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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.

The gamma-strength functions and level densities of in the quasi-continuum of 147,149Sm isotopes have been extracted from particle-gamma coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148,150Sm targets and the reaction products were recorded by the HYPERION array. An upbend in the gSF has been observed. The systematic analysis of the gSF for a range of Sm isotopes show that the scissors mode and the upbend compete with each other. Shell model calculations show a very good agreement with the experimental gSFs and confirm the competition between the upbend and scissors mode.

This thesis focusses on the results of two experiments employing Penning traps to prepare pure beams of the 213Ra ground state and 127Cd, which were then studied with the decay-spectroscopy setup TASISpec. The experiments were conducted with SHIPTRAP at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany, and JYFLTRAP at the IGISOL Accelerator Facility at the University of Jyväskylä, Finland.The α-decay branching ratios of the 213Ra ground state have been revised based on comprehensive Geant4 simulations, i.e. ‘virtual experiments’, which were confronted with the experimental results. These findings are supported by theoretical calculations. This work is published in Papers I and II. Using the same method, the proton-decay branch of the 53Co 3174 keV isomer has been studied, which is the content of Paper IV. In Paper III the results of the 127Cd experiment are presented. There the decay scheme of 127In populated by the β decay of 127Cd was considerably extended and the β feeding into the individual states deduced. Extensive shell-model calculations have been conducted to calculate the energy levels and γ-ray branching ratios of 127In as well as the Gamow-Teller strength distributions of the β decay of the 3/2+ and 11/2− states in 127Cd. Based on these calculations the experimentally observed decay-scheme of 127In could be reproduced remarkably well. The order of the 3/2+ and 11/2− state in 127Cd has been established, identifying the 3/2+ state as the ground state and the 11/2− state as the 283 keV isomer. Furthermore, the phase-depended cleaning method was employed for the first time in an attempt to study the β decay of the 127Cd isomer individually.

Large-scale shell-model calculations were performed for 56Fe, 60Fe, 64Fe and 68Fe. The collective properties of yrast states are reproduced in the used model space. The low-energy enhancement of M1 strength decreases with increasing deformation, while a bump around E = 3 MeV develops, which can be related with the scissors mode. The strength around E = 3 MeV includes transitions from 1+ states to the ground state as well as to excited 0+ states and contributions from other spins. The average M1 strength is rather independent of the excitation energy for Ei > 5 MeV. This validates the Brink-Axel hypothesis in this energy region.

Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal sd interaction (USD) describing nuclei within the sd shell yielded two new interactions—USDA and USDB—causing changes in the theoretical description of these nuclei. Purpose: Transitionmatrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus 26Na with 7 valence neutrons and 3 valence protons outside the doubly-magic 16O core is used as a test case. Method: A radioactive beam experiment with 26Na (T1/2 = 1,07s) was performed at the REX-ISOLDE facility (CERN) using Coulomb excitation at safe energies below the Coulomb barrier. Scattered particles were detected with an annular Si detector in coincidence with γ rays observed by the segmented MINIBALL array. Coulomb excitation cross sections of the beam have been obtained by normalization to the well known Coulomb excitation cross sections of the 104Pd target. Results: The observation of three γ -ray transitions in 26Na together with available spectroscopic data allows us to determine E2- and M1-transitional matrix elements. Results are compared to theoretical predictions. Conclusion: The improved theoretical description of 26Na could be validated. Remaining discrepancies between experimental data and theoretical predictions indicate the need for future experiments and possibly further theoretical improvements. ispartof: Physical Review C vol:91 issue:1 status: published

The beta decays Mn-68 -> Fe-68 -> Mn-69 -> Fe-69 and Mn-70 -> Fe-70 have been measured at the RIBF facility at RIKEN using the EURICA gamma spectrometer combined with an active stopper consisting of a stack of Si detectors. The nuclei were produced as fission fragments from a beam of U-238 at a bombarding energy of (345) MeV/nucleon impinging on a Be target and selected using the BigRIPS separator. Half-lives and beta-delayed neutron emission probabilities have been extracted for these decays, together with first experimental information on excited states populated in Fe-69,Fe-70. The data indicate a continuously increasing deformation for Fe isotopes up to A = 70. This is interpreted, as for Cr isotopes, in terms of the interplay between the quadrupole correlations of the nu 1d(5/2) and nu 0g(9/2) orbitals and the monopole component of the pi 0f(7/2)-nu 0f(5/2) interaction. (C) 2015 The Authors. Published by Elsevier B.V.

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.

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.

Excited states in Pm-146 have been investigated through the Xe-136(N-15,5n) and the Nd-146(d,xn) compound-nucleus reactions. A level scheme extending up to 6.9 MeV of excitation energy and (I = 25HBAR) is proposed. Most of the high-spin levels are interpreted in terms of multi-particle-hole states but at medium spins octupole-phonon excitations are identified. The results are discussed and the level scheme compared with analogous states in neighbouring nuclei. Yrast configurations in Pm-146 are described by the shell-model calculation involving empirical single-particle energies and two-body interactions.

The harmonic oscillator shell closure at N=40 in 68Ni is weak and loses its strength when removing (or adding) pair of protons. Calculations performed in this mass region predict a new island of inversion at N=40 similar to the one at N=20. Using a large valence space, the neutron orbital 2d5/2 is shown to be a crucial ingredient for the interpretation of the nuclear structure at N≈40. The neutron 1g9/2-2d5/2 energy difference has been determined in 69Ni using the d(68Ni,p) transfer reaction in inverse kinematics. The experiment performed at GANIL used a 68Ni beam at 25.14 MeV/u seperated by the LISE3 spectrometer was impinging a CD2 target of 2.6 mg/cm2 thickness. The experimental setup consisted of CATS/MUST2-S1/EXOGAM detectors coupled to an ionization chamber and a plastic scintillator. The angular momenta and spectroscopic factors of the ground state (Jπ = 9/2+) and a doublet of states ( Jπ = 5/2+) around 2.48 MeV corresponding to the population of the 1g9/2 and the 2d5/2 orbitals, were obtained from the comparison between the experimental cross-sections as a function of the proton detection angle and ADWA calculations. The spins of the observed states were assigned by comparaison to large scale Shell-Model calculations. The position of the 2d5/2 orbital in 69Ni has been established for the first time. Our measurements support the hypothesis of a low-lying 2d5/2 orbital (≈2.5 MeV) with respect to the 1g9/2 neutron orbital and thus its major role in the structure of the nuclei around N=40.; La fermeture de couche de l'oscillateur harmonique à N=40 dans le 68Ni est faible et perd sa rigidité après l'enlèvement (ou l'ajout) de paires de protons. Les calculs effectués dans cette région de masse prédisent un nouvel îlot d'inversion à N=40 semblable à celui à N=20 et montrant que le placement de l'orbital neutron 2d5/2 est un ingrédient essentiel pour l'interprétation de la structure nucléaire à N≈40. La différence d'énergie 1g9/2-2d5/2 a été déterminée dans le noyau 69Ni en utilisant la réaction de transfert d'un neutron d(68Ni,p) en cinématique inverse. L'expérience réalisée au GANIL utilisait un faisceau de 68Ni à 25,14 MeV/u. Les noyaux 68Ni séparés par le spectromètre LISE3 ont ensuite interagit avec une cible de CD2 d'épaisseur 2,6 mg/cm2. Le dispositif expérimental était composé principalement des détecteurs CATS/MUST2-S1/EXOGAM couplés à une chambre d'ionisation et un scintillateur plastique. Les moments angulaires et les facteurs spectroscopiques de l'état fondamental (Jπ = 9/2+) et d'un doublet d'états (Jπ = 5/2+) autour de 2,48 MeV, associés à la population des orbitales 1g9/2 et 2d5/2, ont été obtenus après la comparaison des sections efficaces différentielles et des calculs ADWA. Les spins des états observés ont été attribués après comparaison aux calculs de modèles en couches dans un grand espace de valence. La position de l'orbitale 2d5/2 dans 69Ni a été établie pour la première fois. Nos mesures confirment l'hypothèse de la faible différence d'énergie (≈2,5 MeV) entre l'orbitale neutron 2d5/2 et l'orbitale 1g9/2 et son importance pour décrire la structure des noyaux autour de N=40.

The harmonic oscillator shell closure at N=40 in 68Ni is weak and loses its strength when removing (or adding) pair of protons. Calculations performed in this mass region predict a new island of inversion at N=40 similar to the one at N=20. Using a large valence space, the neutron orbital 2d5/2 is shown to be a crucial ingredient for the interpretation of the nuclear structure at N≈40. The neutron 1g9/2-2d5/2 energy difference has been determined in 69Ni using the d(68Ni,p) transfer reaction in inverse kinematics. The experiment performed at GANIL used a 68Ni beam at 25.14 MeV/u seperated by the LISE3 spectrometer was impinging a CD2 target of 2.6 mg/cm2 thickness. The experimental setup consisted of CATS/MUST2-S1/EXOGAM detectors coupled to an ionization chamber and a plastic scintillator. The angular momenta and spectroscopic factors of the ground state (Jπ = 9/2+) and a doublet of states ( Jπ = 5/2+) around 2.48 MeV corresponding to the population of the 1g9/2 and the 2d5/2 orbitals, were obtained from the comparison between the experimental cross-sections as a function of the proton detection angle and ADWA calculations. The spins of the observed states were assigned by comparaison to large scale Shell-Model calculations. The position of the 2d5/2 orbital in 69Ni has been established for the first time. Our measurements support the hypothesis of a low-lying 2d5/2 orbital (≈2,5 MeV) with respect to the 1g9/2 neutron orbital and thus its major role in the structure of the nuclei around N=40.; La fermeture de couche de l'oscillateur harmonique à N=40 dans le 68Ni est faible et perd sa rigidité après l'enlèvement (ou l'ajout) de paires de protons. Les calculs effectués dans cette région de masse prédisent un nouvel îlot d'inversion à N=40 semblable à celui à N=20 et montrant que le placement de l'orbital neutron 2d5/2 est un ingrédient essentiel pour l'interprétation de la structure nucléaire à N≈40. La différence d'énergie 1g9/2-2d5/2 a été déterminée dans le noyau 69Ni en utilisant la réaction de transfert d'un neutron d(68Ni,p) en cinématique inverse. L'expérience réalisée au GANIL utilisait un faisceau de 68Ni à 25,14 MeV/u. Les noyaux 68Ni séparés par le spectromètre LISE3 ont ensuite interagit avec une cible de CD2 d'épaisseur 2,6 mg/cm2. Le dispositif expérimental était composé principalement des détecteurs CATS/MUST2-S1/EXOGAM couplés à une chambre d'ionisation et un scintillateur plastique. Les moments angulaires et les facteurs spectroscopiques de l'état fondamental (Jπ = 9/2+) et d'un doublet d'états ( Jπ = 5/2+) autour de 2,48 MeV, associés à la population des orbitales 1g9/2 et 2d5/2, ont été obtenus après la comparaison des sections efficaces différentielles et des calculs ADWA. Les spins des états observés ont été attribués après comparaison aux calculs de modèles en couches dans un grand espace de valence. La position de l'orbitale 2d5/2 dans 69Ni a été établie pour la première fois. Nos mesures confirment l'hypothèse de la faible différence d'énergie (≈2,5 MeV) entre l'orbitale neutron 2d5/2 et l'orbitale 1g9/2 et son importance pour décrire la structure des noyaux autour de N=40.

Yrast states in the neutron-rich 41S 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 magnetic spectrometer, PRISMA, and the γ -ray array, CLARA, were used in the measurements. γ -ray transitions of energy 449 and 638 keV were observed. Results from published intermediate-energy Coulomb excitation measurements in combination with those from the present work have led to the construction of a new 41S level scheme. Proposed J π values are based on experimental observation and on model-dependent arguments. The level scheme and published electromagnetic transition probabilities are discussed within the context of state-of-art shell-model calculations using the SDPF-U effective interaction. In contrast with the excellent agreement observed in earlier published work, here there are significant discrepancies between experiment and the results of 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.

Lifetimes of low-lying excited states of the neutron-rich 44, 46Ar nuclei, populated via multinucleon transfer reactions, are measured by means of the differential recoil distance Doppler shift method. The extracted electromagnetic transition probabilities are compared with previous intermediate-energy Coulomb-excitation measurements and with large-scale shell-model calculations. The increase in the deduced B(E2 ; 2+→0+) transition probability from 44Ar to the closed-shell nucleus 46Ar contradicts the earlier results of Coulomb-excitation experiments. Shell-model calculations using different effective interactions agree with the new measured values.

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.

We report on a study of the structure of the unbound nucleus He-7 utilizing the proton-removal reaction H-2(Li-8,He-3)He-7. Combining the present results with those of our prior measurements of the neutron-adding reaction H-2(He-6,p)He-7, a consistent picture emerges for the low-lying excitations in He-7. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2(-),1/2(-), and 5/2(-). The stable-beam reactions H-2(Li-7,t)Li-6 and H-2(Li-7,He-3)He-6 were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo calculations.

We report on a study of the structure of the unbound nucleus He-7 utilizing the proton-removal reaction H-2(Li-8,He-3)He-7. Combining the present results with those of our prior measurements of the neutron-adding reaction H-2(He-6,p)He-7, a consistent picture emerges for the low-lying excitations in He-7. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2(-),1/2(-), and 5/2(-). The stable-beam reactions H-2(Li-7,t)Li-6 and H-2(Li-7,He-3)He-6 were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo 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.

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.

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 β decay of 96Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in 96Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8+) and (2+), respectively. For both isomers, the intensities of β transitions to low-lying levels of 96Pd (Z=46,N=50) and β-delayed proton decays to levels in 95Rh (Z=45,N=50) were measured. Several new 96Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of 96Ag are compared to shell-model predictions. A new low-lying level in 95Rh was found at 680keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2+ state built on the proton 9/2+ ground state. The assignments of further excited states in 95Rh 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.

The nuclei $^{91}$Sr and $^{92}$Sr were produced at high spin as fission fragments following the fusion reaction $^{36}$S + $^{159}$Tb at 165 MeV. Gamma rays were detected with the Gammasphere array. The level schemes of $^{91}$Sr and $^{92}$Sr were extended up to $E \approx$ 6 MeV and $E \approx$ 8 MeV, respectively. Level structures in $^{91}$Sr and $^{92}$Sr were interpreted in terms of the shell model. The calculations were performed in the configuration space $(0f_{5/2}, 1p_{3/2}, 1p_{1/2}, 0g_{9/2})$ for the protons and $(1p_{1/2}, 0g_{9/2}, 1d_{5/2})$ for the neutrons. Negative-parity states in the yrast sequences are described in these calculations by coupling $3^-$ proton excitations to the unpaired $1d_{5/2}$ neutrons. A possible reduction of the gap between the proton $1p_{3/2}$ and $1p_{1/2}$ orbitals in $^{92}$Sr is discussed.

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.