Search

The study of hyperon resonances has entered a new era of precision with advent of high-statistics photoproduction data from the CLAS detector at Jefferson Lab. These data have multi-particle final states, allowing clean identification of exclusive reactions associated with strange mesons and baryons. Examples of physics results are: evidence for isospin interference in the decay of the Λ ( 1405 ) resonance; a strong suggestion of meson cloud effects in the structure of the Σ ( 1385 ) resonance; data from K ⁎ photoproduction that will test the existence of the purported K 0 ( 800 ) meson. Properties of other hyperon resonances will also be studied in the near future.

The spin structure functions g 1 for the proton and the deuteron have been measured over a wide kinematic range in x and Q 2 using 1.6 and 5.7 GeV longitudinally polarized electrons incident upon polarized NH3 and ND3 targets at Jefferson Lab. Scattered electrons were detected in the CEBAF Large Acceptance Spectrometer, for 0.05 Q 2 5 GeV 2 and W 3 GeV . The first moments of g 1 for the proton and deuteron are presented – both have a negative slope at low Q 2 , as predicted by the extended Gerasimov–Drell–Hearn sum rule. The first extraction of the generalized forward spin polarizability of the proton γ 0 p is also reported. This quantity shows strong Q 2 dependence at low Q 2 . Our analysis of the Q 2 evolution of the first moment of g 1 shows agreement in leading order with Heavy Baryon Chiral Perturbation Theory. However, a significant discrepancy is observed between the γ 0 p data and Chiral Perturbation calculations for γ 0 p , even at the lowest Q 2 .

The theoretical motivation to look for S=+1 resonances is introduced and searches for such states in the literature are reviewed. The motivation for the recent pentaquark searches is discussed and the experimental details are described for several positive results of the S=+1 resonance with a mass of approximately 1.54 GeV, now called the Θ+. Finally, some new theoretical proposals to explain the recent experimental results are briefly mentioned, followed by a short discussion of future experimental prospects to learn more about pentaquark states.

We describe the upgraded time-of-flight facility at the Indiana University Cyclotron which has been used to measure the polarization transfer induced in ( p → , n → ) reactions at intermediate energies, Ep=100–200 MeV. The Indiana Neutron POLarimeter (INPOL) is able to measure simultaneously two orthogonal neutron spin polarizations induced in charge exchange reactions with polarized proton beams oriented in each of the three spin states, normal ( N → ), sideways ( S → ) and longitudinal ( L → ).

The CEBAF Large Acceptance Spectrometer at 12 GeV (CLAS12) is located in Hall B, one of the experimental halls at Jefferson Lab. The forward part of CLAS12 is built around a superconducting toroidal magnet. The six coils of the toroid divide the detector azimuthally into six sectors. Each sector contains three multi-layer drift chambers for reconstructing the trajectories of charged particles originating from a fixed target. Each of the 18 planar chambers has two “superlayers” of six layers each, with the wires in the two adjacent superlayers oriented at ± 6 ° stereo angles. Each layer has 112 hexagonal cells spanning a range from about 5 ° to 40 ° in polar angle. The six-layer structure provides redundancy in track segment finding and good tracking efficiency even in the presence of some individual wire inefficiency. The design, construction, operation, and calibration methods are described, and estimates of the efficiency and resolution are presented from in-beam measurements.

The GeV photon beam at SPring-8 is produced by backward-Compton scattering of laser photons from 8 GeV electrons. The maximum energy of the photon will be above 3 GeV, and the beam intensity will be 10 7 photons/sec. Polarization of the photon beam will be 100 % at the maximum energy with fully polarized laser photons. We report the outline of the quark nuclear physics project with this high-quality high-intensity beam.

A complete set of spin observables was measured for the 2 H(p,n)2p reaction at 200 MeV at the Indiana University Cyclotron Facility (IUCF) with the high intensity polarized ion source (HIPIOS) and the Indiana Neutron Polarization Facility (INPOL). The incident proton beam was delivered successively in each of the three spin states, normal ( N ), sideways ( S ), and longitudinal ( L ). Two large-volume neutron polarimeters placed along the 0° and 24° beam lines measured the polarizations of the emitted neutrons in each of the three spin states. The measured cross sections and spin observables are compared with three-body Faddeev calculations, which generally agree with the data. The ratio of the longitudinal to transverse response is suppressed rather than enhanced, as predicted by some models.

We have developed an apparatus that can polarize muonic 3He and detect the triton from the reaction μ− + 3He → ν + 3H. With this apparatus, we have measured the vector analyzing power of the reaction. This technique promises to provide a good test of QCD.

We have made simultaneous measurements of singles ($\stackrel{\ensuremath{\rightarrow}}{p}, {\stackrel{\ensuremath{\rightarrow}}{p}}^{\ensuremath{'}}$) spin-transfer observables and coincident ($\stackrel{\ensuremath{\rightarrow}}{p}, {p}^{\ensuremath{'}}\ensuremath{\gamma}$) yields and asymmetries for the 15.11 MeV, ${1}^{+}$, $T=1$ state in $^{12}\mathrm{C}$, at an incident proton bombarding energy of 200 MeV. Data were taken at four proton scattering angles ranging from ${\ensuremath{\theta}}_{p}^{\mathrm{c}.\mathrm{m}.}=5.5\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 16.5\ifmmode^\circ\else\textdegree\fi{}$. Both vertical (normal to the reaction plane) and horizontal (in-plane) incident beam polarizations were used, which allowed us to extract 16 different observables for this transition. In particular, using the ($\stackrel{\ensuremath{\rightarrow}}{p}, {p}^{\ensuremath{'}}\ensuremath{\gamma}$) reaction, we measured the sideways and longitudinal analyzing powers, ${D}_{0S}$ and ${D}_{0L}$, which vanish identically in the ($\stackrel{\ensuremath{\rightarrow}}{p}, {p}^{\ensuremath{'}}$) reaction. Detailed comparisons of all observables to calculations done in both relativistic and nonrelativistic formalisms are presented. Surprisingly, a relativistic description in which knock-on exchange processes are not explicitly included provides the best overall agreement with the data.

Differential cross sections were measured and compared to distorted-wave impulse-approximation calculations for the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${4}^{\mathrm{\ensuremath{-}}}$(\ensuremath{\nu}${\mathit{d}}_{5/2}$,\ensuremath{\pi}${\mathit{p}}_{3/2}^{\mathrm{\ensuremath{-}}1}$) state excited in the $^{12}\mathrm{C}$(n,p${)}^{12}$B (4.52 MeV) reaction, the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${6}^{\mathrm{\ensuremath{-}}}$(\ensuremath{\nu},${\mathit{f}}_{7/2}$\ensuremath{\pi}${\mathit{d}}_{5/2}^{\mathrm{\ensuremath{-}}1}$) state excited in the $^{28}\mathrm{Si}$(n,p${)}^{28}$Al (5.175 MeV) reaction, and the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${10}^{\mathrm{\ensuremath{-}}}$(\ensuremath{\nu}${\mathit{h}}_{11/2}$,\ensuremath{\pi}${\mathit{g}}_{9/2}^{\mathrm{\ensuremath{-}}1}$) state excited in the $^{120}\mathrm{Sn}$(n,p${)}^{120}$In (\ensuremath{\simeq}0.0 MeV) reaction at 300 MeV. We obtained a normalization factor of 0.68 for the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${10}^{\mathrm{\ensuremath{-}}}$(\ensuremath{\nu}${\mathit{h}}_{11/2}$,\ensuremath{\pi}${\mathit{g}}_{9/2}^{\mathrm{\ensuremath{-}}1}$) state excited in $^{120}\mathrm{Sn}$(n,p${)}^{120}$In (\ensuremath{\simeq}0.0 MeV) reaction; this is the first ``1\ensuremath{\Elzxh}\ensuremath{\omega}'' stretched state known in this mass region.

The {sup 70,72}Ge({ital n},{ital p}){sup 70,72}Ga reactions have been measured at a beam energy of 200 MeV in order to study the behavior of Gamow-Teller (GT) strength near the {ital N}=40 subshell closure. The GT quenching factor extracted for {sup 70}Ge is consistent with results for {sup 54}Fe and with calculations done on the quasiparticle random-phase-approximation model if they are renormalized by a factor of about 0.6. The quasiparticle random-phase approximation predicts a drastic reduction in concentrated GT strength from {sup 70}Ge to {sup 72}Ge which is also seen in the data. These results are relevant to models of supernovae.

A gamma-gamma coincidence measurement was performed in order to search for a neutral scalar particle associated with beta decay with a mass near 17 keV. The measurement used a 35 S source and two LEPS-type Ge detectors. A coincidence signal above the background generated by random bremsstrahlung coincidences would be a signature of the two-photon decay of a light neutral scalar particle. No evidence was found for such a particle with a mass near 17 keV with a lifetime shorter than 1 nanosecond.

We present results on the electroexcitation of the low mass resonances Delta(1232)P33, N(1440)P11, N(1520)D13, and N(1535)S11 in a wide range of Q2. The results were obtained in the comprehensive analysis of JLab-CLAS data on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for pion electroproduction off the proton. The data were analysed using two conceptually different approaches, fixed-t dispersion relations and a unitary isobar model, allowing us to draw conclusions on the model sensitivity of the obtained electrocoupling amplitudes. The amplitudes for the Delta(1232)P33} show the importance of a meson-cloud contribution to quantitatively explain the magnetic dipole strength, as well as the electric and scalar quadrupole transitions. They do not show any tendency of approaching the pQCD regime for Q2 N(1520)D13 and N(1535)S11 longitudinal helicity amplitudes with good precision., 23 pages, 17 figures

The light vector mesons ($\rho$, $\omega$, and $\phi$) were produced in deuterium, carbon, titanium, and iron targets in a search for possible in-medium modifications to the properties of the $\rho$ meson at normal nuclear densities and zero temperature. The vector mesons were detected with the CEBAF Large Acceptance Spectrometer (CLAS) via their decays to $e^{+}e^{-}$. The rare leptonic decay was chosen to reduce final-state interactions. A combinatorial background was subtracted from the invariant mass spectra using a well-established event-mixing technique. The $\rho$ meson mass spectrum was extracted after the $\omega$ and $\phi$ signals were removed in a nearly model-independent way. Comparisons were made between the $\rho$ mass spectra from the heavy targets ($A > 2$) with the mass spectrum extracted from the deuterium target. With respect to the $\rho$-meson mass, we obtain a small shift compatible with zero. Also, we measure widths consistent with standard nuclear many-body effects such as collisional broadening and Fermi motion., Comment: 15 pages, 18 figures, 3 tables

Cross sections for the 48 Ti(n, p) reaction have been measured at angles of 0°, 6°, and 12° at an energy of 200 MeV. The measurements are compared with results of DWIA calculations to obtain estimates of transition strengths for L = 0, 1, and ⩾2 up to an excitation energy of 25 MeV. Gamow-Teller strength ( L = 0) is peaked between 3 and 4 MeV excitation energy, with a significant distribution extending to about 12 MeV. The L = 1 strength is found mainly between 6 and 20 MeV while the cross section for transitions with L ⩾2 increases from 10 MeV to the upper limit of the measurements. The distribution of Gamow-Teller strength is in poor agreement with theoretical distributions used to calculate the lifetime for double beta decay of 48 Ca.

Nonrelativistic and relativistic collective deformed potential models have been used to study the excitation of seven states in 58Ni by 280 and 489 MeV unpolarized protons. Optical model potentials were determined at each energy by fitting elastic scattering data using both of the models. Deformation lengths were also obtained using both models with no dependence on incident energy observed for either model. The average value of the hadronic deformation lengths along with the charge deformation lengths were used to calculate neutron to proton multipole matrix elements ( M n M p ). Five transitions, 2+1, 1.45 MeV; 2+3, 3.04 MeV; 2+4, 3.26 MeV; 4+1, 2.46 MeV; and the 4+5, 4.75 MeV state were determined to be isoscalar, i.e. M n M p = N Z . The 4+2, 3.63 MeV state was observed to be a proton-like transition with M n M p = 0.43 ± 0.18. At small scattering angles, the relativistic model gave consistently larger cross sections than the nonrelativistic model. This effect was much larger at 280 MeV than at 489 MeV.

The complete set of Wolfenstein parameters, the polarization, the asymmetry of scattering and the unpolarized double-differential cross section are presented for inclusive quasielastic proton scattering from 12C at a central momentum transfer of q = 1.9 fm−1 and incident energies of 290 and 420 MeV. The spin observables D0, Dx, Dy and Dz as well as the longitudinal-to-transverse ratio of spin-flip probabilities are extracted from the data. Across the quasielastic continuum, the experimental data is compared to the variations expected from a single-scattering Fermi-gas approximation using the free NN amplitudes. Medium effects are evident in the pronounced quenching of the polarization parameter relative to the free value.

Measurements of the spin-flip probability S nn for inclusive inelastic proton scattering around 300 MeV from nuclei between 12 C and 90 Zr show that an enhanced spin response near 40 MeV excitation at q ∼ 100 MeV/ c is a general feature of nuclear structure. Data for 40 Ca at 800 MeV confirm that the enhancement is not a peculiarity of 300 MeV scattering. In addition, measurements in 44 Ca up to 75 MeV show that the enhancement cannot be attributed solely to a relatively narrow resonance. Continuum RPA calculations suggest that the enhancement is due to the exhaustion of most S = 0 strength at lower energy and a shift of S = 1 strength to higher energy.

The experimental evidence for pentaquarks, both old an new, is discussed. Constraints due to $K^+N$ scattering data from previous decades is first reviewed, followed by experiments with positive evidence and those with null results. Finally, the problem of the narrow width of the Theta+ pentaquark is discussed, along with theoretical implications., Comment: Review article for Progress in Particle and Nuclear Physics (34 pages)

A critical look is taken at both positive and null evidence for the $\Theta^+$ pentaquark. Potential problems with experiments will be discussed and the question of what conclusion can be drawn from both the positive and the null results is examined. First the question of existence of the $\Theta^+$ pentaquark is considered, followed by a discussion of new experiments that are either planned or in progress to answer questions about its mass, width and isospin. Finally, indirect evidence for the parity of the $\Theta^+$ is examined, and suggestions for experiments to measure its parity directly are given., Comment: MESON2004 conference proceedings, 10 pages, 1 figure

Cross-sections and recoil polarizations for the reactions gamma + p --> K^+ + Lambda and gamma + p --> K^+ + Sigma^0 have been measured with high statistics and with good angular coverage for center-of-mass energies between 1.6 and 2.3 GeV. In the K^+Lambda channel we confirm a structure near W=1.9 GeV at backward kaon angles, but our data shows a more complex s- and u- channel resonance structure than previously seen. This structure is present at forward and backward angles but not central angles, and its position and width change with angle, indicating that more than one resonance is playing a role. Rising back-angle cross sections at higher energies and large positive polarization at backward angles are consistent with sizable s- or u-channel contributions. None of the model calculations we present can consistently explain these aspects of the data., 5 pages, 3 figures, submitted to Physical Review Letters

The CEBAF large acceptance spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about 30 institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 34 nucleon cm −2 s −1 . These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS.

The fission of nuclei with $159\ensuremath{\le}A\ensuremath{\le}232$ induced by the bombardment of 19.1 to 44.5 MeV $^{3}\mathrm{He}$ ions has been measured using solid-state detectors with time-of-flight measurements. Analysis with statistical fission theory, including precompound nucleon emission, indicates fission barriers which decrease only slightly relative to the liquid-drop model values with decreasing $Z$, approaching about 90% of the liquid-drop model barrier for $A\ensuremath{\approx}160$. These results are in contrast with measurements at higher angular momenta which indicate much lower fission barriers (60 to 70% of the liquid-drop model) for this mass region. The angular correlations indicate complete, or slightly greater than complete momentum transfer to the compound system. This is in opposition to that observed using heavier projectiles where incomplete momentum transfer is probable.NUCLEAR REACTIONS, FISSION $^{159}\mathrm{Tb}$, $^{165}\mathrm{Ho}$, $^{169}\mathrm{Tm}$, $^{\mathrm{nat}}\mathrm{Ta}$, $^{\mathrm{nat}}\mathrm{Re}$, $^{194,195}\mathrm{Pt}$, $^{197}\mathrm{Au}$, $^{202}\mathrm{Hg}$, $^{205}\mathrm{Tl}$, $^{206,208}\mathrm{Pb}$, $^{\mathrm{nat}}\mathrm{Bi}$, $^{\mathrm{nat}}\mathrm{Th}$($^{3}\mathrm{He}$,f), $E(^{3}\mathrm{He})=19.1 \mathrm{to} 44.5$ MeV; measured ${\ensuremath{\sigma}}_{F}(\ensuremath{\theta}, E)$, angular correlations, coincident fragment kinetic energies; deduced relative mass division, total kinetic energy release, statistical-model fission parameters.

Differential cross sections and analyzing powers for the /sup 7/Li(p-arrow-right,..pi../sup +- /) reactions leading to discrete states of /sup 8/B and /sup 8/Li, as well as to the continuum, are presented at T/sub p/ = 280, 354, and 489 MeV. These results are compared with previously published results at 200 and 250 MeV. At fixed four-momentum transfers squared in the region 0.6>t>0.4 GeV/sup 2//c/sup 2/, the energy dependence of the (p,..pi../sup +/) and (p,..pi../sup -/) differential cross sections is quite similar, in sharp contrast to earlier results from the /sup 13/C(p,..pi../sup +- /) reactions. The observed variations in the (p,..pi../sup -/) energy dependence are presumed to reflect differences in the relative importance of resonant and nonresonant amplitudes in the (p,..pi../sup -/) reaction mechanism. The analyzing powers of the (p-arrow-right,..pi../sup -/) and (p-arrow-right,..pi../sup +/) reactions are qualitatively very similar except for a difference in sign.

The cross section at 0° for the reaction 14 C(p, n) 14 N has been measured at energies of 200, 300, 400 and 450 MeV using a nucleon charge-exchange facility recently commissioned at TRIUMF. Energy resolution of 1 MeV or better was obtained at each energy, permitting a reliable measurement of the cross section ratio for the Gamow-Teller transition to the 1 + state at 3.95 MeV and the Fermi transition to the 0 + state at 2.31 MeV. The deried values of ‖ J στ / J τ ‖ 2 are in clear disagreement with impulse approximation calculations using a free NN t -matrix.

Analyzing power and spectral data for the inclusive quasifree ( p ,p ′) reaction on 208Pb at 290 MeV are presented. Cross sections were measured over an angular range of 4°–26° and for excitation energies up to 160 MeV. The free surface response model provides a good description of the shape of the continuum. At the quasifree peak the large angle Ay(θ) data drop below the free nucleon values. This difference is a possible indication of relativistic medium effects.

The208Pb(n, p)208Tl reaction was studied at 198 and 458 MeV in a search for isovector spin giant resonances. Peaks at 5.1 MeV and 13.6 MeV excitation in208Tl are observed and discussed as candidates for the T> spin giant dipole resonance (SGDR), the spin isovector monopole resonance (SIVM), and the spin isovector quadrupole resonance (SIVQ).

Rotational sidebands in 166 Er were observed using the 24 MeV 164 Dy(α, 2nγ) reactions. The ground-state band was observed up to spin 16 + and does not backbend. A strong backbend is, however, observed in a K π = ( O + ) sideband, indicating that the 12 + state of the previously unknown S-band is at 2656 keV. The γ-band shows significant rotational alignment above I = 10 + . Levels of at least two negative-parity bands, one of which is primarily the K π = 2 − octupole vibration, are also observed.

Differences of the polarization ( P ) and analyzing power ( A y ) have been measured between 5° and 14° for the lowest isoscalar 1 + and isovector 1 + and 2 + states in 12 C excited by 400 MeV protons. This is the first measurement of P - A y in an energy regime where the impulse approximation is most valid. Values of P - A y for all states are compared to both nonrelativistic and relativistic model calculations, which only qualitatively describe the data.

Inelastic scattering to the low-lying collective states in 40Ca excited by 500 MeV protons is examined using both relativistic and nonrelativistic microscopic optical model potentials in the Tassie model. The non-standard shapes produced by these microscopic models does not produce different deformation lengths than those obtained using standard Woods-Saxon shapes. For comparison, calculations using the distorted wave impulse approximation are presented.

The half-life of 197g Pb was determined to be 6.2 ± 1.2 min by measuring the γ-decay ingrowth of 197g Pb from sources of 197m Pb (42 min). The sources were produced through the ( 6, 7 Li, x n) reaction on 197 Au using 69–95 MeV beams. Several ambiguities in the decây schemes were resolved based on these γ-decay data.

A newly constructed focal-plane polarimeter for the medium resolution spectrometer at TRIUMF has been used to measure polarizations and polarization transfer coefficients for protons elastically scattered from 208Pb at 290 MeV. These results combined with existing cross section data at 300 MeV completely determine the elastic scattering amplitudes for momentum transfers q

Rotational side-bands in 162Dy have been studied using the 160Gd(α, 2nγ)162Dy reaction. Seven side-bands are observed, with Kπ = 2+, 2−, (0)−, 0+, 5−, 4+ and (6−). Four of these bands have collective structure at low spin: the Kπ = 2+ γ-vibrational band, the Kπ = 0+ β-vibrational band, and the Kπ = 2− and (0)− octupole vibrational bands. Of the remaining bands, the 4+ band is deformation coupled while the 5− and (6−) bands are rotation-aligned. Several bandcrossings are observed in this nucleus. The β and γ-bands are crossed at I = 6 h and 12 h , respectively, by a highly aligned ( i 13 2 )2 S-band; extrapolation of this S-band to higher spin suggests that it crosses the g.s.b. between I = 18 h and 20 h . The 2− octupole band is crossed by the 5− band at I = 9 h and again by the (6−) band at I = 12 h . The latter bandcrossings are discussed in terms of two-quasiparticle plus rotor calculations.

The interactions between a K/sup ..pi../ = 5/sup -/ aligned two-quasineutron band and two octupole bands have been observed in /sup 164/Er. Band crossings occur in both even- and odd-spin sequences. The members of all three bands are observed from the bandheads (L/sup ..pi../ = 1/sup -/, 2/sup -/, and 5/sup -/) to about 12/sup -/.

Proton-induced pion production to the continuum was investigated via the reactions /sup 13/C(p,..pi../sup -/)X, /sup 13/C(p,..pi../sup +/)X, and /sup 16/O(p-arrow-right,..pi../sup +/)X at bombarding proton energies of 250, 354, and 489 MeV, in the kinematic region where the pion has nearly its maximum allowable kinetic energy. Results from the /sup 16/O(p-arrow-right,..pi../sup +/)X reaction indicate that at small missing momenta the analyzing powers can be adequately described by a quasi-free p-arrow-rightp..-->..d..pi../sup +/ process, but as the missing momentum is increased this description becomes less accurate. The energy dependence of the cross section for the inclusive (p,..pi../sup +/) reactions is very similar to that of previously published exclusive (p,..pi../sup +/) data from the same target nuclei. The double differential cross sections for the ..pi../sup -/ data, however, exhibit an energy dependence different from that of the exclusive (p,..pi../sup -/) reaction.

Inclusive measurements of the linear momentum transfer distribution and exclusive studies of light-charged particles as a function of linear momentum transfer have been performed for the reaction of 150-MeV /sup 6/Li ions with /sup 238/U. Linear momentum transfer properties and an upper limit for the complete fusion cross section for this system were deduced from the folding angle between binary fission events and found to be consistent with data for heavier complex projectiles. The exclusive light-charged-particle data demonstrate the existence of fission following the transfer of all possible subdivisions of the /sup 6/Li projectile, as well as inelastic scattering. Absorptive breakup involving /sup 4/He-/sup 2/H cluster structure is found to be the dominant reaction mechanism. In addition, substantial yields of energetic protons associated with full linear momentum transfer are observed in the backward hemisphere. However, the temperature inferred from these spectra is nearly three times as large as that for a fully equilibrated compound nucleus, suggesting a nonequilibrium source for these particles.

We have developed an (n, p) target chamber consisting of six target layers sandwiched between seven gas detector layers. This target chamber is now commonly used with the new (n, p) facility at TRIUMF. With this arrangement, large total (n, p) target thicknesses (> 1 g/cm 2 ) can be used and yet the target contribution to overall energy resolution is moderate, typically less than 500 keV. The simultaneous accumulation of data from six target layers has proven to be highly advantageous with a number of applications, such as; (1) using multiple thicknesses of one target material, (2) including a target of known cross-section in the target stack for normalization, (3) adding a target to obtain simultaneous spectra for later subtraction of contamination lines and (4) the use of several target materials at once.

Energy distributions of A y at backward angles are found to be identical for inclusive proton scattering from Be and C at 303 MeV. While the cross sections scale in the y -variable of West in the same way as electron and pion scattering, the A y values are on the average small and energy dependent, at variance with those expected for a single scattering mechanism.

A polarimeter which uses inclusive scattering from carbon has been mounted after the focal plane of the TRIUMF medium resolution spectrometer. Four drift chambers measure scatterings at all azimuthal angles out to 20° in polar angle over a spectrometer momentum acceptance of ± 5%. A microprocessor rejects events with small scattering angles. The efficiency for 400 MeV protons is 4%, and for 295 MeV deuterons is 1.5%. Analyzing powers for protons are similar to those previously reported for polarimeters of this type.

After crossing the gsb at I = 14, the S-band of 166Yb crosses the γ-band at I = 10 and the β-band at I = 8. The β- and γ-bands are highly aligned below the crossing point, suggesting that the ν( i 13 2 ) 2 strength may be fractionated at low spin.

Angular correlations between binary fission fragments have been measured in coincidence with light charged particles for 64, 129, 199, and 269 MeV {sup 3}He-induced reactions on a {sup 238}U target. Linear momentum transfer and missing linear momentum have been determined for a broad range of light-charged-particle energies {ital E}{sub LCP} and emission angles {theta}{sub LCP}. Average momentum transfer increases from a fraction of beam momentum for small detection angles to nearly full momentum transfer at backward angles. The missing momentum depends primarily on available energy'' {ital E}{sub av}=E{sub beam}{minus}E{sub LCP}, but neither on beam energy {ital E}{sub beam} nor light particle detection angle. Backward proton and deuteron emission is incompatible with statistical evaporation following complete or incomplete fusion.

For the 24 Mg ( →p . →p ′) reaction at Ep=250 MeV and small momentum transfers we have measured cross sections, analysing powers and spin-transfer probabilities up to 40 MeV of excitation in 24Mg. Because of the strong suppression of the S=0 excitations in the spin-flip cross sections, the analogs of Gamow-Teller transitions could be cleanly observed. Up to Eexc=15 MeV about 80% of the L=0 strength predicted by large-scale shell model calculations has been found.

The 166Er(3He, 3nγ) and 164Er(α, 2nγ) reactions were used to populate rotational side-bands in the N = 96 nucleus 166Yb. The aligned v( i 13 2 ) 2 S-band was observed from Iπ = 8+to 12+, while the β- and γ-vibrational bands were observed from the bandheads to Iπ = 10+and 12+, respectively. Negative-parity bands with Kπ = 0−, (2−) and 5− were also observed. Band crossings and interaction effects are seen in both the positive- and negative-parity excitations below about h ω = 0.25 MeV , the frequency at which the first yrast backbend occurs.

Decay properties of /sup 194,195,196/Pb were studied using singles and coincident ..gamma..-ray spectroscopy. Sources were produced by the 95 MeV /sup 197/Au(/sup 6/Li,xn) reactions. No direct evidence for the decay of a low-spin isomer of /sup 195/Pb was observed. Several new levels were observed in /sup 195,196/Tl, and are interpreted in terms of a rotational model.

The 90 Zr(n,p) 90 Y reaction has been studied at a bombarding energy of 198 MeV in a search of GT + strength. Up to 10 MeV excitation in 90 Y, we obtain a firm upper limit of S β + ⩽ 3.6. The majority of the strength at low excitations is identified as spin dipole.

Differential cross section measurements have been made for 250 MeV proton inelastic scattering from /sup 28/Si. Hadronic deformation lengths for the states at 1.78 (2/sup +/), 4.62 (4/sup +/), 6.8 (3/sup -/ and 4/sup +/), 9.70 (5/sup -/), and 10.2 MeV (3/sup -/) have been extracted using a first-order vibration model distorted-wave Born approximation description. Deformation lengths for the 2/sup +/ and 4/sup +/ states are found to be independent of proton energy from 40 to 500 MeV. Cross sections for the excitation of the giant resonance region are found to be highly fragmented between 16 to 25 MeV. This region of excitation is found to contain an energy weighted sum rule depletion of 70% for the isovector giant dipole resonance, 26% for the isoscalar giant quadrupole resonance, and 5% for the isoscalar hexadecapole resonance. No structure was observed in the inelastic continuum region of 25 to 45 MeV of excitation energy.

Inclusive polarized proton-nucleus scattering on 208 Pb has been studied at 290 and 500 MeV. The measurements cover a broad range (0–250 MeV) of excitation energy over the 4°–27° angular range. The measured analyzing powers and cross sections for the continuum were compared with recent relativistic and nonrelativistic distorted-wave impulse approximation calculations. The cross section in the continuum region is found to be dominated by single-step quasi-free scattering. Differences of up to 40% between the analyzing powers measured at the quasi-free peak as opposed to free NN values strongly support the relativistic impulse approximation predictions for the quasi-free region, and indicate the presence of relativistic medium effects. Analyzing powers and cross sections of several low-lying states were compared with both nonrelativistic and relativistic distorted-wave Born approximation predictions.

The ground state differential cross sections for the (n, p) reaction at 0° on 6Li, 12C and 13C have been measured for 198 MeV neutrons with a precision of about 4% relative to the corresponding value for the H(n, p) reaction. These data, together with the accurately known ft values for the β- decay of 6He, 12B and 13B provide three calibrations of the (n, p) reaction as a probe of Gamow-Teller strength for isospin raising transitions.