# Nuclear Physics A

Published by Elsevier

Print ISSN: 0375-9474

Published by Elsevier

Print ISSN: 0375-9474

Publications

Multiplicities of various species of charged secondaries produced in inelastic interactions of 20Ne, 40Ar and 56Fe nuclei with emulsion nuclei at 0.1-0.5 GeV/nucleon have been measured. The data obtained are compared with the results for interactions of higher energy nuclei with emulsion nuclei. The dependences of the nucleus-nucleus interaction parameters on masses and energies of colliding nuclei are examined.

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Nuclear photographic emulsion is used to study the dependence of the characteristics of target-nucleus fragments on the masses and impact parameters of interacting nuclei. The data obtained are compared in all details with the calculation results made in terms of the Dubna version of the cascade-evaporation model (DCM).

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A nuclear photographic emulsion method was used to study the charge-state, ionization, and angular characteristics of secondaries produced in inelastic interactions of 56Fe nuclei at 1.8 GeV/nucleon with H, CNO, and AgBr nuclei. The data obtained are compared with the results of calculations made in terms of the Dubna version of the cascade evaporation model (DCM). The DCM has been shown to satisfactorily describe most of the interaction characteristics for two nuclei in the studied reactions. At the same time, quantitative differences are observed in some cases.

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In intermediate energy nucleus-nucleus collisions, neutron production at forward angles is observed to occur with a Gaussian shape that is centered near the beam energy and extends to energies well above that of the beam. This paper presents an abrasion-ablation model for making quantitative predictions of the neutron spectrum. To describe neutrons produced from the abrasion step of the reaction where the projectile and target overlap, we use the Glauber model and include effects of final-state interactions. We then use the prefragment mass distribution from abrasion with a statistical evaporation model to estimate the neutron spectrum resulting from ablation. Measurements of neutron production from Ne and Nb beams are compared with calculations, and good agreement is found.

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NASA
Researchers explore the use of Bragg Ionization Peak in radiotherapy for tumors. Considerations for the production of a high quality radioactive beam include secondary beam production efficiency, primary beam survival, and multiple scattering. A Positron Emitting Beam Analyzing camera was developed and tested at BEVALAC using a neon-19 beam stopping point. Results indicate that in homogeneous brain tissues, CT measurements and radioactive beam measurements are between 1-2 mm; there can be substantial difference between CT measurements and radioactive beam estimates if the beam stopping point crosses the fossae; random coincidences due to detector activation also appear as diffused images in the image plane of the beam stopping point; and further enhancements are necessary to make reliable measurements in the human trunk and complex brain regions.

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A differential cross section for pi-meson production in peripheral heavy-ion collisions is formulated within the context of a particle-hole model in the Tamm-Dancoff approximation. This is the first attempt at a fully quantum-mechanical particle-hole calculation for pion production in relativistic heavy-ion collisions. The particular reaction studied is an 16O projectile colliding with a 12C target at rest. In the projectile we form a linear combination of isobar-hole states, with the possibility of a coherent isobar giant resonance. The target can be excited to its giant M1 resonance (J pi = 1+, T = 1) at 15.11 MeV, or to its isobar analog neighbours, 12B at 13.4 MeV and 12N at 17.5 MeV. The theory is compared to recent experimental results.

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The analytic results from a microscopic calculation for pion production in heavy-ion collisions at intermediate to relativistic energies both above and below pion threshold are presented and the most important terms that contribute to the pion spectrum are determined. The energy dependence and the effects on the pion spectrum due to the various parameters in the theory are examined. The model is applied to coherent pion-production in 16O + 12C collisions.

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A method is proposed for finding the dependence of mean multiplicities of secondaries on the nucleus-collision impact parameter from the data on the total interaction ensemble. The impact parameter has been shown to completely define the mean characteristics of an individual interaction event. A difference has been found between experimental results and the data calculated in terms of the cascade-evaporation model at impact-parameter values below 3 fm.

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The kaonic (3)He and (4)He [Formula: see text] transitions in gaseous targets were observed by the SIDDHARTA experiment. The X-ray energies of these transitions were measured with large-area silicon-drift detectors using the timing information of the [Formula: see text] pairs produced by the DAΦNE [Formula: see text] collider. The strong-interaction shifts and widths both of the kaonic (3)He and (4)He 2p states were determined, which are much smaller than the results obtained by the previous experiments. The "kaonic helium puzzle" (a discrepancy between theory and experiment) was now resolved.

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This contribution describes a recent experimental study of the reaction on light nuclei, , , and . Final π±Σ∓ pairs arise from π+π−n events. For some nuclei, the π+ momentum spectrum presents peak-strucures in the kinematical interval of formation of Σ-hypernuclear states. The apparatus used for the investigation is the FINUDA spectrometer set at DAΦNE.

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We review the computation of the thermodynamic pressure of the entire minimal standard model to three loop order, performed in hep-ph/0510375 and hep-ph/0512177.

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Eigenvalue problems for Hilbert-Schmidt kernels in two variables related to the three-body problem are investigated numerically. With the aid of these eigenfunctions the solution of the three-body problem is constructed in a purely algebraic manner.

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A set of three integral equations for the wave functions of the three-body problem is proposed. One of these equations is the Lippmann-Schwinger equation, the other two are homogeneous equations and complete the definition of the boundary conditions. The two methods proposed to solve this system reduce to a Hilbert-Schmidt problem in a two-vector space.

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In the framework of pionless nucleon-nucleon effective field theory we study different approximation schemes for the nuclear many body problem. We consider, in particular, ladder diagrams constructed from particle-particle, hole-hole, and particle-hole pairs. We focus on the problem of finding a suitable starting point for perturbative calculations near the unitary limit (k_Fa)->infinity and (k_Fr)-> 0, where k_F is the Fermi momentum, a is the scattering length and r is the effective range. We try to clarify the relationship between different classes of diagrams and the large g and large D approximations, where g is the fermion degeneracy and D is the number of space time dimensions. In the large D limit we find that the energy per particle in the strongly interacting system is 1/2 the result for free fermions. Comment: 23 pages, 8 figures

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Angular distributions of high energy He nuclei, emitted from the target in central 16O-AgBr interactions, are found to be highly forward-peaked at 0.2 GeV/nucleon but almost isotropic at 2 GeV/nucleon. The angular distributions are in qualitative agreement with recent shock-wave calculations. However, we observe no narrow peaks neither in the angular nor in the energy distributions of He nuclei.

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The anisotropy of fragments from the neutron-induced fission of aligned 235U has been measured as a function of neutron energy from 0.2 to 2000 eV. The nuclei were aligned in single crystals of rubidium uranyl nitrate, cooled to about 0.1 K. The anisotropy was found to show a rather small variation over the observed resonances and in the unresolved region, indicating that for the open transition states at the barrier K = 0 and 1 and that some states with K = 2 are partially open.

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Preliminary results on photon production and forward-backward multiplicity correlations in p collisions at √s = 1.8 TeV are presented. Some additional results obtained at lower energies are also shown.

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We have measured the absolute unpolarized cross sections for photon electro-production off the proton ep → epγ with the Three-Spectrometer-Setup at MAMI at a momentum transfer q=600 MeV/c and a virtual photon polarization ɛ=0.62. The momentum q′ of the outgoing real photon range from 33 to 111 MeV/c. We extracted two combinations of the recently introduced generalized polarizabilities [1,2].

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Measurements of the spin-spin effect, σss in the total cross section for polarized neutrons on polarized 165Ho are reported at neutron energies of 0.4 and 1.0 MeV. The absence of an observable effect at 1.0 MeV is in contradiction with a recently reported experimental result. The results of an improved theoretical calculation of σss for neutron energies below 8 MeV are presented and used with the new experimental data to obtain the new limit ‖Vss‖ < 300 keV for the strength of the spin-spin potential.

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We present a total of 273 independent data points of the analyzing powers Aoono (nP) and Aooon (nP) in a large angular interval at four energies between 0.477 and 0.940 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the polarized Saclay frozen-spin proton target. Part of the data was obtained with a CH2 target. A comparison of the two measured observables allows one to determine the polarization of the neutron beam. The present results provide an important contribution to any future theoretical or phenomenological analysis.

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Investigation at fourteen energies from 0.5 to 42 MeV and A ≧ 27 shows that a simple expression describes the σT(A,E) surface in the energy and mass number region mentioned above. For the expression can be interpreted by the nuclear Ramsauer effect, while for E < 10 MeV a better approximation for the black-nucleus formula seems to be useful. The constant amplitude of oscillations suggests a weak volume absorption and a strong surface absorption.

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Momentum spectra of protons emitted at angles of 0.103, 0.139 and 0.157 rad in fragmentation of 9 GeV/c deuterons on 1H, 2H and 12C nuclei have been measured at the JINR synchrophasotron by using a magnetic spectrometer. It is found that the shape of the high-momentum parts of the spectra is defined only by the deuteron structure and the mechanism of deuteron-nucleon interaction and does not depend on a target. The contributions to the differential cross section of the 1H(d, p)X reaction have been determined, which are conditioned by elastic and inelastic scatterings of deuteron nucleons on a proton, stripping, their interference, and also the excitation of the pion degrees of freedom. In the framework of the light front dynamics, calculations of the proton spectra with the deuteron structure functions for the Paris, Reid soft core, and Bonn potentials have been performed; a better agreement with the experiment is achieved with the deuteron wave function for the Paris potential. A conclusion is made that the nucleons in a deuteron keep their individuality up to relative motion momenta of ∼ 1 GeV/c.

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By studying high-energy β− particles the 0.53±0.05 sec decay of 13049In81 and excited states in the two-neutron-hole nucleus 13050Sn80 have been observed. These states have been given the tentative assignments 2+ (1217 keV), 4+ (1992 keV) and 5− (2119 keV).

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Measurements of the (α, 2α) reaction in the GeV region on 16O and 28Si are described. The results are compared with a calculation employing the plane wave impulse approximation (PWIA) and with a calculation employing the distorted wave impulse approximation (DWIA). The PWIA calculation reproduces the shape of the angular distribution of the observed quasi-elastic events. The main effect of the distortion introduced in the DWIA calculation is to attenuate the quasi-elastic cross section by a factor of five. As a consequence, the (α, 2α) reaction in the GeV region is expected to be more useful to measure the spectroscopic factor Neff than in the region below 100 MeV since the attenuation is considerably larger (≈ 103) in the latter case.

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Elastic scattering of α-particles from helium has been measured at bombarding energies of 0.85 and 0.65 GeV over the range of four momentum transfer from 0.9 to 3.8 (GeV/c)2. The results are compared with the predictions of an α-α potential obtained by a folding procedure using a p-4He potential and 4He charge distribution.

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Absolute differential cross sections for elastic p 4He, p 6He and p 8He small-angle scattering were measured in inverse kinematics with secondary 4,6,8He-beams at an energy near 0.7 GeV/u. The experiment was performed using beams from the heavy-ion synchrotron SIS and the fragment separator FRS of GSI Darmstadt. The hydrogen-filled ionization chamber IKAR served simultaneously as a gas target and a detector for the recoil protons. Projectile scattering angles were measured with multi-wire tracking detectors. For proton scattering from the neutron-rich isotopes 6He and 8He, differential elastic-scattering cross sections were deduced in the range 0.002⩽|t|⩽0.05 (GeV/c)2 of the four-momentum transfer squared t. For elastic p 4He scattering, the data obtained in the t-range 0.002⩽|t|⩽0.02 (GeV/c)2 supplement the results from an earlier work performed in direct kinematics. From the differential cross sections the integral elastic-scattering cross sections , the total cross sections , and the total reaction cross sections for the proton–nucleus strong interaction were evaluated. The data obtained on allow the radial matter distributions in the 6He and 8He nuclei to be determined and the corresponding root-mean-square matter radii to be deduced.

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Differential cross sections for the 3H(α, γ)7Li (g.s.) and the 3H(α, γ)7Li (0.478 MeV) reactions have been measured at 0° in the alpha-particle energy range from 0.7 to 2.0 MeV. A Ge(Li) detector has been used to measure the gamma rays. The results have been compared with recent theoretical calculations of Mertelmeier and Hoffman employing the resonanting group method and a good agreement has been found.

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Yields of spallation products after irradiation of the elements 27Al, 51V, 55Mn, 56Fe, 59Co and 75As with bremsstrahlung of maximum energies between 0.8 and 2.1 GeV have been measured by the activation method. For constant Z the yield as a function of the number of ejected particles is similar to that found for proton induced spallation. It is possible to reproduce the spallation data with an analytical formula, the parameters of which have been determined for various energies and mass numbers.

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The separation of the structure functions of the (e,e'p) cross-sections is presented. Results of this separation are given for light nuclei : 2H, 3He and 4He and a comparison with theoretical calculations is made. These results may be interpreted as a modification of the nucleon form-factors in the nuclear medium.

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Projectile fragmentation mechanism and the possible liquid gas phase transition have been studied by extracting the critical exponents using cluster approximation technique. A ‘toy model’, schematically accounting for pre-equilibrium, has been developed and various moments as well as conditional moments have been evaluated with the data obtained from the toy model to see the effect of mass conservation constraint. An exponent δ, related to third order moment, has been evaluated to obtain a set of values of γ, β and τ that follow the corresponding scaling relation. The values of γ, β and τ so obtained are found to be 1.34±0.19, 0.54±0.15 and 2.31±0.06 respectively.

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All the multipole transition densities between the seven T = 0 states in 12C are calculated with the use of the microscopic 3α resonating-group wave functions which are obtained by dynamically solving the 3α relative motion with the total antisymmetrization taken into account exactly. The observed elastic and inelastic electron scattering form factors for the transition to the 21+, 41+, 02+, 11−and 31− states are well reproduced with no additional effective charge. The existence of a deformed intrinsic state for the 01+, 21+and 41+states is deduced by the analysis of the transition densities between them which are derived by the weak-coupling-type 3α wave functions; the intrinsic density distribution is illustrated. The monopole density distribution of the 02+, 22+ and 11−, states is found to be much longer ranged than that of the 01+, 21+ and 41+ states; the 31− state case is intermediate. On the basis of the transition densities between the 01+, 21+, 02+ and 22+ states, analysis is made of the transition between the shell-like states and the molecule-like states with a large spatial-structure change. Specific, effective nucleon-nucleon interactions are folded into the transition densities here obtained. The evident dependence of the radial shape of the folded nucleon-12C form factors on the choice of the interactions and the multi-step form factors for the excitation of the 02+, 11− and 31− states are discussed.

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I summarize theory at Quark Matter '02, stressing the continuing inability model to describe all notable features of the data from √s/A: 55 → 200GeV

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The dibaryon with J = S = 3 and I = 0 has a chance to be “bound”, , in the quark model with QCD residual interaction. We calculate a peripheral reaction mechanism whereby an incoming relativistic deuteron is excited to this dibaryon resonance via the (scalar) mean field of the target nucleus (e.g. 16O). In the projectile system the target nucleus corresponds to an effective number of isoscalar (σ) mesons which produce the (ΔΔ) component via 2π intermediate states. At very high energies we calculate the diffraction excitation via pomeron exchange.

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Based on QCD conformal partial wave expansion to leading order conformal spin accuracy, we present the light-cone distribution amplitudes (DAs) of Σ and Λ baryons up to twist 6. It is concluded that fourteen independent DAs are needed to describe the valence three-quark states of the baryons at small transverse separations. The nonperturbative parameters relevant to the DAs are determined within the framework of QCD sum rule method. With the obtained DAs, a simple investigation on the electromagnetic form factors of these baryons are given. The magnetic moments of the baryons are estimated by fitting the magnetic form factor with the dipole formula.

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The suppression of the yield of high transverse momentum pT hadrons in heavy-ion collisions, referred to as “jet-quenching”, has now developed into a comprehensive science. Jets are now used as probes of a variety of properties of the dense medium through which they propagate. Major theoretical improvements include jet modification in a 3-D fluid dynamical medium, the first set of in-medium Monte-Carlo implementations, an understanding of multi-hadron observables and energy flow within perturbative QCD, along with improvements in the AdS/CFT description of energy loss. On the experimental side, high statistics data are allowing for the first discriminatory test of various theoretical models and approximations while the new measurements of full jet reconstruction pose a challenge to theory.

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DELPHI results are presented on the inclusive production of the neutral mesons rho^0, f_0(980), f_2(1270), K^*0_2(1430) and f'_2(1525) in hadronic Z^0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z^0 decay have been determined to be: 1.19 +/- 0.10 for rho^0; 0.164 +/- 0.021 for f_0(980); 0.214 +/- 0.038 for f_2(1270); 0.073 +/- 0.023 for K^*0_2(1430); and 0.012 +/- 0.006 for f'_2(1525). The total production rates for all mesons and differential cross-sections for the rho^0, f_0(980) and f_2(1270) are compared with the results of other LEP experiments and with models. Comment: LaTeX, 4 pages with 3 eps-figures. In the Proceedings of the 15th International Conference on Particle and Nuclei, Uppsala, Sweden, June 10-16, 1999 (Eds. G. Faldt et al.)

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The renormalization of two-body matrix elements in the 1s 0d shell has been considered by explicitly summing to second and all orders the perturbation theory diagrams of the Tamm-Dancoff and random phase approximations. The equivalence to the phonon coupling approach is demonstrated. Large enhancements are found compared to the first order result, and it is shown that difficulties arise due to the instability of the J″ = T″ = 0 phonon. The spectra and γ-transitions in mass 18 are discussed.

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The shell-model reaction matrix elements for the 0f-1p shell are calculated and tabulated. The matrix elements consist of two parts; the bare reaction matrix elements and the renormalizations due to core polarizations which are both calculated with the Hamada-Johnston nucleon-nucleon potential. The core polarizations are evaluated for two cases; first for a 40Ca core and then for a 48Ca core. As a preliminary test, these matrix elements have been compared with available empirical effective interactions and used to calculate (i) the spectra of the valence particles of 42Ca, 42Sc, 50Ca, 50Sc and 50Ti, (ii) the changes of single-particle (hole) levels such as the changes of single-neutron levels from 41Ca to 49Ca and (iii) the particle-particle states of 38Cl and the corresponding particle-hole states of 40K. In general, the calculated results are in good agreement with the experimental values, and the core polarization effects are usually of great importance.

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New two-body interactions are derived for nuclei in the lower part of the Of 1p shell by fitting semi-empirical potential forms and two-body matrix elements to 61 binding and excitation energy data in the mass range 41 to 49. The shell-model calculations assumed a 40Ca core and valence nucleons distributed over the full fp space. Care was taken to exclude intruder states from the selected data set. The r.m.s. deviations between fitted and experimental energies of 176 keV have been achieved by varying only 6 two-body parameters and 4 single-particle energies in the method utilizing a modified surface one-boson exchange potential (MSOBEP) form. In an alternative fit an r.m.s. deviation of 163 keV has been obtained by fitting 12 linear combinations of single-particle energies and two-body matrix elements, while constraining the remaining two-body matrix elements to values of a G-matrix interaction. The results are comparable in quality to recent similar fits in the 1sOd shell. The effects of a mass dependence of the two-body matrix elements are also investigated. An excellent reproduction of ground-state magnetic moments and quadrupole moments is obtained with the new interactions.

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In this paper we have tried to ascertain the importance of the three-body effective force in the normal parity spectra of nuclei with A = 7, 13 and 14 by calculating their spectra with and without the three-body diagram. It is found that for the heavier nuclei, neglect of this part of the effective force is not justified. The calculations have been done with the Sussex interaction.

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We derive general analytic formulae for the matrix elements of the SU(6) generators for mixed symmetric [Nc−1,1] spin-flavor states with an arbitrary number Nc of quarks. They are relevant for baryon spectroscopy in the 1/Nc expansion method applied to light baryons and can be used to study excited states. In this way previous work on non-strange baryons can be extended to both non-strange and strange baryons.

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

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The 6Li(p, α)3He reaction has been studied with proton energies from 1.0 to 2.6 MeV. The excitation curve and angular distributions were measured by a coincidence method. The results showed that the absolute cross sections for this reaction are lower in this energy region than earlier measurements.

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Neutron time-of-flight techniques and a liquid-helium polarized-neutron analyser were used to measure seven neutron polarization angular distributions for the 3H(d, )4He reaction at deuteron energies from 1.0 to 5.0 MeV. Using Legendre polynomial expansions of σ(θ) and P(θ)σ(θ), values of P(θ) and P2(θ)σ(θ) were calculated, and a contour map of P(θ) was produced for the energy range 1.0 to 5.0 MeV. Various techniques used to measure the 3H(d, )4He polarizations are discussed, and previous and present results are compared.

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Absolute differential cross sections for the scattering of protons by deuterium have been measured at eight proton energies from 1.000 to 10.04 MeV for angles from 10.50° to 166.00° in the centre-of-mass system. The median uncertainty of all measurements is ±0.6%.

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Absolute 55Mn(n, n′γ) γ-ray production cross sections have been measured for 19 transitions from levels up to and including the 2429 keV state in 55Mn over the energy range En = 1.0–3.6 MeV. Angular distributions were also measured for 6 of the transitions. Branching ratios were extracted and total inelastic neutron cross sections were inferred for these 55Mn excited states. The measured and inferred cross sections are compared with calculated cross sections using the statistical compound nucleus theory.

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The γ-decay of 35 resonances of the reaction 27Al(p, γ)28Si was studied in the energy range Ep = 1.01–2.00 MeV by means of a 10cm3 Ge(Li) detector. The proton energies of 20 resonances as well as the energies of 11 bound levels were determined to an accuracy varying between 0.8 and 3 keV. Gamma-ray branching ratios of resonant and bound states were determined. The spins of a number of resonant and bound levels were derived from the γ-ray branching ratios. Mean lifetimes of 5 bound levels were determined from γ-ray Doppler shift measurements.

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The width of the 1.013 MeV level of 27Al was determined in two nuclear resonant scattering experiments. In the first, the source of radiation was a 4000 Ci 60Co source. Gamma rays of the desired energy were obtained by Compton scattering of the 1.33 and 1.17 MeV photons through a precalculated angle. This radiation was then scattered from an Al scatterer and the resonantly scattered quanta observed at an angle of 120° with respect to the incident beam. In the second experiment, Doppler-broadened γ-rays emitted from the 27Al(p, p′γ) reaction were used to excite the state. The weighted mean value of the level width was found to be Λ = 1.3±0.4 MeV. This value is compared with various excited-core model calculations.

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Nuclear resonance fluorescence scattering was observed to measure the lifetime of the second excited state in 27Al at 1.013 MeV. The 27Al(p, p′γ)-reaction in a solid aluminium target served as a Doppler-broadened gamma source. The scattering experiment yielded a mean life of tm = 2.2±0.3 ps, corresponding to a magnetic dipole transition strength of (11.5±1.6)·10−3 Weisskopf units. The low-lying levels of 27Al are discussed in detail in terms of the excited-core model, taking a mixing of the two excited states into account. Agreement between the model predictions and the experimental data are obtained for a 15% quasi-particle admixture to the state at 1.013 MeV. To fit the energies of the multiplet states the core-hole interaction must contain multipoles of orders up to four.

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