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A resonant state at 3.21-0.04+0.12MeV, located just above the one-neutron separation threshold, was observed for the first time in Be12 from the Be11(d,p)Be12 one-neutron transfer reaction in inverse kinematics. This state is assigned a spin-parity of 0- according to the systematics of the level scheme of the N=8 isotones and decay-width analysis. Gamow coupled-channel and Gamow shell-model calculations show the importance of the continuum coupling, which dramatically influences the excitation energy and ordering of low-lying states. Various exotic structures associated with cross-shell intruding configurations in Be12 and in its isotonic nucleus Li11 are comparably discussed.

A detailed investigation of the basic hyperon-nucleon interactions in nuclei is one of the aims of Experiment 91-016, approved with high priority at CEBAF, to study the electroproduction of kaons on targets of deuterium, {sup 3}He, and {sup 4}He. Inasmuch as both the electron and K{sup +} are particles that interact relatively weakly with nucleons, electroproduction of light hypernuclei provides a low-distortion method for investigating the fundamental interactions between nucleons, {Alpha}`s, and {Epsilon}`s in few-body systems. In particular, the (e,e`K{sup +}) reactions on cryogenic targets of D, {sup 3}He, and {sup 4}He will be studied at incident electron energies near 3 GeV with coincident detection of the emergent e and K{sup +} in the HMS and SOS magnetic spectrometers in Hall C. Construction of the He target, operating at {approximately}10 atm, {approximately}50 K and capable of dissipating {approximately}30 W, is expected to be complete prior to commencement of production runs in Hall C. The first data runs for E91-016, expected to begin late in FY 1995, will also be the basis for a doctoral thesis at Hampton University. In addition to providing new information on the phases of hyperon-nucleon interactions, measurements of cross sections for hypernuclear formation, and interference phenomena,more » the data may provide evidence for the presence of bound {Epsilon}`s and strange di-baryonic states that are the subject of considerable theoretical discussion.« less

The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and He. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon., 37 pages, 32 figures, 4 tables

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1n(x, Q2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023

We have measured angular distributions for the {sup 15}N({sup 6}Li,{ital d}){sup 19}F and {sup 16}O({sup 6}Li,{ital d}){sup 20}Ne reactions at a bombarding energy of 22 MeV. Distorted-wave Born approximation and Hauser-Feshbach calculations were used to analyze the data. Alpha spectroscopic factors were obtained for all the states up to 4.1 MeV in {sup 19}F and 6 MeV in {sup 20}Ne. {copyright} {ital 1996 The American Physical Society.}

We develop a new and comprehensive coordinate-space theory of pion-nucleus scattering to facilitate disentangling the conventional aspects of pion scattering from the non-conventional ones relevant to issues of hadron dynamics. We work in coordinate space in order to both unify and extend the relatively extensive and successful analyses of exclusive pion-nucleus reactions previously made within a similar framework. We construct the optical potential microscopically in a shell-model framework by summing particle-hole pair configurations, leading naturally to a coupled-channel formulation. The theory includes a complete treatment of all spin-isospin components of the pion-nucleon scattering amplitude, and Fermi averaging is done explicitly. We present numerical results showing the significance of Fermi motion and spin dependence on charge-exchange angular distributions: Single and double spin flip are shown to play dominant and generally unappreciated roles in charge-exchange reactions, and corrections for Fermi motion are shown to be needed in order to quantitatively separate medium effects from conventional multiple scattering.

A total of 38 angular distributors have been measured for the [sup 19]F([sup 6]Li,[ital d])[sup 23]Na reaction leading to states in the excitation energy region 6.3--13.25 MeV. For many of them, [ital L] values have been assigned and spectroscopic factors extracted, using standard distorted-wave techniques.

In the [sup 20]Ne([ital t],[ital p])[sup 22]Ne reaction at a bombarding energy of 15 MeV, excitation energies have been measured for 81 levels up to [ital E][sub [ital x]]=13.4 MeV. Thirteen new levels were identified. Distorted-wave Born-approximation (DWBA) calculations with spherical and deformed potentials were used to analyze the angular distributions. Two-step processes were found to make important contributions to the reaction. For most low-lying positive-parity levels, results are analyzed with two-particle transfer amplitudes from a realistic shell-model calculation. We have assigned spin-parities to 42 levels above 6.6 MeV based on the success of the DWBA analysis.

By using the {sup 77}Se({ital t},{ital p}){sup 79}Se reaction at 17 MeV, angular distributions have been measured for transitions leading to 34 states or groups of states in {sup 79}Se up to an excitation energy of approximately 3.2 MeV. Twelve of these states are reported for the first time. Comparisons with distorted-wave Born-approximation calculations have allowed the {ital L} transfer for most of the transitions observed to be determined. Four {ital L}=0 transitions are seen, leading to assignments of {ital J}{sup {pi}}=1/2{sup {minus}} to the states populated. The {ital J}{sup {pi}} values for the majority of the other final states have been restricted to one of two values.

The A(e,e'K+)YX reaction has been investigated in Hall C at Jefferson Laboratory for 6 different targets. Data were taken for Q2)approx 0.35 and 0.5 GeV2) at a beam energy of 3.245GeV for 1)H, 2)H, 3)He, 4)He, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of Lambda and Sigma0) hyperon production off the proton, and Sigma-) off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for 3,4)He targets.

The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant., 6 pages, 3 figures, 1 table, revtex

Complete angular distributions are presented (t-italich-italice-italict-italica-italic/sub c.m./ = 9X(de--90/sup 0/) for the reaction /sup 13/C(/sup 13/C, ..cap alpha..)/sup 22/Ne in the energy range E-italic/sub c.m./ = 6.25--9.125 MeV. The data exhibit significant nonstatistical behavior and have been fitted to a linear Legendre polynomial sum using a least-squares procedure. A second procedure makes a grid search to find a best fit to an amplitude squared equation. The correlations with structures in other C+C systems are discussed.

At E(/sup 7/Li) = 22.0 MeV, forward-angle angular distributions have been measured for 37 states (or groups of states) up to an excitation energy of 9.1 MeV, using a multiangle spectrograph and a gas target.

Direct comparison of data for 12 C (α, p ) 15 N and 16 O (α, p ) 19 F allows the identification of 3p4h states in 15 N with J = 5 2 + , 9 2 + and 13 2 + . Correspondence between 19F and 15N is very good, in both transfer strengths and excitation energies.

Twenty levels in K38 up to an excitation energy of 10.26 MeV have been identified in a study of the Ca40(d, )K38 reaction at an incident deuteron energy of 22.8 MeV. Differential cross sections were measured at forty-four angles in an angular range 11°165°. Distorted-wave Born approximation analysis has been performed for eight transitions using two-nucleon spectroscopic amplitudes derived from a full sd shell-model calculation. For other levels, distorted-wave Born approximation calculations were performed assuming simple two-nucleon configurations. The 7.32-MeV level is found to be populated by L=0+2 transfer and hence has J=1+. A newly identified level at 9.88 MeV is found to be excited by L=2 transfer and hence has J=1+, 2+, or 3+. NUCLEAR REACTIONS Ca40(d, )K38, Ed=22.8 MeV, measured E and (, E), DWBA analysis, deduced levels, L transfer. © 1983 The American Physical Society.

The 12 C( 14 N, α) 22 Na reaction has been investigated at 14 N bombarding energies of 30.3, 35.0, 40.0 and 45.5 MeV, and the 14 N( 12 C, α) 22 Na reaction has been investigated at a 12 C bombarding energy of 39.3 MeV. The α-particle reaction products were recorded using a multiple-gap spectrograph. One hundred eighty-five levels below 17.86 MeV have now been observed in 22 Na, many of them for the first time. Though some “resonance”-like behavior is observed, the overall results are consistent with a compound-nucleus reaction mechanism.

Earlier /sup 1/4N(t,p)/sup 1/6N data for levels between 5.5 and 8.5 MeV excitation have been subjected to a distorted-wave Born-approximation analysis in order to extract L values and place limits on J/sup ..pi../. Three 1/sup +/ levels are located at 6422, 6512, and 7006 keV, and possibly at 5520 keV. Several levels are suggested to be unresolved doublets.

Symmetric fission of 24 Mg into two 12 C nuclei following inelastic scattering of 120 MeV α-particles has been studied. The 12 C g.s. + 12 C g.s. and the 12 C g.s. + 12 C(4.44 MeV) decay modes were identified in the excitation energy ranges of 24 Mg, 22 MeV ≦ E x ≦ 26 MeV and 25 MeV ≦ E x ≦ 32 MeV, respectively. Depending on the assumptions made about the α'-inclusive spectrum, lower and upper limits have been obtained for the average partial width 〈 Γ CC / Γ 〉.

States populated in the /sup 15/N(/sup 6/Li,d)/sup 19/F reaction at 22 MeV are compared with those in /sup 16/O(/sup 6/Li,d)/sup 20/Ne at the same energy. Cross section ratios are in good agreement with a weak-coupling model, in contrast to previous observations via the (/sup 7/Li,t) reaction. Two strong transitions are observed to states at E/sub x/ = 8.288 and 8.957 MeV in /sup 19/F. The measured angular-distribution shapes and alpha-transfer strengths for these states are consistent with their being, respectively, the (13/2)/sup -/ and (11/2)/sup -/ members of the K/sup ..pi../ = (1/2)/sup -/ band in /sup 19/F. A comparison between the measured alpha-particle widths for these states and the single-particle alpha widths calculated in a Woods-Saxon well supports the above assignments.

The 24 Mg(t, α) 23 Na reaction has been studied at bombarding energies of 15.0 and 23.5 MeV. Spectroscopic strengths extracted at the two energies are in good agreement and indicate a diffuse, rather than a sharp Nilsson Fermi surface for 23 Na and 24 Mg. Significant population of high-spin states indicates the importance of multistep and/or compound processes. Data were also taken for 28 Si(t, α) 27 Al at 23.5 MeV. A FR/NL DWBA normalization of 11 ± 2 was consistent with all three (t, α) data sets.

Complete angular distributions (theta/sub c.m./ = 9/sup 0/--90/sup 0/) for the reaction /sup 13/C( /sup 13/C,..cap alpha..) /sup 22/ Ne in the energy range E/sub c.m./ = 6.25--13.38 MeV have been subjected to a battery of tests to determine the existence of a significant nonstatistical component in the cross section. The autocorrelation function, distribution of cross sections, and channel correlations were investigated. The data were also compared with the predictions of Hauser-Feshbach calculations. A large nonstatistical component was found in all tests and comparisons.

The reaction 12 C + 13 C → α + 21 Ne has been investigated at a c.m. bombarding energy of 14.5 MeV using beams of both 12 C and 13 C. The α-particle reaction products were recorded using a multiple-angle spectrograph. Seventy-six levels were observed below 12.56 MeV in 21 Ne; 28 levels from 9.42 to 12.56 MeV are reported for the first time. The data are consistent with a compound-nucleus reaction mechanism.

The reaction /sup 41/K(t,p)/sup 43/K has been investigated with a 15-MeV triton beam. Twenty levels of /sup 43/K (many of them unreported previously) have been identified up to about 3.4 MeV excitation energy. Angular distributions were measured for all levels. Comparison with distorted-wave Born-approximation calculations allows extraction of L values for most of them. Three multiplets arising from the couplings of (1f/sub 7/2/)= 2/sup 2/ and (1f/sub 7/2/)= 4/sup 2/ transferred neutrons with the 1d/sub 3/2/ proton hole have been identified in /sup 43/K. Their energy centroids are closely related to the (1f/sub 7/2/)/sup 4/ spectrum of /sup 44/Ca. The general sum rules for two-nucleon transfer reactions and a more specialized sum rule give a good account of the data and suggest spin and parity assignments for many of the observed states. The positive parity states in /sup 43/K are compared with f/sub 7/2//sup 4/(d/sub 3/2/s/sub 1/2/)-1 and f/sub 7/2//sup 3/ p/sub 3/2/d/sub 3/2//sup -1/ shell-model calculations.

Angular distributions have been measured at a bombarding energy of 28 MeV for the reaction /sup 24/Mg(d,/sup 6/Li) /sup 20/Ne, populating most of the known levels below 9.1 MeV excitation. Results were compared with distorted wave Born-approximation calculations, and ..cap alpha.. spectroscopic factors extracted. Those for the g.s. band are in reasonable agreement with theoretical predictions. Members of the 7.20-MeV band are found to possess very large spectroscopic factors, in agreement with the core-excited nature of this band.

The /sup 76/Se(t,p)/sup 78/Se reaction has been studied at an incident energy of 17 MeV. Excitation energies for 80 states (or groups of states) up to 6.16 MeV have been measured. Angular distributions have been obtained for 61 of them, below E/sub x/ = 5.03 MeV. Comparison of the data with distorted-wave Born approximation calculations, using pure configurations for the transfer amplitudes, have enabled the L transfer (and hence J/sup ..pi../ value) to be determined for 58 of these states. Of these assignments, 52 are new.

The $^{39}\mathrm{K}(d, t)^{38}\mathrm{K}$ reaction has been utilized to study states in $^{38}\mathrm{K}$ below an excitation energy of 5 MeV. Spectroscopic factors have been extracted by comparing the data with distorted-wave calculations. For states for which both $l=0$ and $l=2$ transitions are allowed, attempts have been made to extract relative admixtures. Two positive-parity states, not previously reported in neutron-pickup experiments, have been observed at ${E}_{x}=3.44 \mathrm{and} 3.99$ MeV. Two weak negative-parity states have been observed at ${E}_{x}=2.64$ ($l=1$) and 4.66 MeV ($l=3$), indicating the admixture of core-excited configurations in the ground-state wave function of $^{39}\mathrm{K}$.

Angular distributions of the elastic scattering of 3 He by 4 He over an angular range θ cm = 30° to 150° have been measured for five 3 He bombarding energies from 12.0 to 19.0 MeV. A simple optical model with and without a spin-orbit potential has been used to fit the angular distributions. In the resonance free region above 13.5 MeV bombarding energy the optical parameters vary little from U = 100 MeV and W = 10 MeV. These values are more characteristic of alpha-particle scattering than of 3 He scattering. The spin-orbit potential of about 20 MeV is much larger than that found with heavier targets.

Excitation functions for 12 C( 3 He, α) reactions leading to the ground state, first and third excited states of 11 C have been measured at selected angles for E 3 He = 12 to 18 MeV. Angular distributions were measured at bombarding energies of 16,17 and 18 MeV for the ground state and four excited states to study the energy dependence of extracted spectroscopic factors. The ground state reaction is well represented at all energies by a zero-range, local DWBA calculation for neutron pickup with a renormalization factor of R ≈ 40, which is twice as large as the generally accepted value. At E 3 He = 18 MeV angular distributions leading to the ground state and first ten excited states of 11 C were measured. In general the pickup calculations for the excited state reactions do not give a good representation of the measurements when the ground state optical parameters are used.

Gamma-ray branching ratios have been measured for several states near E x = 3.7 MeV in 26 A1 with the 24 Mg(τ, pγ), 25 Mg(τ, dγ) and 27 Al(τ, αγ) reactions. Reaction particles were detected at 0° in coincidence with de-excitation γ-rays. Proton angular distributions were measured at E τ = 11 MeV for the 24 Mg(τ, p) 26 Al reaction to the 3.72 and 3.75 MeV levels. The results yield an assignment of J π = 1 + , T = 0 for the 3.72 MeV state, in disagreement with a recent J π = 0 + , T = 1 assignment, but in agreement with an earlier assignment of J = 1. The 3.75 MeV level is observed to be a close doublet. One member of this doublet is preferentially excited in the 25 Mg(τ, dγ) and 27 Al(τ, αγ) reactions and is associated with a previous assignment of J π = 2 + or 3 + . The second member of the 3.75 MeV doublet is preferentially excited in the 24 Mg(τ, pγ) reaction and is identified as the second 0 + , T = 1 state in 26 A1. Branching ratio results for the 3.68 MeV level establish that this level is also a close doublet. Results for the 3.59 MeV state are in agreement with previous work.

Distorted-wave calculations have been performed for the 36 Ar( 6 Li, d) 40 Ca reaction to the first five 0 + levels of 40 Ca. using the wave functions of Gerace and Green, with up 8p-8h excitations. If we interchange the 0 4 + and 0 5 + models states, agreement with experiment is excellent.

A method is outlined for performing finite-range distorted-wave Born-approximation calculations for pickup reactions in which the ejectile is unbound with respect to the transferred particle.

The reaction /sup 13/C(t,p) has been used to locate 1p-2h and 2p-3h states in /sup 15/C. Results for the negative-parity levels are in good agreement with expectations for (sd)/sup 2/ L = 0, 2, and 4 transfers as given by /sup 14/C(t,p)/sup 16/C.

Wave functions for /sup 18/O derived from fits to particle-transfer and ..gamma..-decay data have been used in finite-range distorted-wave calculations of the reaction /sup 14/C(/sup 7/Li,t)/sup 18/O. The agreement between experimental and theoretical cross sections is excellent.

The resonance previously observed in 12 C( 12 C, α) 20 Ne at E c.m. = 19.0 MeV is assigned J π = 10 + from the shape of the ground-state angular-distribution measured at resonance.

A distorted wave analysis of the 32S(t,p) 34S reaction reveals that the 0+ state at 5.86 MeV, the 2+ state at 7.80 MeV and the 4+ state at 8.42 MeV are the principal components of the (1 f 7 2 2 , T = 1 multiplet.

We have measured a (..pi../sup +/,..pi../sup /minus//) angular distribution for the transition to the double isobaric analog state of a T = 2 target nucleus, /sup 56/Fe, at T/sub ..pi../ = 180 MeV. The data are compared to measurements on T = 1 targets and to theoretical predictions. The angular dependence is different from that observed in measurements on T = 1 targets. Some features of the data are reproduced by the theoretical predictions, but significant discrepancies remain. 15 refs., 3 figs., 1 tab.

L-value decompositions are presented for angular distributions of 22 levels below 3-MeV excitation in /sup 53/V, for the reaction /sup 51/V(t,p)/sup 53/V. Correspondence with /sup 52/Ti is discussed.