Direct observation of new proton rich nuclei in the region 23≦Z≦29 using A 55A.MeV58Ni beam

Using magnetic separation and identification through time of flight andΔExE measurements, the nuclei⁵⁶Cu,⁵²Co (T _z =?1);⁵⁵Cu,⁵¹Co,⁴⁷Mn,⁴³V(T _z =?3/2)⁵²Ni,⁵⁰Co,⁴⁸Fe,⁴⁶Mn,⁴⁴Cr (T _z =?2); and⁵¹Ni (T _z =?5/2) are observed for the first time from interactions of 55A.MeV⁵⁸Ni projectiles with a Ni target. The predicted proton drip-line has probably been reached for the odd elements.     

Beta-decay studies of neutron-rich Sc- Cr nuclei

The neutron-rich nuclei ₂₁^{57, 58}Sc, ₂₂^58-60Ti, ₂₃^60-63V, ₂₄^62-66Cr have been produced at Ganil via interactions of a 61.8A MeV ⁷⁶Ge beam with a ⁵⁸Ni target. Beta-decay studies have been performed using combined - and -ray spectroscopy. Half-lives have been determined and -decay schemes are proposed for ⁵⁸Ti, ⁶¹V and ⁶²Cr. From these studies, new hints for the existence of -decaying isomers in ⁶⁰V and in ⁶²Mn are provided. These results are compared to shell model calculations. The role of the f_7/2- f_5/2 proton-neutron interaction is examined through its influence on the lifetime values.     

Formation and deexcitation of the 32S compound nucleus via the 20Ne+12C and 16O+16O entrance channels

Reaction-product cross sections following ²⁰Ne+¹²C and ¹⁶O + ¹⁶O collisions at several incident energies have been measured with a E-ΔE counter telescope. They are compared to statistical model predictions. Fair agreement is obtained for the high-Z evaporation residue cross sections, but a strong discrepancy is observed for the lower-Z reaction products. Possible explanations are discussed. It is shown that the compound nucleus formation does not depend on the structure of the colliding ions in the entrance channel and also that it is not limited by the ³²S yrast line.     

Spectroscopy of Na: Bridging the two-proton radioactivity of Mg

The unbound nucleus ¹⁸Na, the intermediate nucleus in the two-proton radioactivity of ¹⁹Mg, was studied by the measurement of the resonant elastic scattering reaction H(¹⁷Ne,p)¹⁷Ne performed at 4 A.MeV using a radioactive beam from the SPIRAL Facility. Spectroscopic properties of the low-lying states were obtained in an R-matrix analysis of the excitation function.     

Rapid decrease of fragment emission time in the range of 3–5 MeV/u excitation energy

Multifragment emission processes from highly excited nuclei produced in ⁴⁰Ar + ¹⁹⁷Au reactions at incident energies of 30 and 60 MeV/u are compared. At the lowest bombarding energy and 3.3 MeV/u excitation energy, the composite system decay process supports the hypothesis of long-lived equilibrated nucleu decaying by successive binary splittings. For excited nuclei around 5 MeV/u, the depletion observed at small relative angles in the correlation functions is interpreted as the result of a strong reduction in the fragment emission time scale.     

Momentum transfer in light-ion-induced fission reactions

Angular correlations and angular distributions of the fission fragments produced in the bombardment of a ²³²Th target with protons, deuterons and α-particles in the energy range between 35 and 1000 MeV/nucleon have been measured. From these measurements, the distributions of linear momentum imparted to fissioning nuclei have been deduced in the various energy regimes; dominating reaction mechanisms are classified according to the fraction of the available incident momentum transferred to the target. The experimental results are compared to the predictions of intra-nuclear cascade calculations. An optimum excitation energy supported by the fissioning nuclei could be the dominant limitation to momentum transfer at high incident energies. The angular distributions of the fission fragments were used to extract fission cross sections and upper limits of the angular momentum imparted to the fissioning nuclei.     

(68)(28)Ni(40): Magicity versus superfluidity

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)-->2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy. The B(E2) value for (68)Ni(40) is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the B(E2) values and indicates the erosion of the N = 40 harmonic-oscillator subshell by neutron-pair scattering.     

Spectroscopy of neutron-deficient nuclei around 36Ca

An experiment was performed to extend the knowledge of excited states in neutron-deficient Ca isotopes. In particular, the first excited state in ³⁶Ca was searched for to obtain information on the isospin dependence of the nucleon-nucleon interaction near the proton drip line from a comparison with its stable mirror nucleus, ³⁶S. The ³⁶Ca ions were produced using a two-step fragmentation technique with a ³⁷Ca secondary beam, and in-beam γ-rays were measured. First results are the energy of the first 2⁺ state in ³⁶Ca, E(2⁺)=3036(11) keV, and the cross section for the reaction ³⁷Ca → ³⁶Ca at 61.A MeV. In addition, the de-excitaion of the first 2⁺ state in ²⁸S has been observed.     

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.