Sy Vanderwerf

CA-48(HE-3,T)SC-48 REACTION AT 66 AND 70 MEV REACTION-MECHANISM AND GAMOW-TELLER STRENGTH

Abstract The 48Ca(3He, t)48Sc reaction has been studied at E3He = 66 MeV and 70 MeV. Angular distributions are given from θ = 8° to 35°. The 0+–7+ multiplet in 48Sc is strongly excited at these energies and the spectra are further characterized by some broad structures on a continuous background. Broad peaks at Eex = 7.8, 10.6 and 13.3 MeV have an angular distribution similar to the low-lying 1+ state. The broad peaks are interpreted as envelopes of groups of 1+ states carrying a significant part of the Gamow-Teller strength. The strength distribution is consistent with a shell-model calculation. The reaction mechanism has been examined at 66 MeV. The cross section is calculated for the 0+–7+ multiplet in 48Sc as a coherent sum of one-step and two-step processes. The two-step contribution is calculated in a full finite-range 2nd-order DWBA. The result is similar contributions from (3He, α, t) and (3He, d, t). The calculations account reasonably well for the data with the exception of the transition to 0+, IAS.

DEUTERON INDUCED PICKUP REACTIONS ON CA-41

Abstract The 41 Ca(d, t) 40 Ca and 41 Ca(d, τ) 40 K reactions have been investigated at a bombarding energy of 40 MeV. A distorted-wave analysis of the measured angular distributions and a sum-rule analysis of the resulting spectroscopic factors has enabled the identification of members of various particle-hole multiplets. Values obtained for the matrix elements of the 1 f 7 2 − 1 d 3 2 −1 effective interaction are in poor agreement with values obtained from other nuclei, but are reasonably well reproduced by calculations with a simple force.

STRENGTH DISTRIBUTIONS IN NEODYMIUM ISOTOPES - A TEST OF COLLECTIVE NUCLEAR-MODELS

Abstract Excited states in even Nd isotopes, up to excitation energies of 3–4 MeV, were investigated in proton- and deuteron-scattering experiments performed with high-energy resolution. More than 300 transitions were studied. For several new excited states spin and parity assignments have been suggested. Reduced transition probabilities were extracted for natural-parity states from O + up to 6 + . The experimental strength distributions have been compared with the predictions of the interacting boson model (IBM) and of the quasi-particle-phonon model (QPM). The octupole transition probabilities are well described in both models as produced by the fragmentation of the f-boson or of E3 phonons. IBM-sdf calculations seem to account also for the transitions to the low-lying 1 − states. Quadrupole and hexadecapole distributions are well described in the QPM. The leading configurations are due to 6–8 low-lying one-phonon states. The two- and three-phonon states play an important role especially in 146 Nd. The failure of IBM quadrupole and hexadecapole calculations clearly points out the need of introducing additional bosons lying at high excitation energies. QPM evaluations account also for other features of the experimental data, as the E5 and E6 strength distributions and the isovector components. The limits of the two models are discussed.

NON-SPIN-FLIP (HE-3, T) CHARGE-EXCHANGE AND ISOBARIC ANALOG STATES OF ACTINIDE NUCLEI STUDIED AT THETA=0-DEGREES, E(HE-3)=76 MEV AND 200 MEV

The (He-3, t) charge-exchange reaction has been studied at theta = 0-degree-C and bombarding energies of E(He-3) = 76.5 MeV and 200 MeV. Spectra were measured using magnetic analysis for target nuclei of C-12, C-13, O-16, F-19, Si-28, Si-29, Si-30, Zr-90, Sn-117, Sn-120, (nat)Ta, (nat)W, Au-197, Pb-208, Th-230, Th-232, U-234, U-236, U-238 and Pu-244. The measurements at 76.5 MeV concentrated on the isobaric analog states of several actinide nuclei, particularly on their widths and the branching ratios for proton decay. Cross sections, Q-values and total widths were determined for the transitions to the isobaric analog states. Coulomb displacement energies derived from the measured Q-values display the influence of deformed nuclear shapes. Escape widths GAMMA-up and spreding widths GAMMA-down of the isobaric analog states in five actinide nuclei were deduced from the measured proton-decay branching ratios. They were found to be in agreement with predictions which postulate isospin mixing via the Coulomb force with the (T0-1)-component of the isovector giant monopole resonance. The measurements at 200 MeV were concerned with transitions to isobaric analog states in both light and heavy nuclei, including several actinide nuclei, but Gamow-Teller resonances and transitions to numerous other states were also observed. The measured cross sections for several transitions to isobaric analog states from Si-30 to Pb-208 were used to extract the effective interaction V(tau) for non-spin-flip (He-3, t) charge exchange at E(He-3) almost-equal-to 200 MeV. The interaction strength V(tau) decreases by a factor 0.6 when compared to previously measured values for the energy range E(He-3) = 65 to 90 MeV. An angular distribution from theta(t) = 0-degree to 16-degrees for the transition to the isobaric analog state in Sb-120 measured at E(He-3) = 200 MeV was found to be in very good agreement with microscopic calculations.

γ-decay of the deeply-bound hole states in 101Pd, 105Pd, 107Pd, 111Sn, 117Sn observed in the (3He, αγ) reaction at 70 MeV

Abstract The γ-decay of deep-hole states in 101, 105, 107 Pd was studied via the ( 3 He, αγ) reaction at E 3 he = 70 MeV and supplemented by data from 112, 118 Sn targets to investigate the deep-hole spreading mechanism. The γ-decay pattern for the g 9 2 deep-hole state shows a strong dependence on the spreading width: if the deep-hole state is observed as a sharp peak, it mainly decays to the low-lying 7 2 + state by a spin-flip M1 transition with a large M1-E2 mixing ratio; if the deep-hole state is observed as a broad bump, it decays statistically indicating the complete spreading of the hole strength over the underlying states; if the deep-hole state is observed with a structure intermediate between a sharp peak and broad bump, its γ-decay shows both decay patterns. A sharp peak at E x = 2.396 MeV in 101 Pd which carries a large fraction of the g 9 2 hole strength ( C 2 S = 2.0) was found to be a single state having a width of less than 2.5 keV. For the spin-flip M1 transition the destructive interference between the g 9 2 component and the coupled components of the deep-hole state was found in heavily spread states. A quasiparticle-plus-rotor (QPR) model was applied to calculate the fragmentation in the doorway stage for the g 9 2 neutron deep-hole state in the Pd isotopes. A reasonable agreement between the calculation and the experimental results was obtained for the strength fragmentation, for the nucleus 101 Pd. However, the large M1-E2 mixing ratio experimentally observed was not reproduced.

Low-lying octupole strength in 112Cd

The low-lying octupole strength distribution in 112Cd has been measured by means of inelastic proton scattering. A splitting of the strength has been observed and interpreted as due to the interaction between the quadrupole and octupole degrees of freedom. The splitting can be reproduced by the IBA-1 model if the coupling of f- and d-bosons is considered.

The 197Au(d, 3He)196Pt reaction and the supersymmetry scheme

The 197Au(d,3He)196Pt reaction has been studied at Ed = 108 MeV. An important breakdown of the selection rules of the supersymmetry scheme is observed for the 22+ level. The generally strong excitation of the 22+ level by transfer reactions in the Pt region leads to question the validity of the supersymmetry scheme at least for this level.

The 54Fe(3He, t)54Co reaction at 70 MeV, Gamow-Teller strength

Abstract The 54 Fe( 3 He, t) 54 Co reaction has been studied at 70 MeV with an energy resolution around 70 keV (FWHM). The triton spectra are characterized by sharp peaks up to 10 MeV excitation energy superimposed on a continuum. Most of the sharp peaks have a forward-peaked angular distribution and 38 peaks or groups of peaks are found to have an angular distribution corresponding to an angular momentum transfer of 2. Model considerations lead to the conclusion that most of these states are 1 + states. A shell-model calculation with parameters that account for the Gamow-Teller strength distribution in 48 Ca- 48 Sc divides the β-strength in 54 Co in a ratio 5.7:6.8:1.3 for the T = 0, 1 and 2 states. A comparison is made with the 1 + spectrum in 54 Mn ( T = 2 states) and a tentative assignment of T = 2 states in 54 Co is reached. The cross section has been calculated for the 0 + , 1 + and 3 + states in 54 Co assuming a pure ( π f 7 2 −1 ν f 7 2 −1 ) configuration finite-range DWBA is used and the conclusions are that the ( 3 He, α, t) and ( 3 He, d, t) processes give significant contributions to the cross sections.

TRANSITION CHARGE-DENSITIES OF LOW-LYING COLLECTIVE STATES IN PT 196 FROM INELASTIC ELECTRON-SCATTERING

Abstract Differential cross sections for levels in the excitation-energy range from 0 to 3.0 MeV in 196 Pt have been measured by inelastic electron scattering in a momentum-transfer range up to 2.5 fm −1 . The ground-state charge density and the transition charge densities of nine low-lying collective levels have been extracted in a Fourier-Bessel analysis of these data. The densities are compared with those obtained from microscopic calculations within the quasiparticle phonon model, using the single-particle basis obtained from a density functional approach. Satisfactory agreement has been obtained, in spite of the complicated structure of 196 Pt.

PROTON HOLE RESPONSE FUNCTION ON PT-196 AND AU-197 TRANSITIONAL TARGET NUCLEI UP TO HIGH-EXCITATION ENERGY

Abstract The proton-hole response functions have been studied on the transitional target nuclei 196Pt and 197Au via the (d, 3 He) reaction at Ed = 108.4 MeV, up to 6 MeV and 18.5 MeV excitation energy respectively. 196Pt low-lying levels have been studied in addition at Ed = 50 MeV. Spectroscopic information gained on the low-lying levels in the 195Ir and 196Pt residual nuclei allows the discussion of the 3 s 1 2 and 2 d 3 2 orbital filling. For both 195Ir and 196Pt, new 2d 5 2 and 1 h 11 2 levels or groups are observed. The 196Pt spectra exhibit a broad bump between 6 and 15 MeV excitation energy riding over a continuous background. The study of the excitation energy spectra up to 27 MeV leads to a consistent subtraction of the background. The contributions of the 1 g 9 2 , 2p and 1f inner-hole strengths are deduced by least square fits of DWBA angular distributions. About the whole 1 g 9 2 and 2p inner hole strengths and 50% of the 1f strengths are found below Ex = 18.5 MeV. The background correction is also used to reanalyse previous data obtained via the same reaction on the spherical 208Pb target for comparison. Experimental results on centroid separation energies are compared with Hartree Fock predictions. The spreading widths and specific features of the strength distribution shapes in 195Ir and 196Pt and 207Tl are discussed in connection with the dominant quadrupole collective degrees of freedom of the two first nuclei contrasting with the strong vibrational modes in 207Tl. The valence hole fragmentation in 195Ir is described in the framework of the core quasiparticle coupling model.