4,272 research outputs found
Nonlinear influence of excess Mn on the magnetoelastic transition in (Mn,Cr)<sub>2</sub>Sb
No full textThe influence of excess Mn on the magnetoelastic ferromagnetic-to-antiferromagnetic transition Tt in the magnetocaloric compound (Mn,Cr)2Sb has been studied. With increasing excess Mn the magnetoelastic transition temperature for (Mn,Cr)2Sb initially increases and then decreases. This trend is accompanied by a strong reduction of the (Mn,Cr)Sb secondary phase. With increasing excess Mn a higher Cr content was found in the (Mn,Cr)Sb secondary phase in comparison to the matrix phase. This competition for Cr leads to a nonlinear dependence of Tt with increasing excess Mn at a fixed nominal Cr content. However, we observed that Tt depends linear on the c/a ratio for a wide range of temperatures from 170 to 350 K. A compositional diagram of the c/a ratio was constructed to assist the selection of (Mn,Cr)2Sb alloys with a desired transition temperature.RST/Fundamental Aspects of Materials and Energ
A REVIEW OF THE FISSION DECAY OF THE GIANT-RESONANCES IN THE ACTINIDE REGION
No full textLa décroissance par fission des résonances géantes dans la région des actinides est passée en revue. Les résultats invariablement contradictoires de diverses expériences sont discutés. Celles-ci comprennent des réactions inclusives de fission induite par électron ou positron, et des expériences où les fragments de fission sont détectés en coïncidence avec les électrons ou hadrons diffusés inélastiquement. Nous nous concentrons sur une expérience (α,α'f) récente où l'on étudie la décroissance par fission de la résonance géante monopolaire en détectant les fragments de fission en coïncidence avec les α inélastiques autour de, et à 0°.The fission decay of giant resonances in the actinide region is reviewed. Results from various experiments which are invariably conflicting are discussed. These include inclusive electron and positron induced fission, as well as experiments in which fission fragments were detected in coincidence with inelastically scattered electrons or hadrons. Attention is focussed on a recent (α,α'f) experiment in which the fission decay of the giant monopole resonance was investigated by measuring fission fragments in coincidence with inelastically scattered α-particles at and around 0°
Excitation of isospin and spin-isospin modes in the beta(+) direction
No full textThe excitation of isospin and spin-isospin modes has been a topic of much interest in the last two decades because of their importance to various astrophysical phenomena next to the intrinsic interest in their microscopic structure. (p, n) and other (p,n)-type reactions, such as (He-3,t), at intermediate energies have been used to map spin-isospin-flip strength in the beta(-) direction. For the beta(+) direction the spin-isospin-flip strength can, in principle, be mapped with the (n,p) reaction at intermediate energies. However, the resolution that can be obtained with secondary neutron beams is hardly useful to map accurately this strength. Better reactions could be (d, He-2) and (t,He-3) reactions at intermediate energies. Recently, at KVI a primary triton beam has been accelerated to energies of about 45 MeV/u. It is planned to use this beam to study isospin excitations in 'neutron-rich' nuclei. Furthermore, an unprecedented high resolution of 150 keV has been achieved with the (d,2He) reaction, which is a reaction of essentially pure spin- and isospin-flip character. This allows to map the spin-isospin strength and study its microscopic and multipole structure. Recent experimental results axe discussed.</p
On the excitation of isoscalar dipole strength in the giant resonance region by inelastic electron and hadron scattering
Full text linkThe possible excitation of isoscalar dinole strength in the region of the giant resonances is investigated. The presence of 20% of the isoscalar dipole energy-weighted sum rule (EWSR) in the region of the giant quadrupole resonance (GQR) would have an appreciable cross section as compared to the total cross section attributed to GQR excitation, and would readily account for the forward-backward asymmetries observed in α0-decay of the GQR in light nuclei
GDR excitation by isoscalar probes: a means to determine the neutron-skin thickness
No full textInelastic scattering of a-particles can excite the isovector giant dipole resonance (GDR) via the Coulomb interaction. In spite of their isoscalar nature alpha-particles carl also excite the GDR via the nuclear interaction due to the difference in the radii of the neutron and proton density distributions. The absolute cross section to excite the GDR in inelastic alpha-scattering is therefore a measure of this radial difference, the so-called neutron-skin thickness. Furthermore, since the GDR strength distribution has a centroid energy which depends on the nuclear radius, these studies, when performed in deformed nuclei, can measure the neutron-skin thickness along both the short and the long axes independently. Results of an experiment performed at KVI at E-alpha = 120 MeV and small scattering angles, including 0 degrees, to determine the neutron-skin thickness in Pb-208, Sn-116, Sn-124, and the deformed Nd-150 are discussed and compared to earlier measurements and theoretical predictions. Future improvements in the experimental set-up are also discussed
Hadronic excitation of the octupole bands in deformed nuclei: Necessity of the isoscalar dipole degree of freedom?
Full text linkCoupled channel analysis indicates that an octupole vibration coupled to the quadrupole static deformation is sufficient to explain the inelastic excitation by proton scattering of the K ~r = 0- octupole band in lS2Sm. The isoscalar dipole degree of freedom is found not to be necessary, at least for this mass region, to explain the excitation of the 1- state of the octupole band
EXCITATION OF GROUND-BAND AND GAMMA-BAND IN THE MG-24(ALPHA, ALPHA')MG-24 REACTION AT 120 MEV
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