arXiv subjects
Publications and source records attributed to H. Fujita.
A study of the $β$ decay of the proton-rich $T_{z}$ = -2 nucleus $^{56}$Zn has been reported in a recent publication. A rare and exotic decay mode, $β$-delayed $γ$-proton decay, has been observed there for the first time in the $fp$ shell. Here we expand on some of the details of the data analysis, focussing on the charged particle spectrum.
We report the observation of a very exotic decay mode at the proton drip-line, the $β$-delayed $γ$-proton decay, clearly seen in the $β$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $γ$-proton sequences have been observed after the $β$ decay. Here this decay mode, already observed in the $sd$-shell, is seen for the first time in the $fp$-shell. Both $γ$ and proton decays have been taken into account in the estimation of the Fermi (F) and Gamow Teller (GT) strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.
High resolution experimental data has been obtained for the 40,42,44,48Ca(3He,t)Sc charge exchange reaction at 420 MeV beam energy, which favors the spin-isospin excitations. The measured angular distributions were analyzed for each state separately, and the relative spin dipole strength has been extracted for the first time. The low-lying spin-dipole strength distribution in 40Sc shows some interesting periodic gross feature. It resembles to a soft, dumped multi-phonon vibrational band with $\hbarω$= 1.8 MeV, which might be associated to pairing vibrations around $^{40}$Ca.
The half-lives of the Tz = -2, 56Zn and Tz = -1, 58Zn isotopes and other nuclei were measured in a β-decay experiment at GANIL. The energy levels populated by the 56Zn β decay were determined. The 56Zn results are compared with the results of the mirror process, the charge exchange reaction 56Fe(3He,t)56Co.
An experiment using the 11B(3He,d)12C reaction was performed at iThemba LABS at an incident energy of 44 MeV and analyzed with a high energy-resolution magnetic spectrometer, to re-investigate states in 12C published in 1971. The original investigation reported the existence of an 11.16 MeV state in 12C that displays a 2+ nature. In the present experiment data were acquired at laboratory angles of 25-, 30- and 35- degrees, to be as close to the c.m. angles of the original measurements where the clearest signature of such a state was observed. These new low background measurements revealed no evidence of the previously reported state at 11.16 MeV in 12C.
Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208Pb shows that at very forward angles J^pi = 1- states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9 MeV, i.e., in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the E1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR.
The level density of 2+ states in 40Ca has been extracted in the energy region of the isoscalar giant quadrupole resonance (ISGQR) from a fluctuation analysis of high energy-resolution p,p') data taken at incident energies of 200 MeV at the K600 magnetic spectrometer of iThemba LABS, South Africa. Quasi-free scattering cross sections were calculated to estimate their role as a background contribution to the spectra and found to be small. The shape of the background was determined from the discrete wavelet transform of the spectra using a biorthogonal wavelet function normalized at the lowest particle separation threshold. The experimental results are compared to widely used phenomenological and microscopic models.
A benchmark experiment on 208Pb shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r_skin = 0.156+0.025-0.021 fm in 208Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence, relevant to the description of neutron stars.
The $^{150}$Nd($^3$He,$t$) reaction at 140 MeV/u and $^{150}$Sm($t$,$^3$He) reaction at 115 MeV/u were measured, populating excited states in $^{150}$Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) $ββ$ decay of $^{150}$Nd to $^{150}$Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless $ββ$ decay ($0νββ$) of $^{150}$Nd. The present results thus provide useful information on the neutrino responses for evaluating the $0νββ$ and $2νββ$ matrix elements. The $2νββ$ matrix element calculated from the Gamow-Teller transitions through the lowest $1^{+}$ state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in $2νββ$ direct counting experiments and at least several transitions through $1^{+}$ intermediate states in $^{150}$Pm are required to explain the $2νββ$ half-life. Because Gamow-Teller transitions in the $^{150}$Sm($t$,$^3$He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the $2\hbarω$, $ΔL=0$, $ΔS=1$ isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.
The possibility of observing neutrinoless double beta decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain and the occupations of valence orbits by nucleons active in the decay are likely to be important. The occupation of valence proton orbits in the ground states of 76Ge, a candidate for such decay, and 76Se, the corresponding daughter nucleus, were determined by precisely measuring cross sections for proton-removing transfer reactions. As in previous work on neutron occupations, we find that the Fermi surface for protons is much more diffuse than previously thought, and the occupancies of at least three orbits change significantly between the two 0+ ground states.
We present a nanomechanical device design to be used in a non-volatile mechanical memory point. The structure is composed of a suspended slender nanowire (width : 100nm, thickness 430nm length : 8 to 30$μ$m) clamped at its both ends. Electrodes are placed on each sides of the nanowire and are used to actuate the structure (writing, erasing) and to measure the position through a capactive bridge (reading). The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released, the stressed material relaxes and the beam buckles in a position of lower energy. Such symmetric beams, called Euler beams, show two stable deformed positions thus form a bistable structure. This paper will present the fabrication, simulation and mechanical and electrical actuation of an in plane bistable nanowire. Final paper will include a section on FEM simulations.
We report on experimental data of the three-dimensional bulk Fermi surfaces of the layered strongly correlated Ca1.5Sr0.5RuO4 system. The measurements have been performed by means of hn-depndent bulk-sensitive soft x-ray angle-resolved photoemission technique. Our experimental data evinces the bulk Fermi surface topology at kz~0 to be qualitatively different from the one observed by surface-sensitive low-energy ARPES. Furthermore, stronger kz dispersion of the circle-like gamma Fermi surface sheet is observed compared with Sr2RuO4. Thus in the paramagnetic metal phase, Ca1.5Sr0.5RuO4 compound is found to have rather three-dimensional electronic structure.
The cluster structures of the excited states in $^{11}$B are studied by analyzing the isoscalar monopole and quadrupole strengths in the $^{11}$B($d$,$d'$) reaction at $E_d=200$ MeV. The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the $3/2^-_3$ state at $E_x=8.56$ MeV is well described by the AMD calculation and is an evidence for a developed $2α+t$ cluster structure.
The $^{11}$B($^3$He$, t$), $^{11}$B($d, d'$), and $^{11}$B($p, p'$) reactions were measured at forward scattering angles including $0^\circ$ to study the isovector and isoscalar spin-flip M1 strengths in $^{11}$B. The measured $^{11}$B($^3$He$, t$) cross sections were compared with the results of the distorted-wave impulse-approximation (DWIA) calculation, and the Gamow-Teller (GT) strengths for low-lying states in $^{11}$C were determined. The GT strengths were converted to the isovector spin-flip M1 strengths using the isobaric analog relations under the assumption of the isospin symmetry. The isoscalar spin-flip M1 strengths were obtained from the ($d, d'$) analysis by assuming that the shape of the collective transition form factor with the same $ΔJ^π$ is similar in the $^{11}$B($d, d'$) and $^{12}$C($d, d'$) reactions. The obtained isovector and isoscalar strengths were used in the DWIA calculations for the $^{11}$B($p, p'$) reaction. The DWIA calculation reasonably well explains the present $^{11}$B($p, p'$) result. However, the calculated cross section for the 8.92-MeV 3/2$^-_2$ state was significantly smaller than the experimental values. The transition strengths obtained in the shell-model calculations were found to be 20-50% larger than the experimental strengths. The transition strengths for the neutrino induced reactions were estimated by using the isovector and isoscalar spin-flip M1 strengths. The present results are quantitatively in agreement with the theoretical estimation discussing the axial isoscalar coupling in the neutrino scattering process, and are useful in the measurement of the stellar neutrinos using the neutral- and charged-current reactions on $^{11}$B.
Cross sections and polarization transfer observables in the $^{16}$O$(p,p')$ reactions at 392 MeV were measured at several angles between $θ_{lab}=$ 0$^\circ$ and 14$^\circ$. The non-spin-flip ($ΔS=0$) and spin-flip ($ΔS=1$) strengths in transitions to several discrete states and broad resonances in $^{16}$O were extracted using a model-independent method. The giant resonances in the energy region of $E_x=19-$27 MeV were found to be predominantly excited by $ΔL=1$ transitions. The strength distribution of spin-dipole transitions with $ΔS=1$ and $ΔL=1$ were deduced. The obtained distribution was compared with a recent shell model calculation. Experimental results are reasonably explained by distorted-wave impulse approximation calculations with the shell model wave functions.
A windowless and self-supporting ice target is described. An ice sheet with a thickness of 29.7 mg/cm$^2$ cooled by liquid nitrogen was placed at the target position of a magnetic spectrometer and worked stably in the $^{16}$O$(p,p')$ experiment at $E_{p}=392$ MeV. Background-free spectra were obtained.