Search results for "IONIZATION"
showing 10 items of 1255 documents
Possibility of measuring the amount of intergalactic metals with 14N VII HFS line
2009
AbstractWe discuss possibility of observations of the warm-hot intergalactic medium using the hyperfine structure line of highly charged nitrogen ion 14N VII (rest wavelength λ = 5.652 mm). Observations of this line will allow to separate bulk and turbulent motions in the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition.Wavelength of this line is well-suited for ground-based observation of objects at z ≈ 0.15 − 0.6 when it is redshifted to the widely-used 6.5 − 9 mm spectral band, and, for example, for z ≥ 1.3, when the line can be observed in 1.3 cm band and at lower frequencies.
Multiphoton One-step Ionization of Helium at 1064 nm
1989
Abstract The multiphoton ionization of helium by a strong radiation field having a wavelength of 1064 nm and a field intensity up to 5 × 1014 W cm −2 is considered within a non-perturbative treatment partially accounting for the electron-electron correlations in the initial bound state and approximately for the Coulomb interaction between the residual ion and the ejected electron in the final state. Only single-electron transitions are considered, the main emphasis being on the field polarization effects. The obtained results are compared with the few results available in the literature in the same regime as well as with very recent experimental findings. In particular, the calculated photo…
High‐Resolution X‐Ray Spectroscopy of the Post–T Tauri Star PZ Telescopii
2004
We present an analysis of the Chandra High Energy Transmission Grating Spectrometer observation of the rapidly rotating P_(rot)=0.94 d post T Tauri (~20 Myr old) star PZ Telescopii, in the Tucana association. Using two different methods we have derived the coronal emission measure distribution, em(T), and chemical abundances. The em(T) peaks at log T = 6.9 and exhibits a significant emission measure at temperatures log T > 7. The coronal abundances are generally ~0.5 times the solar photospheric values that are presumed fairly representative of the composition of the underlying star. A minimum in abundance is seen at a first ionization potential (FIP) of 7-8 eV, with evidence for higher abu…
Time-dependent density-functional theory of strong-field ionization of atoms by soft x rays
2014
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.
Zeeman Spectroscopy in Penning Traps
2018
Abstract Penning traps are the instruments of choice to determine the magnetic moments of long lived or stable charged particles. The virtual absence of collisions with background molecules when working in ultra-high vacuum, the small volume which the trapped particles occupy at low kinetic energies, and the extremely long observation and coherence times allow for very high precision in Zeeman spectroscopy. When applied to singly ionized multielectron atoms the experiments serve for tests of atomic structure calculations. The magnetic moments in few-electron systems such as hydrogen- or lithium-like highly charged ions can be calculated with remarkable precision in the frame of bound-state …
Field-free molecular alignment for measuring ionization probability
2007
International audience; We have shown in a recent letter (Loriot et al 2006 Opt. Lett. 31 2897) the possibility of determining the ionization probability of linear molecules by using an all-optical technique that takes advantage of post-pulse molecular alignment. To that end, we have implemented a ‘cross-defocusing' technique producing a signal sensitive to both alignment and ionization. The analysis of the signal provides a quantitative measurement of the ionization probability calibrated with molecular alignment. In the present work, the method is discussed in more detail and applied to the measurement of the ionization probability of N2 as well as to the determination of the ionization r…
Ortho-H2 and the age of prestellar cores
2013
Prestellar cores form from the contraction of cold gas and dust material in dark clouds before they collapse to form protostars. Several concurrent theories exist to describe this contraction but they are currently difficult to distinguish. One major difference is the timescale involved in forming the prestellar cores: some theories advocate nearly free-fall speed via, e.g., rapid turbulence decay, while others can accommodate much longer periods to let the gas accumulate via, e.g., ambipolar diffusion. To tell the difference between these theories, measuring the age of prestellar cores could greatly help. However, no reliable clock currently exists. We present a simple chemical clock based…
High-rate x-ray spectroscopy in mammography with a CdTe detector: A digital pulse processing approach
2010
Purpose:Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. Methods: The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the respon…
Comparison and uncertainty evaluation of different calibration protocols and ionization chambers for low-energy surface brachytherapy dosimetry
2015
Purpose: A surface electronic brachytherapy (EBT) device is in fact an x-ray source collimated with specific applicators. Low-energy (<100 kVp) x-ray beam dosimetry faces several challenges that need to be addressed. A number of calibration protocols have been published for x-ray beam dosimetry. The media in which measurements are performed are the fundamental difference between them. The aim of this study was to evaluate the surface dose rate of a low-energy x-ray source with small field applicators using different calibration standards and different small-volume ionization chambers, comparing the values and uncertainties of each methodology. Methods: The surface dose rate of the EBT unit …