Search results for "Radiative Transfer"
showing 10 items of 551 documents
Preliminary Mechanical Characterization of Thermal Filters for the X-IFU Instrument on Athena
2018
The X-ray Integral Field Unit (X-IFU) is one of the two instruments of the Athena astrophysics space mission approved by ESA in the Cosmic Vision Science Program. The X-IFU consists of a large array of TES microcalorimeters that will operate at ~ 50 mK inside a sophisticated cryostat. A set of thin filters, highly transparent to X-rays, will be mounted on the cryostat thermal shields in order to attenuate the IR radiative load, to attenuate RF electromagnetic interferences, and to protect the detector from contamination. In this paper, we present the current thermal filters design, describe the filter samples developed/procured so far, and present preliminary results from the ongoing charac…
A practicableγ 5-scheme in dimensional regularization
1992
We present a new simpleγ5 regularization scheme. We discuss its use in the standard radiative correction calculations including the anomaly contributions. The new scheme features an anticommutingγ5 which leads to great simplifications in practical calculations. We carefully discuss the underlying mathematics of ourγ5-scheme which is formulated in terms of simple projection operations.
Quasirelativistic transition property calculations by the intermediate Hamiltonian method: Electronic transition dipole moments and radiative lifetim…
2001
We present a quasirelativistic method of ab initio calculations on molecular excited states and electronic transition moments within the relativistic effective potential approximation, based on the construction of intermediate Hamiltonians and spin-free one-particle transition density matrices by means of the many-body multipartitioning perturbation theory. The method is applied to describe the electronic transitions involved in the radiative decay of the ${A0}_{u}^{+},$ ${B0}_{u}^{+},$ and ${B1}_{u}$ states of ${\mathrm{Te}}_{2}.$ Good agreement of the computed transition dipole moment functions with their empirical counterparts is achieved. Theoretical radiative lifetime estimates for sev…
Energy and radiative properties of the low-lying NaRb states
2001
D 1 P ‐B 1 P transition dipole moments, as well as nonadiabatic L-uncoupling matrix elements between the examined 1 P and four lowest 1 S 1 states for both 23 Na 85 Rb and 23 Na 87 Rb isotopomers. The relevant MPPT ab initio matrix elements and energy curves were converted by means of the approximate sum rule to radiative lifetimes and L-doubling constants ( q factors! for the particular rovibronic levels of the B 1 P and D 1 P states. The theoretical lifetimes agree well with their experimental counterparts for both B 1 P and D 1 P states. The q factor estimates obtained in the singlet-singlet approximation are in good agreement with the experimental ones for the D 1 P(1<v8<12;7<J8<50) lev…
A new radiation infrastructure for the Modular Earth Submodel System (MESSy, based on version 2.51)
2016
Abstract. The Modular Earth Submodel System (MESSy) provides an interface to couple submodels to a basemodel via a highly flexible data management facility (Jöckel et al., 2010). In the present paper we present the four new radiation related submodels RAD, AEROPT, CLOUDOPT and ORBIT. The submodel RAD (with shortwave radiation scheme RAD_FUBRAD) simulates the radiative transfer, the submodel AEROPT calculates the aerosol optical properties, the submodel CLOUDOPT calculates the cloud optical properties, and the submodel ORBIT is responsible for Earth orbit calculations. These submodels are coupled via the standard MESSy infrastructure and are largely based on the original radiation scheme of …
Direct measurement of the radiative tail in electron scattering from atomic nuclei
1985
We have made a direct measurement of the radiative tail of the eleastic peak from several tungsten targets. The measured data have been compared to the results expected for both internal and external bremsstrahlung contributions. Even for targets as thick as 4% of a radiation length of tungsten, agreement between the results of the experiment and the predictions of the theory has been found to be unexpectedly good.
ISR Experiment at A1-Collaboration
2019
The discrepancy between the proton charge radius extracted from the muonic hydrogen Lamb shift measurement and the best present value obtained from the elastic scattering experiments, remains unexplained and represents a burning problem of today’s nuclear physics. In a pursuit of reconciling the puzzle an experiment is underway at MAMI, which exploits the radiative tail of the elastic peak to study the properties of electromagnetic processes and to extract the proton charge form factor $ \left( {\mathop G\nolimits_E^p } \right) $ at extremely small Q2. This paper reports on the latest results of the first such measurement performed at the three-spectrometer facility of the A1-Collaboration,…
Radiative kaon capture on nuclei.
1990
Hypernuclear formation through the radiative capture of in-flight ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ is studied in a distorted wave impluse approximation approach. The elementary operator is obtained from first-order Feynman diagrams and is constrained by the reactions ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma} and, via crossing, by \ensuremath{\gamma}p\ensuremath{\rightarrow}${\mathit{K}}^{+}$\ensuremath{\Lambda}. The ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ distortion has been included via a simple optical potential which is in agreement with ${\mathit{K}}^{\mathrm{\ensuremath{-}}}$ elastic scattering on nuclei. Using the…
Radiative capture of protons by the deformed nuclide232Th
1986
The excitation function for the radiative capture232Th(p, γ)233Pa has been determined in the proton energy range 7 to 20 MeV by an activation method. The results are compared with a compound nucleus model prediction and earlier experimental data for another deformed nuclide176Yb. As in previous cases an enhancement over the CN-model prediction is observed and the excitation of the giant dipole resonance via the direct-semidirect reaction process is a likely explanation. Supplementary measurements of the232Th (p, f) excitation function in the proton energy range 11–20 MeV have been performed.
Lifetime Studies in Traps
2009
A knowledge of the radiative lifetimes of excited atomic states is of wide interest, not only in the detailed understanding of intrinsic atomic structure and dynamics but also in the fields of plasma diagnostics and astrophysics. The transition rates of intercombination and electric-dipole forbidden lines are of particular importance, since their low transition probability gives them long optical depths in plasmas and astrophysical environments.