W. Lübcke

Analyzing power in n+d elastic scattering at 67 MeV

The analyzing power Ay of 2H(n, n)2H elastic scattering at En = 67 MeV has been measured in the angular range 30° < θ c.m. < 165°. The data are in good agreement with the results of our rigorous three-nucleon calculations employing the PARIS and the BONN B potential.

Ghost anomaly and first excited state of 8Be in the 9Be(d, tα)4He reaction at 7 MeV

Abstract The three-body reaction 9 Be + d → t + α + α has been investigated in kinematically complete experiments at E d = 7.0 MeV for θ t = −40° and θ t = 40°, θ α = −72.5° to −162.5. The experimental spectra are dominated by sequential processes via intermediate excited states of 8 Be and 7 Li. R -matrix theory was employed to describe the line shape of the first excited state and the ghost anomaly of the ground state of 8 Be. Use was made of the αα phase shifts. The best fits were obtained assuming a channel radius of a αα = 4.5 fm. The average intensity of the ghost anomaly for E αα = 0.35–1.0 MeV is 4.3%/MeV ( θ t = 40°) and 8%/MeV ( θ t = 100°). For the first excited state of 8 Be we find E x = 3.00 MeV and Γ x = 1.23 MeV(FWHM).

Analyzing power of the 2H(n, np)n breakup reaction at 67 MeV in selected kinematical configurations

Abstract The angular distribution of the analyzing power A y for the 2 H( n , np)n breakup reaction at 67 MeV was measured in two kinematical regions: np quasi-free scattering and np final-state interaction. The results are compared with rigorous three-nucleon calculations using the Paris potential and allowing for charge dependence in the 1 S 0 state. According to the actual experimental conditions energy averaging was simulated in the theoretical calculations. In both configurations agreement between experimental and calculated values is found.

Differential cross section for elastic n+d scattering and n+d break-up quasi free-scattering at 67 MeV

Abstract The differential cross sections for the n+d elastic scattering and for the 2 H(n,np)n break-up reaction in the np quasi-free scattering configuration was measured at 67 MeV. The experimental data are compared with results of the calculations based on a rigorous solution of the three-nucleon Faddeev equations using meson-exchange potentials. Good agreement is found between experiment and theory for the n+d elastic-scattering cross section while in the case of np quasi-free scattering the theoretical predictions overestimate the data at neutron angles larger than 40° by about 30%.

Facility for neutron induced few body reactions at Bochum University

Abstract A facility is described which is designed for the measurement of neutron induced three-body breakup. It has been used for the breakup of deuterium and of the nucleus 9 Be. Neutrons are produced by a pulsed beam of deuterons from the Bochum 4MV Dynamitron-Tandem accelerator by bombarding a thick tritium-titanium target or a deuterium gas target. The outgoing beam is collimated by a 4π shielding to a solid angle of about 1 msr. In most cases, a liquid scintillator (NE232 or a mixture of NE232/NE213) serves as a target for the neutron beam. Scattered neutrons are detected by NE213-detectors of different sizes. For testing purposes the differential elastic n-d cross section and simultaneously the response of NE232 have been measured at 22.4 and 7.9 MeV.

Neutron-neutron scattering length in the reaction9Be (n, nn)8Be at 10.3 MeV

In a kinematically complete experiment on9Be(n, nn)8Begs at 10.3 MeV, the absolute differential cross section of then-n FSI configuration at Θlab=30° has been measured. It was our particular object to determine the singlet scattering length of then-n interaction via its final-state interaction being embedded in a multi-nucleon background. An extended and thorough analysis yielded1ann=−16.5±1.0 fm which is consistent with the results of the most recent and most precise kinematically complete measurements with three hadrons in the final state. These, however, altogether contradict the values deduced from π−d→nnγ.

The neutron-proton scattering length in the reaction9Be(p, np)8Be at 7.5 MeV

The relative differential cross section of the9Be(p, np)8Begs reaction at 7.5 MeV has been measured in an FSI geometry. A strongn-p FSI peak was observed with virtually no sequential decay modes interfering. The Watson-Migdal analysis of this peak yields the scattering lengthanp=−23.8−1.2−1.1 fm with the effective rangernp=2.76 fm.

Absolute 2H(n,2n)1H cross section in star geometry

The syymetric star geometry of a three-nucleon System is particularly sensitive to a three-body force. We therefore measured the corresponding absolute cross section of the 2H(n,2n)1H reaction at Elab-10 MeV, with special efforts to achieve an accuracy of better than 10%. Method and results are discussed.

Collinearity in the reaction p+d→p+p+n at Ep = 7.5 MeV

In view of the controversial situation concerning the existence of a “collinearity peak” we continued the series of recent measurements on the p+d-breakup in collinear geometry down to very low energy. Spectra of p-p and n-p coincidence were taken and were compared with Faddeev calculations (one of them including a Tucson 3N-force). Care was taken to achieve good statistics and low background in the spectra. No evidence for a collinearity Peak could be detected.