Total Absorption Cross Section Research Articles

Odderon and photon exchange in pseudoscalar meson production

We consider exclusive π 0 production in ep-scattering. At high energies odderon and photon exchange contribute. The photon exchange contribution is evaluated exactly using data for the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark structure as suggested by the small odderon amplitude in pp and p p forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic π 0 production cross section. Observing our process at HERA would establish the soft odderon.

Scattering of intermediate-energy positrons by C, N, O atoms and the corresponding diatomic molecules: elastic and total cross-sections

Elastic and total (elastic plus absorption) cross-sections for the scattering of positrons by carbon, nitrogen and oxygen atoms and the corresponding diatomic molecules (C2, CN, CO, N2, NO and O2) in the energy range from 100 to 5000 eV are presented. Parameter-free interaction potentials along with the additivity rule are used in the calculations. Good agreement with the experimental data is obtained wherever such comparisons can be made.

Odderon and photon exchange in electroproduction of pseudoscalar mesons

We investigate the reaction \({\rm e}\;{\rm p} \rightarrow{\rm e}\;{\rm PS}\;{\rm X}\) where PS denotes a pseudoscalar meson \(\pi^0\), \(\eta\), \(\eta'\), or \(\eta_c\) and X either a proton or resonance or continuum state into which the proton can go by diffractive excitation. At high energies photon and odderon exchange contribute to the reaction. The photon exchange contribution is evaluated exactly using data for the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark structure as suggested by the small odderon amplitude in pp and \( {\rm p} \bar{{\rm p}}\) forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic PS production cross section. Observation of our reaction at HERA would establish the soft odderon as an exchange object on an equal footing with the soft pomeron and would give us valuable insight into both the nucleon structure and the mechanism of high energy diffractive scattering.

Dynamics of HI photodissociation in the A band absorption via H-atom Doppler spectroscopy

The dynamics of HI photodissociation following absorption in the A band (200 to 300 nm) was investigated by Doppler spectroscopy at the Lyman α transition of the H-atom photofragments. Measurements of both the branching ratios for the formation of spin-orbit excited I(2P1/2) and ground state I(2P3/2) atoms and the angular distributions of the recoil velocity for these two photofragment channels were obtained at nine photolysis wavelengths between 212.5 and 266 nm. These results show that ground state products result from a transition of perpendicular symmetry (ΔΩ=1), while the excited state atoms are produced from a parallel transition (ΔΩ=0). These experimental results, in combination with total absorption cross section data obtained prior to the present study, have enabled a calculation of the potential curves for the dissociative excited states. The outcome of the calculation was found to be in good qualitative agreement with the model of HI electronic structure originally suggested by Mulliken.

Dissociative photoionization of SO2 from 16 to 120 eV

Using synchrotron radiation as a continuum light source, dissociative photoionization of SO2 has been studied in the photon-energy region of 16–120 eV. Ion branching ratios were obtained by analyzing time-of-flight mass spectra and were converted to the absolute partial cross sections for the production of SO2+, SO+, S+(O2+), O+, and SO2+ by using the reported total absorption cross sections of SO2. Ion branching ratios were differentiated with respect to the incident photon energy. The results obtained by this analytical photoion spectroscopy show dissociation pathways of the SO2+ and SO22+ ions, some of which are first observed in the present study. These pathways are discussed by comparing them with the reported electronic states of the ions.

Total and partial pion absorption cross sections on4Hein the Δ resonance region

This paper presents a large solid angle measurement of the positive pion absorption cross section on 4He and its decomposition into partial channels. The total absorption cross sections at incident pion kinetic energies of Tπ+=70, 118, 162, and 239 MeV are 35±5, 52±4, 51±5, and 27±2 mb, respectively. These values are lower than those reported in some previous experiments. At all pion energies a large fraction of the absorption cross section is due to multinucleon channels.Received 2 September 1997DOI:https://doi.org/10.1103/PhysRevC.58.942©1998 American Physical Society

Spin-Dependent Structure Function of Deuteron

Based on the relationship between electron deep inelastic scattering and forward virtual photon Compton scattering, and using the information provided by virtual photon absorption on target, we study spin-dependent structure function of deuteron and its corresponding first moment, which are expressed by total absorption cross sections of virtual photon. The absorption cross section is determined by helicity amplitudes and which are evaluated in quark model with an improved electromagnetic interaction. The method avoids the difficulty for solving nonperturbative QCD which is impossible at present. In general, our theoretical predictions on the first moment and quark polarization in deuteron are in good agreement with data of E143 at SLAC, EMC at CERN and Hermes at DESY.

Q2-dependence of the Gerasimov-Drell-Hearn sum rule

We test the Gerasimov-Drell-Hearn (GDH) sum rule numerically by calculating the total photon absorption cross sections σ 1 2 and σ 3 2 on the nucleon via photon excitation of baryon resonances in the constituent quark model. A total of seventeen, low-lying, non-strange baryon resonances are included in this calculation. The transverse and longitudinal interference cross section, σ 1 2 TL , is found to play an important role in the study of the Q 2 variation of the sum rule. The results show that the GDH sum rule is saturated by these resonances at a confidence level of 94%. In particular, the P 33(1232) dominates at small Q 2. The GDH integral has a strong Q 2-dependence below Q 2 = 1.0 GeV 2 and changes its sign around Q 2 = 0.3 GeV 2. It becomes weakly Q 2-dependent for Q 2 > 1.0 GeV 2 because of the quick decline of the resonance contributions.

On the total absorption cross-section of galaxies - II: The case of λ cosmologies and covering factor variation

In this work we expand the previous discussion of the plausibility of hypothesis of origin of the Ly? forest absorption systems in haloes of normal galaxies in connection with the HubbleDeepField (HDF) data. It is shown that simplistic approach to absorption cross-sections of galaxies with no luminosity scaling is in strong violation of empirical statistics up to redshift of z ? 3.5. Realistic variation of the covering factor in order to account for its increase in the inner parts of observed haloes leads to even bigger discrepancy. Cosmologies with finite cosmological constant are briefly discussed and compared to ? = 0 case. Ways to improve agreement with observational data are indicated. This problem is highly illustrative of the basic tenets of modern observational cosmology.

Observation of strong optical absorption at the surface of small particles

Experiments are presented in which strong optical absorption at the surface of small metal particles is been observed. This was accomplished by the following method. Na clusters with rough surfaces were prepared on a transparent substrate. They provide the possibility of localized electronic excitations in the surface region in addition to the well-known plasmon-polaritons in the bulk. The particles were irradiated with pulsed laser light and their temperature rise was derived from measurements of the kinetic energy distribution of thermally desorbed Na dimers. From the temperature increase, the heat generated in the particles during decay of both surface and bulk excitations was calculated and taken as a measure of the total absorption cross-section. Separation of the bulk and surface contributions was achieved by repeating the experiments after removal of the surface roughness by annealing. We find that the surface contributes as much as 32% to the total optical absorption at λ = 532 nm for Na clusters of a mean radius R of 21 mm.

Multinucleon pion absorption on4He into thepppnfinal state

Results from a 4π solid angle measurement of the reaction π+4He→pppn at incident pion energies of Tπ+= 70, 118, 162, 239, and 330 MeV are presented. Integrated cross sections are given for the reactions where three nucleons participate, leading to energetic (ppp) or (ppn) final states, and for states where four nucleons are involved (pppn). The two three-nucleon absorption modes were investigated in particular, and an energy dependent isospin ratio of the cross sections of σppn/σppp=3.6±1.3, 2.6±0.5, 1.8±0.3, 1.4±0.2, and 1.8±0.6 was determined from 70 to 330 MeV. The differential cross sections were described by a complete set of eight independent variables and compared to simple cascade and phase space models. From this analysis the contributions from initial state interactions to the multinucleon absorption cross sections were found to be more important at higher pion energies, while those from final state interactions are stronger at lower energies. However, both mechanisms combined were found to account for not more than one-third of the total pppn multinucleon yield. The remaining strength is reasonably well reproduced by phase space models, but shows a dependence on the incident pion's orbital angular momentum. The isospin structure of the (ppp) and (ppn) final states is not understood, nor are some structures in their distributions. The four-nucleon yield (pppn) was found to be weak (1–8 % of the total absorption cross section) and shows no evidence for a “double-Δ” excitation.Received 18 June 1997DOI:https://doi.org/10.1103/PhysRevC.56.1872©1997 American Physical Society

Pion absorption cross section for2H and3He in theΔ-isobar region: A phenomenological connection

The absorption of ${\ensuremath{\pi}}^{+}$ on ${}^{3}$He in the $\ensuremath{\Delta}$ region is evaluated with exact inclusion of the final state interaction among the three emerging protons. The absorption is described by a $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\Delta}$ vertex and an $N\ensuremath{\Delta}$-$\mathrm{NN}$ transition $t$ matrix which are calculated from a phenomenological model for $\mathrm{NN}$ and $\ensuremath{\pi}d$ reactions. In a calculation where the initial pion scattering effects are neglected, the predicted peaks of the pion absorption cross sections for ${}^{2}$H and ${}^{3}$He lie too high in energy in relation to the data. The effect of the final-state three-nucleon interaction turns out to be too small for changing the magnitude and shifting the peak position of the total absorption cross section for ${}^{3}$He. We demonstrate that the adjustment of the peak position for the deuteron cross section by small modifications of the $\ensuremath{\Delta}$ parameters automatically leads to the correct peak position in ${}^{3}$He.

Xenon poisoning method for the determination of the average thermal neutron flux, macroscopic fission and total absorption cross sections / Die Xenon-Vergiftungsmethode zur Bestimmung des durchschnittlichen thermischen Neutronenflusses, des makroskopischen Spaltungsquerschnittes und des totalen Absorptionsquerschnittes

The paper presents the xenon poisoning method as an experimental way to determine the average thermal neutron flux (Φ), the average macroscopic fission cross section (Σ f ) and the average total macroscopic absorption cross section (Σ a ) together with the reactivity change due to the 135 Xe poisoning. The predictions for the reactivity change due to the 135 Xe poisoning are in good agreement with the results of the experiments. The results of Φ, Σ f and Σ a obtained by using the xenon poisoning method are also in satisfactorily agreement with the predictions of TRIGAP and WIMS-D/4 computer codes. The temperature coefficients of the reactivity for the fuel and tank water have also been determined experimentally during this study.

Measurements of spectral solar UV irradiance in tropical‐Australia

Measurements of global spectral irradiance in the UV and visible range were carried out during December 1995 and January 1996 in Townsville, Australia (19.33°S, 146.76°E, 30 m above sea level (asl)) using the mobile spectroradiometer of the Fraunhofer Institute for Atmospheric Environmental Research, Germany. These are, to our knowledge, the first reported spectral UV measurements in the tropics of Australia. For cloudless days, the spectral measurements are consistent with results of a radiative transfer model. In the UVA, measurement and model agree within ±10% for solar elevations above 10°. In the UVB, the differences are larger (≈15% at 300 nm), which can be explained by uncertainties in the model input parameters of total ozone column and ozone absorption cross section. The variation of the daily erythemal irradiation was found to be ±24% (±1 σ) for the period of the campaign. The variation of the total ozone column contributes less than ±3% to this variability; the main part is introduced by clouds. These attenuate UV irradiation less than total irradiation (300 nm – 3000 nm); the daily total irradiation averaged over the period of the campaign was reduced by a factor of 0.71 owing to cloudiness compared to the clear‐sky case while the erythemal irradiation was only diminished by a factor of 0.78. Using long‐term records of total irradiation and ozone column, the parameters influencing UV radiation on Earth were found to be typical for the period and site of the campaign. The maximum erythemally weighted irradiance measured during the campaign was 429 mW/m2, and the average daily erythemal irradiation for this period was 6.06 kJ/m2. These high radiation levels were found to exceed the corresponding values for Garmisch‐Partenkirchen (47.5°N, 11.0°E, 730 m asl), Germany, by between 55 and 70%. This pronounced difference in the radiation environment between Australia and Germany is explained by the higher solar elevation and the lower ozone column in the tropics.

An investigation of the photodissociation of molecular oxygen in the 75 to 85 nm region

Abstract The cross section for photodissociation of molecular oxygen in the 75 to 85 nm region has been obtained from data for the total absorption and photoionization cross sections. This spectrum, together with published data, has been used to adjust a theoretical model for photodissociation in which three Rydberg states were each coupled to two newly proposed dissociating states. It was found that the observed photodissociation cross sections can be approximated by a model in which there is no direct transition from the ground state to one of the dissociating states. It is proposed that this dissociating state has the symmetry 3Σu+, while the other has either 3Σu− or 3Πu symmetry.

Collision cross-sections for scattering of electrons from NO molecule

Electron-NO scattering is investigated in the energy range 2–1000eV by using a parameter-free spherical complex optical potential (SCOP) approach in the fixed nuclei approximation. The real part of the optical potential consists of three potentials namely, the static, the exchange and the polarization. For the imaginary part of the SCOP, we employ a semi-empirical model absorption potential. The molecular charge density function is calculated from a single-configuration molecular orbital based on Slater type orbitals. The various potential terms are then determined from these charge density functions. Calculations of the elastic (with and without absorption effects), total absorption, momentum transfer and differential cross-sections are obtained and compared with the available theoretical results and experimental measurements.

Application of magnetic circular dichroism to magnetic thin films

The L 2,3 edge magnetic circular dichroism (MCD) spectra of 3d transition metal magnetic thin films and overlayers is used to identify the presence and alignment of the magnetic moment of overlayers on ferromagnetic and non-magnetic substrates. A controversial application of MCD is the determination of the magnitude of magnetic moments and the extraction of orbital and spin contributions to the moment. To study this, we have measured, in transmission, the helicity-dependent, total absorption cross-section at the L 2 and L 3 absorption edge of Fe and Co ultrathin films deposited on 1 μm parylene foil. Using no artificial background subtraction or curve renormalization, we obtain clean spectra for comparison with theoretical methods of the extraction of the orbital and spin contributions to the total moment.

Pygmy dipole resonances in the calcium isotopes.

We present microscopic density functional theory calculations of the total dipole absorption cross sections of the even-A calcium isotopes from $^{40}\mathrm{Ca}$ through $^{48}\mathrm{Ca}$. The results reveal the onset of a collective dipole oscillation occurring at low energy and decoupled from the giant dipole resonance. The radial density fluctuations associated with this low-lying mode have the character of the pygmy dipole resonance predicted to exist in neutron rich nuclei.

Total cross sections for electron scattering by molecules

The additivity rule is employed to calculate the total (elastic and absorption) cross sections for electron scattering by molecules (O 2, N 2, CO and CO 2) over an incident energy range of 10–800 eV. Compared with other calculations and experimental data when available, excellent agreement has been obtained.

Large-solid-angle study of pion absorption on 3He.

Measurements have been made of pi+ absorption on He3 at T_pi+ = 118, 162, and 239 MeV using the Large Acceptance Detector System (LADS). The nearly 4pi solid angle coverage of this detector minimizes uncertainties associated with extrapolations over unmeasured regions of phase space. The total absorption cross section is reported. In addition, the total cross section is divided into components in which only two or all three nucleons play a significant role in the process. These are the first direct measurements of the total and three nucleon absorption cross sections.