P. von Rossen

Parity violation in proton-proton scattering at 13.6 MeV

Abstract Parity nonconservation in proton-proton scattering has been studied by measuring the angle-integrated longitudinal analyzing power A z . We found A z (13.6 MeV)=(−1.5±0.5)×10 −7 . The error includes uncertainties due to statistics and corrections, as well as upper limits on systematic effects. The experimental result is discussed with respect to recent theoretical calculations.

The α + α → 8Be double resonance at the 16.6 and 16.9 MeV levels

Abstract The elastic scattering 4 He(α, α) has been investigated in the energy range 32.6–35.4 MeV. The level parameters of the overlapping 2 + states in 8 Be at 16.6 and 16.9 MeV were obtained with a double resonance formalism. In R -matrix theory the level energies and widths are 16623 ± 3 keV, 107.7 ± 0.5 keV and 16925 ± 3 keV, 74.4 ± 0.4 keV, respectively. In complex-eigenvalue theory the resonance energies and widths are 16630 ± 3 keV, 108.5 ± 0.5 keV and 16918 ± 3 keV, 73.6 ± 0.4 keV, respectively. The relation between the parameter sets is discussed. The present results are compared with previous investigations where 8 Be is formed as a product nucleus. The isospin mixing of the doublet and the deduced charge-dependent matrix element are discussed with regard to theoretical predictions.

The 16O + p → 17F (T = 32) resonances at Ep = 11.26,12.71 and 14.57 MeV

Abstract Excitation functions for 16 O+p reactions have been measured with high energy resolution in the region of the first, second and seventh T = 3 2 resonances in 17 F at extreme backward angles. The observed resonance shapes have been analyzed with a single-level resonance formula taking the off-resonance spin-flip amplitude into account. The resonance parameters of the 17 F first T = 3 2 state studied with special emphasis are E x = 11193.3 ± 2.3 keV, Γ = 200 ± 40 eV and Γ p 0 = 19 ± 3 eV. This result and other results are compared with previous studies and theoretical predictions. The comparison with data of the mirror nucleus 17 O is discussed with respect to the observed charge asymmetry of the isospin-forbidden particle decay widths.

No evidence for time reversal invariance violation from (3He,p) polarization measurements

Abstract We have measured the proton polarization from the reactions 7Li(3He, p )9Be and 9Be(3He, p )11B between 20° and 75° at 14 MeV using a magnetic spectrograph. In complete disagreement with previous measurements our polarization values agree with analyzing power values in the inverse ( p ,3He) reactions. In contrast to previous claims no evidence for a violation of time reversal invariance was found.

High-resolution study of 16O+n → 17O (T = 32) resonances

Abstract Sharp, isospin-forbidden, T = 3 2 resonances in 17 O have been studied by a measurement of the total neutron cross section of oxygen using the Karlsruhe neutron time-of-flight spectrometer. The transmission of a natural liquid oxygen target was measured at 190 m with a time-of-flight resolution of 5.5 ps m yielding an effective energy resolution of 1:2100 for 10 MeV neutrons. The absolute energy calibration allowed neutron resonance energies to be determined with an accuracy between 10 −5 and 10 −4 . Total and partial decay widths and resonance energies have been determined assuming non-interfering multi-level Breit-Wigner resonances. The c.m. resonance parameters of the 17 O first T = 3 2 state are: E c.m. = 6934.38±0.17 keV, Γ = 2.4±0.3 keV and Γ n 0 = 1.88±0.12 keV. Besides the investigation of 10 known T = 3 2 states a search was undertaken for additional T = 3 2 resonances. The obtained results are compared with shell-model predictions of isospin mixing matrix elements and the systematics of isospin non-conserving particle decays.

Optical model analysis of the elastic scattering of 45 MeV 3He particles on 1p shell nuclei

Abstract Angular distributions of elastically scattered 3He particles from the 1p shell nuclei 6Li, 7Li, 9Be, 10B, 11B, 12C and 16O were measured by using a 45 MeV 3He beam. The absolute differential cross section data obtained were analysed in terms of the standard optical model. Using the fact that the rms radius of the 1p shell nuclei is nearly constant a simple folding model allows finding an optical potential family whose real potential depth varies linearly with the target mass. The best fits exhibit a normalized volume integral of about 400 MeV · fm3 for the real potential. From the best-fit parameters a mean parameter set is deduced which varies smoothly with the target mass AT. The average parameter set compares well with the systematics found for heavier nuclei.

The 9Be+α → 13C(T = 32) resonance at 6.44 MeV

Abstract The first T = 3 2 level in 13C has been studied as an isospin-forbidden resonance in the 9Be(α, n0), 9Be(α, n1) and 9Be(α, α0) reactions at an incident energy of 6443.5±2.0 keV, corresponding to an excitation energy of 15108.9±1.5 keV in 13C. Total and partial decay widths were deduced as Γ = 5.49±0.25 keV and Γ α0 /Γ ≧ 0.017 . The resonance parameters are discussed along the lines of similar investigations in 17O and 21Ne and with respect to the isobaric mass multiplet equation. Combining the present value for Γ with previous measurements of Γγ0/Γ yields the ground-state γ-decay width Γγ0 = 22.8±1.9 eV, which compares well with the most precise value until now known from inelastic electron scattering data. The weighted combination of all available information on the ground-state-γ-decay of the first T = 3 2 states in 13C and 13N leads to B( 13 C )/B( 13 N )−1 = −0.15±0.07 for the reduced M1 transition strengths. The charge asymmetry of the reduced M1 transition strengths is discussed with respect to a charge-dependent mixing in the initial and final states and a possible isotensor component of the M1 transition operator.

Search for the lowest T = 52 resonance in 22Ne + p → 23Na

Abstract In a systematic search for the lowest T = 5 2 resonance in 23Na a candidate has been found in the excitation functions for 22Ne + p reactions at an excitation energy in 23Na of 19 586.1 ± 2.0 keV. Total and partial widths were determined as Γ = 1.9 ± 0.8 keV and (J + 1 2 ) Γ p0 = 44 ± 4 eV , respectively.

Multiple scattering of protons in thick gas targets

Abstract Small angle multiple scattering distributions of 9.9 and 13.9 MeV protons were measured in thick gas targets of H2, D2, He, N2 and Ar. The target thicknesses ranged between 13 and 26 mg/cm2. The data were compared with theoretical predictions of Moliere, Bethe, Fano and Marion and Zimmermann, which differ substantially in the case of hydrogen. Only the predictions of Fano are in good agreement with the experimental results. The simple formula of the Particle Data Group for the 1/e widths yields predictions which deviate less than 10% from the data. Theoretical expressions are summarized for easy application.

Microcomputer controlled energy variation of an isochronous cyclotron and beam handling system

Abstract An automatic 3 MeV variation of a 30 MeV α-beam was performed in 300 steps at the Bonn Isochronous Cyclotron. A microcomputer in connection with a control unit adjusted the cyclotron and the monochromator system parameters. This combination allowed a direct and precise measurement of broad excitation functions. Using fast magnetic field stabilization an energy-shift was accomplished to an accuracy of better than 1 part in 105 within 20 s. The stability of the beam position on the target was about 0.05 mm.