Low Resolution Dipole Research Articles

Time-dependent radioactivity distribution in MAFF

The Munich Accelerator for Fission Fragments is planned to be installed at the FRM II in Garching. It will operate a uranium-carbide-loaded graphite matrix as a target for neutron-induced fission. The radioactive reaction fragments leave the ion source as both, atoms and ions. For radiation safety it is imperative to have a basic understanding of the fragment distribution within the beam line. Atoms leaving the graphite matrix will spread like a gas and stick to surfaces depending on their species. A probabilistic Monte-Carlo approach is used to predict the surface coating of internal surfaces of the beam line for all fission nuclides. To decrease calculation time, the problem is reduced to two dimensions with the surface areas being a measure for the probability, that they are hit by a particle. The program is completely time dependent to implement radioactive decay. Ions leaving the fission ion source are transported by electrostatic means towards the mass pre-separator, a low-resolution dipole magnet with a complex slit system in the focal plane. All unwanted ions are stopped at the slits, resulting in a high level of radioactive contamination. While it is advantageous for shielding purposes to have the majority of the contamination in one point, precautions must be taken to ensure that it stays that way. Material corrosion caused by sputtering will release previously implanted radionuclides. To reduce this effect, different methods are under investigation, one of which is changing the slit geometry. The considered designs will be described and experimental results will be shown.

Absolute photoabsorption oscillator strengths by electron energy loss methods: the valence and S 2p and 2s inner shells of sulphur dioxide in the discrete and continuum regions (3.5–260 eV)

Absolute photoabsorption oscillator strengths (cross-sections) for the valence shell discrete and continuum regions of sulphur dioxide from 3.5 to 51 eV have been measured using high resolution (∼0.05 eV FWHM) dipole ( e, e) spectroscopy. A wide-range spectrum, covering both the valence shell and the S 2p and 2s inner shells, has also been obtained from 5 to 260 eV at low resolution (∼1 eV FWHM), and this has been used to determine the absolute oscillator strength scale using valence shell TRK (i.e., S(0)) sum-rule normalization. The present measurements have been undertaken in order to investigate the recently discovered significant quantitative errors in our previously published low resolution dipole ( e, e) work on sulphur dioxide (Cooper et al., Chem. Phys. 150 (1991) 237; 150 (1991) 251). These earlier measurements were also in poor agreement with other previously published direct photoabsorption measurements. We now report new absolute photoabsorption oscillator strengths using both high and low resolution dipole ( e, e) spectroscopies. These new measurements cover a wider energy range and are much more consistent with the previously published direct photoabsorption measurements. The accuracy of our new measurements is confirmed by an S(−2) dipole sum-rule analysis which gives a static dipole polarizability for sulphur dioxide in excellent agreement (within 3.5%) with previously reported polarizability values. Other dipole sums S( u) ( u=−1,−3 to −6,−8,−10) and logarithmic dipole sums L( u) ( u=−1 to −6) are also determined from the presently reported absolute oscillator strength distributions.

Absolute oscillator strengths for the photoabsorption of silane in the valence and Si 2p and 2s regions (7.5–350 eV)

Abstract Absolute photoabsorption oscillator strengths (cross sections) for the valence and Si 2p discrete regions of silane have been measured using high resolution (∼ 0.05–0.1 eV fwhm) dipole (e, e) spectroscopy. Long range (7.5–350 eV) lower resolution data (1 eV fwhm) have also been obtained, from which the absolute oscillator strength scale has been determined using TRK (i.e. S (0)) sum-rule normalization. The accuracy of the presently reported measurements has been tested using the S (−2) sum-rule: Evaluation of the S (−2) sum using the presently reported data gives a dipole polarizability for silane within 0.2% of the experimental value. The present valence shell measurements were undertaken in order to investigate the differences between earlier low resolution dipole (e, e) work (Cooper et al., Chem. Phys. 140 (1990) 133) and subsequent valence shell synchrotron radiation photoabsorption measurements reported by Kameta et al. (J. Chem. Phys. 95 (1991) 1456). The presently reported high and low resolution absolute phtoabsorption oscillator strengths are much more consistent with the direct photoabsorption measurements than the earlier dipole (e, e) work (within ∼ 15%). The resolution of the present high resolution data is sufficient to allow absolute photoabsorption oscillator strengths to be determined for many of the individual electronic transitions in the Si 2p discrete spectrum.

Discrete and continuum photoabsorption oscillator strengths for the electronic spectrum of nitrous oxide (5.5–203 eV)

The electronic excitation spectrum and the associated absolute optical oscillator strengths for the photoabsorption of nitrous oxide in the energy region 7.4–203 eV have been obtained using low-resolution dipole (e, e) spectroscopy and TRK sum-rule normalization. High-resolution dipole (e, e) spectroscopy (0.048 fwhm) has been used to measure the absolute photoabsorption oscillator strengths in the valence shell discrete region in the energy region 5.5–30 eV. The present results are compared with previously reported experimental and theoretical data.

The electronic spectrum of carbon dioxide. Discrete and continuum photoabsorption oscillator strengths (6–203 eV)

The recently developed high resolution dipole (e,e) method, which is free of Beer—Lambert law “line saturation” errors, has been used to determine absolute photoabsorption oscillator strengths for the discrete electronic excitation of carbon dioxide in the energy region 6–30 eV. Low resolution dipole (e,e) measurements (1 eV fwhm) have also been made in the equivalent photon energy range 8.5–203 eV. The absolute scale of the present measurements was obtained by TRK sum-rule normalization.

The electronic spectrum of water in the discrete and continuum regions. Absolute optical oscillator strengths for photoabsorption (6–200 eV)

The electronic excitation spectrum and the associated absolute optical oscillator strengths for the photoabsorption of water have been determined in the energy region 6–200 eV using low resolution dipole (e, e) spectroscopy and TRK sum-rule normalization. In addition, detailed studies of the absolute photoabsorption oscillator strengths for the valence shell discrete electronic transitions of water have been made using high resolution dipole (e, e) spectroscopy (0.048 eV fwhm), from the first excitation threshold up to 30 eV. The present results are free of “line saturation” (i.e. bandwidth/linewidth interaction) effects which can lead to serious errors when absolute intensity measurements are made using conventional Beer-Lambert law photoabsorption methods.

Absolute optical oscillator strengths for discrete and continuum photoabsorption of carbon monoxide (7–200 eV) and transition moments for the X 1Σ + → A 1Π system

Absolute optical oscillator strengths for the photoabsorption of carbon monoxide have been determined in the energy region 7–200 eV using low resolution dipole (e, e) spectroscopy and TRK sum-rule normalization. High resolution dipole (e, e) spectroscopy has been used to measure the absolute optical oscillator strengths for the photoabsorption of carbon monoxide in the valence shell discrete region from the first excitation threshold to 21 eV. Values of the absolute optical oscillator strengths for excitation of the vibrational levels of the A 1Π, C 1Σ +, B 1Σ + and E 1Π excited electronic states are reported. The variation of transition moment with internuclear distance is investigated for the vibronic bands of the X 1Σ + → A 1Π transition.

Absolute optical oscillator strengths for the electronic excitation of atoms at high resolution. III. The photoabsorption of argon, krypton, and xenon.

Absolute oscillator strengths for the photoabsorption of argon, krypton, and xenon in both the discrete and continuum regions have been measured. The results are compared where possible with previously published experimental and theoretical data. The present work is a continuation of recently reported measurements for helium [Chan et al., Phys. Rev. A 44, 186 (1991)] and neon [Chan et al., Phys. Rev. A 45, 1420 (1992)] obtained using the dipole (e,e) method at both low and high resolution. Using the low-resolution dipole (e,e) spectrometer [with a full width at half maximum (FWHM) of about 1 eV], absolute photoabsorption oscillator strength spectra for the valence and inner shells of argon, krypton, and xenon were obtained up to equivalent photon energies of 500, 380, and 398 eV, respectively. The high-resolution dipole (e,e) spectrometer (FWHM of 0.048 eV) was employed to obtain absolute photoabsorption oscillator strengths for the discrete electronic transitions from the ground states to the ${\mathit{ms}}^{2}$${\mathit{mp}}^{5}$ns and ${\mathit{ms}}^{2}$${\mathit{mp}}^{5}$nd ${(}^{2}$${\mathit{P}}_{3/2,1/2}$) manifolds where m=3, 4, and 5 for argon, krypton, and xenon, respectively. The absolute optical oscillator strength scales were obtained by single-point continuum normalization of the Bethe-Born converted electron-energy-loss spectra using the recently reported absolute optical data of Samson and Yin [J. Opt. Soc. Am. B 6, 2326 (1989)] for argon, krypton, and xenon atoms. High-resolution absolute photoabsorption oscillator strengths were also obtained in the energy regions of the autoionizing resonances corresponding to excitation of the inner-valence s electrons of argon, krypton, and xenon.