Sum Of Cross Sections Research Articles

Osteological and vascular morphology and electrolyte homeostasis of sea turtles.

Sea turtles have well developed lacrimal glands for their electrolyte homeostasis. In turtles, stapedial artery and palatine artery send branches to supply orbital region, but supply artery for lacrimal glands was not identified. Micro-CT scans showed dorsoventrally large lacrimal glands of sea turtle are supplied by both stapedial artery and palatine artery. The circulatory pattern in cranial region was reconstructed based on the micro-CT scans, showing that sea turtle has basically similar pattern with the common snapping turtle: stapedial artery supplies orbital region and mandibular artery is ramified from stapedial artery. We also investigate the foramen stapedio-temporalis in turtles using osteological specimens. The foramen stapedio-temporalis, where the stapedial artery passes through, has different size among four families of turtles. We compared the sum of cross sections of left and right foramen stapedio-temporalis since homeostasis of one individual is maintained by a pair of lacrimal glands. The size difference may reflect primarily the share of stapedial artery against palatine artery in cranial circulation pattern and blood supply of orbital regions. Our observations confirmed a significantly larger cross-section in the foramen stapedio-temporalis of sea turtles than other freshwater/terrestrial turtles. Since the circulatory pattern is shared, the size difference of foramen stapedio-temporalis reflects the amount of arterial blood supply to lacrimal glands. Therefore, the size of the foramen stapedio-temporalis may indicate marine adaptation of turtles and are applicable to both fossil and osteological specimens.

Nuclear data for reactor production of 131Ba and 133Ba

The newest radioisotope for brachytherapy treatment of prostate cancer is 131Cs (t1/2 = 9.69 d, 100% EC). Generated via electron capture decay of 131Ba (t1/2 = 11.6 d, 100% EC), 131Cs has been used in brachytherapy for prostate cancer since 2004. The 131Ba parent is produced through neutron capture of enriched 130Ba in a nuclear reactor. For large-scale production of 131Ba, an accurate knowledge of production and burnup cross sections of 131Ba are essential. In this paper, we report two group cross sections (thermal and resonance integrals) for 130Ba and 131Ba and a new measure of the half-life of 131Ba. Targets consisting of milligram quantities of enriched 130Ba (∼35%) were irradiated in Oak Ridge National Laboratory's High Flux Isotope Reactor at thermal and resonance neutron fluxes of (1.9–2.1) × 1015 and (5.8–7.0) × 1013 neutrons·cm−2 s−1, respectively, for durations ranging from 3 to 26 days. In addition, cadmium covered samples of 130Ba were irradiated for 1 hour at 12.6% full reactor power (10.7 MW). The yield of 131Ba approaches a saturation value of ∼60 GBq (∼1.6 Ci) per mg of 130Ba for 20 days irradiation at a thermal neutron flux of 1.8 × 1015 n·s−1·cm−2, with a thermal/epithermal ratio of ∼30. Under the above experimental conditions, the two group cross sections of 130Ba are 6.9 ± 0.5 b (thermal, σ0) and 173 ± 7 b (resonance, I0). These values represent the sum of cross sections to metastable and ground states of 131Ba. For 131Ba, the empirically measured thermal cross section is 200 ± 50 b assuming an I0/σ0 of 10. This cross section is reported for the first time. Further, the half-life of 131Ba was remeasured to be 11.657 ± 0.008 d. Lastly, this study also resulted in the co-production of 133Ba (t1/2 = 10.52 y, 100% EC). The experimental yield of 133Ba is ∼370 MBq (∼10 mCi) per mg of 132Ba (thin target) for one cycle irradiation in the High Flux Isotope Reactor, and measured two-group 132Ba cross sections are 7.2 ± 0.2 b and 39.9 ± 1.3 b. These values also represent the sum of cross sections to metastable and ground states of 133Ba.

Recent results from COMPASS on the GPD program

The dedicated COMPASS GPD program started in 2012 with a short pilot ’DVCS run’ and the first results from this run on DVCS, exclusive π0 and exclusive ω channels have been obtained. From the sum of cross sections measured with positive and negative beam polarities the DVCS cross-section and its dependence on the squared four-momentum transfer t have been extracted. It allowed a first estimate of the transverse size of the partonic distribution of the nucleon √〈r2⊥〉 i in a range of intermediate xBj with a mean xBj value of 0.056. We report also on the absolute value of the cross section for exclusive π0 production and its dependence on t and azimuthal angle ϕ between the scattering plane and π0 production plane. These measurements are aiming to constrain the GPDs, in particular chiral-odd (transversity) GPDs. Further, we present results on the spin density matrix elements for exclusive ω meson production and discuss the contributions from unnaturaly parity exchanges and from transitions that do not conserve helicity.

COMPASS results on DVCS and exclusive π0 production

The high energy polarised muon beam available at CERN, with positive or negative charge, makes COMPASS a unique place for studies of General Parton Distributions (GPDs). The dedicated COMPASS GPD program started in 2012 with commissioning of a new long liquid hydrogen target and new detectors, such as the large recoil particle detector CAMERA and the large-angle electromagnetic calorimeter. It was followed by a short pilot ‘DVCS run’. The first results on DVCS and exclusive π0 channels have been obtained. From the sum of cross sections measured with positive and negative beam polarities the pure DVCS cross-section and its dependence on the squared four-momentum transfer t have been extracted. It allowed a first estimate of the transverse size of the partonic distribution of the nucleon in a range of intermediate xBj with a mean xBj value of 0.056. We report also on the absolute value of the cross section for exclusive π0 production and its dependence on t and azimuthal angle ϕ between the scattering plane and π0 production plane. These measurements are aiming to constrain the GPDs, in particular chiral-odd (transversity) GPDs. The full data taking for the GPD program approved within the COMPASS-II proposal continues in 2016 and 2017.

α scattering and α -induced reaction cross sections of Zn64 at low energies

Background: alpha-nucleus potentials play an essential role for the calculation of alpha-induced reaction cross sections at low energies in the statistical model... Purpose: The present work studies the total reaction cross section sigma_reac of alpha-induced reactions at low energies which can be determined from the elastic scattering angular distribution or from the sum over the cross sections of all open non-elastic channels. Method: Elastic and inelastic 64Zn(a,a)64Zn angular distributions were measured at two energies around the Coulomb barrier at 12.1 MeV and 16.1 MeV. Reaction cross sections of the (a,g), (a,n), and (a,p) reactions were measured at the same energies using the activation technique. The contributions of missing non-elastic channels were estimated from statistical model calculations. Results: The total reaction cross sections from elastic scattering and from the sum of the cross sections over all open non-elastic channels agree well within the uncertainties. This finding confirms the consistency of the experimental data. At the higher energy of 16.1 MeV, the predicted significant contribution of compound-inelastic scattering to the total reaction cross section is confirmed experimentally. As a by-product it is found that most recent global alpha-nucleus potentials are able to describe the reaction cross sections for 64Zn around the Coulomb barrier. Conclusions: Total reaction cross sections of alpha-induced reactions can be well determined from elastic scattering angular distributions. The present study proves experimentally that the total cross section from elastic scattering is identical to the sum of non-elastic reaction cross sections. Thus, the statistical model can reliably be used to distribute the total reaction cross section among the different open channels.

Photoionization and photofragmentation of theC60+molecular ion

Cross-section measurements are reported for single and double photoionization of ${\mathrm{C}}_{60}^{+}$ ions in the photon energy range 18--150 eV accompanied by the loss of zero to seven pairs of carbon atoms, as well as for fragmentation without ionization resulting in loss of two to eight pairs of C atoms in the photon energy range 18--65 eV. Absolute measurements were performed by merging a beam of ${\mathrm{C}}_{60}^{+}$ molecular ions with a beam of monochromatized synchrotron radiation. Product channels involving dissociation yielding smaller fullerene fragment ions account for nearly half of the total measured oscillator strength in this energy range. The sum of cross sections for the measured product channels is compared to a published calculation of the total photoabsorption cross section of neutral ${\mathrm{C}}_{60}$ based on time-dependent density-functional theory. This comparison and an accounting of oscillator strengths indicate that with the exception of ${\mathrm{C}}_{58}^{+}$, the most important product channels resulting from photoabsorption were accounted for in the experiment. Threshold energies for the successive removal of carbon atom pairs accompanying photoionization are also determined from the measurements.

Skyrme forces and the fusion-fission dynamics of the132Sn+64Ni→196Pt*reaction

The dependence of the fusion-fission process on Skyrme forces is studied by using the dynamical cluster-decay model (DCM) and the $\ensuremath{\ell}$-summed extended-Wong model in the ${}^{132}\mathrm{Sn}+{}^{64}\mathrm{Ni}\ensuremath{\rightarrow}{{}^{196}\mathrm{Pt}}^{*}$ reaction, where the nuclear proximity potential is obtained by using the semiclassical extended Thomas-Fermi (ETF) approach in the Skyrme energy density formalism (SEDF) under the frozen density approximation. The DCM gives an excellent fit to the measured fusion evaporation residue (ER) and the fission cross sections below and above barrier energies, with ER data needing ``barrier lowering'' at below-barrier energies for each Skyrme force (an in-built property of the DCM). The fission cross sections show a contribution of quasifission (qf) at the above-barrier two or three highest energies, depending on the Skyrme force. Calculations are illustrated for three Skyrme forces, GSkI, SSk, and SIII. Another interesting result is that there is a change of fission mass distribution from a predominantly asymmetric one to a symmetric one with a decrease in the $N/Z$ ratio of the compound nucleus, independent of the choice of nuclear interaction potential, which gives an opportunity to address the isospin effects in the Pt${}^{*}$ nucleus. Within the $\ensuremath{\ell}$-summed extended-Wong model we find that the GSkI and SSk forces fit the total fusion cross-section data exactly, whereas the SIII force needs ``barrier modification'' in order to fit the data at below-barrier energies. This happens because the isospin and neutron-proton asymmetry nature of GSkI and SSk forces is different from that of the SIII force, and because the center-of-mass energy ${E}_{\mathrm{c}.\mathrm{m}.}$ dependence of the barrier height for the SIII force and that of Blocki et al. [Ann. Phys. (NY) 105, 427 (1977)] differs strongly (by a constant amount of $\ensuremath{\sim}$7 MeV) from those for GSKI and SSk forces. Note that, because of the associated preformation factor with each fragment, the DCM has the advantage of treating various decay processes separately, whereas the Wong model describes only the total fusion cross section, a sum of cross sections due to all contributing processes.

Coupled channels optical theorem and non-elastic cross section sum rule

Within a coupled channels framework a theorem, similar to the optical theorem, is proved which provides a new formula for total non-elastic (inelastic, rearrangement and absorption) cross sections. An approximate cross section energy sum rule is also developed in terms of the trace of the imaginary part of an energy independent, but non-local optical potential. Corrections to sum rule are found small indicating that the result is a good approximation. The theorem and sum rule are applied to the Lane model describing charge exchange reactions.

Observations of Separator Reconnection to an Emerging Active Region

Extreme-ultraviolet (EUV) observations of an emerging active region are used to study separator reconnection in the corona. We identify each EUV loop connecting the emerging polarity to a nearby existing active region over the 41 hr period beginning at emergence onset. Their geometrical resemblance to post-reconnection field lines from a magnetic model of the active region pair implicates separator reconnection in their production. While some reconnection is evident within 7 hr of emergence onset, the most intense period occurs after a 1 day delay. The sum of cross sections of all observed loops accounts for only one-fifth of the transferred magnetic flux predicted by the model. We suggest that the remaining loops remain at temperatures too high, or at densities too low, to be detected in our EUV data. The most intense reconnection requires as much as 109 V along the coronal separator; however, the observed loops suggests that the flux is transferred as discrete bundles of ~4 × 1018 Mx each. The reconnection appears to directly dissipate only a small fraction of the energy released, while the rest is dissipated within the post-reconnection flux over the ensuing 6 or more hours the loops remain visible. The net energy released, and ultimately dissipated, is consistent with the amount that could be stored magnetically during the 24 hr delay between emergence and reconnection.

Harmonic two-photon intensity sum rule for benzene b 2u modes

A harmonic two-photon cross section sum rule for benzene b 2u modes (ν 14 and ν 15) in the à 1B 2u←X̃ 1A 1g transition is derived. An approximate (but accurate) form of this rule based on skeletal mode displacements is used to obtain absorptivity values for C 6H 6 14 1 0 (6.3×10 −50 cm 4 s mol −1 photon −1) and 15 1 0 (1.6×10 −50 cm 4 s mol −1 photon −1) from the measured absorptivity ratio, δ ↑↑(15)/δ ↑↑(14) and from the measured value of 14 0 1. We also report the sum-rule-predicted hot and cold band absolute absorptivities in the other D 6h benzenes, C 6D 6, 13C 6H 6 and 13C 6D 6.

Knockout and knockout-fusion contributions to the (p,p')-type singles cross sections.

The (p,p')-type singles cross sections are calculated. The knockout of the target nucleons, reabsorption of the knocked-out particle, and particle-hole excitations into bound orbits are taken into account. The sum of cross sections for these three excitation modes is shown to describe nicely the observed continuum cross section data for the /sup 54/Fe(p,p') and /sup 27/Al(p,p') reactions at 62 MeV.

Differential scattering cross sections for collisions of 0.5−, 1.5−, and 5.0‐keV helium atoms with He, H2, N2, and O2

This paper reports the first results of an experimental program established to provide cross section data for use in modeling various atmospheric processes. Absolute cross sections, differential in the scattering angle, have been measured for collisions of 0.5−, 1.5−, and 5.0‐keV helium atoms with He, H2, N2, and O2 at laboratory scattering angles between 0.1° and 5°. The results are the sums of cross sections for elastic and inelastic scattering of helium atoms; charged collision products are not detected. Integration of the differential cross section data yields integral cross sections consistent with measurements by other workers. The apparatus employs a position‐sensitive detector for both primary and scattered particles and uses a short target cell with a large exit aperture to ensure a simple and well‐defined apparatus geometry.

Direct ionization and electron capture inM-shell x-ray production by fluorine ions

Measurements of $M$-shell x-ray production cross sections are reported for thin solid targets of $_{79}\mathrm{Au}$, $_{83}\mathrm{Bi}$, and $_{92}\mathrm{U}$. Fluorine ions of energies 25, 27, and 35 MeV and charge states of 4, 5, 6, 8, and 9 were used. The microscopic cross sections were determined from measurements made with targets ranging in thickness from \ensuremath{\sim}1 to \ensuremath{\sim}300 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$. An enhancement in the target $M$-shell x-ray production cross section was observed for fluorine ions with one or two $K$-shell vacancies over those without a $K$-shell vacancy. The sums of cross sections for direct ionization to the target continuum and electron capture to the projectile's $L,M,N,\dots{}$ shells are inferred from charge state $q=4,5,6$ data. The first Born calculations overpredict the cross-section data at all energies. Cross sections for electron capture from the target $M$ shell to the projectile $K$ shell for one ($q=8$) and two ($q=9$) $K$-shell vacancies in the projectile are also overpredicted by the first Born approximation for electron capture, i.e., the Oppenheimer-Brinkman-Kramers approximation of Nikolaev. The data are in good agreement with the ECPSSR theory of Brandt and Lapicki, which accounts for the energy-loss, Coulomb-deflection, and relativistic effects in the perturbed-stationary-state theory.

Cross sections for inelastic electron-ion scattering in weak-coupling approximations

Coulomb-Born and distorted-wave theories for electron-ion scattering are described and applied to several transitions in H-, He-, Li-, and Be-like isoelectric ions. A number of options are available in these theories and the numerical data plus theoretical arguments are used to define the most accurate alternative. The most complex of these weak-coupling approaches (DWXII) which is a distorted-wave theory that includes initial- and final-state distorting potentials, local-exchange approximations to the exchange terms appearing in the distorting potentials, the retention of the full distorting potential in the $S$-matrix element one-electron exchange terms, and $S$-matrix elements transformed to guarantee a unitary $S$ matrix, is recommended as a survey tool with the potential for reasonable accuracy. Supporting evidence becomes stronger for increasing charge on the ion. The sum of cross sections for the excitation of nearly degenerate or strongly coupled states remains reliable for examples that exhibit the expected weak-coupling inaccuracies in predicting the individual contributions. The long-recognized requirement of using accurate target wave functions, including configuration interaction, is reemphasized.

Production of fast highly excited atoms in proton collisions with atomic hydrogen and argon

The study of keV ${\mathrm{H}}^{+}\ensuremath{-}\mathrm{H}(1s)$ collisions has been extended to the production by electron transfer of highly excited states with principal quantum numbers between 13 and 28. A fast-proton beam was passed through thermally dissociated hydrogen gas, and the resultant fast excited atoms were observed using electric field ionization and proton-counting techniques. The incident proton energy range was from 7 to 60 keV. The observed cross section for production of such excited states possesses a broad maximum near 30 keV. The sum of cross sections over the observed principal quantum numbers is 0.00089 ${\mathrm{\AA{}}}^{2}$ at 7 keV, 0.0070 ${\mathrm{\AA{}}}^{2}$ at 30 keV, and drops again with energy to 0.0023 ${\mathrm{\AA{}}}^{2}$ at 60 keV. Possible error in our cross section scale is \ifmmode\pm\else\textpm\fi{} 30%. Thus the fraction of electron-transfer collisions producing these highly excited states varies from a maximum value of about 0.03% in the range 30-60 keV to the lower value of 0.01% at 7 keV, values not markedly different from those found for inert-gas target atoms; this is contrary to the predictions of the Brinkman-Kramers-Oppenheimer approximation. The data at 60 keV agree with recent calculations by Band using the coupled Born approximation. The present results for ${\mathrm{H}}^{+}$-Ar collisions and $13\ensuremath{\le}n\ensuremath{\le}28$ are in agreement with previous investigations for $9\ensuremath{\le}n\ensuremath{\le}15$, assuming that the Jackson-Schiff scaling rule is valid for this collision system.

TRANSFER OF EIGHT NUCLEONS ON SOME LIGHT NUCLEI

TRANSFER OF EIGHT NUCLEONS ON SOME LIGHT NUCLEI

Test of cross section sum rules for nucleon magnetic moments

Considering forward Compton scattering by nucleons and deuterons and approximating the deuteron by free nucleons above the pion production threshold the three cross section sum rules for the nucleon and deuteron magnetic moments are combined to a relation containing only known constants and a low-energy integral which agrees with the predicted value. The result concerning the validity of the sum rules supports other tests by Gerasimov [4], Drell and Hearn [6] and Pagels [2] based on pion photoproduction data below 1 GeV.

Cross-section sum rules in the static model

On the basis of the unitary sum rules and of the self-consistency condition for the coupling constant ratios of the static model, the cross section sum rules are reduced to the eigenvector problem. It is shown that the meson-baryon scattering is allowed only in those partial waves in which there is a bound state or a resonance. The pion-nucleon scattering is considered in some detail, and the results obtained for it are compared with experiment.

Ionization of lithium by electrons

The cross section for the ionization of lithium by electron impact is calculated using Born's approximation. The total cross section is expressed in terms of the sum of cross sections for each partial wave of the ejected electron, and calculations are made using Hartree-Fock wave functions for the bound states and both Hartree-Fock continuum functions and undistorted Coulomb functions for the ejected electron. The total cross section agrees well with the classical Gryzinski and Thompson cross sections for incident electron energies greater than 54 ev.

Interactions of Cadmium-106 with Alpha Particles

The excitation functions of the ($\ensuremath{\alpha}, \ensuremath{\gamma}$), ($\ensuremath{\alpha}, n$), ($\ensuremath{\alpha}, p$), ($\ensuremath{\alpha}, 2n$), ($\ensuremath{\alpha}, \mathrm{pn}$), $(\ensuremath{\alpha}, 3n)+(\ensuremath{\alpha}, p2n)$, ($\ensuremath{\alpha}, \ensuremath{\alpha}n$), and ($\ensuremath{\alpha}, 2\ensuremath{\alpha}n$) reactions of reactions of ${\mathrm{Cd}}^{106}$ have been determined with alpha particles of 6-39-MeV kinetic energy. Reactions involving charged-particle emission compete quite favorably with those involving neutron emission only; the large Coulomb barrier for charged-particle emission is partially offset by the relatively low separation energies for these charged particles, as compared to those for neutrons. Thus, some of the peak cross sections (and corresponding alpha-particle energies) are: ($\ensuremath{\alpha}, n$), 626 mb (19 MeV); ($\ensuremath{\alpha}, p$), 243 mb (22 MeV); ($\ensuremath{\alpha}, 2n$), 427 mb (32 MeV); ($\ensuremath{\alpha}, \mathrm{pn}$), 230 mb (35 MeV); and ($\ensuremath{\alpha}, \ensuremath{\alpha}n$), 205 mb (37 MeV). Comparison of these data with the previously determined excitation functions for ${\mathrm{Sn}}^{124}$ clearly demonstrates that the reactions leading to charged-particle emission in neutron-deficient ${\mathrm{Cd}}^{106}$ are much probable than are the analogous reactions on neutron-excess ${\mathrm{Sn}}^{124}$. The ratio of the sum of cross sections involving the emission of at least one charged particle to the sum of cross sections for the emission only of neutrons is more than an order of magnitude greater for ${\mathrm{Cd}}^{106}$ than for ${\mathrm{Sn}}^{124}$. This behavior may be reproduced with the statistical theory of nuclear reactions, by using ${r}_{o}=1.7$ F for the radius parameter and $a=1.8/\mathrm{MeV}$ for the level-density parameter. Detailed comparison of the data with compound nucleus theory shows good agreement for the ($\ensuremath{\alpha}, n$), ($\ensuremath{\alpha}, p$), and ($\ensuremath{\alpha}, \ensuremath{\alpha}n$) excitation functions. A brief discussion of the principles of $4\ensuremath{\pi}$ scintillation counting is also presented.