HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. The N=14 shell closure in O viewed through a neutron sensitive probe E. Becheva, Y. Blumenfeld, E. Khan, D. Beaumel, J.M. Daugas, F. Delaunay, C.E. Demonchy, A. Drouart, M. Fallot, A. Gillibert, et al.

The two-proton radioactivity has been observed experimentally in 2002, at projectile fragmentation facilities, more than 40 years after the first theoretical prediction of this process. First observations were indirect measurements, using standard silicon detector devices. Since then, a new generation of experiments allowed for a direct observation, and opened the field of more detailed studies, using tracking devices for the detection of the emitted protons.

The two-proton radioactivity has been evidenced experimentally in 2002 in the ground-state decay of Fe-45, while this new decay mode was predicted since the 60's. The first observations have been done indirectly, from various global quantities measured in the decay process (half-file, Q-value, daughter decay,...). Since then, new devices have been developed in order to perform energy and angular measurements of the emitted particles. The comparison of full experimental observations with theoretical models opens a new access to nuclear structure a the drip-line.

The two-proton radioactivity of 45Fe was studied experimentally with a time projection chamber. The aim of the experiment was the reconstruction of the proton tracks in three dimensions. Energy and angular correlations have been determined and the data are compared with theoretical models, in particular with a three-body model. Moreover, the decay of 43Cr was studied and β-delayed one-, two- and three-proton emission could be established. The correlations observed for β-delayed two-proton emission favour a sequential emission. Finally, β-delayed two-proton emission was observed for the first time for 51Ni.

In the framework of the two proton radioactivity studies, a Time Projection Chamber was recently developed at CENBG, in order to study the correlations between the two protons emitted. In fragmentation experiments performed at LISE3/GANIL, the 2p radioactivity of Fe-45 and Zn-54 was directly observed with the TPC. Results on correlations between the two protons are presented and compared to a recent theoretical model.

Two-proton radioactivity is an exotic decay mode for very proton-rich nuclei. It was observed experimentally for the first time in 2002 for the nucleus Fe-45 but the two protons could not be directly detected. So a new detector has been developed, a Time Projection Chamber, to individually observe the two protons emitted. It was used successfully during two experiments for the study of Fe-45 and Zn-54. Energy correlations have been studied and the relative angle between the two protons is calculated.

After the discovery of two-proton radioactivity in 2002, an important effort has been made in order to observe each emitted particle individually. Energy and angular correlations between the protons should reveal details about the mechanism of this exotic decay mode. In this framework, an experiment has been performed at LISE/GANIL, where the two protons emitted in the decay of Zn-54 have been individually observed for the first time. Angular and energy correlations were determined and allowed a first comparison with theoretical predictions.

The MAYA detector is a Time-Charge Projection Chamber based on the concept of active target. These type of devices use a part of the detection system, the filling gas in this case, in the role of reaction target. The MAYA detector performs three-dimensional tracking, in order to determine physical observables of the reactions occurring inside the detector. The reconstruction algorithms of the tracking use the information from a two-dimensional projection on the segmented cathode, and, in general, they need to be adapted for the different experimental settings of the detector. This work presents some of the most relevant solutions developed for the MAYA detector.

Studies of beta-delayed emission of protons for Cr-43 and Ni-51 were performed with a Time Projection Chamber. This detection setup allows to reconstruct in the three-dimensional space the tracks of the protons emitted. For the first time, beta-delayed emission of two protons is directly observed for Cr-43 and Ni-51. The question about correlations between protons can be accessed. Finally, we show that Cr-43 can emit up to three delayed protons.

The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.

The half-lives of 38Ca and 39Ca have been measured at ISOLDE of CERN. The REXTRAP facility was used to prepare ultra-clean samples of radioactive nuclei for precision decay spectroscopy. 38Ca is one of the T z = - 1 , 0+ \( \rightarrow\) 0+ \( \beta\) -emitting nuclides used to determine the vector coupling constant of the weak interaction and the Vud quark-mixing matrix element. The result obtained, T 1/2 = 443.8(19) ms, is four times more precise than the average of previous measurements. For 39Ca , a half-life of T 1/2 = 860.7(10) ms is obtained, a result in agreement with the average value from the literature.

Light-particles stable high-intensity beams (p, d, He-3,He-4...) will be available from the Linac driver accelerator of SPIRAL-2. Yields of neutron-deficient isotopes as well as of neutron-rich isotopes (by means of reactions with secondary neutrons) are compared with those presently available at the SPIRAL-1 facility. We explore, for light beams (Z< 16) asked in the 'white book' of SPIRAL-2 (1), the production methods taking into account the in -target yield but also the feasibility of making such beams by the ISOL method (considering reaction, target, thermal and release properties). We discuss some of the tests needed and planned. A comparison with the present and potentially attainable yields at SPIRAL-1 is presented.

Two-proton radioactivity was observed in 2002 in the decay of 45Fe. However, the experiments performed at that time did not allow the observation of the two protons directly. We present here a new setup based on the principle of a time-projection chamber that enabled us for the first time to identify directly the two protons. The new setup permits the observation and reconstruction in three dimensions of the traces of the protons and to determine thus their individual energies and their relative angle. We will discuss the setup in all necessary details and describe its performances in the context of two-proton radioactivity and β- delayed two-proton emission studies.

The SPIRAL2 project, currently under construction at GANIL, will include an isotope separator on line based facility for the production and acceleration of radioactive ion beams. A superconducting linear accelerator will accelerate 5 mA deuterons up to 40 MeV and 1 mA heavy ions up to 14.5 MeV/u. These primary beams will be used to bombard both thick and thin targets. We are investigating three different techniques to produce the radioactive ion beams: (1) the neutron induced fission of uranium carbide, (2) the direct interaction of deuterons in a uranium carbide target, and (3) the interaction of a heavy ion beam with a target. All these production systems will be coupled to an ion source. Four kinds of ion sources are foreseen for the ionization of the radioactive atoms: an electron cyclotron resonance ion source, a surface ionization ion source, a forced electron beam induced arc discharge ion source, and a laser ion source depending on the characteristics of the desired radioactive ion beam in terms of intensity, efficiency, purity, etc. A presentation of the SPIRAL2 project and of the different production systems is given.

The H-7 and H-6 nuclear systems were investigated via transfer reactions with a He-8 beam at 15.4A MeV impinging in a C-12 target. The experimental setup allowed a complete reconstruction of the reaction kinematics with the MAYA gas detector, based on the active-target concept, where the carbon atoms of the filling isobutane played also the role of reaction target. The H-7 resonance was observed at 0.57(-0.21)(+0.42) MeV above the H-3+4n threshold with a width of 0.09(-0.06)(+0.94) MeV. The H-6 system was formed at 2.91(-0.95)(+0.85) MeV with a resonance width of 1.52(-0.35)(+1.77) MeV. These results show the availability of nuclear structure information well outside the bounding limits, resulting in an extraordinary input to improve the present models and understanding of nuclear matter.

In the present paper, we present measurements that led to the discovery of two-proton radioactivity. After the first observation of this decay mode for Fe-45, new measurements evidenced this decay mode also for Zn-54 and most likely Ni-48. A new detector based on the time-projection chamber principle allowed now to visualize the two protons directly.

The masses of neutron-deficient nuclides near the N=Z line with A=64-80 have been determined using a direct time-of-flight technique which employed a cyclotron as a high-resolution spectrometer. The measured atomic masses for Se-68 and Y-80 were 67.9421(3) u and 79.9344(2) u, respectively. The new values agree with the 2003 Atomic Mass Evaluation. The result for Se-68 confirms that this nucleus is a waiting point of the rp-process, and that for Y-80 resolves the conflict between earlier measurements. Using the present results and the 2003 Atomic Mass Evaluation compilation, the empirical interaction between the last proton and the last neutron in N=Z nuclei has been revisited and extended.

The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the Ni-56 unstable nucleus by inducing the Ni-56(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 degrees to 7 degrees. 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 masses of neutron-deficient nuclides near the N = Z line with A = 64-80 have been determined using a direct time-of-flight technique which employed a cyclotron as a high-resolution spectrometer. The measured atomic masses for 68 Se and 80 Y were 67.9421(3) u and 79.9344(2) u, respectively. The new values agree with the 2003 Atomic Mass Evaluation. The result for 68 Se confirms that this nucleus is a waiting point of the rp-process, and that for 80 Y resolves the conflict between earlier measurements. Using the present results and the 2003 Atomic Mass Evaluation compilation, the empirical interaction between the last proton and the last neutron in N = Z nuclei has been revisited and extended.