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5 pags., 4 figs., Excited states in Zn were populated following one-neutron removal from a Zn beam impinging on a Be target at intermediate energies in an experiment conducted at the Radioactive Isotope Beam Factory at RIKEN. Three γ rays were observed and tentatively assigned to the 6→4→2→0 yrast sequence. This turns Zn into the heaviest T=−2 nucleus in which excited states are known. The excitation-energy differences between these levels and the isobaric analogue states in the T=+2 mirror partner, Fe, are compared with large-scale shell-model calculations considering the full pf valence space and various isospin-breaking contributions. This comparison, together with an analysis of the mirror energy differences in the A=58, T=±1 pair Zn and Ni, provides valuable information with respect to the size of the monopole radial and the isovector multipole isospin-breaking terms in the region above doubly-magic Ni., We thank the RIKEN Nishina Center accelerator staff and the BigRIPS team for providing excellent beams to the experiment. This work was supported by the Spanish Ministerio de Ciencia e Inno- vación under contracts FPA2017-84756-C4-2-P, PGC-2018-94583, and SEV-2016-0597, the Swedish Research Council (Vetenskap- srådet, VR 2016-3969), and the UK Science and Technology Facil- ities Council (STFC) under grants ST/L005727/1 and ST/P003885/1. FB is supported by the RIKEN Special Postdoctoral Researcher Pro- gram

The fusion-evaporation reaction 32S+28Si at 125-MeV beam energy was used to populate excited states in 55Fe. Combining the Gammasphere spectrometer with ancillary devices including the Microball CsI(Tl) array and a shell of neutron detectors, a comprehensive level scheme could be derived. The experimental results are compared with theoretical results from shell-model calculations. Taking into account isospin-symmetry breaking terms is found to considerably improve the shell-model description for 55Fe. This motivated a predictive case study of near-yrast states in the mirror nucleus 55Cu.

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.

Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T-z = +/-1 nuclei to the common excited states of the T-z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT) transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T-z = 1 with those from the beta-decay of the T-z = -1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT transitions from Ni-58 (T-z = 1) to Cu-58 (T-z = 0) by using the zero-degree (He-3,t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified. The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., Dear to the Q window limitation (Q(EC) = 9.37 MeV) of the beta-decay from Zn-58 (T-z = -1) to Cu-58. The strength distribution is compared with that from shell-model calculations.

Yrast states up to (6+) in the neutron-rich 40S nucleus have been studied using binary grazing reactions produced by the interaction of a 215 MeV beam of 36S ions with a thin 208Pb target. The novel experimental setup that combines the large acceptance magnetic spectrometer, PRISMA, and the high-efficiency γ -ray detection array, CLARA, was used. A new γ -ray transition at an energy of 1572 keV was observed and tentatively assigned to the (6+) → (4+) transition. A comparison of experimental observations and the results of large-scale 0hω sd-pf shell-model calculations indicates that one- and two-proton excitations from the 2s1/2 to the 1d3/2 orbitals play an important role in reproducing the 40S yrast level structure and the published B(E2 ; 0+g.s.→ 2+) value. The structure of the yrast states of the even-A isotopes of sulfur is interpreted in terms of the configurations of valence protons and neutrons within the context of large-scale 0hω sd-pf shell-model calculations.

Excited states of 38Cl were populated in binary grazing reactions during the interaction of a beam of 36S ions of energy 215 MeV with a 208Pb target. The combination of the PRISMA magnetic spectrometer and the CLARA γ-ray detector array was used to identify the reaction fragments and to detect their decay via γ-ray emission. A level scheme for 38Cl is presented and discussed within the context of the systematics of neighboring nuclei and is compared with the results of state-of-the-art shell-model calculations.

The (d,He-2) charge-exchange reaction on the double-beta decay (beta beta) nucleus Zn-64 has been studied at an incident energy of 183 MeV. The two protons in the S-1(0) state (indicated as He-2) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. He-2 spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus Cu-64 with high precision. Zn-64 is one of the rare cases undergoing a beta beta decay in beta(+) direction. In the experiment presented here, Gamow-Teller (GT(+)) transition strengths have been extracted. Together with the GT(-) transition strengths from Ni-64(He-3,t) data to the same intermediate nucleus Cu-64, the nuclear matrix elements of the beta beta decay of Zn-64 have been evaluated. Finally, the GT(+/-) distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

The (d,He-2) charge-exchange reaction on the double-beta decay (beta beta) nucleus Zn-64 has been studied at an incident energy of 183 MeV. The two protons in the S-1(0) state (indicated as He-2) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. He-2 spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus Cu-64 with high precision. Zn-64 is one of the rare cases undergoing a beta beta decay in beta(+) direction. In the experiment presented here, Gamow-Teller (GT(+)) transition strengths have been extracted. Together with the GT(-) transition strengths from Ni-64(He-3,t) data to the same intermediate nucleus Cu-64, the nuclear matrix elements of the beta beta decay of Zn-64 have been evaluated. Finally, the GT(+/-) distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

The (d,2He) charge-exchange reaction on the double-beta decay (beta beta) nucleus 64Zn has been studied at an incident energy of 183 MeV. The two protons in the 1S0 state (indicated as 2He) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. 2He spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus 64Cu with high precision. 64Zn is one of the rare cases undergoing a beta beta decay in beta+ direction. In the experiment presented here, Gamow-Teller (GT+) transition strengths have been extracted. Together with the GT- transition strengths from 64Ni(3He,t) data to the same intermediate nucleus 64Cu, the nuclear matrix elements of the beta beta decay of 64Zn have been evaluated. Finally, the GT± distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell

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.

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

The Ni-58 (t, He-3)Co-58 reaction at 112 MeV/nucleon was measured to identify strength associated with Gamow-Teller transitions in the T-z = +1 direction. The experiment is a test case for future similar studies. The main aim of such studies is to test theoretical models used to predict Gamow-Teller strength distributions that serve as input for supernovae evolution calculations. The results indicate that the (t, He-3) reaction is indeed a powerful tool to perform such tests.

This thesis presents the research performed within two different research groups using heavy-ion induced nuclear reactions. They offer the opportunity to investigate different properties of nuclear matter. The results are based on measurements using a variety of different experimental techniques. The PHENIX experiment measured the production of deuteron and anti-deuterons at mid-rapidity in gold-gold collisions at the Relativistic Heavy-Ion Collider, RHIC. The invariant yields and transverse momentum spectra are presented. The results are not in agreement with a simple coalescence model with a constant coalescence paramete. Excited states of atomic nuclei were populated using fusion-evaporation reactions. The emitted gamma rays were detected in large multi-detector arrays. One experiment was in conjunction with a plunger device. Lifetimes of analogue states in the A=51 mirror nuclei 51Fe and 51Mn were measured using the recoil distance Doppler shift (RDDS) technique. The deduced B(E2) values make possible an investigation of isoscalar and isovector polarization charges. A comparison between the experimental results and large-scale shell-model calculations yields a quantitative estimate of the effective nucleon charges in the fp-shell. I denna avhandling diskuteras olika aspekter av kärnreaktioner inducerade med tunga atomkärnor. En beskrivning av de experiment, detektorer och metoder som har använts återfinns tillsammans med en utförlig redogörelse av analysarbetet. De resultat som presenteras är baserade på dels experimentella data men även från simuleringar och teoretiska beräkningar. Avhandlingen redogör för mätningarna av deuteroner och anti-deuteroner producerade vid acceleratorn RHIC (Relativistic Heavy-Ion Collider) på Brookhaven National Laboratory i USA. Vid tidpunkten för dessa mätningar accelererades guldkärnor upp till en hastighet väldigt nära ljusets innan de tilläts kollidera med varandra. Resultaten från dessa mätningar, vilka är de första för deuteroner och anti-deuteroner vid denna hastighet, presenteras och diskuteras. Vidare i avhandlingen diskuteras mätningar av livstider av exciterade tillstånd i atomkärnor. Dessa mätningar baserar sig på data från experiment utförda vid LNL (Legnaro National Laboratory) i Italien där atomkärnor accelererades upp till ett par procent av ljusets hastighet innan kärnreaktionerna ägde rum. De uppmätta livstiderna kan användas för att undersöka fundamentala elektromagnetiska egenskaper hos kärnorna. Speciellt redogörs för hur livstidsmätningar i så kallade spegelkärnor, vilka är par av kärnor där antalet protoner och neutroner är det omvända, kan användas för att bestämma effektiva nukleonladdningar. Dessa introduceras i gängse teoretiska modeller för att ge en bättre överensstämmelse mellan teori och experiment. Speciellt fokuserar avhandlingen på livstidsresultat för spegelkärnorna 51Fe, som har 26 protoner och 25 neutroner, och 51Mn som har 25 protoner och 26 neutroner. Metodiken och de erhållna resultaten från denna studie diskuteras utförligt.

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.

Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T-z = +/-1 nuclei to the common excited states of the T-z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT) transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T-z = 1 with those from the beta-decay of the T-z = -1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT transitions from Ni-58 (T-z = 1) to Cu-58 (T-z = 0) by using the zero-degree (He-3,t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified. The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., Dear to the Q window limitation (Q(EC) = 9.37 MeV) of the beta-decay from Zn-58 (T-z = -1) to Cu-58. The strength distribution is compared with that from shell-model calculations.

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