774 research outputs found
Measurement of the production branching ratios following nuclear muon capture for palladium isotopes using the in-beam activation method
Background: The energy distribution of excited states populated by the
nuclear muon capture reaction can facilitate an understanding of the reaction
mechanism; however, experimental data are fairly sparse. Purpose: We developed
a new methodology, called the in-beam activation method, to measure the
production probability of residual nuclei by muon capture. For the first
application of the new method, we have measured muon-induced activation of five
isotopically-enriched palladium targets. Methods: The experiment was conducted
at the RIKEN-RAL muon facility of the Rutherford Appleton Facility in the UK.
The pulsed muon beam impinged on the palladium targets and gamma rays from the
beta and isomeric decays from the reaction residues were measured using
high-purity germanium detectors in both the in-beam and offline setups.
Results: The production branching ratios of the residual nuclei of muon capture
for five palladium isotopes with mass numbers A = 104, 105, 106, 108, and 110
were obtained. The results were compared with a model calculation using the
particle and heavy ion transport system (PHITS) code. The model calculation
well reproduces the experimental data. Conclusion: For the first time, this
study provides experimental data on the distribution of production branching
ratios without any theoretical estimation or assumptions in the interpretation
of the data analysisComment: 20 pages, 11 figure
Correlation dynamics between electrons and ions in the fragmentation of D molecules by short laser pulses
We studied the recollision dynamics between the electrons and D ions
following the tunneling ionization of D molecules in an intense short pulse
laser field. The returning electron collisionally excites the D ion to
excited electronic states from there D can dissociate or be further
ionized by the laser field, resulting in D + D or D + D,
respectively. We modeled the fragmentation dynamics and calculated the
resulting kinetic energy spectrum of D to compare with recent experiments.
Since the recollision time is locked to the tunneling ionization time which
occurs only within fraction of an optical cycle, the peaks in the D kinetic
energy spectra provides a measure of the time when the recollision occurs. This
collision dynamics forms the basis of the molecular clock where the clock can
be read with attosecond precision, as first proposed by Corkum and coworkers.
By analyzing each of the elementary processes leading to the fragmentation
quantitatively, we identified how the molecular clock is to be read from the
measured kinetic energy spectra of D and what laser parameters be used in
order to measure the clock more accurately.Comment: 13 pages with 14 figure
Cortical plasticity as a new endpoint measurement for chronic pain
Animal models of chronic pain are widely used to investigate basic mechanisms of chronic pain and to evaluate potential novel drugs for treating chronic pain. Among the different criteria used to measure chronic pain, behavioral responses are commonly used as the end point measurements. However, not all chronic pain conditions can be easily measured by behavioral responses such as the headache, phantom pain and pain related to spinal cord injury. Here I propose that cortical indexes, that indicate neuronal plastic changes in pain-related cortical areas, can be used as endpoint measurements for chronic pain. Such cortical indexes are not only useful for those chronic pain conditions where a suitable animal model is lacking, but also serve as additional screening methods for potential drugs to treat chronic pain in humans. These cortical indexes are activity-dependent immediate early genes, electrophysiological identified plastic changes and biochemical assays of signaling proteins. It can be used to evaluate novel analgesic compounds that may act at peripheral or spinal sites. I hope that these new cortical endpoint measurements will facilitate our search for new, and more effective, pain medicines, and help to reduce false lead drug targets
Coherent Electron Scattering Captured by an Attosecond Quantum Stroboscope
The basic properties of atoms, molecules and solids are governed by electron
dynamics which take place on extremely short time scales. To measure and
control these dynamics therefore requires ultrafast sources of radiation
combined with efficient detection techniques. The generation of extreme
ultraviolet (XUV) attosecond (1 as = 10-18 s) pulses has, for the first time,
made direct measurements of electron dynamics possible. Nevertheless, while
various applications of attosecond pulses have been demonstrated
experimentally, no one has yet captured or controlled the full three
dimensional motion of an electron on an attosecond time scale. Here we
demonstrate an attosecond quantum stroboscope capable of guiding and imaging
electron motion on a sub-femtosecond (1 fs = 10-15 s) time scale. It is based
on a sequence of identical attosecond pulses which are synchronized with a
guiding laser field. The pulse to pulse separation in the train is tailored to
exactly match an optical cycle of the laser field and the electron momentum
distributions are detected with a velocity map imaging spectrometer (VMIS).
This technique has enabled us to guide ionized electrons back to their parent
ion and image the scattering event. We envision that coherent electron
scattering from atoms, molecules and surfaces captured by the attosecond
quantum stroboscope will complement more traditional scattering techniques
since it provides high temporal as well as spatial resolution.Comment: 6 pages, 4 figure
Entanglement and Timing-Based Mechanisms in the Coherent Control of Scattering Processes
The coherent control of scattering processes is considered, with electron
impact dissociation of H used as an example. The physical mechanism
underlying coherently controlled stationary state scattering is exposed by
analyzing a control scenario that relies on previously established entanglement
requirements between the scattering partners. Specifically, initial state
entanglement assures that all collisions in the scattering volume yield the
desirable scattering configuration. Scattering is controlled by preparing the
particular internal state wave function that leads to the favored collisional
configuration in the collision volume. This insight allows coherent control to
be extended to the case of time-dependent scattering. Specifically, we identify
reactive scattering scenarios using incident wave packets of translational
motion where coherent control is operational and initial state entanglement is
unnecessary. Both the stationary and time-dependent scenarios incorporate
extended coherence features, making them physically distinct. From a
theoretical point of view, this work represents a large step forward in the
qualitative understanding of coherently controlled reactive scattering. From an
experimental viewpoint, it offers an alternative to entanglement-based control
schemes. However, both methods present significant challenges to existing
experimental technologies
Development of wide range photon detection system for muonic X-ray spectroscopy
We have developed a photon detection system for muonic X-ray spectroscopy.
The detector system consists of high-purity germanium detectors with BGO
Compton suppressors. The signals from the detectors are readout with a digital
acquisition system. The absolute energy accuracy, energy and timing
resolutions, photo-peak efficiency, the performance of the Compton suppressor,
and high count rate durability are studied with standard -ray sources
and in-beam experiment using
resonance reaction. The detection system was demonstrated at Paul Scherrer
Institute. A calibration method for a photon detector at a muon facility using
muonic X-rays of Au and Bi is proposed
β-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
G. Larusso et al.; 7 pags.; 5 figs.; 2 tabs.; PACS numbers: 23.40.-s, 26.30.Hj, 27.60.+j© 2015 American Physical Society. The β-decay half-lives of 110 neutron-rich isotopes of the elements from 37Rb to 50Sn 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.Part of the WAS3ABi was supported by the Rare
Isotope Science Project which is funded by the Ministry of
Education, Science, and Technology (MEST) and National
Research Foundation (NRF) of Korea. This work was
partially supported by KAKENHI (Grants No. 25247045,
No. 2301752, and No. 25800130), the RIKEN Foreign
Research Program, the Spanish Ministerio de Ciencia e
Innovación (Contracts No. FPA2009-13377-C02 and
No. FPA2011-29854-C04), the U.S. Department of
Energy, Office of Science, Office of Nuclear Physics,
Contract No. DE-AC02-06CH11357, the NASA Grant
No. NNX10AH78G, and the Hungarian Scientific
Research Fund OTKA Contract No. K100835.Peer Reviewe
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