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The unbound O12 nucleus was studied via the two-neutron transfer (p,t) reaction in inverse kinematics using a radioactive O14 beam at 51 MeV/u. Excitation energy spectra and differential cross sections were deduced by the missing mass method using MUST2 telescopes. We achieved much higher statistics compared to the previous experiments of O12, which allowed accurate determination of resonance energy and unambiguous spin and parity assignment. The O12 resonance previously reported using the same reaction was confirmed at an excitation energy of 1.62±0.03(stat.)±0.10(syst.). MeV and assigned spin and parity of 0+ from a distorted-wave Born approximation analysis of the differential cross sections. Mirror symmetry of O12 with respect to its neutron-rich partner Be12 is discussed from the energy difference of the second 0+ states. In addition, from systematics of known 0+ states, a distinct correlation is revealed between the mirror energy difference and the binding energy after carrying out a scaling with the mass and the charge. We show that the mirror energy difference of the observed 0+ state of O12 is highly deviated from the systematic trend of deeply bound nuclei and in line with the scaling relation found for weakly bound nuclei with a substantial 2s1/2 component. The importance of the scaling of mirror asymmetry is discussed in the context of ab initio calculations near the drip lines and universality of few-body quantum systems.

The measurement of the Isoscalar Giant Monopole Resonance(GMR) in unstable nuclei remains a major experimental challenge due to low radioactive beam intensities and unfavourable conditions in reverse kinematics. At GANIL, we have tested a new experimental method based on the unique capabilities of the active target Maya to probe the GMR by the inelastic scattering reaction 56Ni(d,d') at 50 AMeV. The preliminary excitation energy spectrum of 56Ni presents a bump between 12 and 25 MeV where isoscalar resonances are expected. © 2007 Elsevier B.V. All rights reserved.

4 pages, 3 figures.-- PACS nr.: 23.40.-s.-- Printed version published Apr 2004.-- et al., Beta-decay experiments are a primary source of information for nuclear-structure studies and at the same time complementary to in-beam investigations of nuclei far from stability. Although both types of experiment are mainly based on γ-ray spectroscopy, they face different experimental problems. The so-called Pandemonium effect is a critical problem in β-decay if we are to test theoretically calculated transition probabilities. In this contribution we will present a solution to this problem using total absorption spectroscopy methods. We will also present some examples of experiments carried out with the Total Absorption Spectrometer (TAS) at GSI an describe a new device LUCRECIA recently installed at CERN., This work was partially supported by C.I.C.Y.T. (Spain) under contract AEN96-1662, by MCYT (Spain)contract No. FPA2002-04181-C04-03, by C.S.R. (Poland) grant KBN-2Pp03B-039-13, by R.F.B.R. (Russia)-D.F.G. (Germany) contract 436 RUS 113/201/0(R). Support from the HPMF-CT-1999-00394 project as well as from the European Large Scale Facility program at CERN is also aknowledged.

Elastic and inelastic proton scattering to the 21+ state of the single closed shell radioactive nucleus 20 O have been measured in inverse kinematics with a beam energy of 30 MeV/u. The matrix element determined for the 0gs+→21+ transition in this work is compared with the corresponding electromagnetic matrix element to determine the ratio of the neutron and proton multipole matrix elements for this transition, Mn/Mp=2.9(4), which is quite different from the value Mn/Mp=N/Z=1.5 that would be expected for a purely isoscalar transition. A comparison of this result to a corresponding result for 18 O suggests that the strength of the core polarizing interactions between the valence neutrons and the core protons and neutrons is changing significantly with mass.

The proton scattering on unstable38S nuclei has been measured in inverse kinematics by using a38S secondary beam at 39 MeV/nucleon. The first 2+ state is seen at 1.2 MeV excitation energy and its angular distribution is extracted. Optical and folding model calculations are compared with the elastic and the 2 1 + angular distributions and the β2 value is determined to be 0.35±0.04. This value is compared with the corresponding result from a Coulomb excitation measurement and theM n/Mp value is extracted.

Elastic and inelastic scattering of protons on unstable 38 S nuclei has been measured in inverse kinematics by using a 38 S secondary beam at 39 MeV/nucleon. The excitation energy spectrum is measured up to 5 MeV. The first 2 + state is seen at 1.2 MeV excitation energy, and strength at around 3–5 MeV is also observed. Angular distributions for inelastic and elastic scattering are shown and compared to optical potential and folding model calculations. The preliminary β 2 value extracted for the first 2 + state is 0.38±0.05.

An excited state in the proton-rich unbound nucleus $^{12}\mathrm{O}$ was identified at 1.8(4) MeV via missing-mass spectroscopy with the $^{14}\mathrm{O}(p,t)$ reaction at $51\text{ }\text{ }A\mathrm{MeV}$. The spin-parity of the state was determined to be ${0}^{+}$ or ${2}^{+}$ by comparing the measured differential cross sections with distorted-wave calculations. The lowered location of the excited state in $^{12}\mathrm{O}$ indicates the breakdown of the major shell closure at $Z=8$ near the proton drip line. This demonstrates the persistence of mirror symmetry in the disappearance of the magic number 8 between $^{12}\mathrm{O}$ and its mirror partner $^{12}\mathrm{Be}$.

The nuclear break-up of 6He on a 208Pb target was studied at 20A MeV using a secondary beam of 6He produced by the SPIRAL facility at GANIL. $ \alpha$ -particles were detected in coincidence with two neutrons with a large angular coverage and the reaction mechanism was identified. From the distribution of the relative angles between the two neutrons the correlation function was extracted. It shows a strong correlation at small relative angles attributed to the contribution of the di-neutron configuration of 6He .

The reaction 20 O ( d , t ) has been studied in inverse kinematics using a secondary radioactive beam produced with the SPIRAL facility at GANIL. Fragments, light charged particles and gamma rays were measured with the TIARA, MUST2, VAMOS and EXOGAM detectors and preliminary results are reported. The level scheme of 19 O is built and the spin and parity of one state is tentatively assigned using the one-neutron transfer angular distribution.

Expérience GANIL, SPEG, SISSI, Maya; The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the Ni56 unstable nucleus by inducing the Ni56(d,d′) reaction at 50A MeV in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at 19.3±0.5 MeV and 16.2±0.5 MeV, respectively. The corresponding angular distributions are extracted from 3° to 7°. A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energy-weighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediate-energy radioactive beam facilities.

The differential cross section angular distribution and the analyzing powers ${}^{T}{T}_{10},{}^{T}{T}_{20}$, for $^{7}\mathrm{Li}$+$^{16}\mathrm{O}$ elastic scattering were measured at ${E}_{\mathrm{lab}}({}^{7}\stackrel{\ensuremath{\rightarrow}}{\mathrm{Li}}$) = 42 MeV. These and previously published $^{7}\mathrm{Li}$+$^{16}\mathrm{O}$ scattering data measured at ${E}_{c.m.}$ = 6.26\ensuremath{-}34.78 MeV were analyzed with the optical model and coupled-reaction channels (CRC) methods to determine the energy dependence of the parameters of the scattering potential. It was found that the optical model potentials are energy independent for $^{7}\mathrm{Li}$ laboratory bombarding energies above 28 MeV, except for a slight decrease in the real potential strength as the bombarding energy increases. The calculations presented show that the tensor analyzing power ${}^{T}{T}_{20}$ arises from a coherent combination of contributions from the ground-state reorientation and central scattering potential. The energy-dependent CRC potentials were shown to describe the data for the $^{16}\mathrm{O}$($^{7}\mathrm{Li}$,$t$)$^{20}\mathrm{Ne}$ reaction.

A novel method of deducing the deformation of the N=Z nucleus Sr-76 is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of quasi-random-phase approximation calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large total absorption gamma spectrometer, "Lucrecia," newly installed at CERN-ISOLDE.

4 pages, 2 figures.-- Issue title: "Proceedings of the Eighth International Conference on Nucleus-Nucleus Collisions (NN2003, Moscow, Jun 17-21, 2003)"., A new Total Absorption Spectrometer (TAS) called "Lucrecia" has been installed at ISOLDE (CERN) to investigate the β-decay of some nuclei with A≈70-80 in the vicinity of the N=Z line. In this work we report on the decay of the N=Z nucleus 76Sr, measured with a TAS for the first time. The Gamow-Teller strength distribution B(GT) for this decay is presented and compared with theoretical calculations.

A total absorption spectrometer, dedicated to the study of very short-lived atomic species, has been built and installed at the CERN/ISOLDE mass separator. The beta decay of the neutron-deficient Kr-74 nucleus has been studied using this new device. The Gamow-Teller strength distribution has been observed over most of the Q(EC) window, and a total strength of 0.69(3) g(A)(2)/4pi has been measured for states with excitation energy below 3 MeV. Shape mixing in the Kr-74 ground state is inferred from a comparison of the experimental strength distribution with self-consistent, deformed, quasiparticle-random-phase-approximation calculations.

NESTER; Elastic and inelastic proton scattering on 11Be were measured in inverse kinematics up to a 11Be excitation energy of 7 MeV. Continuum discretised coupled-channels (CDCC) calculations using a Click to view the MathML source cluster model of 11Be are able to explain the elastic scattering data. However, for the inelastic scattering angular distributions for 11Be excitation energy bins of 0.5–3 and 3–5.5 MeV the CDCC calculations under-predict the data, indicating the presence of contributions due to the deformed and active 10Be core to the 11Be breakup process.

A new Total Absorption Spectrometer (TAS) called “Lucrecia” has been installed at ISOLDE (CERN) to investigate the β‐decay of some nuclei with A≈70–80 in the vicinity of the N=Z line. In this work we report on the decay of the N=Z nucleus 76Sr, measured with a TAS for the first time. The Gamow‐Teller strength distribution B(GT) for this decay is presented and compared with theoretical calculations.

Measurements of the beta-decay half-lives of neutron-rich nuclei (MgAr) in the vicinity of the N =28 shell closure are reported. Some 22 half-lives have been determined, 12 of which for the first time. Particular emphasis is placed on the results for the Si isotopes, the half-lives of which have been extended from N =25 to 28. Comparison with QRPA calculations suggests that 42 Si is strongly deformed. This is discussed in the light of a possible weakening of the spin–orbit potential.

We report here on a new Total Absorption Spectrometer dedicated to the study of exotic nuclei, presently installed at the CERN/ISOLDE mass separator.

To study the effect of the weak binding energy on the interaction potential between a light exotic nucleus and a target, elastic scattering of ${}^{6}\mathrm{He}$ at 38.3 MeV/nucleon on a ${}^{12}\mathrm{C}$ target was measured at Grand Acc\'el\'erateur National d'Ions Lourds (GANIL). The ${}^{6}\mathrm{He}$ beam was produced by fragmentation. The detection of the scattered particles was performed by the GANIL spectrometer. The energy resolution was good enough to separate elastic from inelastic scattering contributions. The measured elastic data have been analyzed within the optical model, with the real part of the optical potential calculated in the double-folding model using a realistic density-dependent nucleon-nucleon interaction and the imaginary part taken in the conventional Woods-Saxon (WS) form. A failure of the ``bare'' real folded potential to reproduce the measured angular distribution over the whole angular range suggests quite a strong coupling of the higher-order breakup channels to the elastic channel. To estimate the strength of the breakup effects, a complex surface potential with a repulsive real part (designed to simulate the polarization effects caused by the projectile breakup) was added to the real folded and imaginary WS potentials. A realistic estimate of the polarization potential caused by the breakup of the weakly bound ${}^{6}\mathrm{He}$ was made based on a parallel study of ${}^{6}\mathrm{He}{+}^{12}\mathrm{C}$ and ${}^{6}\mathrm{Li}{+}^{12}\mathrm{C}$ optical potentials at about the same energies.

Complete sets of analyzing powers have been obtained for a large number of inelastic scattering and single-nucleon stripping channels for 34-MeV polarized ${}^{7}\mathrm{Li}{+}^{12}\mathrm{C}.$ We present data for inelastic excitation to the 0.478-MeV ${1/2}^{\ensuremath{-}}$ state of ${}^{7}\mathrm{Li},$ the 4.44-MeV ${2}^{+},$ 7.65-MeV ${0}^{+},$ and 9.64-MeV ${3}^{\ensuremath{-}}$ states of ${}^{12}\mathrm{C}$ and for mutual excitation of the ${1/2}^{\ensuremath{-}}$ and ${2}^{+}$ states, single-neutron stripping to the 0.0-MeV ${1/2}^{\ensuremath{-}},$ 3.09-MeV ${1/2}^{+},$ and 3.85-MeV ${5/2}^{+}$ states and an unresolved multiplet centered at 7.6 MeV of ${}^{13}\mathrm{C},$ and single-proton stripping to the 0.0-MeV ${1/2}^{\ensuremath{-}}$ state and an unresolved doublet of the 3.51-MeV ${3/2}^{\ensuremath{-}}$ and 3.55-MeV ${5/2}^{+}$ states of ${}^{13}\mathrm{N}.$ These data are analyzed with the continuum-discretized-coupled-channels approach using cluster-folding model form factors in a calculation that includes all the known physics for these systems.

The Li({sup 7}Li, {sup 10}Be{sup *}{yields}{sup 4}He+{sup 6}He) reactions have been studied at bombarding energies of 34 and 50.9 MeV. For {sup 10}Be{sup *} production near 0{sup o}, decay angular correlations are used to determine the previously unknown spin values and more accurate excitation energies of J=2 at E{sub x}=9.56 MeV and J=3 at E{sub x}=10.15 MeV. New excited states are proposed at higher excitations. A triaxial rotor model calculation and other collective rotation proposals all require a J=4 state in the vicinity of 9 to 11 MeV, which has not been found. Angular correlation methods more general than have been used in the recent past are discussed.

The neutron-rich argon isotope ${}^{43}\mathrm{Ar}$ has been studied by quasielastic and inelastic proton scattering performed in inverse kinematics. The measured inelastic angular distribution for the second excited state is in good agreement with an $L=2$ transition. Assuming this transition to be $E2,$ yields a ${\ensuremath{\beta}}_{2}$ value for this state of $0.25\ifmmode\pm\else\textpm\fi{}0.03$ when compared with distorted-wave Born approximation calculations. This value is comparable to the one reported for the stable isotope ${}^{40}\mathrm{Ar}.$ Moreover it is similar to those measured by Coulomb excitation for the neighboring even-even isotopes ${}^{42}\mathrm{Ar}$ and ${}^{44}\mathrm{Ar}$ indicating that the structure of the argon isotopes is stable as a function of neutron number.

The availability of radioactive beams with reasonable intensities and good optical qualities makes possible the study of direct reactions induced by unstable nuclei. Such experiments can be performed by measuring the energy and angle of light recoiling particles. High resolution position sensitive detectors using silicon strip technology are well suited tools to determine the two-body kinematics of the reaction. The newly built and innovative array MUST, dedicated to such studies, will be presented and its performances discussed in the light of experiments performed at the GANIL accelerator.

Systematic measurements of the first excited states in neutron-rich nuclei in the π(sd)-shell have been performed in the last two years using the technique of intermediate energy Coulomb excitation. These experiments were designed to study the evolution of nuclear shell structure as the neutron-dripline is approached and to provide experimental data which can be easily compared to nuclear model predictions. These measurements indicated a breakdown of the N=20 shell closure for 32Mg and a weakening of the N=28 shell closure below 48Ca, as well as a region of moderate collectivity around 40,42S. However, this experimental technique is sensitive only to the electromagnetic response of the nucleus. To probe the neutron distributions we performed a series of proton scattering experiments in inverse kinematics on neutronrich sulfur and argon isotopes. Proton scattering at energies of about 30 MeV/nucleon is more sensitive to neutrons than to protons by about a factor of three. The combination of the proton scat...

We have recently studied the structure of the neutron rich sulfur isotope 40S by using elastic and inelastic proton scattering in inverse kinematics. Optical potential and folding model calculations are compared with the elastic and inelastic angular distributions. Using coupled-channel calculations, the β2 value for the 21+ excited state is determined to be 0.35±0.05. The extracted value of Mn/Mp ratio indicates a small isovector contribution to the 21+ state of 40S. The microscopic analysis of the data is compatible with the presence of a neutron skin for this nucleus.

A modular array named MUST, based on Silicon strip technology has been built and will be devoted to the measurement of recoiling light particles in direct reactions induced by radioactive beams. The detector is described and the performances illustrated with preliminary results from a (p,p′) scattering experiment recently performed with a secondary 20O beam at GANIL.

Elastic and inelastic scattering to the 21+ state of the single closed shell radioactive nuclei 18Ne and 20O have been measured in inverse kinematics with a beam energies of 30 MeV/u. The matrix element determined for the 0gs+→21+ transitions in these reactions are compared with the corresponding electromagnetic matrix elements to determine Mn/Mp, the ratio of the neutron and proton multipole matrix elements. A comparison between the Mn/Mp values in 20O and 18O suggests that the matrix element ratio is increasing as the neutron number increases. The Mn/Mp result for 18Ne is consistent with one obtained from a comparison of electromagnetic data from the mirror nuclei 18O and 18Ne.

The availability of radioactive beams with relatively high intensities and good optical qualities makes possible the study of direct reactions induced by unstable nuclei. The problems of nuclear matter distributions, deformation and the modification of shell structure far from stability can be addressed through inverse kinematics reactions on light targets. The experimental method is presented and two examples in the case of the 38S (p,p′) and 40S (p,p′) reactions measured at the NSCL-MSU are given. Finally, the newly built silicon strip detector system, MUST, dedicated to such studies, is presented.

This paper describes two beta decay experiments performed at the CERN/ISOLDE mass separator. The structure of 74Kr has been studied using a total absorption gamma spectrometer (TAgS). The measured Gamow-Teller strength is presented and compared to HFBCS+QRPA calculations. The 33Na decay is also presented. The structure of the 33Mg daughter nucleus is compared to shell-model calculations, showing for the first time an inversion of states in the A~35 mass region.

Cross sections for the elastic scattering of 6He radioactive nuclear beam on proton targets have been measured at 38.3 MeV/nucleon. With a view to test the ability of general optical potentials to reproduce the data for scattering of unstable nuclei, the present results, as well as other existing data for 6,8He, have been analyzed within the framework of the microscopic Jeukenne–Lejeune–Mahaux nucleon–nucleus potential. The angular distributions were found to be best reproduced by reducing the real part of the optical potential. This renormalization can be seen as a consequence of the complex polarization potential produced by the coupling to the continuum due to the weakly bound nature of the unstable nuclei. This effect can be simulated in a phenomenological analysis by a surface potential.

International audience; The 10;11Be(p,p) and (12C, 12C) reactions were analyzed to determine the in uence of the weak binding energies of exotic nuclei on their interaction potential. The elastic cross sections were measured at GANIL in inverse kinematics using radioactive 10;11Be beams produced at energies of 39:1 A and 38:4A MeV. The elastic proton scattering data were analyzed within the framework of the microscopic Jeukenne-Lejeune-Mahaux (JLM) nucleon-nucleus potential. The angular distributions are found to be best reproduced by reducing the real part of the microscopic optical potential, as a consequence of the coupling to the continuum. These effects modify deeply the elastic potential. Including the Virtual Coupling Potential (VCP), we show the ability of the general optical potentials to reproduce the data for scattering of unstable nuclei, using realistic densities. Finally, the concepts needed to develop a more general and microscopic approach of the VCP are discussed.

International audience; 26Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in novae outbursts is still uncertain mainly due to the lack of nuclear information concerning the 25Al(p,g )26Si reaction. We report here on a neutron-gamma coincidence measurement of the 24Mg(3He,ng )26Si reaction performed at the Orsay TANDEM facility aiming at the spectroscopic study of astrophysically important 26Si states. A new level in the Gamow peak is observed at EX = 5:888 MeV and the gamma-ray decay scheme of all levels below the proton threshold is confirmed.

Elastic and inelastic proton scattering has been measured in inverse kinematics on the unstable nucleus ${}^{40}\mathrm{S}$. A phenomenological distorted wave Born approximation analysis yields a quadrupole deformation parameter ${\ensuremath{\beta}}_{2}=0.35\ifmmode\pm\else\textpm\fi{}0.05$ for the ${2}_{1}^{+}$ state. Consistent phenomenological and microscopic proton scattering analyses have been applied to all even-even sulfur isotopes from $A=32$ to $A=40$. The second analysis used microscopic collective model densities and a modified Jeukenne-Lejeune-Mahaux nucleon-nucleon effective interaction. This microscopic analysis suggests the presence of a neutron skin in the heavy sulfur isotopes. The analysis is consistent with normalization values for ${\ensuremath{\lambda}}_{v}$ and ${\ensuremath{\lambda}}_{w}$ of 0.95 for both the real and imaginary parts of the Jeukenne-Lejeune-Mahaux potential.