Evidence for a New Compact Symmetric Fission Mode in Light Thorium Isotopes.

Taking benefit of the R3B/SOFIA setup to measure the mass and the nuclear charge of both fission fragments in coincidence with the total prompt-neutron multiplicity, the scission configurations are inferred along the thorium chain, from the asymmetric fission in the heavier isotopes to the symmetric fission in the neutron-deficient thorium. Against all expectations, the symmetric scission in the light thorium isotopes shows a compact configuration, which is in total contrast to what is known in the fission of the heavier thorium isotopes and heavier actinides. This new main symmetric scission mode is characterized by a significant drop in deformation energy of the fission fragments of about 19 MeV, compared to the well-known symmetric scission in the uranium-plutonium region.

The Neutrons for Science Facility at SPIRAL-2.

The neutrons for science (NFS) facility is a component of SPIRAL-2, the new superconducting linear accelerator built at GANIL in Caen (France). The proton and deuteron beams delivered by the accelerator will allow producing intense neutron fields in the 100 keV-40 MeV energy range. Continuous and quasi-mono-kinetic energy spectra, respectively, will be available at NFS, produced by the interaction of a deuteron beam on a thick Be converter and by the 7Li(p,n) reaction on thin converter. The pulsed neutron beam, with a flux up to two orders of magnitude higher than those of other existing time-of-flight facilities, will open new opportunities of experiments in fundamental research as well as in nuclear data measurements. In addition to the neutron beam, irradiation stations for neutron-, proton- and deuteron-induced reactions will be available for cross-sections measurements and for the irradiation of electronic devices or biological cells. NFS, whose first experiment is foreseen in 2018, will be a very powerful tool for physics, fundamental research as well as applications like the transmutation of nuclear waste, design of future fission and fusion reactors, nuclear medicine or test and development of new detectors.

First observation of the unbound nucleus 15Ne.

We report on the first observation of the unbound proton-rich nucleus 15Ne. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u 17Ne. The 15Ne ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to 13O with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2- and 1- states in 14F is observed. The 15Ne ground state is shown to have a strong configuration with two protons in the (sd) shell around 13O with a 63(5)% (1s1/2)2 component.

Study of the 14Be continuum: identification and structure of its second 2+ state.

The coupling between bound quantum states and those in the continuum is of high theoretical interest. Experimental studies of bound drip-line nuclei provide ideal testing grounds for such investigations since they, due to the feeble binding energy of their valence particles, are easy to excite into the continuum. In this Letter, continuum states in the heaviest particle-stable Be isotope, 14Be, are studied by employing the method of inelastic proton scattering in inverse kinematics. New continuum states are found at excitation energies E*=3.54(16) MeV and E*=5.25(19) MeV. The structure of the earlier known 2(1)+ state at 1.54(13) MeV was confirmed with a predominantly (0d5/2)2 configuration while there is very clear evidence that the 2(2)+ state has a predominant (1s1/2, 0d5/2) structure with a preferential three-body decay mechanism. The region at about 7 MeV excitation shows distinct features of sequential neutron decay via intermediate states in 13Be. This demonstrates that the increasing availability of energetic beams of exotic nuclei opens up new vistas for experiments leading towards a new understanding of the interplay between bound and continuum states.

Measurement of the dipole polarizability of the unstable neutron-rich nucleus 68Ni.

The E1 strength distribution in 68Ni has been investigated using Coulomb excitation in inverse kinematics at the R3B-LAND setup and by measuring the invariant mass in the one- and two-neutron decay channels. The giant dipole resonance and a low-lying peak (pygmy dipole resonance) have been observed at 17.1(2) and 9.55(17) MeV, respectively. The measured dipole polarizability is compared to relativistic random phase approximation calculations yielding a neutron-skin thickness of 0.17(2) fm. A method and analysis applicable to neutron-rich nuclei has been developed, allowing for a precise determination of neutron skins in nuclei as a function of neutron excess.

Observation of two-proton radioactivity of 19Mg by tracking the decay products.

We have observed the two-proton radioactivity of the previously unknown (19)Mg ground state by tracking the decay products in-flight. For the first time, the trajectories of the 2p-decay products, (17)Ne+p+p, have been measured by using tracking microstrip detectors which allowed us to reconstruct the 2p-decay vertices and fragment correlations. The half-life of (19)Mg deduced from the measured vertex distribution is 4.0(15) ps in the system of (19)Mg. The Q value of the 2p decay of the (19)Mg ground state inferred from the measured p-p-(17)Ne correlations is 0.75(5) MeV.

Observation of a rotational band in the odd-Z transfermium nucleus 101251Md.

A rotational band has been unambiguously observed in an odd-proton transfermium nucleus for the first time. An in-beam gamma-ray spectroscopic study of 101/251Md has been performed using the gamma-ray array JUROGAM combined with the gas-filled separator RITU and the focal plane device GREAT. The experimental results, compared to Hartree-Fock-Bogolyubov calculations, lead to the interpretation that the rotational band is built on the [521]1/2(-) Nilsson state.

Enhanced core polarization in (70)Ni and (74)Zn.

The reduced transition probabilities B(E2;0(+) --> 2(+)(1)) of the neutron-rich (74)Zn and (70)Ni nuclei have been measured by Coulomb excitation in a (208)Pb target at intermediate energy. These nuclei have been produced at Grand Accélérateur National d'Ions Lourds via interactions of a 60A MeV (76)Ge beam with a Be target. The B(E2) value for (70)Ni(42) is unexpectedly large, which indicates that neutrons added above N=40 strongly polarize the Z=28 proton core. In the Zn isotopic chain, the steep rise of B(E2) values beyond N=40 continues up to (74)Zn(44). The enhanced proton core polarization in (70)Ni is attributed to the monopole interaction between the neutron in the g(9/2) and protons in the f(7/2) and f(5/2) spin-orbit partner orbitals. This interaction could result in a weakening of magicity in (78)Ni(50).

Chemical activation of thin-fiber phrenic afferents. 2. Cardiovascular responses.

To assess the effects of groups III and IV (thin-fiber) phrenic afferents on arterial pressure, heart rate, and distribution of cardiac output, we injected capsaicin into phrenic arteries of in situ isolated and innervated left diaphragms of dogs anesthetized with chloralose, vagotomized, and mechanically ventilated. Blood flow in the ascending aorta, common carotid, renal, superior mesenteric, and femoral arteries was measured by electromagnetic and Doppler flow probes. Injection of 1 mg capsaicin into the left phrenic artery produced congruent to 15% increase in mean arterial pressure and congruent to 7% increase in heart rate with no change in aortic flow. Phrenic arterial flow decreased by 64%, renal arterial flow by 16%, and superior mesenteric arterial flow by 10%, whereas carotid flow increased by 13% and flow to the right gastrocnemius muscle did not change. Mean arterial pressure, heart rate, and blood flow distribution (with the exception of the decline in phrenic blood flow) returned to baseline within 60 s of the injection. Injection of 1.5 mg capsaicin into the right isolated and innervated gastrocnemius produced congruent to 35% increase in mean arterial pressure, 17% rise in heart rate, and no change in aortic blood flow. Phrenic and carotid arterial flow rose by 240 and 41%, respectively, whereas renal and superior mesenteric flow declined by 50 and 20%, respectively. In conclusion, thin-fiber phrenic afferents have an excitatory effect on arterial pressure and heart rate. They redistribute blood flow away from the renal and intestinal vascular beds and toward the carotid vascular bed. On the other hand, the cardiovascular reflex from thin-fiber phrenic afferents seems less potent than that from limb muscle afferents.

Chemical activation of thin-fiber phrenic afferents: respiratory responses.

In supine chloralose-anesthetized and mechanically ventilated dogs, we assessed the effects of group III and IV thin-fiber phrenic afferents on cardiorespiratory control by injecting capsaicin into the phrenic artery of an in situ isolated and innervated left diaphragm. Inspiratory motor drive was assessed by measuring the electromyogram of left and right diaphragm, left parasternal, and mylohyoid muscles in five protocols. 1) Three boluses (2 ml) of capsaicin (1, 10, and 50 micrograms/ml) were injected 30 min apart. Only the 50-micrograms/ml injection elicited a significant increase in arterial pressure, heart rate, and inspiratory motor drive. 2) Repeated doses of capsaicin were tested. The pressor and hyperpneic responses were weakened. 3) High doses of capsaicin (100 and 500 micrograms/ml) were given. Hyperpneic and pressor responses were similar to those elicited by the 50-micrograms/ml dose. 4) When the left phrenic nerve was sectioned, the pressor and hyperpneic responses to the 50-micrograms/ml injection were abolished. 5) Capsaicin (50 micrograms/ml) was infused into the arterial supply of the in situ vascularly isolated and innervated gastrocnemius. Arterial pressure, breathing frequency, and inspiratory motor drive to all inspiratory muscles increased significantly and to a greater degree than in the diaphragm. In conclusion, diaphragmatic thin-fiber afferents have an excitatory effect on the inspiratory motor drive and arterial pressure that is similar to that seen in limb muscles.

Importance of perceived similarity in improving children's attitudes toward mentally retarded peers.

Effects of perceived similarity on fifth- and sixth-grade children's attitudes toward mentally retarded peers were examined. Children were selected from schools that contained segregated classes of retarded pupils (exposed setting) and schools that had no retarded pupils enrolled (nonexposed). Attitudes were defined in terms of children's affective feelings and behavioral intentions. Results showed that children responded more positively toward a retarded target who was depicted as similar to them than toward one who was not. Unexpectedly, the positive effects of perceived similarity were observed only among children in the exposed schools. Also, girls were more positive toward a female target than boys were to a male target, regardless of whether the target was perceived as similar. The importance of developing strategies based on theories of interpersonal attraction to improve children's attitudes toward their retarded peers was discussed.