Search

In the context of the investigation of collectivity in the A = 100 mass region an experiment to measure the low-spin excitations of 100Pd was performed at the Cologne Tandem accelerator with the HORUS cube spectrometer. Besides the determination of excitation and transition energies and branching ratios, data on spins and multipole mixing ratios resulted from the γγ angular correlation analysis. The level scheme was extended and clarified. Nearly 70γ transitions were identified, thereof 16 for the first time. In addition 11 new energy levels were assigned and 13 multipole mixing ratios were measured for the first time. The newly gained data are compared with theoretical predictions from collective models and the shell model.

The 116Cd(p,n) experiment at 300 MeV has been performed for deducing the Gamow-Teller (GT) transition strengths B(GT−) in 116In. For the transition to the ground state, the B(GT−) value of 0.26 ± 0.02 is obtained. From this B(GT−) value and the B(GT+) value by a beta-decay experiment, the contribution of the intermediate ground state of 116In to the nuclear matrix element is deduced to be 0.070 ± 0.003. The B(GT−) value obtained herein is a factor of 8 less than that obtained from a previous (3He,t) measurement. This discrepancy, as well as differences in the distribution of low energy GT strength, and the width and peak energy of the GT giant resonance may be explained if the target used in the (3He,t) measurement is a Cd target with natural abundance.

Inclusive cross sections (d(2)sigma/d Omega dE, d sigma/dE, d sigma/d Omega and sigma(T)) for the production of neutron and light charged particles induced by protons of 26.5, 48.5 and 62.9 MeV and alpha-particles of 25.4, 45.5 and 57.8 MeV on Si-nat targets have been measured. The secondary particles (p, d, t, He-3, alpha, Li-6, Li-7 and Be-7) were detected at angles from 10 degrees to 165 degrees in steps of +/- 10 degrees with respect to the beam axis. Neutrons emitted in these reactions were only recorded in coincidence with, at least, one detected light charged particle. A comparison of the proton- and neutron-induced reactions on Si at E = 62 MeV shows evidence of charge independence of the nuclear force. The proton spectra from the two reactions scale as expected from the difference in proton-neutron and proton-proton quasi-free scattering cross sections. The new data are reproduced with moving source fits and are also compared with state-of-the-art nuclear reaction models. The codes used for this purpose, GNASH and TALYS, consider direct nuclear reactions as well as pre-equilibrium and compound nucleus emission, and were found to reproduce the general features of the experimental data, especially for the (p, p x) channel. More detailed comparisons with the data indicate that there is still room for improvement in these codes. (c) 2006 Elsevier B.V. All rights reserved.

Resonances in 6Be and 5Li have been investigated by deuteron transfer reactions with radioactive ion beams, 2H(8B,α)6Be, 2H(7Be,α)5Li, respectively. There is an indication of a possible resonance at excitation energy of 9.6 MeV in 6Be, just below the 3He+3He threshold. The structure of the 6Li nucleus has been also investigated by the neutron transfer reaction 3He(7Li,α)6Li. In 6Li, a new resonance is observed at about 12.4 MeV in excitation energy and the presence of a resonance at 15.2 MeV is confirmed. The data are preliminary and a detailed analysis is in progress. The instalation of a Radioactive Ion Beam facility in Brazil (RIBRAS) is also reported.

The A(e,e{prime}K{sup +})YX reaction on H, D, {sup 3}He, and {sup 4}He was investigated in Hall C at CEBAF. Data were obtained for Q{sup 2} {approx} 0.35 and 0.5 GeV{sup 2} at 3.245 GeV. The missing mass spectra for both H and D are fitted with Monte-Carlo simulations incorporating peaks corresponding to {Lambda} production on the proton and {Sigma} production on both the proton and neutron. For D, the cross section ratio {Sigma}{sup 0}/{Sigma}{sup {minus}} {approx} 2, and excess yield close to the thresholds for {Lambda} and {Sigma} production can be attributed to final-state interactions that are compared to the data. The analysis of the data for the He targets is in a more preliminary state with broader quasi-free peaks resulting from the higher Fermi momenta. Evidence for bound {Lambda}-hypernuclear states is seen and other structure may be present.

The new superconducting accelerator Nuclotron have been operated for the first time at 3.8 and 6.2 GeV/c deuteron momentum and the run on the internal target have been carried out in March'94. The various scintillation counters for ΔE-E and time-of-flight (TOF) measurements, the silicon and CsI(Tl) crystal detectors for ΔE-E measurements as well, and the lead glass EM calorimeters were used. The secondary particles γ, π, K, p, d, and t as well as He fragments produced by deuterons on the internal targets were detected and identified relaibly, thus manifestating a broad perspective of the relativistic nuclear physics research on Nuclotron in the nearest future.

Nuclear-rainbow effects in elastic and inelastic scattering and transfer reactions by the 3He + 12C and 4He + 12C interactions at E(3He) = 98 MeV and E(4He) = 90 MeV respectively are observed analyzing the angular distributions of the 2,3H, 3,4He and 6Li particles. The data have been analyzed by a near/far-side formalism using Fuller's model. It has been shown that the far-side component plays the main role in all studied processes. The present investigation proposes a method for the optical model parameter choice for entrance and exit channels. We also observe the different characteristics of the rainbow effects and of the shape of the angular distributions for very deep inelastic processes (high excitation energies) and transfer reactions.

Our progress in understanding the properties of 3 H and 3 He in terms of a nonrelativistic Hamiltonian picture employing realistic nuclear forces is reviewed. Trinucleon model properties are summarized for a number of contemporary force models, and predictions for physical observables are presented. Disagreement between theoretical model results and experimental results are highlighted.

The dependence on deuteron energy of the polarization of the neutrons emitted at 45° from the 2H(d, n)3He reaction in the range 35 to 275 keV, was determined from the asymmetry in the scattering of the neutrons by 4He. There is no indication of the much discussed possible resonance at about 100 keV deuteron energy. The results are discussed in relation to the general theoretical treatment of the 2H-2H interaction put forward by Boersma.

Angular distributions of 3 He polarization in elastic scattering from 9 Be and 12 C, and in inelastic scattering to the 4.44 MeV state of 12 C were measured using a 33 MeV polarized 3 He beam. The polarization and cross-section data were successfully analysed in terms of the standard optical model. Selectively of the 3 He elastic polarization for various potential sets was established in both optical model and coupled-channel analyses. While it is possible to determine unambiguously the geometry of the spin-orbit term, its strength is strongly correlated with other optical model parameters.

Inclusive cross sections for the emission of 3H, 3He and 4He at laboratory angles of 45°, 90° and 135° in collisions of 4He with targets of 9Be, 12C, 27Al, 64Cu, 108Ag and 197Au at a beam kinetic energy of 3.33 GeV/nucleon are presented. Assuming the existence of an intermediate object emitting fragments, we have found its velocity and temperature for different fragment energies. It is shown that the velocity and temperature continuously increase with the fragment energy under consideration. The evaporation mechanism is discussed, and it is argued that the evaporation significantly contributes to the yield of fragments with energy less than 50 MeV. The considered 3H to 3He ratio is found to be larger than the neutron to proton ratio in the emitting system. Comparing 3H and 3He spectra, an important role of the Coulomb barrier is shown. The At dependence of the yield of the fragments is studied. The experimental spectra are compared with thermodynamic firestreak model predictions. The model is successful in describing the emission of fragments with energy greater than 50 MeV.

Relativistic effects in the atomic and nuclear few-body systems are classified and discussed with the emphasis on electromagnetic transitions. The size of relativistic corrections, calculational techniques and ambiguities, and comparison of theory and experiment are considered.

The elastic scattering of 3 He from nuclei in the mass range A T = 10–208 at projectile energies from 10 MeV to 220 MeV is analyzed in the frame of the simple optical model. An empirical parametrization of the central potential for the whole mass and energy range is given that satisfies all qualitative requirements put on optical potentials by theories. The discrete ambiguity is phenomenologically resolved by the parametrization presented in this work.

The 115 In(d, 3 He) 114 Cd reaction was studied at E d = 50 MeV. For transitions to states in 114 Cd in the excitation energy range 0–5.3 MeV angular distributions were obtained, most of them corresponding to l p = 1(2 p 1 2 , 2 p 3 2 ) or l p = 4(1g 9 2 ) transfer. From DWBA analysis spectroscopic factors were extracted and compared with sum rules. An 8 + state at 3.25 MeV is proposed. A comparison with semi-microscopic model calculations is made.

The polarization of neutrons from the reaction 2 H(d, n) 3 He has been measured with unpolarized incident particles and target nuclei. A new type of helium recoil polarimeter is used. The results indicate a monotonic increase of the degree of neutron polarization P n with increasing deuteron energy E d in the range 50–700 keV. Typical values are P n = −0.099, −0.126, −0.162 and −0.173 for E d = 52, 154, 268 and 586 keV respectively and a neutron emission angle of 52–53° in the c.m. system. The measured dependence of P n on E d approximately agrees with the energy dependence calculated from measured anisotropies of the neutron angular distribution by means of the theoretical relations of Blin-Stoyle and Boersma.

The angular distributions of the differential cross sections and the analyzing powers for the 3 He(p,p)dp and 3 He(p,pd) 1 H reactions have been measured in the FSI region. The multiple scattering calculation including to double scattering terms has reproduced the differential cross sections well.

The isospin mixing of states in 8 Be near 17 MeV was investigated by comparison of cross sections for the 9 Be(d, t) 8 Be and 9 Be(d, 3 He) 8 Li reactions. For the 2 + doublet at 17 MeV, our results are inconsistent with previous measurements of the isospin mixing unless the theoretical T = 0, p 3 2 spectroscopic amplitude is changed by ≈ 20%. For the 1 + states near 18 MeV we find an isospin amplitude impurity of 0.21±0.03. For the 3 + states near 19 MeV no new information could be obtained due to the complex peak shape.

The 64 Ni and 64 Zn(d, 3 He) reactions have been studied at a deuteron energy of 55 MeV. Proton pickup strengths for l = 1 transitions in 63 Co and 63 Cu amounted to 0.4 and 1.7, respectively, in comparison to l = 3 strengths of 7.6 and 8.3, respectively. Proton pickup strength from the 2 s 1 2 and 1d deeply bound states is also observed in both nuclei with about half of the sum rule limit for each configuration.

We present an event-by-event study of the breakup of the 16 O in 16 O + emulsion nucleus interactions at 75, 175 and 2000 MeV/ A . The events are categorized according to their multiplicity of projectile He nuclei. The multiplicity depends on the degree of target destruction. Although the fragmentation model describes the gross features of inclusive He spectra, an event-by-event study reveals deviations from the model. The momenta of the He nuclei, emitted from the projectile, depend on helium multiplicity and the breakup properties of the target nucleus. The probability that the 16 O projectile breaks up into multiple He fragments is larger at 75 MeV/ A than at 2000 MeV/ A . At 75 MeV/ A the mean velocity of projectile He is on the average 0.06 c below the projectile velocity. This recoil velocity depends on the target nucleus destruction also for the most peripheral collisions.

Energy spectra of 130 MeV 3 He scattered from 24 Mg, 90 Zr, 120 Sn and 208 Pb have been measured. The spectra exhibit a pronounced giant resonance (GR) structure in the excitation energy region around E x ≈ 63A − 1 3 MeV . The GR angular distributions as well as those corresponding to the first 2 + levels in 24 Mg and 120 Sn have been obtained for angles 7° ≦ θ L ≦ 35°. Distorted wave calculations using the optical model parameters fitting the elastic data resulted in good fits to the 2 + levels. For 24 Mg, 90 Zr and 120 Sn the shapes of the GR angular distributions are well fitted by L = 2 curves alone. However, for 208 Pb both L = 2 and L = 4 curves give fits of comparable quality.

The angular distribution of 3 He polarization was measured in the scattering of a polarized 3 He beam by protons at a mid-target energy of 31.5 MeV. The results together with the available cross section and proton polarization data were analysed in terms of phase shifts and mixing parameters. The measured left-right asymmetry of recoil protons was used in the design of a 3 He polarimeter.

Results on the Δ excitation by heavy ion charge exchange are presented. 900 MeV per nucleon 12C, 16O, 20Ne and 1100 MeV per nucleon 12C have been used. The Δ excitation strength depends on the projectile — ejectile nature and on the incident energy. The role of the target mass is also discussed. The peak for the Δ in nuclei is energy shifted from the free Δ peak.

Total cross sections and angular distributions in the 6 Li(p, 3 He) 4 He reaction have been measured over the energy range E p = 100−700 keV. The extrapolation of the cross section to the energy region which is of interest in controlled thermonuclear reactors is given. The values of the “astrophysical S -function” are deduced from the cross sections.

The polarization angular distribution of 3 He elastically scattered from 12 C at 28 MeV has been measured using the double scattering method. The 3 He polarization reached −28 % at θ c.m. = 47°. An optical model analysis of the polarization and differential cross section requires a spin-orbit potential of ≈ 4 MeV to fit the data over the angular range of 12.5° c.m. to 72.5° c.m. This spin-orbit potential is higher than the theoretical prediction for simple constituent-nucleon coupling.

Asymptotic wave functions for nuclear reactions with two fragments are expanded into supermultiplets. The expansion coefficients turn out to be essentially coefficients of fractional parentage for the spin-isospin part.

A simultaneous analysis of the elastic p 3 H and p 3 He scatterings and of the charge exchange p 3 H → n 3 He reaction at 415 and 600 MeV is made, using, at all orders of the Glauber multiple scattering expansion, fully spin/isospin-dependent NN amplitudes. The calculated cross sections are compared to the experimental data and their sensitivity to various ingredients of the model is discussed.

The 3 He spin analysing power of hydrogen (protons) has been measured at a c.m. energy of 20 MeV at 14 c.m. angles from 40° to 160°. The measurement of 3 He target polarization was calibrated by measuring the 3 He spin analysing power of 4 He at an energy and angle where it was −1.00. The proton- 3 He differential elastic scattering cross section is also reported at a c.m. energy of 20.0 MeV for 36 c.m. angles from 20° to 170°.

The (d, τ) proton pick-up reactions on 36Ar and 38Ar have been studied at an incident energy of 52 MeV. Differential cross sections were measured and spectroscopic factors were extracted for transitions to 14 states of 35Cl and 13 states of 37Cl, respectively. Many new 5 2 + states and nearly the complete 1 d 5 2 strength have been observed in both nuclei. The width of the 1 d 5 2 spectral distribution is appreciably smaller for the semi-closed shell nucleus 38Ar than for 36Ar and 40Ar. The results are compared with those from the 40Ar(d, τ) reaction and proton stripping reactions on each of the three argon isotopes. Recent shell model calculations proved to be well suited to describe excitation energies as well as spectroscopic factors for the low-lying positiveparity states. Mirror relations were established for the nuclei 35Ar and 35Cl. In 37Cl we succeeded in observing a weak component of a 1p proton hole state at a separation energy of only 18 MeV.

The quadrupole deformation of 11 B has been investigated by means of inelastic helion scattering at E 3 He = 74 MeV. Optical model and coupled-channels parameters determined in this work are reported.

The Saturne I quasi-monokinetic triton beam has been used to measure the p 3 H → n 3 He differential cross section at 415 and 600 MeV per nucleon and the p 3 H → p 3 H differential cross section at 415 MeV per nucleon. We covered the four-momentum transfer squared t domain from 0 down to −0.7 GeV/ c ) 2 . A spin-independent Glauber-model interpretation of the data is discussed.

The polarization of neutrons produced in the 2 H(d, n) 3 He reaction was measured at deuteron bombarding energies between 60 and 380 keV in 20 keV intervals. Except for an angular distribution of polarization at 340 keV, all measurements were performed at a neutron emission angle of 47° in the lab system. The deuterium target was a thick layer of heavy ice. A helium polarimeter was employed for these measurements. The results of the present experiment indicate that the polarization does not vary rapidly in the energy range investigated.

Angular distributions for 3He elastic scattering, have been measured to 155° at 37.7 MeV on 48Ti, 58Fe and 90Zr, and at 36.8, 37.4, 37.5 and 38.1 MeV on 58Ni. These have been analysed in terms of the optical model. Ambiguities in the real well depth and in the geometrical form of the imaginary potential have been studied. The usefulness of a surface-peaked imaginary potential, particularly in fitting the backward angle data, is indicated by these analyses. The utility of a spin-orbit term in fitting large angle data was investigated. Multiset fits were performed to the data. No conclusions concerning the necessity of either an isospin or asymmetry term in the optical potential at these energies could be drawn. Other information gained from extending 3He elastic scattering measurements into the backward hemisphere is discussed.

The differential cross sections for the one-nucleon stripping reactions and the elastic scattering of 104 MeV α-particles on 12 C, 27 Al and 40 Ca were measured. The experimental results show that the (α, τ) cross sections are larger than those obtained from (α, t) reactions on the same target nuclei. The reaction data were analyzed in the framework of the DWBA. The calculations using the zero-range approximation are able to reproduce the measured angular distributions. In addition the effect of finite-range corrections were studied in the local energy approximation. From the analysis it becomes evident, that the inner part of the target nucleus contributes significantly to the reaction cross section. The larger yield of 3 He particles compared to that of tritons can be explained mainly by different normalization factors for the (α, τ) and (α, t) reactions, respectively.

The polarization in p-3He elastic scattering at 30 MeV in the angular range 33° to 160° c.m. has been measured. The magnitude of the polarization is very much greater than that predicted from an optical-model analysis of cross section data, but is consistent with the values found at lower energies.

Differential cross sections of 29 MeV 3 He nuclei elastically scattered by C, Mg, Al, Si, Ca, 56 Fe, 63 Cu, Zn, Y, Ag, In and Sn in the angular range 15°–110° (lab) are presented, and discussed in terms of the optical model.

Thick-target yields for reactions of 3 He particles with B, N, Be and Na were determined by irradiating boron, beryllium nitride and sodium iodide with 3 He ions of energies from 6 to 18 MeV. Excitation functions for the reactions 11 B( 3 He, n) 13 N, 10 B( 3 He, d) 11 C, 14 N( 3 He, α) 13 N, 14 N( 3 He, d) 15 O, 9 Be( 3 He, n) 11 C and 23 Na( 3 He, 2p) 24 Na were obtained by numerical differentiation of the smoothed yield versus energy curves. The distorted-wave theory of nuclear reactions was used to compute excitation functions for comparison with the data for the 14 N( 3 He, α) 13 N reaction and for the ( 3 He, d) reactions on 14 N and 10 B. Optical-model potentials, not for the particular nucleides observed, but determined for neighbouring light nuclei, were used in the calculations. The results of this comparison of theory with experiment indicate that the 14 N( 3 He, α) and 10 B( 3 He, d) reactions appear to proceed mainly by direct pick-up and stripping processes, respectively. For the 14 N( 3 He, d) reaction, a stripping calculation that considered only those 15 O states with known spins and parities yielded a lower limit of ≈30% of the observed excitation function.

Differential cross sections have been measured for the elastic scattering of 21 MeV 3 He particles by 40 Ca, 52 Cr, 54 Fe, 62 Ni, 64 Ni, 90 Zr, 92 Zr, 94 Zr and 118 Sn. These data are compared with recently published 20 MeV triton elastic scattering data for the same targets in a simultaneous optical-model analysis. The strength of the isospin contribution to the optical potential obtained from the elastic scattering studies is compared with that required to describe ( 3 He, t) quasi-elastic scattering data. The major part of the asymmetry dependence previously observed in triton optical potentials is shown to be unrelated to isospin.

Differential cross sections have been measured for the elastic scattering of 33 MeV 3 He particles from targets of 58,60,62,64 Ni, 63,65 Cu and 64,66,68 Zn over the angular range 5° to 175°. The data have been analysed with the optical model, with particular emphasis on the investigation of the ambiguities in the real potential, the form of the imaginary potential and the use of a spin-orbit term.

The differential cross section for elastic scattering of 42 MeV α-particles from 3 He has been measured between 20° and 160° c.m. A phenomenological description of the elastic scattering data is given by an optical-model calculation. To reproduce the shape of the differential cross section it was found that the absorptive potential was required to extend radially beyond the real potential. Including a small spin-orbit potential in the calculation improves the agreement with the experiment and predicts a polarization which is consistent with one measurement at a nearby energy. The reaction cross section given by the optical-model calculation is close to a lower limit estimated from integration of inelastic events observed. The two-body reactions 3 He(α, p) 6 Li ground and first excited state, were measured between 20° and 160° c.m. Optical potentials determined from elastic scattering data were used in a distorted wave Born approximation prediction for these cross sections. Qualitative agreement was obtained assuming only the 3 He stripping mode.

The polarized proton beam from the Wisconsin tandem accelerator has been used to measure the proton polarization in p- 3 He elastic scattering at five energies between 4 and 11 MeV in the angular range θ c.m. = 24°–156°. A phase-shift analysis of all available data between 1 and 11 MeV has been performed. A broad solution region has been found which includes solutions found earlier by Tombrello 1 ) and Drigo et al. 2 )

Charged-particle reactions resulting from the bombardment of thin isotopic 7Li targets have been studied at an incident proton energy of 30.3 MeV. Differential cross sections have been obtained for the (p, d) reaction to the ground state and first two excited states of 6Li and for the (p, t), (p, 3He) and (p, α) reactions to the ground states of the respective residual nuclei. A DWBA analysis has been used to fit the (p, d) experimental data, and relative spectroscopic factors have been extracted. The 7Li(p, pd)5He angular correlation has been studied; the results were compared with those obtained for the 6Li(p, pd)4He reaction at the same energy.

The photodisintegration of 3 He is discussed in the light of the non-relativistic version of the Cabibbo-Radicati sum rule, which amounts to a new decomposition of the standard bremsstrahlung-weighted electric dipole sume rule according to the isobaric spin, I = 1 2 or I = 3 2 , of the final state. Experiment shows that, most remarkably, the sum rule for I = 1 2 is exhausted by the two-body breakup into d + p, to the practical exclusion of three-body states with I = 1 2 . We point out some implications of the sum rules for attempts to calculate the disintegration cross sections.

Using a polarized proton beam and a polarized 3 He target, measurements of proton polarization, 3 He polarization, and the spin correlation parameters A yy and A xx in p- 3 He elastic scattering at 19.4 MeV have been obtained in a range of laboratory scattering angles from 38° to 115°. A phase-shift analysis, which is consistent with analyses at lower energies, is presented

The angular distributions of 3 He particles elastically scattered from carbon, nitrogen, oxygen, magnesium, aluminium, argon and iodine have been analysed in terms of the strong absorption model of Frahn and Venter and the best-fit values of the parameters T , Δ and μ have been obtained. An overall satisfactory agreement was obtained except in light nuclei. The interaction radius, surface diffuseness and the total reaction cross section have been calculated from the parameter values.

Comparison of the ratio of yields of the 26 Mg( 3 He, p) 28 Al and 27 Al(d, p) 28 Al transitions shows a strong enhancement for transitions to the 5.989 MeV state of 28 A1. This and the ( 3 He, p) angular distribution, support an assignment T = 2 for this level.

The nn and pp final-state interaction spectra were measured at 2.5° and 7.5° in the mirror reactions 3 H(d, 3 He)2n and 3 He(d, t)2p at 83 MeV deuteron energy. The Watson-Migdal treatment does not give a good description of these spectra. Application of the comparison method of Slobodrian et al. gives a mean value for a nn of −15.5 fm, and very large values for r on : the variation of the production form factor with the relative energy of the two nucleons seems also very large. The coherent addition of a constant amplitude to the Watson-Migdal amplitude introduces only a limited number of parameters: this method gives for r on a mean value of 3.3 fm, but the values found for a nn (around −12 fm) are in general smaller than the theoretical predictions. A more rigorous theoretical treatment of these deuteron induced reactions seems necessary. Measurements have also been performed on the mirror reactions 3 H(d, t)pn, 3 He(d, 3 He)pn and 3 H(d, t) 2 H, 3 He(d, 3 He) 2 H.

The cross sections for the elastic scattering of ^3He from tritium and ^3He have been measured for bombarding energies from 4.3 to 21.4 MeV and from 11.9 to 18.9 MeV, respectively. The results agree well with a recent resonating-group calculation in which the marked change in the shape of the angular distributions above 15 MeV is attributed to a broad resonance in the l = 3 partial wave.

The 3 He+ 3 He differential scattering and reaction cross-section data in the energy range of 1.5 to 15 MeV (c.m.) is analyzed with a one-channel resonating-group method to which is added a phenomenological imaginary potential in order to approximately account for open reaction channels. With a nucleon-nucleon potential of near-Serber exchange mixture it is found that satisfactory results can be obtained with such a formalism. The presence of the imaginary potential is shown to be important, especially at higher energies; it affects the magnitude of the differential cross section mainly, but can also accentuate the diffraction features at certain energies.