Upper Pleistocene Stratigraphy, Paleoecology, and Archaeology of the Northern Yukon Interior, Eastern Beringia. I. Bonnet Plume Basin

New stratigraphic and chronometric data show that Bonnet Plume Basin, in northeastern Yukon Territory, was glaciated in late Wisconsinan time rather than during an earlier advance of Laurentide ice. This conclusion has important ramifications not only for the interpretation of all-time glacial limits farther north along the Richardson Mountains but also for non-glaciated basins in the Porcupine drainage to the northwest. The late Wisconsinan glacial episode in Bonnet Plume Basin is here named the Hungry Creek advance after the principal Quaternary section in the basin. Sediments beneath the till at Hungry Creek have produced well-produced pollen, plant macrofossils, insects, and a few vertebrate remains. The plant and invertebrate fossils provide a detailed, if temporally restricted, record of a portion of the mid-Wisconsinan interstadial, while the vertebrate fossils include the oldest Yukon specimen of the Yukon wild ass. Some of the mid-Wisconsinan sediments have also yielded distinctive chert flakes that represent either a previously unreported product of natural fracturing or a by-product of stone tool manufacture by human residents of Bonnet Plume Basin. In addition to presenting new data on these diverse but interrelated topics, this paper serves as an introduction to a series of reports that will treat in turn the Upper Pleistocene record of Bluefish, Old Crow, and Bell basins, respectively.&nbsp

Linear Responses in Time-dependent Hartree-Fock-Bogoliubov Method with Gogny Interaction

A numerical method to integrate the time-dependent Hartree-Fock Bogoliubov (TDHFB) equations with Gogny interaction is proposed. The feasibility of the TDHFB code is illustrated by the conservation of the energy, particle numbers, and center-of-mass in the small amplitude vibrations of oxygen 20. The TDHFB code is applied to the isoscalar quadrupole and/or isovector dipole vibrations in the linear (small amplitude) region in oxygen isotopes (masses A = 18,20,22 and 24), titanium isotopes (A = 44,50,52 and 54), neon isotope (A = 26), and magnesium isotopes (A = 24 and 34). The isoscalar quadrupole and isovector dipole strength functions are calculated from the expectation values of the isoscalar quadrupole and isovector dipole moments.Comment: 10 pages, 13 figure

Yrast decays in K43

High-spin states in K43 were studied using the Be9(36S,pn)43K reaction. Threefold (p12) coincidence data and -ray intensity ratios were used to establish a decay scheme and identify negative- and positive-parity yrast decay chains. The 15/2- yrast state is relatively poorly aligned prior to decay. Energies of positive-parity levels predicted by Johnstone are in good agreement with experiment

γ spectroscopy of states in Cl 32 relevant for the S 31 (p,γ) Cl 32 reaction rate

Background: The S31(p,γ)Cl32 reaction becomes important for sulfur production in novae if the P31(p,α)Si28 reaction rate is somewhat greater than currently accepted. The rate of the S31(p,γ)Cl32 reaction is uncertain, primarily due to the properties of resonances at Ec.m.=156 and 549 keV. Purpose: We precisely determined the excitation energies of states in Cl32 through high-resolution γ spectroscopy including the two states most important for the S31(p,γ)Cl32 reaction at nova temperatures. Method: Excited states in Cl32 were populated using the B10(Mg24,2n)Cl32 reaction with a Mg24 beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils in the Fragment Mass Analyzer, and precise level energies were determined by detecting γ rays with Gammasphere. Results: We observed γ rays from the decay of six excited states in Cl32. The excitation energies for two unbound levels at Ex=1738.1 (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the S32(He3,t)Cl32 reaction [1]. Conclusions: An updated S31(p,γ)Cl32 reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in Cl32

Decay properties of the new isotopes 172Hg and 173Hg

The α decays of the two neutron-deficient nuclei 172Hg and 173Hg were observed for the first time using the 78Kr(96Ru,2n) and 80Kr(96Ru,3n) reactions, respectively. The reaction products were dispersed according to their mass-to-charge state ratios in the Argonne Fragment Mass Analyzer and implanted in a double-sided silicon strip detector, where their subsequent decays were studied using spatial and time correlations between implants and decays. A half-life of 250(+350-90) μs and an energy of 7350(12) keV were deduced for the α decay of 172Hg. In 173Hg the half-life was measured to be 0.93(+0.57-0.26) ms and the corresponding energy is 7211(11) keV. In addition, the half-life and energy of the α decay of 174Hg were measured more precisely. The reduced widths deduced for these Hg isotopes indicate that the observed decays correspond to unhindered Δl = 0 transitions. The α-decay Q values are compared with the values calculated using mass tables by Möller and Nix, and by Liran and Zeldes. The latter mass tables show better agreement with the data

Superdeformation and prolate-oblate competition in Tl nuclei

Spectroscopic studies of weakly populated proton i13/2 bands in superdeformed Tl nuclei (around mass 190) and in the normally deformed, very light 183Tl nucleus are discussed. Among the results presented, the first measurement of a superdeformed quadrupole moment in an odd-Z nucleus, 191Tl, is reported. The experiments were conducted with the Gammasphere array as "stand-alone" device and coupled with the Argonne Fragment Mass Analyzer

Identification of γ -decaying resonant states in 26Mg and their importance for the astrophysical s process

The 22Ne(α, n) reaction is expected to provide the dominant neutron source for the weak s process in massive stars and intermediate-mass (IM) Asymptotic Giant Branch (AGB) stars. However, the production of neutrons in such environments is hindered by the competing 22Ne(α,γ)26Mg reaction. Here, the 11B(16O,p) fusion-evaporation reaction was used to identify γ-decay transitions from 22Ne + α resonant states in 26Mg. Spin-parity restrictions have been placed on a number of α-unbound excited states in 26 Mg and their role in the 22Ne(α,γ)26Mg reaction has been investigated. In particular, a suspected natural-parity resonance at Ec.m. = 557(3) keV, that lies above the neutron threshold in 26Mg, and is known to exhibit a strong α-cluster character, was observed to γ decay. Furthermore, a known resonance at Ec . m .= 466 (4 ) keV has been definitively assigned 2+ spin and parity. Consequently, uncertainties in the 22Ne(α,γ) stellar reaction rate have been reduced by a factor of ∼ 20 for temperatures ∼ 0.2 GK

Revised decay properties of the key 93-keV resonance in the Mg 25 (p,γ) reaction and its influence on the MgAl cycle in astrophysical environments

The γ-decay properties of an excited state in Al26 at 6398.3(8) keV have been reexamined using the B11+O16 fusion-evaporation reaction. This level represents a key 93.1(8)-keV resonance in the Mg25+p system and its relative branching to the Al26 ground state, f0, has been determined to be 0.76±0.03 (stat.) ±0.10 (syst.). This is a significantly higher value than the most recent evaluation and implies a considerable increase in the production of cosmic γ rays from Al26 radioactivity

Prolate collectivity in Tl187

High-spin states of Tl187 populated in the Gd156(35Cl,4n) reaction have been investigated with -ray coincidence techniques. Two decoupled bands feeding the oblate 9/2- isomeric state have been established. These bands are built on h9/2 and i13/2 configurations associated with prolate shapes. The first observation of a low-K h9/2 structure in an odd-A Tl nucleus is used to draw conclusions on the role of this proton orbital in stabilizing the prolate minimum seen in light Hg isotopes

Low-lying T=0 states in the odd-odd N=Z nucleus 62Ga

New, low-lying levels in the odd-odd, N=Z nucleus 62Ga have been identified using a sensitive technique, where in-beam γ rays from short-lived nuclei are tagged with β decays following recoil mass identification. A comparison of the results with shell-model and IBM-4 calculations demonstrates good agreement between theory and experiment, with the majority of predicted low-lying, low-spin T=0 states now identified. There is a dramatic change in the level density at low excitation energies for the N=Z nucleus 62Ga when compared with neighbouring odd-odd Ga isotopes where, in contrast, the low-lying level structure is dominated by configurations with T=1 pairing interactions between excess neutrons. This illustrates the distinctively different aspects of nuclear structure exhibited by nuclei with N=Z