G. Tibell

Inelastic scattering of 185 MeV protons from light nuclei

Abstract Differential cross sections have been measured for scattering of 185 MeV protons from excited levels of the seven light nuclei Li 6 , Li 7 Be 9 , B 10 , B 11 , C 12 and O 16 . The energy analysis of the inelastically scattered protons has been performed in a magnetic spectrometer giving a resolution of 0.4–0.5 MeV (full width at half maximum) of peaks in the energy spectra. The measurements cover an angular region of 3°.5–45°.5 in the laboratory system and excitation energies up to 30 MeV. For 31 peaks in the energy spectra angular distributions are presented. Excitation energies and in some cases intrinsic widths are given for a total of 68 levels excited in this experiment. The results are compared with those of previous experiments using incoming protons of about the same energy and in, a few cases, with theoretical analyses of inelastic proton scattering

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.

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.

Delayed fission from the antiproton annihilation in 209Bi — evidence for hypernuclear decay

Abstract Delayed fission following the annihilation of stopped antiprotons in 209 Bi has been observed with a yield of approximately 3 × 10 −4 . The lifetime for delayed fission as measured by the recoil-distance technique is (2.5 +2.5 −1.0 )×10 −10 s. The observed delayed fission is interpreted as resulting from the decay of hypernuclei in the region of masses near 200 produced in the annihilation of antiprotons in 209 Bi.

The asymmetry of 155 MeV protons elastically and inelastically scattered from carbon, oxygen, and calcium

Abstract The asymmetry of protons scattered elastically and inelastically from oxygen and calcium has been studied with the conventional double scattering technique using range telescopes. Results are given for the asymmetry in scattering from oxygen and calcium together with improved values of previously reported carbon data. The angular distributions of the elastic asymmetry are quite similar for the three elements. For the inelastic asymmetry of oxygen and calcium it has been possible to obtain only qualitative results.

Proton emission in 58A and 86A MeV 12C-induced heavy-ion reactions

Abstract Inclusive proton spectra from 12 C-induced heavy-ion interactions at 58 A and 86 A MeV have been obtained by using a ΔE − E time-of-flight telescope. The shapes of the energy spectra above 30 MeV for 32°⩽ θ ⩽142° are very similar for five targets ranging from C to Au. The backward spectra can be reproduced both in the picture of a thermalized source characterized by an 11–17 MeV temperature Boltzmann distribution moving with half the beam velocity and in the picture of quasi-elastic nucleon-nucleon scattering from two interacting Fermi spheres. The forward spectra are difficult to reproduce unless a combination of the two descriptions is accepted. The 58 A MeV spectra peak substantially closer to the beam energy per nucleon and show significantly steeper slopes than 86 A MeV spectra.

THE C-12(N,P)B-12 REACTION AT E(N)=98 MEV

Double-differential cross sections of the C-12(n, p) reaction have been measured at 98 MeV in the angular range 0-degrees-33-degrees for excitation energies up to 35 MeV. The spectra have been analysed in terms of multipole components, using peak fitting and decomposition techniques. The data have been compared with cross sections obtained in the distorted-wave Born approximation, using matrix elements from shell-model calculations. The unit cross section and the related strength of the spin-isospin part of the nucleon-nucleon interaction were determined from the extracted Gamow-Teller strength. Cross sections and fractions of strength exhausted by dipole and higher-multipole transitions were extracted and compared with data available in the literature.

The elastic scattering of 160 MeV protons from lithium, aluminum, indium and gold

Abstract The differential cross-sections and asymmetries of protons scattered elastically from lithium, aluminum, indium and gold have been measured in the angular range 3–30°. The results are compared with calculations using the optical model, and overall agreement is found.

Inelastic scattering of 185 MeV protons from Mg and Al

Abstract A magnetic spectrometer was used for the energy analysis of protons scattered from targets of magnesium (natural isotopic composition) and aluminium. The mean energy of the incident protons in the targets was 185 MeV. A total energy resolution of 350 keV (FWHM) was achieved, which made possible the observation of the excitation of a large number of discrete levels. Energy spectra were measured in the angular region of 4° to 40° (lab system). The results are presented partly in the form of tables giving measured excitation energies and maximum cross sections for resolved levels and partly in the form of graphs of angular distributions of the differential cross sections. A qualitative discussion of the results is given in terms of the multipolarities of the transitions involved and comparisons are made with similar results from other experiments in inelastic scattering and in a few cases with theoretical predictions.

The polarization of 155 MeV protons elastically and inelastically scattered from carbon

Abstract The polarization of 155 MeV protons elastically and inelastically (4.43 MeV level) scattered from carbon has been measured for angles up to 35° (lab. system). The energy spread of the protons was small enough to allow separation of energy levels by absorbers in a range telescope. The asymmetries were determined for two absorber settings, one corresponding to elastically scattered protons, and the other to elastically plus inelastically scattered protons. The elastic polarization rises from zero at 2° to a maximum of 99.5 % at 21°, then goes through a minimum of −18 % at 32°.5 and reaches 28.4 % at 35°. The inelastic polarization appears to increase from 59 % to 96 % in the angular region 16°.2 to 27°.4 and then to decrease to 2 % at 35°.