Microscopic DWBA Calculations Research Articles

Invariant Mass Spectroscopy of 23O via the (p, p′) Reaction in Inverse Kinematics

The neutron-rich oxygen isotope 23O has been investigated via proton inelastic scattering on a liquid hydrogen target at 63.5 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum. A sharp resonance state was observed at 42(5) keV above the neutron threshold. A comparison of the differential cross section leading to this state with a microscopic DWBA calculation allowed a Jπ assignment of 5/2+ for this state.

Invariant Mass Spectroscopy for the Neutron Rich Nuclei

The neutron-rich carbon isotopes (19,17)C and a boron isotope (14)B are investigated respectively via proton inelastic and charge-exchange reactions on a liquid hydrogen target at around 70 MeV/nucleon at RIKEN. The invariant mass method in inverse kinematics involving coincidence detection of a charged fragment and a neutron both emitted at forward angles is employed to map the energy spectrum above the neutron decay threshold. Several resonance structures are revealed in the invariant mass spectra, and the nature for some of them is discussed from comparisons of differential cross section data with predictions of microscopic DWBA calculations based on spsdp f shell model wave functions and a recent parametrization of semi-microscopic nucleon-nucleus optical model potential (JLMB). By extrapolating the (p, n) cross sections leading to the 1(+) state at 1.27 MeV in (14)B to zero momentum transfer the Gamow-Teller transition strength is deduced. The value is found to compare well with that reported in a beta-delayed neutron emission study.

Unbound excited states in 19,17C

The neutron-rich carbon isotopes 19,17C have been investigated via proton inelastic scattering on a liquid hydrogen target at 70 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum, in which fast neutrons and charged fragments were detected in coincidence using a neutron hodoscope and a dipole magnet system. A peak has been observed with an excitation energy of 1.46(10) MeV in 19C, while three peaks with energies of 2.20(3), 3.05(3), and 6.13(9) MeV have been observed in 17C. Deduced cross sections are compared with microscopic DWBA calculations based on p-sd shell model wave functions and modern nucleon–nucleus optical potentials. Jπ assignments are made for the four observed states as well as the ground states of both nuclei.

Sn120homologous levels via the123Sb(p→,α)Sn120reaction: Experimental evidence and microscopic calculations

The $^{123}\mathrm{Sb}$$(\stackrel{\ensuremath{\rightarrow}}{p},\ensuremath{\alpha})$$^{120}\mathrm{Sn}$ reaction has been studied in a high resolution measurement at incident energy of 24 MeV using a polarized proton source and a Q3D spectrometer. The differential cross sections and asymmetries for transitions to levels of $^{120}\mathrm{Sn}$ homologous to the lowest energy states of $^{119}\mathrm{In}$ have been measured and interpreted in terms of the experimental differential cross sections and asymmetries of the parent $^{119}\mathrm{In}$ states, on the basis of the weak-coupling model. Several (17) states of the $^{120}\mathrm{Sn}$ residual nucleus, not previously reported in the literature, have been detected and spins and parities have been proposed for seven of them, while parities have been proposed for five other previously known levels. In order to analyze the transitions populating the homologous levels, for both differential cross sections and asymmetries, microscopic DWBA calculations have been performed using spectroscopic amplitudes obtained from a shell-model study.

Spin-flip probability via the 26Mg(3He,tγ)26Al reaction

The spin-flip probability for the charge-exchange reaction Mg-26(He-3,tgamma)Al-26 (1+; 1.06 MeV) has been measured at E = 53 MeV and theta(lab) = 10-degrees. The extracted value is 0.41 +/- 0.04. A microscopic DWBA calculation with empirically determined effective interactions reproduces the observed cross sections fairly well but the spin-flip probability poorly. To supplement the (He-3,tgamma) study, the spin-flip probability has been measured for the same state by the charge-exchange (p,ngamma) reaction at 35 MeV and theta(lab) = 30-degrees and found to be 0.52 +/- 0.11. Though statistically not significant the lower value of S in the (He-3,t) reaction may reflect on the more complex nature of this reaction at the present bombarding energy.

Microscopic and dirac macroscopic analyses of elastic and inelastic scatterings of 135 MeV and 800 MeV polarized protons from16O

Microscopic DWBA calculations and Dirac coupled-channel calculations have been performed to analyse cross-sections and analysing powers data for elastic and inelastic scatterings of 135 MeV and 800 MeV polarized protons from some low-lying states in16O. Good agreement, in general, between the microscopic DWBA calculations and the data has been obtained, the analysing powers for the inelastic scattering are less well described; however, better agreement has been obtained with Dirac coupled-channel collective model calculations for all these states investigated.

Spin-flip and non-spin-flip isovector excitations observed in the (12C,12N) reactions at and the (13C,13N) reactions at

The charge-exchange reactions ( 12 C, 12 N) at E A = 135 MeV and ( 13 C, 13 N) at E A = 100 MeV have been studied for several nuclei. These two reactions have different selectivity for the spin transfer. The differential cross sections for the 12 C( 12 C, 12 N) 12 B charge-exchange reaction leading to the 12 B (1 + ) ground state, Ex = 4.5 MeV and Ex = 7.5 MeV states were well described by the microscopic DWBA calculations suggesting the dominance of the one-step process.

Excitation of spin-dipole states by the 12C( 12C, 12N) 12B reaction at E/ A = 135 MeV

The spin-dipole resonances in 12B have been studied with the charge-exchange reaction 12C( 12C, 12N) 12B at E/ A = 135 MeV, which has the str excitation. The differential cross sections for the states around E x = 4.5 MeV and 7.5 MeV were well described by the microscopic DWBA calculation. The spin-dipole strength concentrated around E x = 7.5 MeV was found to be dominated by J π = 2 −.

Spin-Isospin Resonances Observed in the (d, 2He) and ( 12C, 12N) Reactions at E/A = 135 MeV

The (d, 2He) and ( 12C, 12N) charge-exchange reactions have been studied at E/A = 135 MeV using the high resolution spectrograph SMART at RIKEN. The similarities were found in the energy spectra of both reactions, indicating the strong selectivity of ΔS = 1 and ΔT = 1 transitions. The 12C( 12C, 12N) 12B reaction has been studied using the microscopic DWBA calculation, suggesting that the reaction predominantly goes thorough a one-step process. The dominance of the L = 0 component was also found.

Charge-exchange reaction 12C( 12C, 12N) 12B at [formula omitted

The charge-exchange reaction 12C( 12C, 12N) 12B has been studied at E A = 135 MeV . The elastic scattering of 12C from 12 C was also measured to determine the optical potential parameters. The differential cross sections for the charge-exchange reaction leading to the 12B ground state (1 +) were well described byh the microscopic DWBA calculation, suggesting the dominance of the one-step process. The L = 0 component was found to be about five times stronger than the L = 2 component at 0°.

Excitation of the 2 1+ and 2 2+ states in the 88Sr(p, p′) reaction at 25 and 31 MeV: A look behind the nuclear surface

Data for the excitation of the 2 1 + and 2 2 + states in the 88Sr(p, p′) reaction at 25 and 31 MeV indicate substantial contributions from the interior of the nucleus, Microscopic DWBA calculations reproduce this and yield a fair description of the data. A detailed description, especially of the 2 2 + state, is sensitive to the effective nucleon-nucleon interaction used and the non-locality of the optical potential, which are insufficiently known at present.

Excitation of M1 states in 58Ni and 60Ni by 65 MeV polarized proton inelastic scattering

We studied the 1 + states in 58Ni and 60Ni by using the 58 Ni( p , p′) 58 Ni and 60 Ni( p , p′) 60 Ni reactions at 65 MeV with high resolution, in order to search for the fragmentation of the 1 + states at excitation energies of E x = 7–11 MeV. From the similarity in experimental shapes of both cross sections and analyzing powers for the well-known 1 + states and from comparison with microscopic DWBA calculations under the assumptions of pure (f 7 2 −1f 5 2 ) and ν(p 3 2 P 1 2 ) configurations, four states in 58Ni and one state in 60Ni have been identified as the candidates of the 1 + states of a (f 7 2 −1f 5 2 ) or ν(p 3 2 P 1 2 ) configuration in the M1 giant resonance region of E x = 7–10 MeV, though the strengths are very weak.

12C(p,n)12N spin-transfer measurement at O degrees and the effective nucleon-nucleon interaction

The spin-transfer coefficient Kyy'(0 degrees ) has been measured for the reaction 12C(p,n)12N at Ep=65 MeV using the neutron double scattering technique. Microscopic DWBA calculations with the M3Y effective interaction give a qualitative account of the Kyy'( degrees ) data for the 1+ transition. Better agreement is obtained if the high-q component of the tensor force is reduced.

ISOSCALAR CHARACTER OF THE 5,845 MeV 1+ STATE IN 208 Pb

A strong 1+ state which has a large component of the π(h11-1/2hg/2) configuration was found at 5.845 MeV in 208Pb from the reactions 208Pb(p,p') and 209Bi(d,3He). Microscopic DWBA calculations of (p,p') cross sections show that the 1+ state has a predominant isoscalar nature. This conclusion is consistent with the large spectroscopic factor deduced from the (d,3He) experiment.

Absolute normalisation in microscopic DWBA analysis of the three-nucleon transfer-reaction cross sections

Theoretical and experimental normalisation constants for the three-nucleon transfer reactions are determined. Zero-range and finite-range analyses have been performed. Theoretical cross sections obtained from microscopic DWBA calculations are two to three orders of magnitude smaller than experimental values.

Alpha particle scattering to negative parity states of14N

Inelastic4He scattering on melamine targets is studied for negative parity excitations of14N. ElevenΔL=3 excitations are presented, for states up to 15.41 MeV; threeΔL=1 transitions are also studied. A microscopic DWBA calculation accounts for several of the octupole excitations, requiring an isoscalar effective strength about twice that expected for free alpha-nucleon scattering. Great purity of the structure of the three lowest 2− states is noted, with the 5.11 MeV and 9.13 MeV levels excited byΔL=3, but with the 7.97 MeV state excited purely byΔL=1.

A microscopic DWBA analysis of ( 6Li, 6He) reactions

The spin-isospin flip ( 6Li, 6He) reaction has been studied. The experiment was performed with a 34 MeV 6Li beam incident upon 25, 26Mg and 27Al targets. Angular distributions associated with the lowest 5 2 +, 1 2 +, 7 2 + 25 Al, 5 +, 3 +, 1 + 26 Al and 5 2 + 27 Si states were measured. Microscopic DWBA calculations were performed using Yukawa central and r 2. Yukawa ( r 2 · Y) tensor ( μ = 1.0 fm −1) potentials averaged over the 6Li( 6He) cluster model wave functions. Knock-on (KO) exchange corrections corresponding to the central interaction are included using the local-energy approximation (LEA) method. The conclusion is that the quasi-elastic process is of major importance in the ( 6Li, 6He) transition studied in this work.

On the mechanism of the 27Al(α, d) 29Si reaction

The 27Al(α, d) 27Si reaction has been studied at three bombarding energies: 26.2, 26.45 and 26.7 MeV. The energy-averaged angular distributions for states populated in 29Si have been compared with the microscopic and macroscopic DWBA calculations and Hauser-Feshbach theory. Spectroscopic amplitudes were calculated using the available shell-model wave functions.

Neutron particle-hole multiplet states in 90Zr studied by proton inelastic scattering

The ν(g 9/2) −1(d 5/2) multiplet states in 90Zr have been identified using proton inelastic scattering at 65 MeV. The measured angular distributions were compared with microscopic DWBA calculations using simple shell-model wave functions. Remarkable agreement has been obtained for all the unnatural parity states of J π = 3 +, 5 + and 7 +.

Single and mutual excitation of projectile and target in α-scattering

Abstract The projectile excitation of 4He exciting the J π = 0 + state at E x = 20.1 MeV (α ∗ ) and the mutual excitation of projectile and target has been studied in α-scattering from 24Mg, 28Si, 40Ca, 58Ni and 90Zr at Eα = 65 MeV. The monopole excitation of 4He has been detected by its breakup α ∗ → p + t in a coincidence setup. The double folding approach for the description of the single and mutual excitation is discussed in which the rather large effect of recoil in the microscopic calculation of the inelastic form factor is taken into account. The microscopic DWBA calculation yields a good description of the structure of the angular distributions for the single excitation, but fails to reproduce the absolute cross sections. A possible explanation in terms of a drastically larger absorption for the final (α∗ + target) channel is discussed. As compared to the single excitation the mutual excitation is enhanced and in two cases even more strongly than the single excitation. For larger angles this effect is well reproduced by our calculations; however, at small angles an anomalous behaviour in the cross section for mutual excitation is observed.