414 research outputs found
Neutral Plasma Oscillations at Zero Temperature
We use cold plasma theory to calculate the response of an ultracold neutral
plasma to an applied rf field. The free oscillation of the system has a
continuous spectrum and an associated damped quasimode. We show that this
quasimode dominates the driven response. We use this model to simulate plasma
oscillations in an expanding ultracold neutral plasma, providing insights into
the assumptions used to interpret experimental data [Phys. Rev. Lett. 85, 318
(2000)].Comment: 4.3 pages, including 3 figure
A Systematic Study on Energy Dependence of Quasi-Periodic Oscillation Frequency in GRS 1915+105
Systematically studying all the RXTE/PCA observations for GRS 1915+105 before
November 2010, we have discovered three additional patterns in the relation
between Quasi-Periodic Oscillation (QPO) frequency and photon energy, extending
earlier outcomes reported by Qu et al. (2010). We have confirmed that as QPO
frequency increases, the relation evolves from the negative correlation to
positive one. The newly discovered patterns provide new constraints on the QPO
models
Photoionization of ultracold and Bose-Einstein condensed Rb atoms
Photoionization of a cold atomic sample offers intriguing possibilities to
observe collective effects at extremely low temperatures. Irradiation of a
rubidium condensate and of cold rubidium atoms within a magneto-optical trap
with laser pulses ionizing through 1-photon and 2-photon absorption processes
has been performed. Losses and modifications in the density profile of the
remaining trapped cold cloud or the remaining condensate sample have been
examined as function of the ionizing laser parameters. Ionization
cross-sections were measured for atoms in a MOT, while in magnetic traps losses
larger than those expected for ionization process were measured.Comment: 9 pages, 7 figure
Evidence for Shape Co-existence at medium spin in 76Rb
Four previously known rotational bands in 76Rb have been extended to moderate
spins using the Gammasphere and Microball gamma ray and charged particle
detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV.
The properties of two of the negative-parity bands can only readily be
interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model
calculations if they have the same configuration in terms of the number of g9/2
particles, but they result from different nuclear shapes (one near-oblate and
the other near-prolate). These data appear to constitute a unique example of
shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters
The influence of νh11/2 occupancy on the magnetic moments of collective 21+ states in A∼100 fission fragments
AbstractThe magnetic moments of Iπ=21+ states in even–even A∼100 fission fragments have been measured using the Gammasphere array, using the technique of time-integral perturbed angular correlations. The data are interpreted within the context of the interacting boson model (IBA2) leading to the suggestion of a strong νh11/2 component in the deformed 21+ states of this region
α decay of 97249Bk and levels in 95245Am
α decay of 249Bk has been investigated by measuring its α and γ-ray spectra, both in singles and in coincidence modes. The α spectrum of a freshly purified 249Bk sample was measured with a high-resolution, double-focusing magnetic spectrometer. γ singles, γ-γ coincidence, and γ-α coincidence spectra were also recorded. The absolute intensity of the 327.45-keV γ ray has been determined to be (1.44±0.08)×10-5% per 249Bk decay. Assignments of previously known single-particle states were confirmed. A new rotational band was identified in the α singles spectrum and Am K x rays have been observed in its decay. This single-particle state, with an energy of 154 keV, has been assigned to the 3/2-[521] Nilsson state. This is the lowest excitation energy for this orbital in any Am nucleus. More precise energies and intensities of the 249Bk α groups and γ-ray transitions are provided
Precise absolute γ -ray and β- -decay branching intensities in the decay of Cu 2967
Absolute γ-ray emission probabilities in the β- decay of Cu67 were measured by means of γ-ray and β - decay singles and β - γ coincidences. The new results, together with the known decay scheme of Cu67, were used to determine absolute β - decay branching intensities. The present data differ significantly from previously published values. In addition, the half-life of the Iπ=12- isomer in Zn67 was measured as T1/2=9.37(4) μs, in a good agreement with earlier measurements. From the analysis of the Fermi-Kurie plots, Qβ-(g.s.)=560.3(10) keV was deduced, which differs from the previously measured value of 577(8) keV but is in good agreement with Qβ-(g.s.)=561.3(15) keV recommended in the latest Atomic Mass Evaluation
M3 and E4 K-forbidden decays of the Kπ=23/2- isomer in 177Lu
Decay of the long-lived (T1/2=160.44 d) Kπ=23/2- isomer in 177Lu was investigated using a chemically purified source and the Gammasphere array. New, high-multipolarity M3 and E4 deexcitation branches to the known Iπ=17/2- and 15/2- members of the π9/2-[514] band were discovered. The reduced hindrance factors per degree of K forbiddenness deduced for these two transitions are found to be relatively large when compared to similar decays from the Kπ=37/2- (T1/2=51.4 min) and Kπ=16+ (T1/2=31 yr) isomers in 177Hf and 178Hf, respectively. This is attributed to significant configuration changes that occur in the decay of this 177Lu isomer
Quasiclassical description of transport through superconducting contacts
We present a theoretical study of transport properties through
superconducting contacts based on a new formulation of boundary conditions that
mimics interfaces for the quasiclassical theory of superconductivity. These
boundary conditions are based on a description of an interface in terms of a
simple Hamiltonian. We show how this Hamiltonian description is incorporated
into quasiclassical theory via a T-matrix equation by integrating out
irrelevant energy scales right at the onset. The resulting boundary conditions
reproduce results obtained by conventional quasiclassical boundary conditions,
or by boundary conditions based on the scattering approach. This formalism is
well suited for the analysis of magnetically active interfaces as well as for
calculating time-dependent properties such as the current-voltage
characteristics or as current fluctuations in junctions with arbitrary
transmission and bias voltage. This approach is illustrated with the
calculation of Josephson currents through a variety of superconducting
junctions ranging from conventional to d-wave superconductors, and to the
analysis of supercurrent through a ferromagnetic nanoparticle. The calculation
of the current-voltage characteristics and of noise is applied to the case of a
contact between two d-wave superconductors. In particular, we discuss the use
of shot noise for the measurement of charge transferred in a multiple Andreev
reflection in d-wave superconductors
Multinucleon transfer in the interaction of 977 MeV and 1143 MeV Hg 204 with Pb 208
A previous study of symmetric collisions of massive nuclei has shown that current models of multinucleon transfer (MNT) reactions do not adequately describe the transfer product yields. To gain further insight into this problem, we have measured the yields of MNT products in the interaction of 977 (E/A=4.79 MeV) and 1143 MeV (E/A=5.60 MeV) Hg204 with Pb208. We find that the yield of multinucleon transfer products are similar in these two reactions and are substantially lower than those observed in the reaction of 1257 MeV (E/A=6.16 MeV) Hg204+Pt198. We compare our measurements with the predictions of the GRAZING-F, dinuclear systems (DNS), and improved quantum molecular dynamics (ImQMD) models. For the observed isotopes of the elements Au, Hg, Tl, Pb, and Bi, the measured values of the MNT cross sections are orders of magnitude larger than the predicted values. Furthermore, the various models predict the formation of nuclides near the N=126 shell, which are not observed
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