A. Algora a,b , B. Rubio a , E. Nácher a , D. Cano-Ott c,a , JL Tain a , A. Gadea d,a , L. Batist... more A. Algora a,b , B. Rubio a , E. Nácher a , D. Cano-Ott c,a , JL Tain a , A. Gadea d,a , L. Batist e , MJG Borge f , R. Collatz g , ... S. Courtin h , Ph. Dessagne h , LM Fraile i , W. Gelletly j , M. Hellström g , Z. Janas k , A. Jungclaus f , R. Kirchner g , ... M. Karny k , G. Le Scornet l , Ch. Miehé h ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997
A comparison is made of the performance of RIST and ISOLDE tantalum targets used on-line at the C... more A comparison is made of the performance of RIST and ISOLDE tantalum targets used on-line at the CERN-ISOLDE isotope separator. The data is taken from a combination of recent measurements at the CERN-PSB and from the former ISOLDE facility at the CERN-SC. Developments in the target geometry have been necessary for the RIST project which aims to design a target capable of dissipating the power developed by an 800 MeV, 100 PA proton beam. These designs are being tested at the ISOLDE-PSB facility and the initial results are reported in comparison with data obtained from typical ISOLDE tantalum-foil targets. The study shows that improvements in the release properties of a number of elements can be made by a judicious choice of target matrix geometry. The target represents a complex system where, in general, modelling alone involves too many parameters to generate a reliable model of the target. From this study, it is clear that further practical work, following simple ideas such as those based on modifications of the target geometry, is necessary in order to obtain progress in the optimisation of the target design.
The unbound nucleus 7 He, produced in neutron-knockout reactions with a 240 MeV/u 8 He beam in a ... more The unbound nucleus 7 He, produced in neutron-knockout reactions with a 240 MeV/u 8 He beam in a liquid-hydrogen target, has been studied in an experiment at the ALADIN-LAND setup at GSI. From an Rmatrix analysis the resonance parameters for 7 He as well as the spectroscopic factor for the 6 He(0 +) + n configuration in its ground-state have been obtained. The spectroscopic factor is 0.61 confirming that 7 He is not a pure single-particle state. An analysis of 5 He data from neutron-knockout reactions of 6 He in a carbon target reveals the presence of an s-wave component at low energies in the α + n relative energy spectrum. A possible low-lying exited state in 7 He observed in neutron knockout data from 8 He in a carbon target and tentatively interpreted as a I π = 1/2 − state, could not be observed in the present experiment. Possible explanations of the shape difference between the 7 He resonance obtained in the two knockout reactions are discussed in terms of target-dependence or different reaction mechanisms at relativistic energies.
Experiments on halo nuclei at energies around the Coulomb barrier can provide good quality data o... more Experiments on halo nuclei at energies around the Coulomb barrier can provide good quality data on elastic, inelastic, breakup and nucleon transfer reactions. This information turns out to be very important to understand the structure and dynamics of these exotic nuclei. In this work we present relevant results obtained from recent scattering experiments of "Be and 'He on heavy targets at energies around the Coulomb barrier. Our data exhibit strong absorption effects in the elastic channel. The role played by transfer and breakup channels, and the coupling to the continuum, are studied using CDCC and DWBA calculations.
The 76Sr (N=Z=38) and the 72Kr (N=Z=36) beta+ EC decay have been studied at the CERN/ISOLDE PSB f... more The 76Sr (N=Z=38) and the 72Kr (N=Z=36) beta+ EC decay have been studied at the CERN/ISOLDE PSB facility where their beta-gamma and delayed particle decay modes have been investigated. The established decay schemes yield new information on the Gamow-Teller (GT) strength spread over the Jpi=1+ states in the daughter nuclei. The delayed proton emission of an N=Z nucleus is observed for the first time in the case of 76Sr. The experimental GT strength intensities and distributions are discussed in the light of the theoretical estimates for oblate and prolate deformations.
The collision induced by the three Beryllium isotopes, 9,10,11 Be, on a 64 Zn target were investi... more The collision induced by the three Beryllium isotopes, 9,10,11 Be, on a 64 Zn target were investigated at Ec.m. ≈ 1.4 the Coulomb barrier. The experiments with the radioactive 10,11 Be beams were performed at the Rex-Isolde facility at CERN. In the case of 9,10 Be, elastic scattering angular distributions were measured whereas, in the 11 Be case, the quasielastic scattering angular distribution was obtained. A strong damping of the quasielastic cross-section was observed in the 11 Be case, in the angular range around the Coulomb-nuclear interference peak. In this latter case a large totalreaction cross-section is found. Such a cross-section is more than a factor of two larger than the ones extracted in the reactions induced by the non-halo Beryllium isotopes. A large contribution to the total-reaction cross-section in the 11 Be case could be attributed to transfer and/or break-up events.
We studied i7Ca P+ decays using a mass-separated ' Ca beam and a proton telescope with 16-keV res... more We studied i7Ca P+ decays using a mass-separated ' Ca beam and a proton telescope with 16-keV resolution. Delayed p's were detected in coincidence with y's to identify p decays of K daughter levels to excited states of Ar. We observed 43 previously undetected proton groups, yielding an integrated B(GT) twice as large as that observed previously. Although our result increases the efficiency of the CI detector for counting solar v's by 6%, its main effect is to reduce uncertainties in this e%ciency arising from discrepancies between previous Ca P decay and 'Cl(p, n) results.
The triple-α-particle breakup of states in the triple-α continuum of 12 C has been investigated b... more The triple-α-particle breakup of states in the triple-α continuum of 12 C has been investigated by way of coincident detection of all three α particles of the breakup. The states have been fed in the β decay of 12 N and 12 B, and the α particles measured using a setup that covers all of the triple-α phase space. Contributions from the breakup through the 8 Be(0 +) ground state as well as other channels-interpreted as breakup through excited energies in 8 Behave been identified. Spins and parities of 12 C triple-α continuum states are deduced from the measured phase-space distributions for breakup through 8 Be above the ground state by comparison to a fully symmetrized sequential R-matrix description of the breakup. At around 10 MeV in 12 C, the breakup is found to be dominated by 0 + strength breaking up through the ghost of the 8 Be(0 +) ground state with L = 0 angular momentum between the first emitted α particle and the intermediate 8 Be nucleus. For 12 C energies above the 12.7 MeV 1 + state, however, L = 2 breakup of a 12 C 2 + state through the 8 Be(2 +) excited state dominates. Furthermore, the possibility of a 2 + excited state in the 9-12 MeV region of 12 C is investigated.
The electric monopole strength p2 for the oi~ot transition and the B (E2) value for tbe oi~2t tra... more The electric monopole strength p2 for the oi~ot transition and the B (E2) value for tbe oi~2t transition were deduced from internal electron conversion and r-ray spectroscopy and from the measurement of the lifetime of tbe oi state, performed by means of the Doppler shift attenuation method in gases. In addition, an upper limit was deduced for tbe EO component of the 2i~2t transition. The available spectroscopic data on low-lying positive parity levels in 78,80, 82 Kr are compared to tbe predictions of the interacting boson model (IBM-2).
Journal of Physics G: Nuclear and Particle Physics, 2005
Pb in the angular ranges of 20 • − 64 • and 135 • − 170 •. A significant amount of 4 He events is... more Pb in the angular ranges of 20 • − 64 • and 135 • − 170 •. A significant amount of 4 He events is found at energies well below the Coulomb barrier, that becomes dominant above it. Optical Model calculations have been performed including a dynamic polarization potential. Very large imaginary diffuseness parameter is needed in order to describe the experimental distributions.
We present a study of the 'hypothetical', doubly magic and extremely neutron-rich nucleus 280. In... more We present a study of the 'hypothetical', doubly magic and extremely neutron-rich nucleus 280. In our description 280 is a bound nucleus and exhibits some of the features of a neutron halo, where a particular channel for beta delayed deuteron emission is evident.
Due to an error during writing the manuscript, the information given for both the beam and the en... more Due to an error during writing the manuscript, the information given for both the beam and the energy used for normalizing the data are not correct. The phrase ".. . of a beam of α particles at the energy of 12 MeV. .. " in the last paragraph of sect. 2 should be replaced by ".. . of a beam of 12C at the energy of 27 MeV. .. ". This change is not substantial for the study described and does not affect to the final conclusions presented in this work.
Challenged by recent theoretical work, a study of the β +-EC decay of the N = Z even-even nucleus... more Challenged by recent theoretical work, a study of the β +-EC decay of the N = Z even-even nucleus 76 Sr has been undertaken in order to assign the parent ground-state deformation. In this study 13 levels with J π = 1 + have been located in 76 Rb. The beta-delayed proton emission has been observed for the first time in an N = Z even-even nucleus. The βp branching ratio has been determined to be (3.4 ± 0.8) • 10 −5. The 76 Sr half-life has been remeasured and a more precise value of 7.89 ± 0.07 s has been obtained. On the basis of the comparison of measured Gamow-Teller strength with calculated strength distributions for both oblate and prolate deformation, it is concluded that the 76 Sr has strong prolate deformation in the ground state.
The quasi-elastic scattering angular distribution of the collision 11 Be + 64 Zn was measured and... more The quasi-elastic scattering angular distribution of the collision 11 Be + 64 Zn was measured and compared with the elastic scattering angular distribution for its core, the 10 Be nucleus on the same target. Optical model and continuum-discretized coupled-channel calculations of the 11 Be+ 64 Zn reaction were performed in order to interpret the effect of coupling with the break-up channels on the measured cross-sections.
The properties of states in "C above the 3a-threshold are of high current interest for nuclear as... more The properties of states in "C above the 3a-threshold are of high current interest for nuclear astrophysics and for the nuclear many-body problem in general. We have initiated a series of experiments aimed at elucidating this region by using the P-decays of 12N and "B. By applying the ISOL method for producing these radioactive isotopes, in combination with modern segmented charged particle detectors, our approach has significant advantages over previous studies of this region.
In this contribution examples of the application of new technologies to disentangle the mechanism... more In this contribution examples of the application of new technologies to disentangle the mechanism of beta-delayed multi-particle emission are given. In particular the mechanism of beta-delayed two-proton emission from 31Ar is resolved and proved to be sequential, both for isospin allowed and isospin forbidden transitions. The analysis of the 9C decay has been focused in the study of the 12.2
Clustering Aspects of Quantum Many-Body Systems - Proceedings of the International Symposium on Post-Symposium of YKIS01, 2002
New data is presented on alpha-particles emitted in the beta-decay of 12N. By developing a low en... more New data is presented on alpha-particles emitted in the beta-decay of 12N. By developing a low energy isotope separated (ISOL) beam of 12N, and employing a modern segmented particle detector setup, a dramatic improvement in the possibility for studying this challenging decay has been reached. We present preliminary results on properties of states in 12C just above the 7.65 MeV state, which are of interest for nuclear astrophysics, and nuclear structure physics in general.
A. Algora a,b , B. Rubio a , E. Nácher a , D. Cano-Ott c,a , JL Tain a , A. Gadea d,a , L. Batist... more A. Algora a,b , B. Rubio a , E. Nácher a , D. Cano-Ott c,a , JL Tain a , A. Gadea d,a , L. Batist e , MJG Borge f , R. Collatz g , ... S. Courtin h , Ph. Dessagne h , LM Fraile i , W. Gelletly j , M. Hellström g , Z. Janas k , A. Jungclaus f , R. Kirchner g , ... M. Karny k , G. Le Scornet l , Ch. Miehé h ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997
A comparison is made of the performance of RIST and ISOLDE tantalum targets used on-line at the C... more A comparison is made of the performance of RIST and ISOLDE tantalum targets used on-line at the CERN-ISOLDE isotope separator. The data is taken from a combination of recent measurements at the CERN-PSB and from the former ISOLDE facility at the CERN-SC. Developments in the target geometry have been necessary for the RIST project which aims to design a target capable of dissipating the power developed by an 800 MeV, 100 PA proton beam. These designs are being tested at the ISOLDE-PSB facility and the initial results are reported in comparison with data obtained from typical ISOLDE tantalum-foil targets. The study shows that improvements in the release properties of a number of elements can be made by a judicious choice of target matrix geometry. The target represents a complex system where, in general, modelling alone involves too many parameters to generate a reliable model of the target. From this study, it is clear that further practical work, following simple ideas such as those based on modifications of the target geometry, is necessary in order to obtain progress in the optimisation of the target design.
The unbound nucleus 7 He, produced in neutron-knockout reactions with a 240 MeV/u 8 He beam in a ... more The unbound nucleus 7 He, produced in neutron-knockout reactions with a 240 MeV/u 8 He beam in a liquid-hydrogen target, has been studied in an experiment at the ALADIN-LAND setup at GSI. From an Rmatrix analysis the resonance parameters for 7 He as well as the spectroscopic factor for the 6 He(0 +) + n configuration in its ground-state have been obtained. The spectroscopic factor is 0.61 confirming that 7 He is not a pure single-particle state. An analysis of 5 He data from neutron-knockout reactions of 6 He in a carbon target reveals the presence of an s-wave component at low energies in the α + n relative energy spectrum. A possible low-lying exited state in 7 He observed in neutron knockout data from 8 He in a carbon target and tentatively interpreted as a I π = 1/2 − state, could not be observed in the present experiment. Possible explanations of the shape difference between the 7 He resonance obtained in the two knockout reactions are discussed in terms of target-dependence or different reaction mechanisms at relativistic energies.
Experiments on halo nuclei at energies around the Coulomb barrier can provide good quality data o... more Experiments on halo nuclei at energies around the Coulomb barrier can provide good quality data on elastic, inelastic, breakup and nucleon transfer reactions. This information turns out to be very important to understand the structure and dynamics of these exotic nuclei. In this work we present relevant results obtained from recent scattering experiments of "Be and 'He on heavy targets at energies around the Coulomb barrier. Our data exhibit strong absorption effects in the elastic channel. The role played by transfer and breakup channels, and the coupling to the continuum, are studied using CDCC and DWBA calculations.
The 76Sr (N=Z=38) and the 72Kr (N=Z=36) beta+ EC decay have been studied at the CERN/ISOLDE PSB f... more The 76Sr (N=Z=38) and the 72Kr (N=Z=36) beta+ EC decay have been studied at the CERN/ISOLDE PSB facility where their beta-gamma and delayed particle decay modes have been investigated. The established decay schemes yield new information on the Gamow-Teller (GT) strength spread over the Jpi=1+ states in the daughter nuclei. The delayed proton emission of an N=Z nucleus is observed for the first time in the case of 76Sr. The experimental GT strength intensities and distributions are discussed in the light of the theoretical estimates for oblate and prolate deformations.
The collision induced by the three Beryllium isotopes, 9,10,11 Be, on a 64 Zn target were investi... more The collision induced by the three Beryllium isotopes, 9,10,11 Be, on a 64 Zn target were investigated at Ec.m. ≈ 1.4 the Coulomb barrier. The experiments with the radioactive 10,11 Be beams were performed at the Rex-Isolde facility at CERN. In the case of 9,10 Be, elastic scattering angular distributions were measured whereas, in the 11 Be case, the quasielastic scattering angular distribution was obtained. A strong damping of the quasielastic cross-section was observed in the 11 Be case, in the angular range around the Coulomb-nuclear interference peak. In this latter case a large totalreaction cross-section is found. Such a cross-section is more than a factor of two larger than the ones extracted in the reactions induced by the non-halo Beryllium isotopes. A large contribution to the total-reaction cross-section in the 11 Be case could be attributed to transfer and/or break-up events.
We studied i7Ca P+ decays using a mass-separated ' Ca beam and a proton telescope with 16-keV res... more We studied i7Ca P+ decays using a mass-separated ' Ca beam and a proton telescope with 16-keV resolution. Delayed p's were detected in coincidence with y's to identify p decays of K daughter levels to excited states of Ar. We observed 43 previously undetected proton groups, yielding an integrated B(GT) twice as large as that observed previously. Although our result increases the efficiency of the CI detector for counting solar v's by 6%, its main effect is to reduce uncertainties in this e%ciency arising from discrepancies between previous Ca P decay and 'Cl(p, n) results.
The triple-α-particle breakup of states in the triple-α continuum of 12 C has been investigated b... more The triple-α-particle breakup of states in the triple-α continuum of 12 C has been investigated by way of coincident detection of all three α particles of the breakup. The states have been fed in the β decay of 12 N and 12 B, and the α particles measured using a setup that covers all of the triple-α phase space. Contributions from the breakup through the 8 Be(0 +) ground state as well as other channels-interpreted as breakup through excited energies in 8 Behave been identified. Spins and parities of 12 C triple-α continuum states are deduced from the measured phase-space distributions for breakup through 8 Be above the ground state by comparison to a fully symmetrized sequential R-matrix description of the breakup. At around 10 MeV in 12 C, the breakup is found to be dominated by 0 + strength breaking up through the ghost of the 8 Be(0 +) ground state with L = 0 angular momentum between the first emitted α particle and the intermediate 8 Be nucleus. For 12 C energies above the 12.7 MeV 1 + state, however, L = 2 breakup of a 12 C 2 + state through the 8 Be(2 +) excited state dominates. Furthermore, the possibility of a 2 + excited state in the 9-12 MeV region of 12 C is investigated.
The electric monopole strength p2 for the oi~ot transition and the B (E2) value for tbe oi~2t tra... more The electric monopole strength p2 for the oi~ot transition and the B (E2) value for tbe oi~2t transition were deduced from internal electron conversion and r-ray spectroscopy and from the measurement of the lifetime of tbe oi state, performed by means of the Doppler shift attenuation method in gases. In addition, an upper limit was deduced for tbe EO component of the 2i~2t transition. The available spectroscopic data on low-lying positive parity levels in 78,80, 82 Kr are compared to tbe predictions of the interacting boson model (IBM-2).
Journal of Physics G: Nuclear and Particle Physics, 2005
Pb in the angular ranges of 20 • − 64 • and 135 • − 170 •. A significant amount of 4 He events is... more Pb in the angular ranges of 20 • − 64 • and 135 • − 170 •. A significant amount of 4 He events is found at energies well below the Coulomb barrier, that becomes dominant above it. Optical Model calculations have been performed including a dynamic polarization potential. Very large imaginary diffuseness parameter is needed in order to describe the experimental distributions.
We present a study of the 'hypothetical', doubly magic and extremely neutron-rich nucleus 280. In... more We present a study of the 'hypothetical', doubly magic and extremely neutron-rich nucleus 280. In our description 280 is a bound nucleus and exhibits some of the features of a neutron halo, where a particular channel for beta delayed deuteron emission is evident.
Due to an error during writing the manuscript, the information given for both the beam and the en... more Due to an error during writing the manuscript, the information given for both the beam and the energy used for normalizing the data are not correct. The phrase ".. . of a beam of α particles at the energy of 12 MeV. .. " in the last paragraph of sect. 2 should be replaced by ".. . of a beam of 12C at the energy of 27 MeV. .. ". This change is not substantial for the study described and does not affect to the final conclusions presented in this work.
Challenged by recent theoretical work, a study of the β +-EC decay of the N = Z even-even nucleus... more Challenged by recent theoretical work, a study of the β +-EC decay of the N = Z even-even nucleus 76 Sr has been undertaken in order to assign the parent ground-state deformation. In this study 13 levels with J π = 1 + have been located in 76 Rb. The beta-delayed proton emission has been observed for the first time in an N = Z even-even nucleus. The βp branching ratio has been determined to be (3.4 ± 0.8) • 10 −5. The 76 Sr half-life has been remeasured and a more precise value of 7.89 ± 0.07 s has been obtained. On the basis of the comparison of measured Gamow-Teller strength with calculated strength distributions for both oblate and prolate deformation, it is concluded that the 76 Sr has strong prolate deformation in the ground state.
The quasi-elastic scattering angular distribution of the collision 11 Be + 64 Zn was measured and... more The quasi-elastic scattering angular distribution of the collision 11 Be + 64 Zn was measured and compared with the elastic scattering angular distribution for its core, the 10 Be nucleus on the same target. Optical model and continuum-discretized coupled-channel calculations of the 11 Be+ 64 Zn reaction were performed in order to interpret the effect of coupling with the break-up channels on the measured cross-sections.
The properties of states in "C above the 3a-threshold are of high current interest for nuclear as... more The properties of states in "C above the 3a-threshold are of high current interest for nuclear astrophysics and for the nuclear many-body problem in general. We have initiated a series of experiments aimed at elucidating this region by using the P-decays of 12N and "B. By applying the ISOL method for producing these radioactive isotopes, in combination with modern segmented charged particle detectors, our approach has significant advantages over previous studies of this region.
In this contribution examples of the application of new technologies to disentangle the mechanism... more In this contribution examples of the application of new technologies to disentangle the mechanism of beta-delayed multi-particle emission are given. In particular the mechanism of beta-delayed two-proton emission from 31Ar is resolved and proved to be sequential, both for isospin allowed and isospin forbidden transitions. The analysis of the 9C decay has been focused in the study of the 12.2
Clustering Aspects of Quantum Many-Body Systems - Proceedings of the International Symposium on Post-Symposium of YKIS01, 2002
New data is presented on alpha-particles emitted in the beta-decay of 12N. By developing a low en... more New data is presented on alpha-particles emitted in the beta-decay of 12N. By developing a low energy isotope separated (ISOL) beam of 12N, and employing a modern segmented particle detector setup, a dramatic improvement in the possibility for studying this challenging decay has been reached. We present preliminary results on properties of states in 12C just above the 7.65 MeV state, which are of interest for nuclear astrophysics, and nuclear structure physics in general.
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Papers by O. Tengblad