Low-energy measurement of the 7Be(p,gamma)8B cross section

We have measured the cross section of the 7Be(p,gamma)8B reaction for E(c.m.) = 185.8, 134.7, and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta+ and alpha particles from 8B and 8Be* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5+/-2.4 eV b and a weighted mean value of 18.8+/-1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.     

Fast neutron irradiation of YBa2Cu3O7

The influence of fast neutron irradiation on the superconducting transition temperature,T _c , the transition width, upper critical field,B _c2 , and critical current density,j _c , has been investigated in YBa₂Cu₃O₇ up to a fluence of 10¹⁹ cm^–2 (E>1 MeV). TheT _c degradation with fluence is slightly less than in PbMo₆S₈, but larger than in A 15 compounds. The irradiation induced increase of the normal state resistivity is accompanied by a remarkable decrease of both the intergrainj _c and the superconducting volume fraction.     

Measurement of the ionization probability of the 1s σ MO on the way into the nuclear fusion reaction58Ni+54Fe

The total excitation probability of the 1s σ molecular orbital on the way into the nuclear reaction⁵⁸Ni+⁵⁴Fe at 238 MeV has been directly measured. The result found is (3.1±0.6) 10^?2. The method is based on the detection at zero degree with respect to the beam direction of the x-rays emitted in the reaction, in coincidence with the gamme rays following the deexcitation of the evaporation residues produced in the nuclear reaction. The difference in the doppler shift of the x-ray energies enables to discriminate between the internal conversion x-rays and the prompt atomic x-rays following the decay of the vacancies made in the approach of the nuclear reaction. The experimental data is compared with numerical evaluations of different mechanisms which can produce a vacancy in theK-shell of the united atom at the end of the collision. The best agreement is found with the value of the direct ionization of the 1sσ MO evaluated in the framework of the Brigg's model.     

Uniform magnetic properties for an ultrahigh-density lattice of noninteracting co nanostructures

We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of 26 Tera/in2 (1 Tera=10(12)), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.     

Über thermische,eine Amino-Claisen-Umlagerung einschliessende. Reaktionen von N-Propargyl-naphthylaminen

N-Propargyl-1-naphthylamine ( 1 ), the corresponding N-butinylcompound 5 and N-propargyl-2-naphthylamine ( 2 ) - unlike N-propargyl-anilines - on heating to 250° are converted to a mixture of py-tetrahydro-benzoquinolines and benzoquinolines (scheme 1). The mechanism of these reactions which are induced by a [3s, 3 s] rearrangement of the propargyl group and include a [1,5s] H-shift is depicted in scheme 4. N-Methylation of 1 and 2 reduces for steric reasons the rate of the [1,5s] H-shifts; therefore ring closure of the allenylnaphthylamine intermediates to indols 13 and 14 is favoured (schemes 2 and 5).