Laboratory Angles Research Articles

Measurement of (d,p) and (d,α) differential cross-sections for 14N

The differential cross-sections for 14N(d,p0)15N, 14N(d,p1+2)15N, 14N(d,α0)12C and 14N(d,α1)12C have been measured in the energy range from 0.7 to 2.2MeV at the laboratory angle of 150°. The obtained results are compared with data published in the literature. Discrepancies between new and previously acquired data are discussed. The cross-sections measured in the present work were uploaded to the IBANDL data base <http://www-nds.iaea.org/ibandl/>.

Cross-section for proton–tritium scattering from 1.4 to 3.4 MeV at the laboratory angle of 165°

The elastic scattering cross-section for proton scattering from tritium was measured at a laboratory angle of 165° and over an incident proton energy range from 1.4 to 3.4MeV. A thin solid target containing 1.62×1017Tatoms/cm2 was prepared by absorption of tritium into a film of titanium on aluminium foil backing. The cross-section increases almost linearly with decreasing energy in the higher energy region of 2–3.4MeV. The currently measured cross-section data are compared with data available in the literature values and they show a similarly linear trend in a similar higher energy range. The maximum difference in the cross-section at almost the same scattering angle between current data and the previous results is no worse than 2.3%.

Secondary Neutron-Production Cross Sections from Heavy-Ion Interactions between 230 and 600 MeV/Nucleon

Secondary neutron-production cross sections have been measured from interactions of 230 MeV/nucleon He, 400 MeV/nucleon N, 400 MeV/nucleon Kr, 400 MeV/nucleon Xe, 500 MeV/nucleon Fe, and 600 MeV/nucleon Ne interacting in a variety of elemental and composite targets. We report the double-differential production cross sections, angular distributions, energy spectra, and total cross sections from all systems. Neutron energies were measured using the time-of-flight technique and were measured at laboratory angles between 5 and 80 deg. The spectra exhibit behavior previously reported in other heavy-ion-induced neutron-production experiments, namely, a peak at forward angles near the energy corresponding to the beam velocity, with the remaining spectra generated by preequilibrium and equilibrium processes. The double-differential spectra are fitted with a moving-source parameterization. Observations on the dependence of the total cross sections on target and projectile mass are discussed.

Reaction mechanisms inO16+Ca40at an incident energy ofE(O16)=86MeV through inclusive measurements of α and proton spectra

The {alpha} and proton spectra from the {sup 16}O+{sup 40}Ca reaction is measured at E({sup 16}O) =86 MeV at several laboratory angles between 54 deg. and 138 deg. Analysis in terms of the statistical model for compound nuclear reactions show that an event-by-event calculation of the evaporation spectra removes discrepancy observed with standard calculations.

Microscopic interpretation of the (t, 3He) reaction at 130 MeV on 90Zr and isovector monopole strength

The 130-MeV primary tritium beam of the AGOR facility with an intensity of up to 108 pps and the Big Bite Spectrometer experimental setup have been used to study the (t, 3He) reaction between 0° and 5° lab angles on 12C and 90Zr targets. The standard ray-tracing procedure has allowed us to obtain excitation-energy spectra up to 30 MeV in six angular bins for each residual nucleus, with an average energy resolution of 350 keV. We have used the DWBA reaction mechanism model to reproduce those spectra and their angular distributions. In this approximation, the form factor was treated as a folding of an effective projectile-nucleon interaction with a transition density. The effective projectile-nucleon interaction has been adjusted to reproduce the 0° cross section of the 1+ ground state of 12B populated in the 12C(t, 3He) reaction. We have employed RPA wave functions of excited states to construct the form factors. This DWBA+RPA analysis is used to compare calculated and experimental cross sections directly and to discuss the giant resonance excitations in the 90Y nucleus. In this talk, we give some details on this analysis. We show that there are important contributions of L = 2 transitions in the observed cross sections for the 1+ final states that explain the previous difficulties in clearly identifying the monopole strength distributions. We then have a better indication of where the L = 0 part is located with this reaction and its microscopic analysis.

Light charged-particle production in 96 MeV neutron-induced reactions on carbon and oxygen

In recent years, an increasing number of applications involving fast neutrons have been developed or are under consideration, e.g. radiation treatment of cancer, neutron dosimetry at commercial aircraft altitudes, soft-error effects in computer memories, accelerator-driven transmutation of nuclear waste and energy production and determination of the response of neutron detectors. Data on light-ion production in light nuclei such as carbon, nitrogen and oxygen are particularly important in calculations of dose distributions in human tissue for radiation therapy at neutron beams, and for dosimetry of high-energy neutrons produced by high-energy cosmic radiation interacting with nuclei (nitrogen and oxygen) in the atmosphere. When studying neutron dose effects, it is especially important to consider carbon and oxygen, since they are, by weight, the most abundant elements in human tissue. Preliminary experimental double-differential cross sections of inclusive light-ion (p, d, t, (3)He and alpha) production in carbon induced by 96-MeV neutrons have been presented. Energy spectra were measured at eight laboratory angles: 20, 40, 60, 80, 100, 120, 140 and 160 degrees. Measurements were performed at The Svedberg Laboratory (TSL), Uppsala, using the dedicated MEDLEY experimental setup. The authors have earlier reported experimental double-differential cross sections of inclusive light-ion production in oxygen. In this paper, the deduced kerma coefficients for oxygen has been presented and compared with reaction model calculations.

Measurements of partial cross sections and photoelectron angular distributions for the photodetachment ofFe−andCu−at visible photon wavelengths

Photodetachment cross sections and the angular distributions of photoelectrons produced by the single-photon detachment of the transition metal negative ions ${\mathrm{Fe}}^{\ensuremath{-}}$ and ${\mathrm{Cu}}^{\ensuremath{-}}$ have been measured at four discrete photon wavelengths ranging from 457.9 to $647.1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ $(2.71--1.92\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ using a crossed-beams laser photodetachment electron spectrometry (LPES) apparatus. Photodetachment cross sections were determined by comparing the photoelectron yields from the photodetachment of ${\mathrm{Fe}}^{\ensuremath{-}}$ to those of ${\mathrm{Cu}}^{\ensuremath{-}}$ and ${\mathrm{C}}^{\ensuremath{-}}$, which have known absolute photodetachment cross sections. Using the measured photodetachment cross sections, radiative electron attachment cross sections were calculated using the principle of detailed balance. Angular distributions were determined by measurements of laboratory frame, angle-, and energy-resolved photoelectrons as a function of the angle between the linear laser polarization vector and the momentum vector of the collected photoelectrons. Values of the asymmetry parameter have been determined by nonlinear least-squares fits to these angular distributions. The measured asymmetry parameters are compared to predictions of photodetachment models including Cooper and Zare's dipole approximation theory [J. Cooper and R. N. Zare, J. Chem. Phys. 48, 942 (1968)], and the angular momentum transfer theory developed by Fano and Dill [Phys. Rev. A 6, 185 (1972)].

Evidence of Simultaneous Double-Electron Promotion inF+Collisions with Surfaces

A high-flux beam of mass-filtered F+ at low energy (100-1300 eV) was scattered off Al and Si surfaces to study core-level excitations of F0 and F+. Elastic scattering behavior for F+ was observed at energies <300 (500) eV off Al (Si) for a 90 degrees lab angle. However, above this energy threshold, orbital mixing in the hard collision step results in electronic excitation of F via molecular orbital promotion along the 4f sigma (F-2p), significantly reducing the observed ion exit energy. In addition, despite the electronegativity of F, scattering at energies >450 (700) eV off Al (Si) produces F2+-behavior which is remarkably similar to Ne+ off the same surfaces. Inelasticities measured for single collision events agree well with the energy deficits required to form (doubly excited) F** and F+** states from F0 and F+, respectively; these excited species most likely decay to inelastic F+ and F2+ via autoionization.

Cross section measurements of the reactions induced by deuteron particles on 13C

Nuclear reactions induced by deuterons have been found to be an ideal analysis tool for depth profiling of light elements in the first microns of materials. In particular, the nonresonant nuclear reactions (d,p), (d,α) and (d,t) are well adapted to determine depth distributions of 12C and 13C in a single measurement. Nevertheless, only the cross section of the 12C(d,p0)13C nuclear reaction is well known for various experimental configurations. Thus, we measured the differential cross sections of the 13C(d,p0)14C, 13C(d,α0)11B, 13C(d,α1)11B and 13C(d,t0)12C nuclear reactions. A thin 13C foil (83nm thick) was used and the measurements were performed at deuteron energies from 0.5 to 1.65MeV for different laboratory angles of detection (135°, 150° and 165° with respect to the incident beam). Then, the results obtained in this work were compared to cross sections measured by Marion and Weber for a detection angle of 135°.

Extensive investigation of0+states in rare earth region nuclei

The nature of 0+ excitations, especially in transitional and deformed nuclei, has attracted new attention. Following a recent experiment studying 158Gd, we investigated a large group of nuclei in the rare-earth region with the (p,t) pickup reaction using the Q3D magnetic spectrograph at the University of Munich MP tandem accelerator laboratory. Outgoing tritons were recorded at various lab angles, and their angular distributions are compared to those calculated using the distorted-wave Born approximation. Using the unique shape of the L=0 angular distribution, more than double the number of 0+ states than were previously known are identified. The distribution of 0+ energies and cross sections is discussed in terms of collective and noncollective degrees of freedom, and the density of low-lying 0+ states is discussed as a corroboration of a characteristic feature of phase transition regions. The degree of level mixing, as extracted from Brody distribution fits to the energy spacings of adjacent 0+ levels, is also explored.

Pulse-shape analysis of signals from monolithic silicon [formula omitted]– [formula omitted] telescopes produced by the quasi-selective epitaxy

Two monolithic E – Δ E charged particle telescopes with Δ E layers of 11 and 20 μ m thick, respectively, produced with the Quasi-Selective Epitaxy method were tested at the Heavy Ion Laboratory in Warsaw. Thorium source α -particles and 12C( 14N,X) reaction products at 80 MeV beam energy were used. During on-beam tests, detectors were placed at 20 ∘ laboratory angle with respect to the beam axis. Among the reaction products, ions of Li, Be, B, C, N, O, F were identified (using the telescope with 20 μ m Δ E layer). Pulses from both E and Δ E components of the telescope were digitalized with a digital oscilloscope, sent to a PC machine and recorded. Pulse shape analysis technique was then applied to obtain the final two dimensional spectrum. The E – Δ E two-dimensional scatter plots obtained after irradiation of the monolithic E – Δ E telescopes by α -particles from the calibration source are presented. The energy resolution of the monolithic E – Δ E telescope measured using α -particles was about 0.7 MeV for telescope with 20 μ m thick Δ E layer and 0.4 MeV for telescope with 11 μ m Δ E layer. Response of the monolythic E – Δ E telescopes for Po 212 8.78 MeV α -particles registered at different impact positions at the telescope face was measured. Cross-talk signals in the monolithic E – Δ E telescope as a function of position and the Δ E detector capacitance were simulated using the numerical solution of the telegraphic equation describing time-dependent evolution of the cross-talk potentials in the Δ E detector RC network.

Light-ion production in the interaction of 96 MeV neutrons with oxygen

Double-differential cross sections for light-ion (p, d, t, He-3 and alpha) production in oxygen, induced by 96 MeV neutrons are reported. Energy spectra are measured at eight laboratory angles from 20 degrees to 160 degrees in steps of 20 degrees. Procedures for data taking and data reduction are presented. Deduced energy-differential and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data at lower neutron energies in the literature. The measured proton data agree reasonably well with the results of the model calculations, whereas the agreement for the other particles is less convincing. The measured production cross sections for protons, deuterons, tritons and alpha particles support the trends suggested by data at lower energies.

Erratum: Light-ion production in the interaction of 96 MeV neutrons with silicon [Phys. Rev. C69, 064609 (2004)

Double-differential cross sections for light-ion (p, d, t, He-3 and alpha) production in silicon, induced by 96 MeV neutrons are reported. Energy spectra are measured at eight laboratory angles, ranging from 20 degrees to 160 degrees in steps of 20 degrees. Procedures for data taking and data reduction are presented. Deduced energy-differential, angle-differential and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data in the literature.

Low-lying states in the unboundN11nucleus

We have investigated the low-energy states of $^{11}\mathrm{N}$ by the resonant elastic-scattering method in inverse kinematics using a $^{10}\mathrm{C}$ beam and a (CH${}_{2}){}_{n}$ target at the CYCLONE facility at Louvain-la-Neuve. Recoil protons were detected at laboratory angles ${\ensuremath{\theta}}_{\mathrm{lab}}=5.{2}^{\ifmmode^\circ\else\textdegree\fi{}}\text{\ensuremath{-}}18.{3}^{\ifmmode^\circ\else\textdegree\fi{}}$ in a $\ensuremath{\Delta}E\text{\ensuremath{-}}E$ detector system. The absolute $^{10}\mathrm{C}$+p elastic cross-section data were analyzed in the R-matrix framework. We found $^{11}\mathrm{N}$ to be unbound with respect to proton emission by $1.54\ifmmode\pm\else\textpm\fi{}0.02$ MeV, with a decay width of $0.83\ifmmode\pm\else\textpm\fi{}0.03$ MeV. These results are used to calculate the two-proton decay width of the $^{12}\mathrm{O}$ ground state.

The (t,He3) reaction at 43 MeV/nucleon onCa48andNi58: Results and microscopic interpretation

We have used the 43 MeV/nucleon primary tritium beam of the AGOR facility with an intensity of 4x10(7) pps and the BBS experimental setup to study the (t,He-3) reaction between 0 degrees and 5 degrees lab angles on C-12, Ca-48, and Ni-58 targets. The standard ray-tracing procedure has allowed us to obtain excitation-energy spectra up to 30 MeV in six angular bins for each residual nucleus, with an average energy resolution of 350 keV. The reaction mechanism has been described in distorted-waves Born approximation (DWBA) using the DWBA98 code. In this approximation, the form factor is treated as a folding of an effective projectile-nucleon interaction with a transition density. The effective projectile-nucleon interaction has been adjusted to reproduce the 0(degrees) cross section of the 1(+) ground state of B-12 populated in the C-12(t,He-3) reaction. We have employed random-phase approximation (RPA) wave functions of excited states to construct the form factor instead of the normal modes wave functions used earlier. This new DWBA+RPA analysis is used to compare calculated and experimental cross sections directly and to discuss the giant resonance excitations in K-48 and Co-58 nuclei.

Measurement of Neutron Emission Spectra in Li(d,xn) Reaction with Thick and Thin Targets for 40-MeV Deuterons

To improve the data accuracy of the neutron emission spectra of the natLi(d,xn) reaction that will be used as the neutron source in the International Fusion Materials Irradiation Facility, the authors have measured the neutron emission spectra from thick and thin lithium targets bombarded by 40-MeV deuterons at the AVF cyclotron (K = 110) facility of Tohoku University. The neutron spectra were measured at nine laboratory angles between 0 and 110 deg with the time-of-flight method using a beam-swinger system and a well-collimated neutron flight channel, obtained over almost the entire energy range of secondary neutrons using a two-gain method. The data obtained revealed the shape and angular dependence of emission spectra up to the high-energy region called a “high-energy tail.” The experimental results are compared with other experimental data and calculations.

Inclusive pion double charge exchange inHe4at intermediate energies

A systematic experimental study of inclusive pion double charge exchange in $^{4}\mathrm{He}$ has been undertaken. The reaction $^{4}\mathrm{He}$$({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}})4p$ was observed at incident energies of 120, 150, 180, 240, and 270 MeV; the $^{4}\mathrm{He}$$({\ensuremath{\pi}}^{\ensuremath{-}},{\ensuremath{\pi}}^{+})4n$ reaction was observed at incident energies of 180 and 240 MeV. At each incident energy, the doubly differential cross section was measured at three to five outgoing pion laboratory angles between ${25}^{\ifmmode^\circ\else\textdegree\fi{}}$ and ${130}^{\ifmmode^\circ\else\textdegree\fi{}}$. At each angle, cross sections were measured over the range of outgoing pion energies from 10 MeV to the kinematic limit for the reaction in which the final state consists of the oppositely charged pion plus four free nucleons. The spectra of outgoing pions are strikingly different from those observed for the inclusive double charge exchange reaction in heavier nuclei but resemble those observed in the $({\ensuremath{\pi}}^{\ensuremath{-}},{\ensuremath{\pi}}^{+})$ reaction in $^{3}\mathrm{He}$. The forward-angle spectra in the $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ reactions exhibit a prominent peak at high outgoing pion energies. Interpretation of the peaks in $^{3}\mathrm{He}$ ($^{4}\mathrm{He}$) as a three-nucleon (four-nucleon) resonance is ruled out by kinematic analysis. The results of a calculation, wherein the double charge exchange reaction is assumed to proceed as two sequential single charge exchange interactions, suggest that the high-energy peak is naturally explained by this double scattering mechanism. Nonstatic treatment of the $\ensuremath{\pi}N$ interactions and the inclusion of nuclear binding effects appear to be important in reproducing the shape of the energy spectra at forward angles.

Systematic exploration of 0+ states in structurally diverse nuclei

The puzzling nature of 0+ excitations, especially in transitional and deformed nuclei, has attracted new attention. Following a recent experiment studying 158Gd, we investigated 15 additional nuclei in and near the rare earth region. Our aim was to map out the energies of as many 0+ states as possible. A series of (p, t) experiments was performed at the Q3D magnetic spectrograph at the University of Munich MP tandem accelerator laboratory. These reactions are particularly sensitive to 0+ states. Outgoing tritons were recorded at various lab angles, and their relative cross sections are compared to those calculated using the distorted wave Born approximation (DWBA). The L = 0 angular distribution is easily discerned. New 0+ states are found in each of these nuclei, and their systematics are discussed.

14N(α,p) 17O nuclear reaction cross-section at 4.9–6.1 MeV

The 14N(α,p) 17O nuclear reaction cross-section was measured in the energy range 4.9–6.1 MeV at the laboratory angle θ = 172° in order to apply ion beam analysis to the detection of N in metal oxynitride layers. Comparison between the new calculation and data in literature was performed, highlighting important discrepancies between the new results and old cross-section data. Application of the new calculations to a standard TiN film suggests improved accuracy for the data in the present work.

Two-photon exchange contribution to elastic electron-nucleonscattering at large momentum transfer

We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer by using a quark-parton representation of virtual Compton scattering. We thus can relate the two-photon exchange amplitude to the generalized parton distributions which also enter in other wide-angle scattering processes. We find that the interference of one- and two-photon exchange contribution is able to substantially resolve the difference between electric form factor measurements from Rosenbluth and polarization transfer experiments. Two-photon exchange has additional consequences which could be experimentally observed, including nonzero polarization effects and a positron-proton/electron-proton scattering asymmetry. The predicted Rosenbluth plot is no longer precisely linear; it acquires a measurable curvature, particularly at large laboratory angle.