M.N. Harakeh

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.

The effective 3he-nucleon force in a microscopic DWBA approach to the (3He, t) charge-exchange reaction

Abstract The ( 3 He, t) reaction has been studied on the targets 12 C, 16 O, 24 Mg, 26 Mg, 28 Si, 32 S, 42 Ca, 48 Ca, 54 Fe, 58 Ni and 90 Zr at incident energies 66–90 MeV. From angular distributions of transitions to selected states the parameters V ρ , V σρ , V Tρ and V LSρ of an effective projectile-nucleon force parametrized with single Yukawa potentials have been obtained for this energy domain. Differences from the force proposed earlier by Schaeffer for a lower energy are found, notably in the tensor component.

Experimental determination of monopole strength in 40Ca between 10 and 20 MeV excitation energy

The distribution of isoscalar monopole strength in 40Ca was determined from singles 40Ca(α, α′) and from coincident 40Ca(α,α′α0) data at Eα =120 MeV and scattering angles from 0° to 3°. Between 10.5 and 15.7 MeV excitation energy (23±5)% of the EO EWSR was located from the singles and from the coincidence measurements independently, while (30 ±6)% of the EO EWSR was found in the interval 10.5–20 MeV from the singles data only.

Isospin decomposition of the Gamow-Teller strength in Cu-58

Abstract The Gamow-Teller (GT) strength excited by a (p, n)-type reaction on a nucleus with isospin T0 and N > Z is shared by isospin components T0 − 1, T0 and T0 + 1. A good energy resolution (3He, t) reaction on 58Ni revealed the fine structure of the GT strength in 58Cu. The isospin of each level constituting the fine structure was assigned by comparing to results from inelastic electron and proton scatterings and (n, p)-type reactions, thus resolving the isospin structure of the GT strength in 58Cu. The ratio of the summed GT strengths among the three isospin components is well described by a shell-model calculation.

Isoscalar excitations in the lead region observed in inelastic α-scattering at Eα = 120 MeV

Abstract Inelastic α-scattering from 197 Au, 206 Pb, 208 Pb and 209 Bi has been measured at an α-bombarding energy of 120 MeV. In the giant resonance region an isoscalar resonance (GR2) at E x ∼ 80A − 1 3 , in addition to the well-known GQR resonance (GR1) at E x ∼ 63 A − 1 3 , is observed. DWBA calculations were performed with the collective form factor prescription. The angular distribution of the GQR bump is found to be better fit if a small admixture of 20 % of the E4, energy-weighted sum rule (EWSR) is added to ∼ 100 % of the E2, EWSR. The angular distribution of the higher bump (GR2) is well fit both with an L = 2 and L = 0 transfer in our angular range. If it is L = 0, it then exhausts 100 % of the monopole EWSR. Angular distributions to low-lying states in 208 Pb were also obtained. DWBA calculations with collective form factors were performed to fit these data. Around 33 %, 15 % and 7 % ofE3, E4 and E5 EWSRs are exhausted in these low-lying transitions in addition to the 15 % E2, EWSR in the 2 + state at 4.10 MeV.

OCTUPOLE EXCITATIONS IN VIBRATIONAL NUCLEI AND THE SDF INTERACTING BOSON MODEL

Abstract Proton and deuteron inelastic scattering experiments, performed with an energy resolution of 12–15 keV, have been used to study negative-parity states of vibrational and transitional nuclei with mass between 98 and 150. The analysis has been focussed on the isovector components, on the quadrupole-octupole two-phonon states and on the fragmentation of the octupole strength. This latter displays a regular dependence on the product of proton and neutron valence particle numbers and is satisfactorily reproduced by IBM-1 + f-boson calculations. Other features of the experimental spectra, as the relative positions of the 3− states, exhibit a dependence on the ratio of valence particle numbers and indicate that a IBM-2 approach might be more appropriate.

Measuring the (d,He-2) reaction with the focal-plane detection system of the BBS magnetic spectrometer at AGOR

At intermediate energies, the (d, He-2) charge-exchange reaction can be used to observe Gamow-Teller strength in the direction. He-2 denotes the two-proton system being in the singlet S-1(0) state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the (d, He-2) cross-section. Nevertheless, background-free He-2 spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our (d 2 He) experiments possible are described. Two nuclei, C-12 and Mg-24, have been used as a test case

Interplay between single-particle and collective degrees of freedom in the excitation of the low-lying states in 142Nd

Abstract The low-lying excited states in 142 Nd were investigated by inelastic electron scattering. The momentum transfer range covered was 0.5–2.8 fm −1 . Transition charge densities were extracted for natural-parity states from 0 + up to 9 − and up to an excitation energy of 3.5 MeV. For several new excited states spin and parity assignments have been suggested. The experimental transition charge densities have been interpreted with the aid of the quasiparticle-phonon model (QPM). The QPM is well-suited to investigate the contribution of collective and single-particle degrees of freedom to excited states in spherical nuclei. On the basis of the QPM calculations it is shown that in 142 Nd both degrees of freedom play an important role, as well as the interplay between them. Both the strength distribution and the structure of the transition charge densities of the low-lying excited states are well described by the calculations. The origin of the structure in the nuclear interior usually predicted by microscopic calculations but not observed experimentally is explained. An argument for the proton number dependence of the excitation energy of the 3 1 − state in the N = 82 isotones is given.

The (150)Nd((3)He,t) and (150)Sm(t,(3)He) reactions with applications to beta beta decay of (150)Nd

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Collective and quasiparticle structures in 192Pb

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