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Spin-isospin excitations of the medium-mass nucleus Co-58 were studied using the (n, p)-type (d,He-2) charge-exchange reaction at an incident energy E-d = 170 MeV and small scattering angles. The achieved energy resolution of 130 keV, full width at half maximum, allowed the extraction of Gamow-Teller strength to 13 peaks at excitation energies lower than 4.1 MeV in the residual nucleus Co-58 and is consistent with the results of a multipole-decomposition analysis. The identification of Gamow-Teller transitions is possible by comparison of the measured cross sections with DWBA calculations. The results are used to discuss the relevance of the Gamow-Teller strength distribution at low excitation energy with regard to electron-capture rates used in calculations for the final stage of a massive star. (C) 2003 Elsevier B.V. All rights reserved.

The proton-rich isotope Cu-56 was produced at the GSI On-Line Mass Separator by means of the Si-28(S-32, p3n) fusion-evaporation reaction. Its beta -decay properties were studied by detecting beta -delayed gamma rays and protons. A half-Life of 93 +/- 3 ms was determined for Cu-56. Compared to the previous work, six new gamma rays and three new levels were assigned to the daughter nucleus Ni-56. The measured Gamow-Teller strength values for five Ni-56 levels are compared to shell-model predictions. (C) 2001 Elsevier Science B.V. ALI rights reserved.

The proton-rich isotope Cu-56 was produced at the GSI On-Line Mass Separator by means of the Si-28(S-32, p3n) fusion-evaporation reaction. Its beta -decay properties were studied by detecting beta -delayed gamma rays and protons. A half-Life of 93 +/- 3 ms was determined for Cu-56. Compared to the previous work, six new gamma rays and three new levels were assigned to the daughter nucleus Ni-56. The measured Gamow-Teller strength values for five Ni-56 levels are compared to shell-model predictions. (C) 2001 Elsevier Science B.V. ALI rights reserved.

The Gamow-Teller (GT) transition strengths in fp-shell nuclei are important parameters in presupernova models. A high-energy-resolution (He-3,t) experiment was performed on the T-z=1 nucleus Ti-46 at 0(degrees) and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final T-z=0 nucleus V-46. With an energy resolution of 33 keV, individual GT transitions were observed and GT strengths were derived for them up to the excitation energy of 4.5 MeV. The GT strengths were compared with shell-model calculations using various effective interactions. In this low-lying region, most GT states have isospin T=0. A few GT states with isospin T=1 were identified from the existence of the corresponding (analog) M1 states in Ti-46. By comparing the GT strength with the corresponding (analogous) M1 transition strength studied in Ti-46(e,e(')) or (gamma,gamma(')) measurements, a large constructive interference of orbital and spin terms was suggested for one of these M1 transitions.

The Gamow-Teller (GT) transition strengths in fp-shell nuclei are important parameters in presupernova models. A high-energy-resolution (He-3,t) experiment was performed on the T-z=1 nucleus Ti-46 at 0(degrees) and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final T-z=0 nucleus V-46. With an energy resolution of 33 keV, individual GT transitions were observed and GT strengths were derived for them up to the excitation energy of 4.5 MeV. The GT strengths were compared with shell-model calculations using various effective interactions. In this low-lying region, most GT states have isospin T=0. A few GT states with isospin T=1 were identified from the existence of the corresponding (analog) M1 states in Ti-46. By comparing the GT strength with the corresponding (analogous) M1 transition strength studied in Ti-46(e,e(')) or (gamma,gamma(')) measurements, a large constructive interference of orbital and spin terms was suggested for one of these M1 transitions.

Electron capture and beta decay play important roles in the evolution of presupernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in Co-58 from the Ni-58(t,He-3) reaction with a secondary triton beam of an intensity of similar to 10(6) pps at 115 MeV/nucleon and a resolution of similar to 250 keV. Previous measurements with the Ni-58(n,p) and the Ni-58(d,He-2) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell-model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from Ni-58(He-3, t) are described and turn out to be nonnegligible due to large interferences between the Delta L=0,Delta S=1 Gamow-Teller amplitude and the Delta L=2,Delta S=1 amplitude.

Electron capture and beta decay play important roles in the evolution of presupernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in Co-58 from the Ni-58(t,He-3) reaction with a secondary triton beam of an intensity of similar to 10(6) pps at 115 MeV/nucleon and a resolution of similar to 250 keV. Previous measurements with the Ni-58(n,p) and the Ni-58(d,He-2) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell-model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from Ni-58(He-3, t) are described and turn out to be nonnegligible due to large interferences between the Delta L=0,Delta S=1 Gamow-Teller amplitude and the Delta L=2,Delta S=1 amplitude.

Electron capture and beta decay play important roles in the evolution of presupernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in Co-58 from the Ni-58(t,He-3) reaction with a secondary triton beam of an intensity of similar to 10(6) pps at 115 MeV/nucleon and a resolution of similar to 250 keV. Previous measurements with the Ni-58(n,p) and the Ni-58(d,He-2) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell-model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from Ni-58(He-3, t) are described and turn out to be nonnegligible due to large interferences between the Delta L=0,Delta S=1 Gamow-Teller amplitude and the Delta L=2,Delta S=1 amplitude.

The Gamow-Teller (GT) transition strengths in fp -shell nuclei are important parameters in presupernova models. A high-energy-resolution ( 3 He ,t ) experiment was performed on the T z = 1 nucleus 46 Ti at 0 ◦ and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final T z = 0 nucleus 46 V. With an energy resolution of 33 keV, individual GT transitions were observed and GT strengths were derived for them up to the excitation energy of 4.5 MeV. The GT strengths were compared with shell-model calculations using various effective interactions. In this low-lying region, most GT states have isospin T = 0. A few GT states with isospin T = 1 were identified from the existence of the corresponding (analog) M 1 states in 46 Ti. By comparing the GT strength with the corresponding (analogous) M 1 transition strength studied in 46 Ti( e, e )or( γ,γ ) measurements, a large constructive interference of orbital and spin terms was suggested for one of these M 1 transitions ispartof: Physical Review C, Nuclear Physics vol:73 issue:2 status: published

Cross sections for the charge-exchange reaction (d,He-2) on V-50, the only odd-odd stable nucleus in the pf shell, have been measured at an incident energy of 171 MeV. The two correlated protons of the unbound He-2 system were both momentum analyzed and detected by the same spectrometer and detector. Measurements have been carried out at forward center-of-mass angles up to 6degrees. The GT(+) strength distribution has been extracted up to about 12 MeV of excitation energy. Because charge-exchange reactions from V-50 provide a unique opportunity to probe Gamow-Teller response from an odd-odd nucleus of the pf shell, the present study serves as important test case for model calculations and astrophysical processes that proceed through GT-type transitions. Consequently, the experimental result is compared with a large-scale shell-model calculation, and the implications for electron-capture processes in presupernova environments are discussed.

Cross sections for the charge-exchange reaction (d,He-2) on V-50, the only odd-odd stable nucleus in the pf shell, have been measured at an incident energy of 171 MeV. The two correlated protons of the unbound He-2 system were both momentum analyzed and detected by the same spectrometer and detector. Measurements have been carried out at forward center-of-mass angles up to 6degrees. The GT(+) strength distribution has been extracted up to about 12 MeV of excitation energy. Because charge-exchange reactions from V-50 provide a unique opportunity to probe Gamow-Teller response from an odd-odd nucleus of the pf shell, the present study serves as important test case for model calculations and astrophysical processes that proceed through GT-type transitions. Consequently, the experimental result is compared with a large-scale shell-model calculation, and the implications for electron-capture processes in presupernova environments are discussed.

The V-51(d,He-2)Ti-51 charge-exchange reaction has been investigated at an incident energy of 171 MeV and scattering angles near 0degrees. The two protons in the S-1(0)(pp) state (denoted as He-2) were both momentum analyzed and detected by the same spectrometer and detector. Spectra with a resolution of about 125 keV (full width at half maximum) have been obtained allowing identification of many levels in Ti-51 with high precision. The GT(+) strength distribution for transitions to levels up to about 6 MeV of excitation energy has been extracted. The results are compared with a large-scale shell-model calculation in the full pf shell.

The V-51(d,He-2)Ti-51 charge-exchange reaction has been investigated at an incident energy of 171 MeV and scattering angles near 0degrees. The two protons in the S-1(0)(pp) state (denoted as He-2) were both momentum analyzed and detected by the same spectrometer and detector. Spectra with a resolution of about 125 keV (full width at half maximum) have been obtained allowing identification of many levels in Ti-51 with high precision. The GT(+) strength distribution for transitions to levels up to about 6 MeV of excitation energy has been extracted. The results are compared with a large-scale shell-model calculation in the full pf shell.

The V-51(d,He-2)Ti-51 charge-exchange reaction has been investigated at an incident energy of 171 MeV and scattering angles near 0degrees. The two protons in the S-1(0)(pp) state (denoted as He-2) were both momentum analyzed and detected by the same spectrometer and detector. Spectra with a resolution of about 125 keV (full width at half maximum) have been obtained allowing identification of many levels in Ti-51 with high precision. The GT(+) strength distribution for transitions to levels up to about 6 MeV of excitation energy has been extracted. The results are compared with a large-scale shell-model calculation in the full pf shell.

The proton-rich isotope Cu-56 was produced at the GSI On-Line Mass Separator by means of the Si-28(S-32, p3n) fusion-evaporation reaction. Its beta -decay properties were studied by detecting beta -delayed gamma rays and protons. A half-Life of 93 +/- 3 ms was determined for Cu-56. Compared to the previous work, six new gamma rays and three new levels were assigned to the daughter nucleus Ni-56. The measured Gamow-Teller strength values for five Ni-56 levels are compared to shell-model predictions. (C) 2001 Elsevier Science B.V. ALI rights reserved.

Our collaboration has set up a focal plane detection system and a focal plane polarimeter at the large acceptance Big-Bite Spectrometer at AGOR. The detector systems are equipped with a high performance readout and online data processing system, which allows polarization transfer and charge transfer measurements at extreme forward angles with high precision. Preliminary results on GT+ strength distributions obtained in (d,2He) measurements revealing the fine structure of the distributions are presented. Their relation to recent calculations of stellar weak interaction rates is discussed., Comment: 8 pages, 4 figures, conference proceeding GR2000, Osaka, June 2000