium yoelii reportedly requiring AMI for suppression and P. chabaudi requiring CMI. To assess this characterization in terms of the current T(H1)/T(H2)-CMI/AMI hypothesis, we infected gene-targeted "knockout" mice lacking either a type-1 cytokine (IL-2 or IFN-gamma) or a type-2 cytokine (IL-4 or IL-10) with one or the other species of Plasmodium. We observed that type-1 cytokine-deficient mice developed exacerbated malaria with either P. yoelii or P. chabaudi, compared with that seen in heterozygote controls. Moreover, type-2 cytokine knockout mice showed a similar time course of infection with either parasite compared with that seen with their controls. We conclude that the mechanism of resolution of these well characterized malarial infections cannot be linked definitely to these T(H1)- and T(H2)-associated cytokines as predicted by the T(H1)/T(H2)-CMI/AMI hypothesis.

Expansion of the gammadelta T cell subset in vivo during bloodstage malaria in B cell-deficient mice.

Mice rendered B cell-deficient either by chronic anti-mu treatment initiated at birth or by gene knockout (JHD and mu-MT mice) suppressed acute Plasmodium chabaudi infections with a time course similar to intact control mice. Moreover, both kinds of B cell-deficient mice showed a 50- to 100-fold increase in splenic gammadelta T cell number after suppression of parasitemia compared with uninfected B cell-deficient controls; the magnitude of this increase resulted in significantly (P< 0.05) greater numbers of splenic gammadelta T cells in the B cell-deficient mice than in infected B cell-intact controls (about 10-fold). In contrast, the number of splenic CD4+ alphabeta T cells was only slightly elevated (< 2-fold) in both kinds of B cell-deficient mice compared with their intact controls. The number of splenic gammadelta T cells following suppression of P. vinckei parasitemia was approximately ninefold greater in JHD mice than in C57BL/6 controls, whereas similar numbers of splenic CD4+ alphabeta T cells were detected. Maximal numbers of gammadelta T cells were in cell-cycle in both JHD and C57BL/6 mice during descending P. chabaudi parasitemia, but the number of gammadelta T cells in cell-cycle was greater in B cell-deficient mice than in intact controls. Interleukin-10 (IL-10), a potent TH1 cell-suppressive molecule, does not appear to down-regulate the gammadelta T cell response during malaria in B cell-intact mice because the magnitude of the gammadelta T cell response was not significantly greater in IL-10 knockout mice compared with heterozygote controls. These findings collectively indicate that a markedly enhanced expansion of the gamma delta T cell population occurs in the absence of B cells, and this expansion occurs predominantly during acute malaria when parasite burdens are similar in B cell-deficient animals and intact controls.

Patterned wafer inspection using spatial filtering for the cluster environment.

Automated-process tool clusters are becoming increasingly prevalent in advanced semiconductor manufacturing plants, necessitating integrated inspection of patterned semiconductor wafers for defects and particulates. Integrated inspection tools must be small, sensitive, inexpensive, and fast in order to be compatible with the cluster environment. We show that intensity spatial filtering, with some refinements, can provide the required sensitivity and speed in a small, inexpensive package. By using dark-field illumination and a nonrectangular azimuthal orientation (e.g., 45 degrees ) to the primarily rectangular pattern, we show that the strongest diffraction from the pattern can be made to bypass the optical system entirely. This technique alleviates stringent scatter and antireflection requirements on the optics, and it permits the use of off-the-shelf components.