N. Olsson

A facility for studies of neutron-induced reactions in the 50–200 MeV range

A facility for studies of neutron-induced reactions has been built at the upgraded Gustaf Werner cyclotron of the The Svedberg Laboratory, Uppsala, Sweden. Well-collimated, monoenergetic neutron beams are produced with a fairly long distance between the neutron source and the reaction target, to reduce background radiation. A magnetic spectrometer with large angular and momentum acceptance has been constructed to allow measurements of energy and angular distributions of light ions produced in neutron-induced reactions. Initially, studies will be undertaken of isovector monopole and Gamow-Teller resonances, induced by the (n,p) reaction in various nuclei. The performance is illustrated in a measurement of the doubly differential cross section of the 12C(n,p)12B reaction at 100 MeV.

SCANDAL - a facility for elastic neutron scattering studies in the 50-130 MeV range

A facility for detection of scattered neutrons in the energy interval 50 130 MeV, SCAttered Nucleon Detection AssembLy (SCANDAL), has recently been installed at the 20-180 MeV neutron beam facility of The Svedberg Laboratory, Uppsala. It is primarily intended for studies of elastic neutron scattering, but can be used for (n,p) and (n,d) reaction experiments as well. The performance of the spectrometer is illustrated in measurements of the (n,p) and (n,n) reactions on H-1 and C-12. In addition, the neutron beam facility is described in some detail

The 54,56Fe(n, p)54,56Mn reactions at En = 97 MeV

Abstract Double-differential cross sections of the 54,56Fe(n, p) reactions have been measured at 97 MeV in the angular range 0–30° for excitation energies up to 40 MeV. The spectra have been decomposed into different multipolarities by a technique based on the use of sample angular distributions calculated within the distorted-wave Born approximation. From the identified Gamow-Teller strength, Sβ+ values were obtained for 54Fe and 56Fe. Comparisons with available shell-model calculations of the GT strength were made. The results are important for models of supernova explosions since electron-capture rates, which are proportional to Sβ+, in 1f2p-shell nuclei affect the dynamics of the star. At higher excitation energies, the spectra are dominated by L = 1 strength in broad distributions with a maximum at about 12 MeV. Microscopic calculations based on the random-phase approximation were performed and compared with the experimental data.

Nucleon-induced reactions at intermediate energies: New data at 96 MeV and theoretical status

Double-differential cross sections for light charged particle production (up to A=4) were measured in 96 MeV neutron-induced reactions, at the TSL Laboratory Cyclotron in Uppsala (Sweden). Measurements for three targets, Fe, Pb, and U, were performed using two independent devices, SCANDAL and MEDLEY. The data were recorded with low-energy thresholds and for a wide angular range (20 deg. -160 deg. ). The normalization procedure used to extract the cross sections is based on the np elastic scattering reaction that we measured and for which we present experimental results. A good control of the systematic uncertainties affecting the results is achieved. Calculations using the exciton model are reported. Two different theoretical approaches proposed to improve its predictive power regarding the complex particle emission are tested. The capabilities of each approach is illustrated by comparison with the 96 MeV data that we measured, and with other experimental results available in the literature.

Development and Validation of the 7Li(p, n) Nuclear Data Library and Its Application in Monitoring of Intermediate Energy Neutrons

Systematics have been created for neutron spectra from the 7Li(p, n) reaction at 0° in the 50-200 MeV proton energy region. The available experimental data in the continuum part of the spectra show satisfactory overall agreement with a representation based on the phase-space distribution corresponding to the three-body breakup process 7Li(p, n 3He)α, with empirical correction factors, which depend regularly on incident energy. Validation of the systematics included folding of the predicted neutron spectra with standard 238U neutron fission cross section. Modeled in this way distributions of neutron-induced fission events agree reasonably with experimental data.

A facility for measurements of nuclear cross sections for fast neutron cancer therapy

A facility for measurements of neutron-induced double-differential light-ion production cross-sections, for application within, e.g., fast neutron cancer therapy, is described. The central detectio ...

Microscopic and conventional optical model analysis of neutron elastic scattering at 21.6 MeV over a wide mass range

Abstract Differential fast neutron elastic scattering angular distributions have been measured at 21.6 MeV for the natural elements Mg, Al, Si, S, Ca, Cr, Fe, Co, Ni, Y, Ce, Pb r (radiogenic lead) and Bi by employing pulsed beam time-of-flight techniques. The energy resolution was about 0.5 MeV (FWHM) throughout the measurements. The experimental data have been analysed in terms of a standard phenomenological spherical optical model. Potential depths and geometrical parameters were determined from individual best fits to the data. Volume integrals of the real and imaginary parts of the potential were calculated using these parameters. A similar technique was utilized to calculate root mean square radii of the real potential, from which radii of point matter distributions were obtained for comparison with α-particle scattering data at 166 MeV and with charge distribution radii from electron scattering. Microscopic folding models for the optical potential according to Jeukenne, Lejeune and Mahaux, Brieva and Rook, and Yamaguchi et al . have been tested by calculating angular distributions, volume integrals and root mean square radii for the real and imaginary potential parts. The results of these calculations are compared with those of the phenomenological analyses. The microscopic potentials have also been intercompared by studying introduced normalizing parameters of the real and imaginary potential parts as well as isovector and isoscalar contributions to the volume integrals.

Light‐Ion Production in the Interaction of 96 MeV Neutrons with Silicon

Double-differential cross sections for light-ion (p, d, t, He and α) production in oxygen, induced by 96 MeV neutrons are reported. Energy spectra are measured at eight laboratory angles from 20◦ to 160◦ in steps of 20◦. Procedures for data taking and data reduction are presented. Deduced energydifferential and production cross sections are reported. Experimental cross ∗Corresponding author, Tel. +46 18 471 6850, Fax. +46 18 471 3853, E-mail: stephan.pomp@tsl.uu.se

The giant isovector E2 resonance in calcium observed in radiative neutron capture

Abstract The reaction 40 Ca(n, γ 0 ) 41 Ca has been studied in the neutron energy range 20 28 MeV, where the isovector giant quadrupole resonance is expected. Interference between El and E2 radiation gives rise to a fore-aft asymmetry of the emitted γ-rays. The measured asymmetries are compared with calculations based on the direct-semidirect capture model. Good agreement with the experimental data is obtained assuming an isovector E2 resonance located at 32 MeV with a strength exhausting about 35%, of the isovector sum rule. This corresponds to the full strength of the T component.

Can self-reported encoding strategy and recognition skill be diagnostic of performance in eyewitness identifications?

The relationship between 3 witness factors and identification accuracy, as well as calibration and diagnosticity of confidence, was investigated. A total of 384 participants in an eyewitness experiment rated their facial recognition skill, general memory skill, and self-reported encoding strategy on a questionnaire presented after the photo-confrontation. Participants who rated themselves to be good face recognizers showed a slightly higher overall accuracy with a more diagnostic confidence-accuracy relation. Participants who reported that they relied on a holistic encoding strategy were associated with more accurate identifications and a stronger confidence-accuracy relation than those who reported an analytic encoding strategy. Degree of self-reported general memory skill was not diagnostic of identification performance.