Energy-integrated Cross Section Research Articles

Measurement of the spin-wave stiffness and energy gap in the magnon spectrum of amorphous ferromagnets by small-angle scattering of polarized neutrons

This work studies the magnetic excitations of amorphous ferromagnetic alloys (Fe40Ni40P14 11B6 and Fe48Ni34P18) by small-angle polarized neutron scattering in the geometry when the magnetic field is inclined towards the neutron beam direction. Polarized neutrons are used in order to extract the scattering arising from the spin waves only. In this case, the energy-integrated neutron cross section contains a component which depends on neutron polarization and has a left–right asymmetry in the plane determined by the directions of the field and the neutron beam. Small-angle polarized neutron scattering measurements on spin waves in amorphous iron–nickel alloys were performed at different values of the external magnetic field H and neutron wavelength λ. The spin-wave spectrum is quadratic in terms of the momentum transfer and contains both a field gap and an inherent gap Δ of a non-field nature: E q = Aq 2 + gμB H + Δ. Only by measuring simultaneously two dependencies of the cut-off angle θc – on the applied magnetic field and on the neutron wavelength – is it possible to obtain reliable information about the spin-wave stiffness and the spin-wave gap in these amorphous ferromagnetic systems.

Measurement of neutron-production double-differential cross sections of [formula omitted]C, 27Al, [formula omitted]Fe, and [formula omitted]Pb by 20, 34, 48, 63, and 78 MeV protons in the most-forward direction

In this study, the neutron-production double-differential cross sections (DDXs) of natC, 27Al, natFe, and natPb bombarded by 20, 34, 48, 63, and 78 MeV protons were measured in the most-forward direction by the time-of-flight (TOF) method using a liquid organic scintillator. Characteristic peak structures were observed in the measured neutron spectra, especially for light nuclei. The experimental data were compared with the results from the Monte Carlo simulation code “Particle and Heavy Ion Transport code System” (PHITS) using the theoretical model Liège Intranuclear Cascade (INCL) or using the Japanese evaluated nuclear data library (JENDL-4.0/HE). While the results of JENDL-4.0/HE were in agreement with the experimental data better than those of INCL, neither could reproduce the measured peak structures for some combinations of the beam and target. For the energy-integrated cross sections, JENDL-4.0/HE reproduced the experimental data within a factor of two in all cases. On the other hand, INCL gave values up to approximately six times larger than the experimental ones.

Systematic measurement of double-differential neutron production cross sections for deuteron-induced reactions at an incident energy of 102 MeV

Double-differential neutron production cross sections (DDXs) for deuteron-induced reactions on Li, Be, C, Al, Cu, and Nb at 102MeV were measured at forward angles ≤25° by means of a time of flight (TOF) method with NE213 liquid organic scintillators at the Research Center of Nuclear Physics (RCNP), Osaka University. The experimental DDXs and energy-integrated cross sections were compared with TENDL-2015 data and Particle and Heavy Ion Transport code System (PHITS) calculation using a combination of the KUROTAMA model, the Liege Intra-Nuclear Cascade model, and the generalized evaporation model. The PHITS calculation showed better agreement with the experimental results than TENDL-2015 for all target nuclei, although the shape of the broad peak around 50MeV was not satisfactorily reproduced by the PHITS calculation.

Angle-Dependent Double-Differential Neutron Emission Cross Sections of 3H(t,n) between 5.98 and 19.14 MeV and Evidence of 4H as Intermediate Reaction Product

Neutrons for fusion applications stem not only from monoenergetic sources but also from “white” neutron sources. In this regard, the reaction 3H(t,n) is of particular interest. Continuous neutron spectra of the 3H(t,n) reactions were measured at 5.98-, 7.47-, 10.45-, 16.41-, and 19.14-MeV triton energy at typically seven angles between 0 and 145 deg. The spectra at the three lowest energies contain only neutrons from 3H(t,n)5He and 3H(t,2n)4He reactions and therefore can more easily be interpreted than the spectra at 16.41 and 19.14 MeV, which are too complex to allow a straightforward decomposition except for estimation of the neutron emission cross section following the reaction 3H(t,d)4H. Angle-dependent double-differential and neutron energy—integrated cross sections are given at the five energies. In most cases the peak of the two-body ground state transition could be deconvolved reliably resulting in cross sections of the reaction 3H(t,n)5He. Although the basic scale uncertainty is >5%, severe background, in particular, at the higher triton energies, increases the total uncertainty of integrated cross sections up to 9%. Naturally, the uncertainty of each energy bin of the double-differential cross sections, which depend on bin width, is considerably higher. As no previous data are reported at or near these energies, no direct comparison with other data was feasible. Evidence is provided of the formation of the short-lived neutron-rich nuclei 5He and at higher energies of 4H.

Measuring the Neutron Signature of the t→d+n Triton Breakup Reaction and the Angle-Dependent Differential Cross Section of 6Li(n,t)4He at 2.32 MeV

The continuous neutron spectrum from the t→d+n breakup reaction can best be extracted in the 3H(p,n)3He and 4He(t,n)6Li reactions because of minimum neutron background in both cases. Only for the latter reaction are neutron background spectra also available. These data were measured at 11.88-MeV triton energy at eight angles between 0 and 120 deg. As a test for the validity of the procedure, angle-dependent differential cross sections of 4He(t,n)6Li were extracted and converted to 6Li(n,t)4He at En = 2.32 MeV by detailed balance calculation thus contributing to the R-matrix analysis of the 7Li system. The double-differential and neutron energy integrated cross sections at that energy are given as well as those for the triton breakup of the time-reversed reaction.

Cross section measurements at neutron energies 71 and 112 MeV and energy integrated cross section measurements (0.1 < En < 750 MeV) for the neutron induced reactions O(n,x)10Be, Si(n,x)10Be, and Si(n,x)26Al

The cross sections for the reactions O(n,x)10Be, Si(n,x)10Be, and Si(n,x)26Al were measured at neutron energies 71 and 112MeV. The neutron cross sections for O(n,x)10Be are higher than the corresponding proton cross sections at 70–110MeV and the neutron induced cross section for Si(n,x)10Be at 112MeV is slightly higher than the corresponding proton cross section. Cross sections for the production of 26Al from Si are similar to those from protons at low energies (<40MeV) while at higher energies the measured neutron cross sections for Si(n,x)26Al are lower than the corresponding proton cross sections. Energy integrated (average) cross sections for these reactions were measured using ‘white’ neutron beams (0.1<En<750MeV). The 26Al/10Be production rate ratio from SiO2 measured using ‘white’ neutrons is considerably lower than that observed in terrestrial quartz (SiO2).

Many-electron character of Rydberg series converging to the ionization thresholds of the 4p 45s states of KrII

The photoionization cross sections of the 4p shell and the 4s main level and 4p 4(3 P) 5s 4 P 5/2, 3/2 satellite subvalence levels of KrII have been calculated in the 4s-near-threshold range of excitation energies from 28.48 to 28.70 eV. The calculation takes into account the core relaxation by the methods of the theory of non-orthogonal orbitals, the interaction between resonant states through autoionization channels by solving the complex secular equation, and the interaction between the channels of the continuous spectrum in all orders of the perturbation theory by the K-matrix method. Good quantitative agreement between the energy-integrated theoretical and experimental photoionization cross sections for the satellite levels has been obtained for the first time. It is shown that only simultaneous consideration of the above-mentioned effects leads to such agreement. The resonant structure of the photoionization cross sections in this excitation energy range is related to the autoionization decay of the 4p 45s(4 P 1/2)np and 4p 45s(2 P 3/2)np Rydberg series. The specificity of this process is that both series manifest themselves not independently but owing to their strong electrostatic interaction with the prominent 4p 4(1 D)5s 2 D 5/2 6p 3/2 resonance, which lies in this excitation energy range.

Cross section measurements for neutron-induced reactions in Ti, Fe and Ni at several neutron energies ranging from 70.7 to 151.6 MeV

Cross sections for neutron-induced reactions producing relatively short-lived radionuclides were measured in natural targets of Ti, Fe and Ni using quasi-monoenergetic neutron beams at several different neutron energies between 70.7 and 151.6 MeV. Comparisons of these new measurements were made with energy integrated cross section measurements and reported data measured at low neutron energies as well as with MC-ALICE calculations. These cross section measurements are part of a systematic study to measure relevant cross sections needed to better understand cosmic ray interactions with extraterrestrial materials.

Measurements of energy integrated cross sections for reactions producing relatively short-lived radionuclides using neutron beams with an energy range of 0.1–750 MeV

Energy integrated cross sections for neutron-induced reactions producing relatively short lived radionuclides were measured using ‘white’ neutron beams with an energy range of 0.1–750 MeV at the Los Alamos Neutron Science Center (LANSCE). Cross sections for neutron-induced reactions are needed as input to the theoretical models used to understand the production of the radionuclide and stable isotopes produced by cosmic ray interactions with extraterrestrial bodies. Although most primary cosmic rays are protons, significant quantities of short- and long-lived radionuclides and stable isotopes are produced by spallation reactions initiated by secondary neutrons produced in primary cosmic ray interactions. Materials irradiated contained the elements commonly found in lunar rocks and meteorites, including SiO 2 (for O), Si, CaCO 3 (for Ca), Al, Mg, Fe, Ni and KNO 3 (for K).

Experimental and theoretical electron energy spectra due to ionizing collisions of metastable Ar*(3P2), Ar*(3P0) and Kr*(3P0) atoms with ground-state Hg atoms

Using a crossed-beams set-up, we have studied the electron energy spectra due to Penning and associative ionization in thermal energy collisions of state-selected metastable Ar*(4s 3P2, 3P0) and Kr*(5s 3P0) atoms with ground-state Hg atoms at an electron energy resolution of 30 meV. In all three cases the energy spectra exhibit a prominent peak located close to the energy difference between the metastable excitation energies and the Hg ionization energy; they show a sharp drop to lower and an extended tail towards higher electron energy with shapes which differ for the three systems. The energy-integrated ionization cross section for Ar*(3P0) exceeds that for Ar*(3P2) by about 30%. Excitation transfer to autoionizing Hg** states, resulting in a sharp additional structure, is only observed—as a weak channel—in Ar*(3P0) + Hg collisions. For the three investigated systems calculations of the electron energy spectra have been carried out within the local optical potential approximation. As input we use ab initio potential curves for the ionic exit channels as well as for the complex entrance channel potentials. Using these potentials (involving a scaled width for Kr* + Hg), impressive agreement with the experimental electron spectra is observed. In contrast, earlier empirical model potentials for the entrance channel are found to be inadequate. The calculated ionization rate coefficients at T = 300 K amount to (3.72, 5.26) × 10−10 cm3 s−1 for Ar*(3P2, 3P0) + Hg, respectively.

Search for x-ray induced acceleration of the decay of the 31-yr isomer of (178)Hf using synchrotron radiation.

Enhanced decay of the 31-yr isomer of (178)Hf induced by x-ray irradiation has been reported previously. Here we describe an attempt to reproduce this result with an intense "white" x-ray beam from the Advanced Photon Source. No induced decay was observed. The upper limits for the energy-integrated cross sections for such a process, over the range of energies of 20--60 keV x rays, are less than 2 x 10(-27) cm(2) keV, below the previously reported values by more than 5 orders of magnitude; at 8 keV the limit is 5 x 10(-26) cm(2) keV.

Coulomb excitation of double giant dipole resonances

We implement the Brink–Axel hypothesis for the excitation of the double giant dipole resonance (DGDR): the background states which couple to the one-phonon giant dipole resonance are themselves capable of dipole absorption. These states (and the ones which couple to the two-phonon resonance) are described in terms of the gaussian orthogonal ensemble of random matrices. We use second-order time-dependent perturbation theory and calculate analytically the ensemble-averaged cross section for excitation of the DGDR. Numerical calculations illuminate the mechanism and the dependence of the cross section on the various parameters of the theory, and are specifically performed for the reaction 208Pb + 208Pb at a projectile energy of 640 MeV /nucleon. We show that the contribution of the background states to the excitation of the DGDR is significant. We find that the width of the DGDR, the energy-integrated cross section and the ratio of this quantity over the energy-integrated cross section for the single giant dipole resonance, all agree with experiment within experimental errors. We compare our approach with that of Carlson et al. who have used a similar physical picture.

Inclusive proton production cross sections in(d,xp)reactions induced by 100 MeV deuterons

Energy spectra and angular distributions of protons emitted from the inclusive $(d,xp)$ reaction on ${}^{9}\mathrm{Be},$ ${}^{12}\mathrm{C},$ ${}^{27}\mathrm{Al},$ ${}^{58}\mathrm{Ni},$ ${}^{93}\mathrm{Nb},$ ${}^{181}\mathrm{Ta},$ ${}^{208}\mathrm{Pb},$ and ${}^{238}\mathrm{U}$ were measured at an incident deuteron energy of 100 MeV. The protons were detected at laboratory scattering angles of $6\ifmmode^\circ\else\textdegree\fi{}$ to $120\ifmmode^\circ\else\textdegree\fi{}$ and $8\ifmmode^\circ\else\textdegree\fi{}$ to $120\ifmmode^\circ\else\textdegree\fi{}$ for the targets with $9&lt;~A&lt;~27$ and $A&gt;~58,$ respectively. Two triple-element and three double-element detector telescopes allowed for a low energy detection threshold of 4 to 8 MeV. The experimental results are presented in double-differential as well as angle- and energy-integrated cross sections. For all the nuclei studied, the energy spectra at forward angles show pronounced deuteron breakup peaks centered around approximately half of the incident deuteron energy. Qualitatively the energy spectra are similar for all nuclei at a given angle except in the region of the low-energy evaporation peak. As a function of target mass the evaporation cross sections are found to increase up to $A=58$ after which they decrease again. The total preequilibrium proton cross section is roughly $(280\ifmmode\pm\else\textpm\fi{}{60)A}^{1/3} \mathrm{mb}.$ The angular distributions at the high emission energies are strongly forward peaked while the distributions of the low-energy protons are almost isotropic. The LAHET code system (LCS) was applied to calculate the proton production cross sections. Standard LCS calculations are found to underpredict the experimental cross sections at the very forward angles on the heavy target nuclei $(A\ensuremath{\gtrsim}58).$ By adding incoherently the Coulomb breakup cross section of the deuteron to the LCS calculations the experimental cross sections are reproduced to within 10%. Although preequilibrium processes are a necessary ingredient in the LCS calculations of the large-angle cross sections, this code still fails to predict the experimental evaporation distributions.

Photodisintegration of9Bewith laser-induced Compton backscatteredγrays

Photoneutron cross sections were measured for ${}^{9}\mathrm{Be}$ in the energy range from 1.78 to 6.11 MeV with laser-induced Compton backscattered $\ensuremath{\gamma}$ rays. Resonance parameters $[{E}_{R},B(E1),{\ensuremath{\Gamma}}_{n}]$ for the ${1/2}^{+}$ and ${5/2}^{+}$ states were deduced from the least-squares fit to the data, while ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ for the ${5/2}^{\ensuremath{-}}$ state was deduced from the energy-integrated cross section. The reaction rate $〈\ensuremath{\alpha}\ensuremath{\alpha}n〉$ is discussed.

Theoretical investigation of the autoionization process in molecular collision complexes: He*(2 3S)+Li(2 2S)→He+Li++e−

A complete ab initio treatment is applied to the autoionization process in the He*(2s 3S)+Li(2s 2S) collisional complex. Feshbach projection based on orbital occupancy, implemented in a multireference configuration interaction (MRCI) code, defines the resonance state and provides the entrance channel potential curve as well as all pertinent information on the resonance–continuum coupling. The l-dependent coupling elements in local approximation are obtained by projecting a compact one-electron function, named Penning molecular orbital (PMO), onto the wave function of the ejected electron with proper energy. The continuum wave function is obtained by coupled channel calculations in the static-exchange approximation. A converged set of seven complex coupling matrix elements, used in the nuclear dynamics calculation based on a complex Numerov algorithm, fully describes the electron angular momentum transfer. The calculated angle-dependent spectra, as well as the total, angle-, and energy-integrated ionization cross sections agree well with available experimental data.

Strong absorption radii from reaction cross section measurements for neutron-rich nuclei

Energy-integrated reaction cross sections have been measured at energies ranging from 38 to 80 MeV/nucleon for various exotic neutron-rich isotopes of Al, Si, P, S, Cl, Ar, K, Ca, Sc, and Ti stopping in Si. An experimental technique is employed where Si detectors are used for both particle identification and to serve as the target material. The reduced strong absorption radii r[sub 0][sup 2] are deduced and compared with other experimental results. The radius dependence on the neutron number was studied and a trend of increasing reduced radius with neutron excess was found. This behavior is similar to that seen in lighter systems, although less pronounced than found there. The implications of this result on the conjectured existence of neutron halo or skin nuclei is discussed. [copyright] [ital 1999] [ital The American Physical Society]

Calculation of dielectronic recombination cross sections and rate coefficients for heliumlike carbon

A simplified relativistic configuration interaction method is used to calculate the dielectronic recombination cross sections and rate coefficients for heliumlike carbon. In this method, the infinite resonant doubly excited states can be treated conveniently in the frame of Quantum Defect Theory. Our calculated cross sections are in agreements with the experimental measurements except for the 1s2lnl'(n=6,7) resonances. The total energy-integrated cross sections and rate coefficients over all dielectronic resonances are in agreements with the experimental measurements within percent.

The NN → NNη reaction close to threshold

The pp → ppη and np → npη reactions at energies near the η production threshold are studied in a non-relativistic one boson exchange model, where the N∗ (1535 MeV) S11 resonance is excited through the exchange of π, η, ϱ and ω mesons and subsequently decays into an ηN pair. Energy integrated cross sections and energy spectra of the out going η's are reported. Providing NN and ηN final state interactions are taken into account coherently, the model reproduces both the scale and energy dependence of the cross section for the pp → ppη reactions up to 100 MeV. Final state interaction corrections due to the nucleon-nucleon and meson-nucleon forces influence strongly the scale and shape of the cross sections. The shape of the energy spectra of the outgoing η's provides a clear signature of the ηN force.

High-resolution measurement of the dielectronic recombination of fluorinelike selenium ions.

We have measured the dielectronic recombination cross section of Se{sup 25+} ions at center-of-mass energies from 1 to 1800 eV using merged electron and ion beams in the Heidelberg heavy-ion Test Storage Ring (TSR). All dielectronic resonances involving changes of {Delta}{ital N}=0 and {Delta}{ital N}=1 of the core principal quantum number {ital N} are covered with high-energy resolution (ranging from {lt}0.6 eV at {lt}90 eV to {approx_equal}6 eV at 1600 eV). A strong contribution of {Delta}{ital N}=1 Rydberg resonances at 1200{endash}1700 eV is observed. The results are compared with isolated-resonance intermediate-coupling calculations of the cross section. Good agreement is found for the {Delta}{ital N}=0 and the low-lying {Delta}{ital N}=1 resonances. For the {Delta}{ital N}=1 Rydberg series the resonant pattern continues to be well reproduced by theory, whereas the total energy-integrated cross section significantly exceeds the theoretical prediction. From experimental and theoretical results rate coefficients for isotropic plasma temperatures between 100 and 2000 eV are also derived. {copyright} {ital 1996 The American Physical Society.}

Cross sections and asymmetries for the [formula omitted] reaction from threshold to 1 GeV

Total cross sections, differential cross sections and asymmetries for the reaction p( p,π 0)pp from threshold to 1 GeV have been measured. The outgoing π 0 was detected by a 4π neutral meson spectrometer. Our data are compared with the corresponding np→NN π ± reactions. The isoscalar partial cross sections are extracted from the relevant total cross sections. They are significant throughout the whole energy range. Below the Δ-region, energy-integrated differential cross sections show a large anisotropy difference between the neutral and charged pion channels, respectively. A partial-wave fit shows that the initial T = 0 state is dominated by the 3D 1 wave in this energy region. Finally, predictions of phenomenological models give reasonable good account of the measured observables but cannot reproduce the sign of the asymmetries.