The polarization and differential cross section of fast neutrons scattered from 6Li and an R-function analysis of the interaction below 4 MeV

The analyzing power of ⁶Li for the elastic scattering of polarized neutrons with energies between 2 and 4 MeV, has been measured at six angles ranging from 25° to 150°. The polarized neutrons were generated from the reactions Pb(γ, n) and ¹²C(n, $\text{n}$), and their polarization was measured using the double-scattering method. The neutron energies were determined with a nanosecond timeof-flight spectrometer. In addition, the differential cross section was measured at three angles in the same energy range; the cross section was determined relative to the well-known n-¹²C cross section. The present results have been combined with existing data for the neutron total, (n, α), and differential elastic cross sections, in a reduced R-function analysis. Clear evidence of a p-wave triplet of shellmodel states emerges from the analysis.     

Scattering of negative pions on helium

Differential cross sections for negative pion scattering on ⁴He have been measured at five pion kinetic energies between 110 and 260 MeV in the angular range from 5° to 180°. Total cross sections have also been measured at eleven energies between 67 and 285 MeV. The differential cross sections have been fitted with a phenomenological expression for the nuclear scattering amplitude. Conventional phase shifts have been reconstructed starting from the parameters of the fits.     

Differential cross sections of proton compton scattering at photon laboratory energies between 700 and 1000 MeV

Differential cross sections of proton Compton scattering have been measured at the Bonn 2.5 GeV synchrotron. 78 data points are presented as angular distributions at photon lab energies of 700, 750, 800, 850, 900, and 950MeV. The c.m. scattering angle ranges from 40°–130°, corresponding to a variation of the four momentum transfer squared betweent=?0.10 tot=?0.96 GeV² at 700 and 950 MeV, respectively. Two additional differential cross sections have been measured at 1000MeV, 35.6° and 47.4°. The angular distributions show forward peaks whose extrapolations to 0° are consistent with calculated forward cross sections taken from literature. The small angle data (|t| ?0.2 GeV²) together with the calculated cross sections at 0° are also consistent with the assumption of a slope parameterB of 5 GeV^?2. For the first time a rerise of the angular distributions towards backward angles has been observed. It becomes less steep with increasing energy. The most interesting feature of the angular distributions is a sharp structure which appears betweent=?0.55 GeV² at 700MeV andt=?0.72 GeV² at 950 MeV. Such a rapid varation of the differential cross section witht has never been ovserved in elastic hadron-hadron scattering or photoproduction processes. It indicates the existence of a dynamical mechanism which could be a peculiarity of Compton scattering.     

Inclusive π4He scattering and the πN interaction in the nuclear medium

Double differential cross sections for the inclusive reaction ⁴He(π, π′)X have been measured for six pion energies between 90 and 320 MeV and an angular range from 30° to 135°. The data are interpreted in terms of the Δ-hole formalism. Medium corrections to the free π-nucleon scattering operator are important for a quantitative understanding of our results. Total inelastic cross sections are obtained and estimates for the absorption cross section are given.     

The elastic scattering of 3He on 4He at medium energies

The differential cross section of the elastic scattering ³He(⁴He, ⁴He)³He has been measured at center of mass energies E_c.m. between 28 and 44 MeV and in the c.m. angular range of 20° to 160°. The ³He polarization P at E_c.m. = 42 MeV and θ_c.m. = 132° was determined in a double scattering experiment. The analysis of the cross section data with the optical and the cluster model has been described previously. The phase shifts obtained in the cluster model calculations were used as starting values in a phase shift analysis. The resulting final real phase shifts and elasticity parameters give good fits to the cross section data. At 44 MeV the elasticity parameters show a pronounced odd-even dependence on angular momentum which had been found already in the case of the real phase shifts. The result of the polarization experiment |P| < 0.22 is consistent with cluster model predictions.     

Differential cross section,analyzing power and phase shifts for p-3He elastic scattering below 1.0 MeV

Differential cross sections and analyzing powers for the elastic scattering of polarized protons by unpolarized ³He nuclei have been measured at eight energies between 0.3 MeV and 1.0 MeV for scattering angles θ_c.m. = 52.4°–173.3°. The cross-section values were normalized to the Rutherford cross section for proton-krypton scattering. The analyzing powers have been measured with a statistical accuracy of about 0.001. The phase-shift analysis based on these data included all phases for orbital angular momenta l ≦ 1 and the channel-spin mixing parameter for the P waves. An energy parametrization of the phase shifts by an effective-range approximation allowed a simultaneous utilization of all data.     

Cross section and analyzing powers for the reaction pd→3He + γ at intermediate energies

We report the results of measurements of the differential cross section and analyzing power for the reaction pd → γ³He at six energies in the range 200 < E_p < 500 MeV. The cross-section data are in good agreement with the most recent results for the inverse process assuming detailed balance; thus no evidence for time-reversal violation is inferred. In addition, the shapes of the measured angular distributions are in general overall accord with those measured in the photodisintegration reaction. The data are compared with several theoretical calculations showing inclusion of meson-exchange current contributions to be important in reproducing the measured cross section. The analyzing powers measured at E_p = 500 MeV are not yet explained by microscopic models.     

Elastic proton scattering from He in the forward direction at 200, 350 and 500 MeV

The differential cross section for the elastic scattering of protons from ⁴He has been measured at 200, 350, and 500 MeV over an angular range from 3.5° to 15° in the lab system. In addition, the analyzing power was measured in the same angular range at 350 and 500 MeV. The experiment makes use of a tenuous gas target in which the recoil -energy is measured with solid-state detectors. The proton scattering angle is measured outside the target by a system of multi-wire proportional counters. The differential cross sections have a nearly exponential dependence on momentum transfer in this kinematic range and grow with increasing energy. The analyzing power shows strong positive asymmetry.     

The reaction 14C(3He,n)16O and the coexistence model of 16O

The reaction ¹⁴C(³He, n)¹⁶O has been measured at a ³He bombarding energy of 25.4 MeV. The zero-degree differential cross section for the excitation of the three low lying 0⁺T = 0 states, at energies 0.0, 6.05 and 12.05 MeV are, respectively, 1.33 ± 0.10, 0.49 ± 0.10, and 0.50 ± 0.10 mb/sr These measured cross sections are in rough agreement with single-step zero-range DWBA calculations using an empirically determined ¹⁴C ground state wave function and in which the Brown and Green coexistence-model wave functions are used to describe the ¹⁶O 0⁺ states. The angular distribution of the transition to the ground state is measured between 0° and 32°.     

Polarization of protons from the C(d,p)C reaction

The polarization of protons from the ¹²C(d, p)¹³C reaction has been measured for deuteron bombarding energies between 3.9 and 5.8 MeV. Angular distributions of the polarization for protons leaving ¹³C in its ground state have been measured for laboratory angles between 10° and 135° at several energies in the vicinity of a resonance at 4 MeV in order to determine the effect of that resonance on the polarization. Additional measurements were made at 0.4 MeV intervals throughout the energy range. These measurements demonstrate that the compound-nuclear resonances observed in the cross section do not significantly alter the polarization angular distributions except at back angles. The shape of the observed polarization angular distributions at all energies is quite similar to previous results obtained for deuteron bombarding energies up to 15 MeV.     

Measurement of the two-body photodisintegration of3He in theΔ(1236) resonance region

The³He(γ, p)d reaction has been measured in the photon energy region between 200 MeV and 450 MeV at proton c.m. angles between 20° and 150°. Protons and deuterons were detected in coincidence with two time-of-flight spectrometers consisting of scintillation counters; both particles were identified and their energies and angles were measured. The angular distributions show a strong forward peak. The differential cross sections fall off with increasing photon energy without showing a significant influence of theΔ resonance.     

Electromagnetic polarizabilities of nucleons bound in 40Ca, 16O and 4He

Differential cross sections for elastic scattering of photons have been measured for ⁴⁰Ca at energies of 58 and 74 MeV and for ¹⁶O and ⁴He at 61 MeV, in the angular range from 45° to 150°. Evidence is obtained that there are no significant in-medium modifications of the electromagnetic polarizabilities except for those originating from meson exchange currents.     

Observation of deuteron D-state and compound nucleus effects in (d,p) reactions on 46Ti and 52Cr with a polarized deuteron beam

The cross section and the vector and tensor analyzing powers have been measured for ⁴⁶Ti(d, p)⁴⁷Ti at deuteron energies of 6 and 10 MeV and ⁵²Cr(d, p)⁵³Cr at 6 MeV. Transitions were observed to the states at E_x=0.159, 1.549 and 1.793 MeV in ⁴⁷Ti and the states at E_x=0.0, 0.564, 1.006 and 2.321 MeV in ⁵³Cr. In addition, the cross sections and vector analyzing powers for deuteron elastic scattering were measured for the same targets and deuteron energies and compared to optical model calculations. The choice of optical parameters for the DWBA analysis of the (d, p) reactions is discussed. Calculations made with the DWBA method show that the deuteron D-state must be included to reproduce even qualitatively the (d, p) tensor analyzing power measurements. The j-dependence of the tensor analyzing power T₂₂ is discussed. The validity of the local energy approximation (which was used to incorporate the deuteron D-state into the DWBA calculations) is evaluated by comparison to finite range calculations. The contribution of compound nucleus reactions to the measured cross sections and analyzing powers was investigated. In order to determine the compound cross section, the Ericson fluctuations in excitation functions of cross section and vector analyzing power were measured from 5 to 7 MeV on each target. The formulas used to calculate the polarization observables from the Hauser-Feshbach theory are presented.     

Photoproduction of neutral pions on hydrogen at photon energies between 200 and 440 MeV

At the Bonn 500 MeV electron synchrotron the differential cross section of the reaction γ+p → π⁰+p has been measured detecting the recoil proton by a magnetic spectrometer. Angular distributions between pion c.m. angles of 50 ° and 160 ° were taken at photon energies between 220 and 420 MeV.     

The complex transfer reaction (14C, 15O) on Ni,Zn and Ge targets: Existence and mass of 69Ni

The (¹⁴C, ¹⁵O) complex transfer reaction has been studied at 72 MeV incident energy on ^58,60,62.64Ni ^68,70Zn and ^74,76Ge targets. Spectra and differential cross sections have been measured in a 5° angular range centred around a laboratory angle of 6°. The nucleus ⁶⁹Ni has been observed for the first time and its mass determined.     

Pion production from deuterium bombarded with polarized protons of 277 and 500 MeV

Analyzing power measurements of the $\text{p}\text{→ tτ}{}^{\mathrm{+}}$ reaction are reported at incident proton energies of 277 and 500 MeV. The 277 MeV results span the angular range from 70° to 130° in the centre of mass while the two 500 MeV measurements at large angles were taken as a check of published results. With the angular distribution of the analyzing power at 277 MeV now known, it is possible to show that the energy dependence of the analyzing power exhibits characteristics closely resembling the shape and magnitude of the analyzing power distribution observed for 1p shell nuclei of similar excitation energies.     

Analyzing powers and cross sections in elastic p-d scattering at 65 MeV

Analyzing powers and differential cross sections for $\text{p}\text{-}\text{d}$ elastic scattering have been measured at 64.8 MeV. The angular distributions cover center-of-mass angles between 8° and 169°. The relative uncertainties of the analyzing power measurement are typically ± 0.005 at c.m. angles less than 80° and are in general ± 0.015 at the remaining angles. The absolute scale of the analyzing power measurement has an uncertainty of ± 0.013. The data are compared with three-body calculations based on the Faddeev theory. In contrast with the differential cross sections, the analyzing powers could not be reproduced without the D-wave nucleon-nucleon interactions.     

A study of the 6Be system by use of the reaction 3He(3He,p)5Li(g.s.) between 17 and 30 MeV with a polarized target

The differential cross section of the reaction ³He(³He, p)⁵Li(g.s.) has been measured at 26 MeV and the analyzing power A_γ in the energy range 17–30 MeV with the use of a polarized ³He target. The data are compared with existing microscopic multi-channel calculations to the ⁶Be system. The influence of the J^π = 4⁺ channels turned out to be too strong. The deviations from the antisymmetry to 90° c.m. of the analyzing power angular distribution _γ(θ) are discussed with respect to the purely direct transfer model for identical particles in the entrance channel.     

12C + 7Li Reaction measurements and the 12C(7Li,t)16O reaction

A measurement of the residues from the ¹²C + ⁷Li reaction has been obtained for ⁷Li energies from 10 to 38 MeV. From these measurements the fusion cross sections and critical angular momenta for the ¹²C + ⁷Li system have been deduced. Cross sections for the ⁷Li(¹²C, t)¹⁶O reaction have been obtained for ¹²C energies from 54 to 62 MeV at θ_lab = 2.7°. The critical angular momenta obtained from the fusion cross sections have been used to perform Hauser-Feshbach calculations for the ¹²C(⁷Li, t)¹⁶O reaction. These calculations have been compared to measured angular distributions over a wide energy range. By comparing the fusion cross sections required by the Hauser-Feshbach calculations to fit the ¹²C(⁷Li, t)¹⁶O(8.87 MeV) reaction and the measured residue cross section it is estimated that at least 80 % of the measured residues are fusion products. The calculations also indicate that direct processes dominate the population of many ¹⁶O levels at forward angles and the 10.35 MeV state at backward angles. The necessity for using a critical angular momentum in Hauser-Feshbach calculations is discussed.     

Two-body pion production d(p, π+)t AT 470 and 590 MeV

The differential cross section for the reaction d(p, π⁺)t has been measured for c.m. angles between 37° and 160°, at incident proton energies of 470 and 590 MeV. The results are in qualitative agreement with the predictions of a two-nucleon model of the reaction when the D-state contribution is included, except for the existence of a backward peak at 470 MeV. Other models of the reaction are discussed; none of them gives a rationale for the backward peak at 470 MeV. A similar peak is present in older data at 325 MeV.