Search

A search for the J(pi) = 1/2(-) spin-orbit partner of the J(pi) = 3/2(-) ground state in He-7 has been performed with the Li-7(d, He-2) charge-exchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on Li-7 as well as on triton and He-4 clusters in the Li-7 ground state. A possible resonance at an excitation energy E-x approximate to 1.45 MeV with a width Gamma approximate to 2.0 MeV is suggested when the quasifree charge-exchange process on Li-7 is constrained by a measurement of the Li-6(d, He-2) reaction. Gamow-Teller strengths for transitions to the lowest states in He-7 deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations. (c) 2006 Elsevier B.V. All rights reserved.

The two charge exchange reactions 14N(d, 2He)14C and 14N(3He, t)14O were studied with high resolution in order to identify the Gamow–Teller (GT) strength distribution starting from the ground state (g.s.) of 14N in the β− and β+ directions. The isospin symmetry in the A = 14 mass system is investigated. An overview of the main features of the experimental investigation is summarized here.

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.

We are investigating the feasibility of nuclear physics experiments designed to overcome the loopholes of observer-dependent reality and satisfying the counterfactuality condition. In a first approach, we have measured polarization correlations of proton pairs produced in 12C(d, 2He) and 1H(d, 2He) reactions in one setting. The results of these measurements are used to test the Bell and Wigner–Belinfante inequalities against the predictions of quantum mechanics.

Two different experimental approaches were combined to study the electric dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold. Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and nearly mono-energetic linearly polarized photons with energies between 6.6 and 9.51 MeV provided strength distribution and parities, and an (\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for an isoscalar probe. The unexpected difference observed in the dipole response is compared to calculations using the first-order random-phase approximation and points to an energy-dependent isospin character. A strong isoscalar state at 7.6 MeV was identified for the first time supporting a recent theoretical prediction., Comment: 6 pages, 5 figures, as accepted in Phys. Lett. B

For the medium-energy proton polarimeter mounted at the focal-plane of the Big-Bite Spectrometer at Kernfysisch Versneller Instituut Groningen, a new wire-chamber readout has been developed. The charge-sensitive preamplifier is based on the ASD-8 B chip which has an input impedance of 115 Omega. This low impedance and the short integration time of 6 ns at a usable sensitivity of 5 fC allow high readout rates and low gas amplifications. This front-end circuit is mounted on all four multi-wire proportional chambers and on two vertical-drift chambers with 3872 wires in total. Measurements have been made using sources and intermediate energy protons. Special attention was given to determine the time-over-threshold properties of the circuit, The time-over-threshold capabilities of the readout system extend future applications to particle discrimination, or, in connection with other detector types, to energy-resolving readout, The operational performance of the readout system is presented.

The (96)Mo(d,(2)He)(96)Nb charge-exchange reaction was investigated at an incident energy of E(d)=183.5 MeV. An excitation-energy resolution of 110 keV was achieved. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0(degrees),2.5(degrees), and 6(degrees). We found that below 6 MeV almost the entire Gamow-Teller (GT(+)) strength is concentrated in a single state at 0.69 MeV excitation energy. As (96)Mo is the daughter of the beta beta decay nucleus (96)Zr, the present result provides information about the nuclear matrix elements active in the 2 nu beta beta decay of (96)Zr.

The (96)Mo(d,(2)He)(96)Nb charge-exchange reaction was investigated at an incident energy of E(d)=183.5 MeV. An excitation-energy resolution of 110 keV was achieved. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0(degrees),2.5(degrees), and 6(degrees). We found that below 6 MeV almost the entire Gamow-Teller (GT(+)) strength is concentrated in a single state at 0.69 MeV excitation energy. As (96)Mo is the daughter of the beta beta decay nucleus (96)Zr, the present result provides information about the nuclear matrix elements active in the 2 nu beta beta decay of (96)Zr.

The (96)Mo(d,(2)He)(96)Nb charge-exchange reaction was investigated at an incident energy of E(d)=183.5 MeV. An excitation-energy resolution of 110 keV was achieved. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0(degrees),2.5(degrees), and 6(degrees). We found that below 6 MeV almost the entire Gamow-Teller (GT(+)) strength is concentrated in a single state at 0.69 MeV excitation energy. As (96)Mo is the daughter of the beta beta decay nucleus (96)Zr, the present result provides information about the nuclear matrix elements active in the 2 nu beta beta decay of (96)Zr.

The (d,(2)He) charge-exchange reaction on (76)Se was studied at an incident energy of 183 MeV. The outgoing two protons in the (1)S(0) state, referred to as (2)He, were both momentum analyzed and detected by the same spectrometer and detector. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0(degrees),2.5(degrees), and 5(degrees). Excitation-energy spectra of the residual nucleus (76)As were obtained with an energy resolution of about 120 keV (FWHM). Gamow-Teller (GT(+)) transition strengths were extracted up to 5 MeV and compared with those from an (n,p) experiment at low resolution. Together with the GT(-) transition strengths from the (76)Ge(p,n) experiment leading to the same intermediate nucleus, the nuclear matrix element of the two-neutrino double-beta decay of (76)Ge was evaluated.

The (d,(2)He) charge-exchange reaction on (76)Se was studied at an incident energy of 183 MeV. The outgoing two protons in the (1)S(0) state, referred to as (2)He, were both momentum analyzed and detected by the same spectrometer and detector. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0(degrees),2.5(degrees), and 5(degrees). Excitation-energy spectra of the residual nucleus (76)As were obtained with an energy resolution of about 120 keV (FWHM). Gamow-Teller (GT(+)) transition strengths were extracted up to 5 MeV and compared with those from an (n,p) experiment at low resolution. Together with the GT(-) transition strengths from the (76)Ge(p,n) experiment leading to the same intermediate nucleus, the nuclear matrix element of the two-neutrino double-beta decay of (76)Ge was evaluated.

Taking advantage of the spin, isospin and J(pi) selectivity of cross sections and analysing powers of the tensor polarised C-12 (d(->), He-2) reaction, the J(pi) = 0(-), 1(-), 2(-) components of the spin-dipole resonance in B-12 have been investigated. The experiment was performed at the Big-Bite Spectrometer of the KVI taking advantage of purely tensor polarised deuteron beams provided by the AGOR cyclotron. The unique energy resolution achieved at KVI allowed determination of analysing powers for well resolved transitions up to 5 MeV excitation energy. The analysing powers of states with known spin and parity provided the means for the first-time for verification of model-independent predictions of analysing powers at extreme for-ward angles. In the continuum region, the analysing powers allowed identification of the J(pi) components of the IVSGDR, including a 0(-) component located at E-x = 9.3 MeV.

Taking advantage of the spin, isospin and J(pi) selectivity of cross sections and analysing powers of the tensor polarised C-12 (d(->), He-2) reaction, the J(pi) = 0(-), 1(-), 2(-) components of the spin-dipole resonance in B-12 have been investigated. The experiment was performed at the Big-Bite Spectrometer of the KVI taking advantage of purely tensor polarised deuteron beams provided by the AGOR cyclotron. The unique energy resolution achieved at KVI allowed determination of analysing powers for well resolved transitions up to 5 MeV excitation energy. The analysing powers of states with known spin and parity provided the means for the first-time for verification of model-independent predictions of analysing powers at extreme for-ward angles. In the continuum region, the analysing powers allowed identification of the J(pi) components of the IVSGDR, including a 0(-) component located at E-x = 9.3 MeV.

The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios.

The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios.

A search for the J(pi) = 1/2(-) spin-orbit partner of the J(pi) = 3/2(-) ground state in He-7 has been performed with the Li-7(d, He-2) charge-exchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on Li-7 as well as on triton and He-4 clusters in the Li-7 ground state. A possible resonance at an excitation energy E-x approximate to 1.45 MeV with a width Gamma approximate to 2.0 MeV is suggested when the quasifree charge-exchange process on Li-7 is constrained by a measurement of the Li-6(d, He-2) reaction. Gamow-Teller strengths for transitions to the lowest states in He-7 deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations. (c) 2006 Elsevier B.V. All rights reserved.

A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the {beta} decay of the A = 14 multiplet is presented. The GT strength distributions to excited states in {sup 14}C and {sup 14}O was studied in high-resolution (d,{sup 2}He) and ({sup 3}He,t) charge-exchange reactions on {sup 14}N. No-core shell-model (NCSM) calculations capable of reproducing the suppression of the {beta} decays predict a selective excitation of J{sup {pi}} = 2{sup +} states. The experimental confirmation represents a validation of the assumptions about the underlying structure of the {sup 14}N ground state wave function. However, the fragmentation of the GT strength over three 2{sup +} final states remains a fundamental issue not explained by the present NCSM using a 6 {h_bar}{omega} model space, suggesting possibly the need to include cluster structure in these light nuclei in a consistent way.

We have used the 43 MeV/nucleon primary tritium beam of the AGOR facility with an intensity of 4x10(7) pps and the BBS experimental setup to study the (t,He-3) reaction between 0 degrees and 5 degrees lab angles on C-12, Ca-48, and Ni-58 targets. The standard ray-tracing procedure has allowed us to obtain excitation-energy spectra up to 30 MeV in six angular bins for each residual nucleus, with an average energy resolution of 350 keV. The reaction mechanism has been described in distorted-waves Born approximation (DWBA) using the DWBA98 code. In this approximation, the form factor is treated as a folding of an effective projectile-nucleon interaction with a transition density. The effective projectile-nucleon interaction has been adjusted to reproduce the 0(degrees) cross section of the 1(+) ground state of B-12 populated in the C-12(t,He-3) reaction. We have employed random-phase approximation (RPA) wave functions of excited states to construct the form factor instead of the normal modes wave functions used earlier. This new DWBA+RPA analysis is used to compare calculated and experimental cross sections directly and to discuss the giant resonance excitations in K-48 and Co-58 nuclei.

We have used the 43 MeV/nucleon primary tritium beam of the AGOR facility with an intensity of 4x10(7) pps and the BBS experimental setup to study the (t,He-3) reaction between 0 degrees and 5 degrees lab angles on C-12, Ca-48, and Ni-58 targets. The standard ray-tracing procedure has allowed us to obtain excitation-energy spectra up to 30 MeV in six angular bins for each residual nucleus, with an average energy resolution of 350 keV. The reaction mechanism has been described in distorted-waves Born approximation (DWBA) using the DWBA98 code. In this approximation, the form factor is treated as a folding of an effective projectile-nucleon interaction with a transition density. The effective projectile-nucleon interaction has been adjusted to reproduce the 0(degrees) cross section of the 1(+) ground state of B-12 populated in the C-12(t,He-3) reaction. We have employed random-phase approximation (RPA) wave functions of excited states to construct the form factor instead of the normal modes wave functions used earlier. This new DWBA+RPA analysis is used to compare calculated and experimental cross sections directly and to discuss the giant resonance excitations in K-48 and Co-58 nuclei.

We have used the (d,He-2) reaction to obtain the GT(+) strength distribution for Sn-116 ->In-116 transitions. Here, In-116 is the intermediate nucleus in the second-order perturbative description of Cd-116 double beta (beta beta) decay. In this paper we will review what is known about the nuclear matrix elements for the Cd-116 2 nu beta beta decay, discuss the single-state dominance hypothesis and combine our new data with other existing data from charge-exchange reactions to obtain a 2 nu beta beta-decay half-life. The deduced value T-1/2=(4 +/- 1)x10(19)y compares well with the one known from direct counting experiments.

We have used the (d,He-2) reaction to obtain the GT(+) strength distribution for Sn-116 ->In-116 transitions. Here, In-116 is the intermediate nucleus in the second-order perturbative description of Cd-116 double beta (beta beta) decay. In this paper we will review what is known about the nuclear matrix elements for the Cd-116 2 nu beta beta decay, discuss the single-state dominance hypothesis and combine our new data with other existing data from charge-exchange reactions to obtain a 2 nu beta beta-decay half-life. The deduced value T-1/2=(4 +/- 1)x10(19)y compares well with the one known from direct counting experiments.

We have used the (d,He-2) reaction to obtain the GT(+) strength distribution for Sn-116 ->In-116 transitions. Here, In-116 is the intermediate nucleus in the second-order perturbative description of Cd-116 double beta (beta beta) decay. In this paper we will review what is known about the nuclear matrix elements for the Cd-116 2 nu beta beta decay, discuss the single-state dominance hypothesis and combine our new data with other existing data from charge-exchange reactions to obtain a 2 nu beta beta-decay half-life. The deduced value T-1/2=(4 +/- 1)x10(19)y compares well with the one known from direct counting experiments.

We have studied spin-isospin excitations in Co-58 via the (n,p) type Ni-58(d,He-2)Co-58 reaction at small angles and an incident deuteron energy of 170 MeV. An energy resolution of 130 keV, full width at half maximum, was obtained allowing the extraction of Gamow-Teller strength to 13 individual levels in Co-58 below an excitation energy of 4.1 MeV. These DeltaL=0 transitions were identified by comparing the measured angular distributions with distorted-wave Born approximation (DWBA) calculations. A multipole decomposition analysis based on those DWBA calculations allowed the determination of the fractions of the DeltaL=0, 1, 2 components in the excitation spectrum. The experimental results are in reasonable agreement with large-scale shell-model calculations.

The two-neutrino double-beta (2nubetabeta) decay represents a test case for our knowledge about the nuclear structure of the involved isobars. The decay of Ca-48 is an especially interesting case because it holds an anomaly of a uniquely high Q(betabeta) value and a comparatively long half-life, which points to a peculiar nuclear structure situation. The nuclear matrix element relevant for betabeta decay can be calculated, if the complete set of Gamow-Teller (GT) matrix elements for the two virtual transitions in the perturbative description are known. Using the high-resolution (d, He-2) probe, we have measured the GT(+) strength distribution in Sc-48, which is the intermediate nucleus in the Ca-48 betabeta decay. By combining our measured GT distribution with data from a Ca-48(p, n) experiment and taking into account relative phases between individual matrix elements, which can be gained from theoretical models, one can compute the double-GT matrix element and deduce the half-life of the Ca-48 2nubetabeta decay.

The two-neutrino double-beta (2nubetabeta) decay represents a test case for our knowledge about the nuclear structure of the involved isobars. The decay of Ca-48 is an especially interesting case because it holds an anomaly of a uniquely high Q(betabeta) value and a comparatively long half-life, which points to a peculiar nuclear structure situation. The nuclear matrix element relevant for betabeta decay can be calculated, if the complete set of Gamow-Teller (GT) matrix elements for the two virtual transitions in the perturbative description are known. Using the high-resolution (d, He-2) probe, we have measured the GT(+) strength distribution in Sc-48, which is the intermediate nucleus in the Ca-48 betabeta decay. By combining our measured GT distribution with data from a Ca-48(p, n) experiment and taking into account relative phases between individual matrix elements, which can be gained from theoretical models, one can compute the double-GT matrix element and deduce the half-life of the Ca-48 2nubetabeta decay.

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.

We are investigating the feasibility of nuclear physics experiments designed to overcome the loopholes of observer-dependent reality and satisfying the counterfactuality condition. In a first approach, we have measured polarization correlations of proton pairs produced in 12C(d, 2He) and 1H(d, 2He) reactions in one setting. The results of these measurements are used to test the Bell and Wigner–Belinfante inequalities against the predictions of quantum mechanics.

We investigated the feasibility of quantum-correlation measurements in nuclear physics experiments. In a first approach, we measured spin correlations of singlet-spin (1S0) proton pairs, which were generated in 1H(d,2He) and 12C(d,2He) nuclear charge-exchange reactions. The experiment was optimized for a clean preparation of the 2He singlet state and offered a 2pi detection geometry for both protons in the exit channel. Our results confirm the effectiveness of the setup for theses studies, despite limitations of a small data sample recorded during the feasibility studies., 13 pages, 7 figures

For proton-induced reactions, a formalism is presented to determine polarization observables using a focal-plane polarimeter in combination with a large-acceptance spectrometer, where also the effect of the scattering in the nondispersive plane of the spectrometer is taken into account. The inclusive proton-carbon analyzing power needed for the determination of spin observables was studied over a wide angular range and a new parameterization for this quantity was deduced. (C) 2003 Elsevier Science B.V. All 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

Angular distributions for elastic and inelastic deuteron scattering on C-12. Mg-24, and Ni-58 have been measured at a bombarding energy of 170 MeV. The data are analyzed in terms of the optical model. The extracted optical model parameters are compared to existing deuteron global optical potentials.

Angular distributions for elastic and inelastic deuteron scattering on C-12. Mg-24, and Ni-58 have been measured at a bombarding energy of 170 MeV. The data are analyzed in terms of the optical model. The extracted optical model parameters are compared to existing deuteron global optical potentials.

Angular distributions for elastic and inelastic deuteron scattering on C-12. Mg-24, and Ni-58 have been measured at a bombarding energy of 170 MeV. The data are analyzed in terms of the optical model. The extracted optical model parameters are compared to existing deuteron global optical potentials.

Angular distributions for elastic and inelastic deuteron scattering on C-12. Mg-24, and Ni-58 have been measured at a bombarding energy of 170 MeV. The data are analyzed in terms of the optical model. The extracted optical model parameters are compared to existing deuteron global optical potentials.

For the medium-energy proton polarimeter mounted at the focal-plane of the Big-Bite Spectrometer at Kernfysisch Versneller Instituut Groningen, a new wire-chamber readout has been developed. The charge-sensitive preamplifier is based on the ASD-8 B chip which has an input impedance of 115 Omega. This low impedance and the short integration time of 6 ns at a usable sensitivity of 5 fC allow high readout rates and low gas amplifications. This front-end circuit is mounted on all four multi-wire proportional chambers and on two vertical-drift chambers with 3872 wires in total. Measurements have been made using sources and intermediate energy protons. Special attention was given to determine the time-over-threshold properties of the circuit, The time-over-threshold capabilities of the readout system extend future applications to particle discrimination, or, in connection with other detector types, to energy-resolving readout, The operational performance of the readout system is presented.

Une revue des plus récentes réalisations en matière d'accélérateurs de particules en mettant l'accent sur les dispositifs concernant l'accélération d'ions lourds. Dans ce contexte on présente successivement l'accélérateur électrostatique VIVITRON implanté à Strasbourg puis les plus récentes réalisations en matière de cyclotron travaillant soit à la température ambiante (GANIL) ou cryogénique (MSU, Chalk River, Milan-Catane, AGOR...). Les dispositifs du type synchrotron sont également présentés ainsi que les problèmes liés aux sources d'ions et leurs intensités.