Search

A neutron facility for the study of (n,p) reactions was set up at the Indiana University Cyclotron Facility. The neutrons were produced by the reaction 7 Li(p,n) 7 Be. The energy spread of the neutron beam is dominated by the thickness of the 7 Li production target. At the (n,p) target the collimated neutron-beam intensity is about 10 5 n/s/cm 2 for a 1 μA proton beam at 120 MeV on a 7 Li target 100 mg/cm 2 thick. The distance between the neutron production target and the (n,p) target, 3.14 m, makes it possible by time-of-flight to eliminate neutrons degraded below the maximum energy by scattering. Protons from the (n,p) reaction are detected simultaneously at three laboratory angles (7.5°, 12.5°, and 17.5°), in three particle telescopes each consisting typically of three hyperpure Ge elements. All three telescopes are mounted in a common cryostat. Spectra are obtained at other angles including zero by magnetically deflecting the (n,p) protons. Spectra recorded at E n = 118 MeV for (n,p) reactions on several light nuclei are presented.

Complete sets of polarization transfer coefficients have been measured for quasifree ([ital [rvec p]],[ital [rvec n]]) scattering from [sup 2]H, [sup 12]C, and [sup 40]Ca at 494 MeV and scattering angles of 12.5[degree], 18[degree], and 27[degree] ([ital q]=1.2,1.7,2.5 fm[sup [minus]1]). These measurements yield separated transverse ([sigma] [times]/I[ital q]) and longitudinal ([sigma] [center dot]/I[ital q]) isovector spin responses. Comparison of the separated responses to calculations and to electron-scattering responses reveals a strong enhancement in the spin transverse channel. This excess transverse strength masks the effect of pionic correlations in the response ratio.

Measurements of the gamma-ray and neutron distributions produced by cosmic-ray bombardment of planetary surfaces can provide important information about water content and near-surface elemental compositions. Accurate interpretation of such measurements depends heavily on comparisons with radiation-transport calculations, which involve not only the soil composition but also assumptions about (1) particle types and energy distributions of cosmic rays, (2) interaction mechanisms for high-energy protons and neutrons, (3) neutron transport at low energies, and (4) production of prompt gamma rays and radionuclides in proton- and neutron-induced reactions. The present experiment simulates the planetary situation by directing a beam of 800 MeV protons onto a large container of Martian-like sand. Measurements were made of (1) the spatial distributions for protons and neutrons inside the container via activation foils and (2) the energy spectrum for neutron leakage out of the container via time of flight. Several configurations of the target were used to represent different Martian surfaces. The measured neutron-energy spectra are in good agreement with calculations made using a computer code that couples medium-energy neutron production to low-energy neutron transport, and the measured spatial distributions match those predicted using calculated fluxes and known cross sections for radionuclide production. The analyses include discussions of soil water content, finite-size effects, and the implications for data from possible planetary missions.

Differential cross sections and analyzing powers for neutron elastic scattering from {sup 93}Nb have been measured at energies from 8 to 17 MeV using pulsed-beam time-of-flight methods. These data plus total cross-section data from 1 to 20 MeV are interpreted in terms of the spherical optical model. Several sets of optical potential parameters with systematic energy dependences have been derived in searches that used different initial parameter sets. In addition, comparisons of the data to calculations based on previously reported optical potentials are presented. It is concluded that the data favor the inclusion of a small imaginary spin-orbit term.

Because polyethylene-moderated {sup 3}He counters are rugged and reliable, they are generally the instruments of choice for field detection of fast neutrons in gamma-ray backgrounds. Their main drawback is the bulky, massive moderator needed to reduce the incident neutron energies to the sensitive range of the {sup 3}He+n capture reaction. This report discusses an optimization approach that provides a detector with uniform angular response and the maximum detection efficiency per unit mass. The key assumption is that each parameter has a geometrical interpretation and its effect on the response can be evaluated independently from that of the others. Specifically, the detection efficiency can be written as a product of separate functions for the moderator mass, gas pressure, tube position, etc., and the uniformity of the angular response is determined by the symmetry of the moderator dimensions. This analytical model was tested by compiling a comprehensive database of detector efficiencies as functions of the different parameters, including one- versus two-tube detectors, moderator masses from 1 to 6 kg, gas pressures from 1 to 20 atm, etc. In general, the model reproduced both the magnitude and angular dependence of the efficiency to within about 10%. To a high degree, the most important more » parameters are polyethylene mass and the quantity of {sup 3}He gas; because of neutron diffusion out of the moderator, the optimum tube positions are near the center of the detector. The highest value of the efficiency per unit mass occurs near 3 kg, a result that requires the most compact detectors to use more than a single {sup 3}He tube. In this case, the optimum detector has two tubes and a total mass of 3.0 kg. Although they could use 4-atm tubes with 2.54-cm diameters, increasing the gas volume could easily provide a 20% increase in efficiency with no changes in other parameters. « less

The imaging Compton telescope COMPTEL on the Gamma Ray Observatory has unusual spectroscopic capabilities for measuring solar γ-ray and neutron emissions. Flares can be observed above the 800 keV γ-ray threshold of the telescope. The telescope energy range extends to 30 MeV with high time resolution burst spectra available from 0.1 to 10 MeV. Strong Compton tail suppression facilitates improved spectral analysis of solar flare γ-ray emissions. In addition, the high signal-to-noise ratio for neutron detection and measurement provides new neutron spectroscopic capabilities. For example, a flare similar to that of 1982 June 3 will yield spectroscopic data on > 1500 individual neutrons, enough to construct an unambiguous spectrum in the energy range of 20 to 150 MeV. Details of the instrument response to solar γ-rays and neutrons are presented.

Differential cross sections at 16.44 and 17.57 MeV and analyzing powers at 8.0, 9.1, 11.1, 13.5 and 15.0 MeV have been measured for the 9Be(p, n0)9B reaction and combined with previous measurements for 9Be(p, p0)9Be, 9Be(p, n0)9B and 9Be(n, n0)9Be to form the first model-complete data base for a Lane model analysis. Energy dependences of the model parameters (including Coulomb corrections) have been handled in a consistent manner. The real central part of the isovector Lane model potential exhibits no surface peaking for this nucleus. Strong evidence is found for a complex spin-orbit part of the isovector potential describing nucleon scattering from 9Be.

Differential cross sections for neutron scattering from 58 Ni and 60 Ni to the ground state and first excited state have been measured at 8, 10, 12 and 14 MeV. In addition, analyzing powers were measured for scattering to the same states for 58 Ni at 10 and 14 MeV, and for 60 Ni at 10 MeV. The data were analyzed in the framework of a coupled-channel formalism in which the vibrational model was assumed with deformed central and spin-orbit potentials. A spherical-optical-model analysis of the elastic scattering data was also performed following the coupled-channel analysis. Predictions for (p, p) and (p, p') scattering observables have been made and compared with measurements previously published. This approach permits neutron and proton deformation parameters to be deduced similarly from (n, n') and (p, p') scattering measurements for 58,60 Ni. These deformation parameters are compared in the framework of the core-polarization model of Madsen, Brown and Anderson.

The transverse polarization transfer coefficient Kyy′ has been measured for the breakup reaction 2H( p , n ) 2p at θ = 0° for five incident energies in the range from 10.6 to 15.1 MeV. The results are presented at each incident proton energy as a function of neutron energy. All of the Kyy′ (0°) data have positive values around 0.4 for low neutron energies and negative values around −0.2 for high neutron energies. The data are compared to predictions from a three-body separable-potential model calculation.

The analyzing power A/sub y/(theta) for scattering of neutrons from deuterons at 10 MeV for 30/sup 0/ to 145/sup 0/ (c.m.) was measured to an accuracy better than +- 0.005. The results are compared to published p-d data at 10 MeV, and convincing differences are noted for the first time. These differences provide a sensitive test both of calculations for the three-nucleon system and, more importantly, of the fundamental nucleon-nucleon interaction.

Cross sections at six angles from 0/sup 0/ out to 20/sup 0/ in the c.m. system have been measured for 1/sup +/..-->..0/sup +/ transition in the reaction /sup 6/Li(n,p)/sup 6/He at E/sub n/ = 118 MeV. The 0/sup 0/ cross section is in good agreement with measurements of the same quantity on /sup 6/Li(p,n)/sup 6/Be at similar energies. The 0/sup 0/ (n,p) cross section gives a value of 161 +- 17 MeV fm/sup 3/ for the volume integral of the central part of the spin-isospin interaction; a theoretical value of 161 MeV fm/sup 3/ is in good agreement. A distorted wave calculation for a pure, Gamow-Teller transition is in fair agreement with the measured (n,p) angular distribution. An approximate resolution of the weak 1/sup +/..-->..2/sup +/ transition to the first excited state of /sup 6/He at 1.8 MeV shows an angular distribution of a very different character corresponding to a transition of mixed angular momenta.

A large-volume large-acceptance neutron polarimeter consisting of two parallel planes of plastic scintilators has been used to measure transverse polarization transfer in (p, n) reactions in the energy range 80 MeV < Ep < 160 MeV. The effective analyzing power obtained from 1H(n, n)1H reactions in the plastic scintillator has been measured by observing neutrons from the 14C(p, n)14N (2.31 MeV) reaction at θ = 0°. Neutron energies are determined by time-of-flight with a resolution of about 1 MeV for 160 MeV neutrons. At this same energy the effective left-right analyzing power is 0.34±0.02 and the effective area is (1.9±0.3) cm2.

The analyzing power and differential cross section for elastic neutron scattering from calcium have been measured at 9.9, 11.9 and 13.9 MeV using the 2 H(d, n) 3 He source reaction and neutron time-of-flight (t.o.f.) techniques to detect the scattered neutrons. Polarized neutron beams were produced via the polarization transfer reaction 2 H( d , n ) 3 He at θ = 0°. The data have been corrected for finite geometry and multiple scattering effects. None of the global neutron-nucleus optical model parameter sets usually referred to in the literature reproduces the present cross-section and analyzing power data. Individual as well as energy-averaged fits of the data resulting from new optical model searches are presented. It is shown that the quoted uncertainties of a recent empirical determination of the real part Δ V c of the Coulomb correction term are probably underestimated. Our imaginary Coulomb correction term Δ W c agrees quite well with both a very recent empirical determination and theoretical studies. Although the quality of the fits to the data can be improved by adding l -dependent potentials to the general optical potential, no definite conclusions can be drawn from the present data as to whether or not l -dependent potentials are important in neutron-calcium scattering in the energy range investigated. The data have also been analyzed using a Fourier-Bessel series description of the real central optical potential. Comparing the X 2 values, the experimental data are better reproduced by the Fourier-Bessel method than by our Woods-Saxon optical model analyses. The Fourier-Bessel potentials obtained show strong deviations from the standard Woods-Saxon shape but are in good agreement with calculations using the nuclear structure approach.

Differential cross sections and analyzing powers for neutron elastic scattering from /sup 89/Y have been measured at energies from 8 to 17 MeV using a neutron time-of-flight facility. The data have been analyzed with the spherical optical model and excellent representations are achieved at all energies with the derived optical potential parameters, which were constrained to vary linearly with energy. Comparisons have been made to two previously reported global spherical optical models as well.

The analyzing power Aγ(θ) for neutron-proton scattering has been measured for θ = 90°(c.m.) from 13.5 to 16.9 MeV and from θ = 50° to 145°(c.m.) at 16.9 MeV. Extensive Monte Carlo calculations have been made to correct for multiple scattering effects. Overall uncertainties are about ± 0.002. All the Aγ(θ) data, but primarily those at 16.9 MeV, disagree with predictons based on the phase-shift sets which have been derived previously by way of global analyses of nucleon-nucleon scattering data. Data for the product σ(θ)Aγ(θ) have been fitted with an expansion of the form (sin θ)(a0 + a1 cos θ + a2 cos 2θ). For the first time the need for a non-zero a2 has been illustrated for energies below 20 MeV. This parameter is shown to be related to the nucleon-nucleon F-state spin-orbit phase parameter. In addition, the P, D, and F spin-orbit phase parameter values derived from the present data differ significantly from the ones based on the Yale-IV and Liver-more-X global analyses. The derived D and F spin-orbit phase parameters also differ from those obtained in the recent analysis of nucleon-nucleon scattering data by Arndt et al.

Angular distributions of the cross section for the (p, n 0 ) reaction on 15 N and the (p, n 0 ), (p, n 1 ) and (p, n 2 + n 3 ) reactions on 13 C have been measured at energies from 9 to 17 MeV using neutron time-of-flight techniques. The (p, n 0 ) results are extensively compared to previous measurements. A coupled-channels Lane model based on isospin-conserving potentials was used to describe the available (p, p), (p, n) and (n, n) data in this energy range. Although the behavior of the 15 N + nucleon system is reasonably well described, no satisfactory potential was found for the 13 C case.

A Lane-model analysis of the /sup 9/Be + nucleon system has provided a detailed description of both cross-section and polarization data for (p,p) elastic, (n,n) elastic, and (p,n) quasielastic scattering over a range of energies. Emphasis is placed on consistency in isospin conservation, data-set completeness, and multichannel constraints. Results favor a symmetry potential which is energy dependent with volume and surface form factors for the real and imaginary wells, respectively. A symmetry spin-orbit (lxsigma-arrow-right)(txT) interaction was found to be unnecessary.

Data for the analyzing power A/sub y/(theta) for elastic scattering of neutrons from deuterons have been measured at 14.1 MeV for the range from 30/sup 0/ to 153/sup 0/ (c.m.) to accuracies between +- 0.003 and +- 0.006. The results are compared to previous n-d data at 14 MeV and are in significant disagreement with the most recent measurement. The present data are in excellent agreement with a Faddeev calculation by Doleschall. The data are also very similar to p-d scattering data at 14.1 MeV, although systematic deviations are observed at forward angles and near the maximum of A/sub y/(theta) at 130/sup 0/. Recent calculations indicate that Coulomb effects can explain most of these differences, although some features will require further investigation.

The quantities A/sub y/ and P/sub y/ were remeasured for E/sub p/

Time-of-flight techniques were used to measure the analyzing power for the scattering of neutrons from 9 Be at energies from 9 to 17 MeV. Because of the high nuclear density of beryllium, particular attention was paid to finite-geometry and multiple-scattering effects. For representing the data, an unusual method of Legendre-coefficient analysis was used to establish the smooth energy dependence of both the cross section σ(θ) and the analyzing power A y ( θ ). Spherical optical-model calculations were able to describe the σ(θ) and A y ( θ ) data simultaneously, but only after the introduction of an imaginary spin-orbit potential W s.o. ( r ). The geometry of the W s.o. ( r ) term was found to be the same as that of the surface-peaked imaginary central potential. Coupledchannels calculations using a quadrupole-deformed rotational model built on the 3 2 − ground state were able to describe inelastic scattering to the 5 2 − and 7 2 − excited states, but also required a W s . o . r potential.

Accurate analyzing power data have been obtained for scattering of 10- and 14-MeV neutrons from /sup 54/Fe and /sup 65/Cu with use of a new combination of techniques to produce pulsed, polarized neutron beams. Parametrization with the conventional optical model yields a spin-orbit interaction which is consistent with that observed for proton-nucleus scattering. This combined experimental and theoretical study represents the most sensitive test of similarities between proton and neutron spin-orbit potentials for medium-weight nuclei.

The evidence for a useful proportionality relationship between 0° (p, n) cross sections and the corresponding Gamow-Teller and Fermi beta-decay transition strengths is examined in detail. A simple parameterization for small momentum transfer L = 0 transitions is developed and used in the analysis of (p, n) data in the bombarding energy range 120–200 MeV. The parameterization describes the (p, n) differential cross section in terms of momentum transfer, energy loss, mass number, and bombarding energy and provides a straightforward way of extrapolating to zero momentum transfer. It is found that a single proportionality constant can serve to relate all Gamow-Teller transitions originating from the same target nucleus. The target dependence of this proportionality constant, however, is found to be unpredictable at the 20%–50% level, even within isotopic chains. Such large variations cannot be easily explained in the context of the standard single-step direct-reaction distorted-waves impulse approximation model.

The tensor analyzing power A/sub y//sub y/(theta), vector analyzing power A/sub y/(theta), and cross section sigma(theta) of the /sup 2/H(d-italic-arrow-right,..gamma..)/sup 4/He reaction have been measured for the angular range of 55/sup 0/--149/sup 0/ in the center of mass system at an incident deuteron energy of 95 MeV. The reaction is dominated by the transition involving the S-state component of /sup 4/He, as indicated by the approximately sin/sup 2/2theta angular distribution of the cross section. The observed deviation of sigma(theta) from this shape is due to either M2 strength, tensor force effects, or both. The tensor analyzing power A/sub y//sub y/(theta) is nearly isotropic, with a typical value of approximately 0.3 +- 0.1. The vector analyzing power A/sub y/ is zero within the statistical precision (typically +- 0.2) of this data set, indicating a reduced contribution from E1 and M2 transitions compared to lower energies. Direct capture calculations in the plane-wave Born approximation do not reproduce even the sign of A/sub y//sub y/.

Neutron time-of-flight measurements have been performed on the 81 Br(p,n) 81 Kr reaction at E p = 190 and 200 MeV. Gamow-Teller transition strengths have been deduced for final 81 Kr states accessible through solar neutrino capture on 81 Br. For the standard solar model, 81 Br is most sensitive to 8 B neutrinos, not — as previously believed — 7 Be neutrinos.

The polarization P y for the 3 H(p, n) 3 He reaction was measured for energies between 2 and 4 MeV. Special care was given to minimizing the effects of background and to interpreting the experimental spectra. The new values for P y are significantly higher than previous values, and comparison to the available data for the analyzing power A y for the same reaction now shows that in this energy range P y and A y are equal within experimental uncertainties. This equality negates earlier conclusions that sizeable differences existed between these observables. In particular, our new results demonstrate that in this reaction the effects of charge symmetry breaking on differences between these observables must be small.

Neutron time-of-flight techniques were used to measure the 9 Be(p, n 0 ) 9 B cross section from 0° to 160°(lab) at 10 energies between 8.15 and 15.68 MeV. The data are combined with previous results below 30 MeV in a Legendre coefficient analysis to evaluate the differential and integral behavior of the 9 Be(p,n) and 9 Be(p, n 0 ) 9 B cross sections. A coupled-channels Lane analysis of cross sections and analyzing powers for (p,n) quasi-elastic scattering and (p, p) and (n, n) elastic scattering is presented and compared to previous single-channel models.

The analyzing power A y ( θ ) and polarization P y ( θ ) for the 15 N(p, n 0 ) 15 O reaction have been measured for E p = 4.5–11.3 MeV. The values of the two observables are nearly the same above 11 MeV, where a “quasi-elastic” view of the (p, n) reaction to the analog state should be applicable. Below 10 MeV, however, large spin-flip amplitudes and isospin-mixing ratios provide the two major conditions needed to obtain P y ( θ ) ≠ A y ( θ ), and dramatic differences between the two observables are observed. The size of the differences and their dependence on energy are similar to the results predicted by shell-model calculations. The P y ( θ ) and A y ( θ ) measurements have been combined with existing cross-section data to provide information about spin-flip processes. We also comment on the connection between comparisons of P y ( θ ) and A y ( θ ) in charge-symmetric (p, n) reactions and the recent controversial measurements of a difference between the values of P y ( θ ) for a reaction and A y ( θ ) for the inverse reaction.

Differential cross sections for neutron elastic scattering and inelastic scattering to the first 2/sup +/ and 3/sup -/ excited states have been measured at 10, 14, and 17 MeV for /sup 120/Sn and at 10 and 14 MeV for /sup 116/Sn. Analyzing powers have also been measured at 10 and 14 MeV for elastic scattering from both isotopes and at 10 MeV for inelastic scattering from /sup 120/Sn. These data have been analyzed in the framework of the coupled-channels formalism for vibrational nuclei. Previously reported neutron scattering measurements performed below 25 MeV, along with total cross-section measurements from 10 keV to 100 MeV, and s- and p-wave strength functions were also considered in the analysis in order to place additional constraints on the optical potential parameters. Neutron scattering deformations have been deduced for the quadrupole and octupole vibrations. These deformations have been compared with those derived from earlier (n,n') and (p,p') scattering measurements which were reanalyzed in the present work.

Measurements and a Lane model analysis were Performed for σ(Θ) and Ay (Θ) for 11B(n,n)11B, and 11B(p,n)11C. Measurements for 10B(n,n)10B σ(Θ) and Ay(Θ) were analyzed with complementary (n,n) and (p...

Analyzing powers A/sub y/(theta) for inelastic scattering of 10-MeV neutrons to the first excited states of /sup 54/Fe, /sup 56/Fe, /sup 58/Ni, /sup 60/Ni, /sup 120/Sn, and /sup 208/Pb have been measured at a few selected angles. These data were analyzed using a coupled channels code in which the full Thomas form of the spin-orbit potential is assumed. The magnitudes of the observed spin-orbit deformations, which were found to be similar to those for (p,p') in each case, contradict recent suggestions based on microscopic nuclear structure considerations.

Measurements of the differential cross sections and analyzing powers have been made for /sup 28/Si(n,n/sub 0/) and /sup 28/Si(n,n/sub 1/) for incident neutron energies between 8 and 17 MeV. These data have been combined with previous differential and total cross-section data to obtain the most complete data set for neutron scattering from /sup 28/Si over the 8--40 MeV energy range. The data have been described within the framework of a symmetric rotational model using phenomenological coupled-channels calculations. Nuclear moments were deduced and they are in good agreement with those obtained from electron scattering and Coulomb excitation measurements. Various calculations were performed to determine the sensitivity of the data and calculations to the signs of the potential deformation parameters ..beta../sub 2/ and ..beta../sub 4/. The systematic analysis of the analyzing power data enabled the determination of the deformation length for the spin-orbit potential. Comparisons between neutron- and proton-scattering data and calculations were made to test the sensitivity of this type of data to charge symmetry breaking in the nuclear force and to investigate the isospin dependence of the absorptive part of the nucleon-nucleus scattering potential for /sup 28/Si. The results of these comparisons suggest that the differences between /sup 28/Si+n andmore » /sup 28/Si+p scattering can be attributed solely to Coulomb effects.« less

The analyzing power ${A}_{y}(\ensuremath{\theta})$ and differential cross section $\ensuremath{\sigma}(\ensuremath{\theta})$ have been measured for elastic scattering of 10-MeV neutrons from $^{208}\mathrm{Pb}$. These data were analyzed with a spherical optical model which has a real spin-orbit potential with either a three-parameter conventional form or a one-parameter semimicroscopic form. The predictions with both spin-orbit potentials reproduce the data equally well, suggesting that fewer free parameters can be used in spherical optical model calculations. Including an imaginary spin-orbit term ${W}_{\mathrm{SO}}(r)$ in the optical potential greatly improves the fits to the ${A}_{y}(\ensuremath{\theta})$ measurements and establishes the need for ${W}_{\mathrm{SO}}(r)\ensuremath{\ne}0$ in the n + $^{208}\mathrm{Pb}$ potential.NUCLEAR REACTIONS $^{208}\mathrm{Pb}$(n, n); $E=10$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$, ${A}_{y}(\ensuremath{\theta})$; deduced complex spin-orbit potential; spherical optical model calculations.

Considerable improvement in the quality of analyzing power experiments performed with polarized fast neutrons has been achieved during the last few years by using neutrons from the polarization transfer reaction 2 H ( d , n ) 3 He at a reaction angle of θ = 0°. To compromise in these experiments between intensity problems and finite geometry corrections, it is desirable in some instances to subtend a full-width angle Δθ of 20° (lab) centered about θ = 0°. In order to investigate the suitability of this reaction as a source of polarized neutrons for cases where the scatterer is close to the neutron source, the neutron polarization of the reaction 2 H ( d , n ) 3 He has been studied with Δθ of about 3° of 3° steps out to θ = 20° (lab). An incident deuteron energy near 8 MeV was chosen to yield outgoing neutrons at 11.0 MeV, a typical energy for neutron analyzing power experiments. It is found that the “effective” neutron polarization, a combination of the two polarizations measured when the direction of the deuteron polarization is inverted or “flipped” at the polarized ion source, is large and nearly constant for angles between θ = 0° and θ = 10° (lab).

The reactions $^{90}\mathrm{Zr}$, $^{208}(\mathit{p}$,xn) have been measured with 80.5 MeV protons in the neutron continuum ${E}_{n}$g20 MeV and the angular range 0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}145\ifmmode^\circ\else\textdegree\fi{}. Whereas the angle-integrated spectrum can be explained by semiclassical preequilibrium models, this nucleon-nucleon scattering approach fails at far backward angles. In contrast, the quantum statistical multistep calculations give good agreement. They are indicative of a decrease of the effective nucleon-nucleon interaction with increasing nucleon energy.

The analyzing power A y ( θ ) for the 9 Be(p, n) 9 B reaction was measured at seven energies between 8.1 to 15.0 MeV for reaction angles between 0° and 100° (c.m.). The A y ( θ ) values are predominantly negative and exhibit a smooth variation with energy. The significance of these results in Lane optical- model calculations for the 9 Be + nucleon system and in comparisons between the observables P y ( θ ) and A y ( θ ) is indicated.

The Gamow-Teller strength function in $^{71}\mathrm{Ge}$ has been measured by use of the reaction $^{71}\mathrm{Ga}(p, n)$ at ${E}_{p}=120 \mathrm{and} 200$ MeV. While a significant fraction of the total strength is associated with excited states located below particle-emission threshold, the first excited state exhibits little strength. Excited-state contributions to the total solar-neutrino capture rate for a $^{71}\mathrm{Ga}$ detector are about 14 solar neutrino units for the neutrino spectrum of the standard solar model and about 3-4 solar neutrino units for representative nonstandard solar models.

The spin correlation parameter C NN has been measured for n-p elastic scattering at 181 MeV. A comparison with predictions from various phase shift sets and potential models reveals sizeable deviations from the for the data Paris potential and Saclay phase shifts. For the Paris potential the deviations are directly related to an overprediction of the 3 D 2 phase shift parameter.

In connection with studies of differences between the polarization and analyzing power observables for the 15N(p, n)15O reaction, differential cross sections at ten proton energies between 5.5 and 9.3 MeV were measured using time-of-flight techniques. These new measurements allowed all previous data to be evaluated through use of the extensive total cross sections measured by Barnett in a study of the mass-16 system. Although some previous data were clearly discrepant, a simple renormalization of Barnett's measurements results in consistency of most of the data.

Angular distributions of the analyzing power ${A}_{y}(\ensuremath{\bigominus})$ have been measured for elastic scattering of neutrons from $^{54}\mathrm{Fe}$ and $^{65}\mathrm{Cu}$ at 10 and 14 MeV and for inelastic scattering to the first ${2}^{+}$ state of $^{54}\mathrm{Fe}$ at 10 MeV. We have combined the results with previous measurements and analyses of the differential cross sections in the same energy range and have carried out new deformed optical model calculations where the major concern was to study the spin-orbit interaction. The need for an imaginary spin-orbit term ${W}_{\mathrm{SO}}(r)$ is discussed. The (n, n\ensuremath{'}) data are important in reducing an ambiguity found between the deformation ${\ensuremath{\beta}}_{\mathrm{SO}}$ of the real spin-orbit potential and the strength ${W}_{\mathrm{SO}}$ of the imaginary spin-orbit potential.

Transverse vector polarization transfer coefficients K/sup y/'/sub y/ have been measured at a reaction angle of 0/sup 0/ for the processes /sup 12/C(d,n)/sup 13/N, /sup 14/N(d,n)/sup 15/O, /sup 16/O(d,n)/sup 17/F, and /sup 28/Si(d,n)/sup 29/P. The deuteron beam energy ranged from about 5 to 15 MeV for most cases. For the /sup 12/C(d,n)/sup 13/N reaction an excitation function of the differential cross section at 0/sup 0/ also was obtained from 6 to 14 MeV for the ground state and first excited state transitions. The polarization transfer coefficients were all positive and typically just slightly lower than the value of 2/3. This indicates that the contribution from spin transfer s = 3/2 is small at 0/sup 0/. Theoretical predictions of K/sup y/'/sub y/(0/sup 0/) using the distorted-wave Born approximation agree with the data to within about 10%.

The analyzing power A y ( θ ) for the 2 H(d, n) 3 He g.s. , reaction was measured from 0° to about 150° (c.m.) at 5.5, 7.0, 8.5, 10.0 and 11.5 MeV. The experiment was conducted with a newly developed pulsing and bunching system for the polarized deuteron beam and used standard time-of-flight neutron detection. The present results disagree in some angular regions with measurements of the same observable reported recently by a Zurich group who detected the 3 He particles, but agree with the limited angular distribution measured at 10 MeV by Hilscher and Liers, who also detected 3 He particles. The present results are reported in terms of associated Legendre polynomial expansions of the product σ ( θ ) A y ( θ ).

Triple coincidences between intermediate mass fragments (IMFs) and angle-correlated fission fragments were measured in the 270 MeV 3 He + 232 Th reaction. These measurements demonstrate that on the average IMF emission occurs prior to fission from a source which carriers 75–80% of the beam momentum. It was deduced that the average number of IMFs per fragmentation event is close to unity. The dependence of the fission probability on the IMF emission angle and atomic number suggests that fragments emitted at forward angles come from more peripheral collisions than those emitted at very backward angles.

The cross section and transverse polarization transfer for the $^{2}\mathrm{H}$(p,n)2p reaction at ${E}_{\mathrm{p}=160}$ MeV and theta=0\ifmmode^\circ\else\textdegree\fi{} have been measured with good energy resolution (1 MeV). An asymmetric peak shape characteristic of the $^{1}\mathrm{S}_{0}$ final-state interaction of the residual two-proton system has been clearly observed. The measured transverse polarization transfer coefficient for this peak is ${D}_{\mathrm{NN}}$(0?(de)=-0.43\ifmmode\pm\else\textpm\fi{}0.04. A simple impulse approximation calculation including the $^{1}\mathrm{S}_{0}$ final-state interaction reproduces the main features of the observed peak shape and polarization transfer. Small discrepancies observed in the peak tail region can be accounted for by including the $^{3}\mathrm{P}_{0}$,1,2 final state interaction.

The tensor analyzing power ${A}_{\mathrm{yy}}$, vector analyzing power ${A}_{y}$, and cross section \ensuremath{\sigma}(\ensuremath{\theta}) of the reaction $^{1}(\mathrm{d}\ensuremath{\rightarrow}$,\ensuremath{\gamma}${)\mathrm{}}^{3}$He have been measured at a deuteron energy of 95 MeV, corresponding to photo- disintegration with 37 MeV photons. The total cross section is in good agreement with $^{3}(\ensuremath{\gamma}$,p${)}^{2}$H measurements; ${A}_{y}$ and ${A}_{\mathrm{yy}}$ were both small and negative. ${A}_{\mathrm{yy}}$ is known to be sensitive to the $^{3}\mathrm{He}$ D-state amplitude, and all previous measurements of tensor analyzing powers have been made in an energy region where the initial state interaction between the proton and deuteron is strong. These data were interpreted using a plane-wave Born approximation model which has been successful in describing other measurements of ${A}_{\mathrm{yy}}$ at lower energies. Within the framework of this model, these measurements were found to be consistent with an asymptotic D-S state normalization ratio \ensuremath{\eta}=-0.029.

Angular distributions of the analyzing power A/sub y/(theta) have been measured for neutron elastic scattering and for neutron inelastic scattering to the first 2/sub 1//sup +/ states of /sup 54,56/Fe and /sup 58.60/Ni at 10 MeV, and for /sup 54/Fe and /sup 58/Ni at 14 and 17 MeV. The differential cross sections sigma(theta) for the same processes were measured at 17 MeV for /sup 54/Fe and /sup 58/Ni. These measurements have been combined with other measurements of sigma(theta) and A/sub y/(theta) and also with total cross sections to form a sizable data set for incident neutron energies up to 80 MeV. This data set has been described in the context of the coupled channels formalism to determine the energy dependences of the various terms of the deformed optical potential. Some emphasis was placed on investigating the magnitude of the deformation parameter ..beta../sub so/ of the neutron spin-orbit potential and the possibility that it might be energy dependent.

Data for the analyzing power ${A}_{y}(\ensuremath{\theta})$ for $n\ensuremath{-}p$ scattering at 16.9 MeV have been measured for the range from 50 to 145\ifmmode^\circ\else\textdegree\fi{} (c.m.). Eleven values are reported to an accuracy of about \ifmmode\pm\else\textpm\fi{}0.002, the highest overall precision ever obtained in any fast-neutron polarization experiment. Predictions based on phase-shift sets obtained from global analyses of nucleon-nucleon scattering disagree significantly with the new data. The data are sufficiently precise to show a dependence on the $f$-wave spin-orbit phase parameter.

The analyzing power A y ( θ ) for 12 C(n,n) 12 C elastic scattering and for inelastic scattering to the first excited state ( J π = 2 + , Q = −4.44 MeV) of 12 C was measured in the energy range from 8.9 to 14.9 MeV in 1 MeV steps. A pulsed polarized neutron beam was produced via the su2rmH( d , n ) 3 He polarization transfer reaction. Monte Carlo simulations were used to correct the data for finite geometry and multiple scattering effects. The A y data, together with published crosssection data, were analyzed in the framework of the spherical optical model and in the coupled-channels formalism. A good description of the data has been achieved.

The transverse polarization transfer for the $^{90}\mathrm{Zr}$(p,n) reaction has been measured for ${E}_{\mathrm{p}=160}$ MeV and theta=0\ifmmode^\circ\else\textdegree\fi{}. A sequence of alternating unnatural parity and natural parity excitations is clearly revealed. Some of the observed features are consistent with the known or predicted excitation energies of \ensuremath{\Delta}L=0 and \ensuremath{\Delta}L=1 resonances.

Accurate neutron analyzing powers have been obtained using a new pulsed polarized neutron facility. Data are presented for elastic scattering of 14-MeV neutrons from /sup 40/Ca, /sup 54/Fe, /sup 65/Cu, /sup 120/Sn, and /sup 208/Pb between 18/sup 0/ and 36/sup 0/. Our data exhibit no evidence for the anomalously large values which were reported previously at 20/sup 0/.

The polarization of neutrons from the reaction /sup 2/H(d, n)/sup 3/He has been measured for a deuteron energy E/subd/ = 2.44 MeV at emission angles of 45degree and 55degree (lab). The polarization values are discussed in relation both to previously reported discrepant data and to measured differences between p/suby/ and A/suby/ in the reaction /sup 3/H(p, n)/sup 3/He. (AIP)