Search

A 130 MeV primary tritium beam, newly developed at the superconducting cyclotron AGOR, has been used for the investigation of 1 hw and 2 hw isovector giant resonances in Co-58 via the r(+) channel. The angular distributions of double-differential cross sections have been extracted between E-x and 30 MeV from theta(lab) = 0degrees to 6degrees. A DWBA analysis have been extracted between E. with normal-mode (NM) wave functions and a multipole-decomposition analysis (MDA) indicate strength for the monopole resonances (dominated by the spin-flip transition) fragmented between 10 and 27 MeV excitation energy, in rather good agreement with preliminary RPA calculations.

The microscopic structure of the Gamow-Teller resonance (GTR) and spin-dipole resonance (SDR) in Bi-208 has been investigated in the Pb-208(He-3,tp)Pb-207 reaction at E(He-3) = 450 MeV and very forward scattering angles. The partial and total branching ratios and the escape widths for GTR and SDR decay to the residual neutron-hole states in Pb-207 were deduced. These are found to be in good agreement with recent theoretical estimates. The (He-3,tp) reaction on Pb at E(He-3) = 177 MeV was also studied in order to locate isovector monopole strength corresponding to 2 (h) over bar w transitions. Monopole strength at excitation energies above 25 MeV was discovered and compared to calculated strength due to the isovector giant monopole resonance and the spin-flip isovector monopole resonance. Calculations in a normal-mode framework show that all isovector monopole strength can be accounted for if the branching ratio for decay by proton emission is 20%.

Spin-isospin excitations in B-12 and N-12 have been studied using the C-12(d,He-2)B-12 and C-12(He-3,t)N-12 charge-exchange reactions at theta = 0 degrees and at E-d=200 MeV and E(He-3)=450 MeV, respectively. Neutron decay from B-12 to B-11 and proton decay from N-12 to C-11 have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in B-12 and N-12 are discussed on the basis of the experimental observations of particle decays and their angular correlations.

Spin-isospin excitations in B-12 and N-12 have been studied using the C-12(d,He-2)B-12 and C-12(He-3,t)N-12 charge-exchange reactions at theta = 0 degrees and at E-d=200 MeV and E(He-3)=450 MeV, respectively. Neutron decay from B-12 to B-11 and proton decay from N-12 to C-11 have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in B-12 and N-12 are discussed on the basis of the experimental observations of particle decays and their angular correlations.

The (He-3,t) charge-exchange reaction has been studied at E(He-3) = 200 MeV and angles near 0-degrees on targets of Sn-117 and Sn-120. Fragmentation of the giant Gamow-Teller resonance into separate components of the particle-hole type has been observed in good agreement with theoretical predictions. These components are connected with what is usually referred to in the literature as direct-, core-polarization-, and back-spin-flip Gamow-Teller strength. The observed cross sections near theta = 0-degrees suggest contributions from the isovector spin-flip interaction as well as the isovector tensor interaction. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components involving the 1h11/2 neutron orbital could not uniquely be identified. The data are compatible, though, with such a splitting since the observed widths of the main Gamow-Teller components in Sb-117 and Sb-120 exceed the predicted splittings.

The (He-3,t) charge-exchange reaction has been studied at E(He-3) = 200 MeV and angles near 0-degrees on targets of Sn-117 and Sn-120. Fragmentation of the giant Gamow-Teller resonance into separate components of the particle-hole type has been observed in good agreement with theoretical predictions. These components are connected with what is usually referred to in the literature as direct-, core-polarization-, and back-spin-flip Gamow-Teller strength. The observed cross sections near theta = 0-degrees suggest contributions from the isovector spin-flip interaction as well as the isovector tensor interaction. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components involving the 1h11/2 neutron orbital could not uniquely be identified. The data are compatible, though, with such a splitting since the observed widths of the main Gamow-Teller components in Sb-117 and Sb-120 exceed the predicted splittings.

Double-differential cross sections of the Fe-54,Fe-56(n, p) reactions have been measured at 97 MeV in the angular range 0-30-degrees for excitation energies up to 40 MeV. The spectra have been decomposed into different multipolarities by a technique based on the use of sample angular distributions calculated within the distorted-wave Born approximation. From the identified Gamow-Teller strength, S(beta)+ values were obtained for Fe-54 Fe and Fe-56. Comparisons with available shell-model calculations of the GT strength were made. The results are important for models of supernova explosions since electron-capture rates, which are proportional to S(beta)+, in 1f2p-shell nuclei affect the dynamics of the star. At higher excitation energies, the spectra are dominated by L = 1 strength in broad distributions with a maximum at about 12 MeV. Microscopic calculations based on the random-phase approximation were performed and compared with the experimental data.

Double-differential cross sections of the Fe-54,Fe-56(n, p) reactions have been measured at 97 MeV in the angular range 0-30-degrees for excitation energies up to 40 MeV. The spectra have been decomposed into different multipolarities by a technique based on the use of sample angular distributions calculated within the distorted-wave Born approximation. From the identified Gamow-Teller strength, S(beta)+ values were obtained for Fe-54 Fe and Fe-56. Comparisons with available shell-model calculations of the GT strength were made. The results are important for models of supernova explosions since electron-capture rates, which are proportional to S(beta)+, in 1f2p-shell nuclei affect the dynamics of the star. At higher excitation energies, the spectra are dominated by L = 1 strength in broad distributions with a maximum at about 12 MeV. Microscopic calculations based on the random-phase approximation were performed and compared with the experimental data.

Double-differential cross sections of the Zr-90(n, p) reaction have been measured at 98 MeV in the angular range 0-degrees-30-degrees for excitation energies up to 40 MeV. The spectra have been interpreted in terms of direct and multistep reactions. The contributions from the latter have been calculated using a statistical theory of multistep direct reactions. The direct parts of the spectra have been decomposed into their different multipole components by using peak-fitting and multipole-decomposition techniques, based on sample angular distributions calculated within the distorted-wave Born approximation. An extensive microscopic calculation based on the random-phase approximation has also been performed and the results are compared with the experimental data. A value S(beta)+ = 1.7 +/- 0.2 is extracted for the Gamow-Teller strength, suggesting an occupancy nu-2 = 0.09 +/- 0.01 for the 1g9/2 proton orbital. This value has been compared with recent results from (d, He-3) proton pickup and (e, e'p) knockout reactions.

Double-differential cross sections of the Zr-90(n, p) reaction have been measured at 98 MeV in the angular range 0-degrees-30-degrees for excitation energies up to 40 MeV. The spectra have been interpreted in terms of direct and multistep reactions. The contributions from the latter have been calculated using a statistical theory of multistep direct reactions. The direct parts of the spectra have been decomposed into their different multipole components by using peak-fitting and multipole-decomposition techniques, based on sample angular distributions calculated within the distorted-wave Born approximation. An extensive microscopic calculation based on the random-phase approximation has also been performed and the results are compared with the experimental data. A value S(beta)+ = 1.7 +/- 0.2 is extracted for the Gamow-Teller strength, suggesting an occupancy nu-2 = 0.09 +/- 0.01 for the 1g9/2 proton orbital. This value has been compared with recent results from (d, He-3) proton pickup and (e, e'p) knockout reactions.

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.

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.

A 130 MeV primary tritium beam, newly developed at the superconducting cyclotron AGOR, has been used for the investigation of 1 hw and 2 hw isovector giant resonances in Co-58 via the r(+) channel. The angular distributions of double-differential cross sections have been extracted between E-x and 30 MeV from theta(lab) = 0degrees to 6degrees. A DWBA analysis have been extracted between E. with normal-mode (NM) wave functions and a multipole-decomposition analysis (MDA) indicate strength for the monopole resonances (dominated by the spin-flip transition) fragmented between 10 and 27 MeV excitation energy, in rather good agreement with preliminary RPA calculations.

The microscopic structure of the Gamow-Teller resonance (GTR) and spin-dipole resonance (SDR) in Bi-208 has been investigated in the Pb-208(He-3,tp)Pb-207 reaction at E(He-3) = 450 MeV and very forward scattering angles. The partial and total branching ratios and the escape widths for GTR and SDR decay to the residual neutron-hole states in Pb-207 were deduced. These are found to be in good agreement with recent theoretical estimates. The (He-3,tp) reaction on Pb at E(He-3) = 177 MeV was also studied in order to locate isovector monopole strength corresponding to 2 (h) over bar w transitions. Monopole strength at excitation energies above 25 MeV was discovered and compared to calculated strength due to the isovector giant monopole resonance and the spin-flip isovector monopole resonance. Calculations in a normal-mode framework show that all isovector monopole strength can be accounted for if the branching ratio for decay by proton emission is 20%.

The microscopic structure of the Gamow-Teller resonance (GTR) and spin-dipole resonance (SDR) in Bi-208 has been investigated in the Pb-208(He-3,tp)Pb-207 reaction at E(He-3) = 450 MeV and very forward scattering angles. The partial and total branching ratios and the escape widths for GTR and SDR decay to the residual neutron-hole states in Pb-207 were deduced. These are found to be in good agreement with recent theoretical estimates. The (He-3,tp) reaction on Pb at E(He-3) = 177 MeV was also studied in order to locate isovector monopole strength corresponding to 2 (h) over bar w transitions. Monopole strength at excitation energies above 25 MeV was discovered and compared to calculated strength due to the isovector giant monopole resonance and the spin-flip isovector monopole resonance. Calculations in a normal-mode framework show that all isovector monopole strength can be accounted for if the branching ratio for decay by proton emission is 20%.

Spin-isospin excitations in B-12 and N-12 have been studied using the C-12(d,He-2)B-12 and C-12(He-3,t)N-12 charge-exchange reactions at theta = 0 degrees and at E-d=200 MeV and E(He-3)=450 MeV, respectively. Neutron decay from B-12 to B-11 and proton decay from N-12 to C-11 have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in B-12 and N-12 are discussed on the basis of the experimental observations of particle decays and their angular correlations.

Spin-isospin excitations in B-12 and N-12 have been studied using the C-12(d,He-2)B-12 and C-12(He-3,t)N-12 charge-exchange reactions at theta = 0 degrees and at E-d=200 MeV and E(He-3)=450 MeV, respectively. Neutron decay from B-12 to B-11 and proton decay from N-12 to C-11 have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in B-12 and N-12 are discussed on the basis of the experimental observations of particle decays and their angular correlations.

Spin-isospin excitations in B-12 and N-12 have been studied using the C-12(d,He-2)B-12 and C-12(He-3,t)N-12 charge-exchange reactions at theta = 0 degrees and at E-d=200 MeV and E(He-3)=450 MeV, respectively. Neutron decay from B-12 to B-11 and proton decay from N-12 to C-11 have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in B-12 and N-12 are discussed on the basis of the experimental observations of particle decays and their angular correlations.

The (He-3,t) charge-exchange reaction has been studied at E(He-3) = 200 MeV and angles near 0-degrees on targets of Sn-117 and Sn-120. Fragmentation of the giant Gamow-Teller resonance into separate components of the particle-hole type has been observed in good agreement with theoretical predictions. These components are connected with what is usually referred to in the literature as direct-, core-polarization-, and back-spin-flip Gamow-Teller strength. The observed cross sections near theta = 0-degrees suggest contributions from the isovector spin-flip interaction as well as the isovector tensor interaction. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components involving the 1h11/2 neutron orbital could not uniquely be identified. The data are compatible, though, with such a splitting since the observed widths of the main Gamow-Teller components in Sb-117 and Sb-120 exceed the predicted splittings.

Double-differential cross sections of the Fe-54,Fe-56(n, p) reactions have been measured at 97 MeV in the angular range 0-30-degrees for excitation energies up to 40 MeV. The spectra have been decomposed into different multipolarities by a technique based on the use of sample angular distributions calculated within the distorted-wave Born approximation. From the identified Gamow-Teller strength, S(beta)+ values were obtained for Fe-54 Fe and Fe-56. Comparisons with available shell-model calculations of the GT strength were made. The results are important for models of supernova explosions since electron-capture rates, which are proportional to S(beta)+, in 1f2p-shell nuclei affect the dynamics of the star. At higher excitation energies, the spectra are dominated by L = 1 strength in broad distributions with a maximum at about 12 MeV. Microscopic calculations based on the random-phase approximation were performed and compared with the experimental data.

Double-differential cross sections of the Zr-90(n, p) reaction have been measured at 98 MeV in the angular range 0-degrees-30-degrees for excitation energies up to 40 MeV. The spectra have been interpreted in terms of direct and multistep reactions. The contributions from the latter have been calculated using a statistical theory of multistep direct reactions. The direct parts of the spectra have been decomposed into their different multipole components by using peak-fitting and multipole-decomposition techniques, based on sample angular distributions calculated within the distorted-wave Born approximation. An extensive microscopic calculation based on the random-phase approximation has also been performed and the results are compared with the experimental data. A value S(beta)+ = 1.7 +/- 0.2 is extracted for the Gamow-Teller strength, suggesting an occupancy nu-2 = 0.09 +/- 0.01 for the 1g9/2 proton orbital. This value has been compared with recent results from (d, He-3) proton pickup and (e, e'p) knockout reactions.

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.