Magnetic excitations of the singlet ground state antiferromagnet CsFeBr3 in a magnetic field

Abstract The magnetic excitations in the quasi-one-dimensional singlet ground state antiferromagnet CsFeBr3 have been studied by inelastic neutron scattering in the presence of an applied magnetic field, H‖c and H⊥c. With H‖c, the dispersion curves renormalise so that the exchange interaction has a decreasing influence with increasing field. H⊥c has little or no effect on the dispersion of the magnetic excitations.

Invariant mass spectrum and α-n correlation function studied in the fragmentation of 6He on a carbon target

13 pags, 5 figures.-- PACS nrs.: 24.60.−t; 25.70.Ef; 27.20.+n.

Trends in infant leukaemia in West Germany in relation to in utero exposure due to Chernobyl accident.

A temporary increase in the incidence of infant leukaemia in Greece was reported by Petridou et al., which was attributed to in utero exposure to ionising radiation resulting from the Chernobyl accident. We performed a similar analysis based on the data of the German Childhood Cancer Registry in order to check whether the observation could be confirmed by means of independent data. Applying the same definitions as Petridou et al., we also observed an increased incidence of infant leukaemia in a cohort of children born after the Chernobyl accident. More detailed analyses, regarding areas with different contamination levels and dose rate gradients over time after the accident, showed, however…

Study of the β-delayed neutron decay of 17C and 18C

Abstract The β-delayed neutron decays of 17C and 18C have been studied using a time-of-flight array with a high detection efficiency. The 17C and 18C ions were produced by fragmentation of an E A = 69 MeV 22Ne beam. Transitions to several neutron unbound states have been observed for the first time for both decays with total branching ratios of (10.8 ± 2.2)% and (21.4 ± 4.4)%. Half-lives of 193 ± 6 ms and 92 ± 2 ms were found for 17C and 18C, respectively. The results are compared with previous measurements of the β-decays and with shell-model calculations.

Magnetostrictive and quadrupolar anisotropy in nuclear magnetic fcc systems

The spin hamiltonian for nuclear magnetic order in copper is investigated with respect to magnetoelastic couplings to the lattice. These arise due to the dipolar, Ruderman Kittel and the quadrupolar interaction. While the latter is quenched for the ideal fcc-lattice, it is found that for copper it will dominate the magnetoelastic terms of the nuclear spin hamiltonian. The absolute size of the quadrupole contribution is determined by the effective charge and (anti-) shielding effects. This interaction can give rise to an effective anisotropy in the fcc-system which can be quite large compared to the small stabilisation energies for nuclear order in copper. Consequences for the nuclear orderi…

Estimation of isometric strength: Intensity and holding time

Crossing the dripline to11Nusing elastic resonance scattering

The level structure of the unbound nucleus N-11 has been studied by C-10+p elastic resonance scattering in inverse geometry with the LISE3 spectrometer at GANIL, using a C-10 beam with an energy of 9.0 MeV/ nucleon. An additional measurement was done at the A1200 spectrometer at MSU. The excitation function above the C-10+p threshold has been determined up to 5 MeV. A potential-model analysis revealed three resonance states at energies 1.27(-0.05)(+0.18) MeV (Gamma = 1.44 +/- 0.2 MeV), 2.01(-0.05)(+0.15) MeV (Gamma = 0.84 +/- 0.2 MeV), and 3.75 +/- 0.05 MeV (Gamma = 0.60 +/- 0.05 MeV) with the spin-parity assignments I-pi=1/2+,1/2,-,5/2+, respectively. Hence, N-11 is shown to have a ground …

Study of the Spin Wave Linewidth in a 1-D Easy-Plane Ferromagnet Using Neutron Polarization Analysis

An anomalous wavevector dependence in the spin wave linewidth associated with fluctuations out of the easy plane is observed for the first time in the one-dimensional easy-plane ferromagnet CsNiF3 by means of inelastic polarized neutron scattering. The linewidths of the spin waves, one attributed to spin fluctuations out of the easy plane and another in the easy plane, are studied separately throughout the Brillouin zone. The zone boundary narrowing of the linewidth associated with the spin fluctuations in the easy plane is observed for the first time in agreement with the classical spin wave theory. The deviations from the classical result at large qc and high temperature are interpreted a…

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Abstract Background Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18–49, 50–69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results NNVs were more favourable in su…

Continuum excitations in6He

T. Aumann et al. ; 11 pags.; 6 figs.; 2 tabs. ; PACS number(s): 27.20.1n, 25.60.Gc, 25.70.De, 29.30.Hs

Realization of a broad band neutron spin filter with compressed, polarized 3He gas

The strongly spin dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to a gas amount of the order of 1 barl. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mbar. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3 × 1018 3He-atoms/s are polarized up to 64%. Subsequent polarization preserving compression by a two stage compressor system enables to prepare NSF cells of ab…

Inelastic neutron scattering measurements on Nd2Fe14B and Y2Fe14B single crystals

Abstract Inelastic neutron scattering measurements have been carried out on Nd 2 Fe 14 B and Y 2 Fe 14 B single crystals. Temperature dependent acoustic magnon dispersion curves have been found along the high-symmetry directions [0,0,1] and [1,0,0] with a gap at (0,0,2). Soft mode behaviour at spin wave vector q = 0 was observed for Nd 2 Fe 14 B near the spin reorientation temperature. The inelastic scattering intensity decreases steeply for larger q . Therefore, the dispersion curves could be measured until the middle of the Brillouin zone only. The experimental results are discussed in the frame of a classical spin wave model.

Crossing the Dripline to 11N Using Elastic Resonance Scattering

The level structure of the unbound nucleus 11N has been studied by 10C+p elastic resonance scattering in inverse geometry with the LISE3 spectrometer at GANIL, using a 10C beam with an energy of 9.0 MeV/u. An additional measurement was done at the A1200 spectrometer at MSU. The excitation function above the 10C+p threshold has been determined up to 5 MeV. A potential-model analysis revealed three resonance states at energies 1.27 (+0.18-0.05) MeV (Gamma=1.44 +-0.2 MeV), 2.01(+0.15-0.05) MeV, (Gamma=0.84 +-$0.2 MeV) and 3.75(+-0.05) MeV, (Gamma=0.60 +-0.05 MeV) with the spin-parity assignments I(pi) =1/2+, 1/2- and 5/2+, respectively. Hence, 11N is shown to have a ground state parity inversi…

Magnetic excitations and phase transition of CsFeBr3 in an external magnetic field

In CSFeBr3 the Fe2+ ion with effective spin one has locally a singlet ground state (m=0). The antiferromagnetic interactions between neighbouring Fe-ions are too weak as compared with the anisotropy constant to introduce long range order in the absence of an external field. By inelastic neutron scattering we studied the magnetic excitations in an external magnetic field up to 5 Tesla applied along thec-axis. A linear Zeeman splitting was observed with a Lande factorg=2.4. The field renormalizes the dispersion curves in such a way that the exchange interaction has decreasing influence with increasing field. Theoretical calculations according to the excitonic model of Lindgard describe the ex…

Realization of a broad-band neutron spin filter with compressed, polarized 3He gas

The strongly spin-dependent absorption of neutrons in nuclear spin polarized 3He opens the possibility to polarize beams of thermal and epithermal neutrons. An effective 3He neutron spin filter (NSF) requires high 3He nuclear polarization as well as a filter thickness corresponding to amount of gas in the order of 1 bar 1. We realized such a filter using direct optical pumping of metastable 3He∗ atoms in a 3He plasma at 1 mb. Metastable exchange scattering transfers the angular momentum to the whole ensemble of 3He atoms. At present 3.6 × 1018 3He-atoms s−1 are polarized up to 68%. Subsequent polarization preserving compression by a two-stage compressor system enables to prepare NSF cells o…

Magnetic resonances in low-dimensional spin systems

Abstract We present magnetic resonance experiments in the frequency range of 35 to 460 GHz at low temperatures (1.5 K) for the two compounds CsNiCl 3 and (CH 3 ) 4 NMnCl 3 (TMMC). In both cases the large frequency range enables us to make a precise determination of the various coupling constants (exchange interactions and anisotropy parameters). For CsNiCl 3 we found a larger interchain exchange than previously determined. These constants can then be used for a critical evaluation of other related experiments. In TMMC we found resonances which cannot be explained by existing models.

The phase diagram and the magnetic structure of nuclear spins in elemental copper below 60 nK

Abstract The phase diagram for nuclear magnetic order is elemental copper and the corresponding ordering vectors were investigated by neutron diffraction at nanokelvin temperatures. The intermediate phase is characterized by an ordering vector (O 2 3 2/3 . This is the first time that this type of order is observed in an fcc antiferromagnet.

Radioactive ion beams in the region of 100Sn and 78Ni at the NSCL

The regions around the doubly magic nuclei 100 Sn and 78 Ni are of great interest from a nuclear structure standpoint. These nuclei also play a key role in the astrophysical rp- and r-processes, respectively. Recently, nuclei in these regions were studied at the Coupled Cyclotron Facility at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University.

Solitary excitations in one-dimensional magnets

Abstract The present status of theoretical and experimental investigations of solitary excitations in one-dimensional magnetic systems is reviewed. A survey of exact solutions to the nonlinear equations of motion for pertinent classical chain systems (sine-Gordon chain and ferromagnetic Heisenberg chains with various anisotropies) is given. Particular emphasis is devoted to the role of solitons in the thermodynamics of such systems. Models corresponding to real quasi-one-dimensional magnets are broadly discussed to demonstrate the properties of their solitary excitations. The experimental significance of such nonlinear excitations in the static and dynamic quantities of such systems is disc…

Poster contributions

Magnetic field and temperature dependent correlations in the singlet ground state system CsFeBr3

Abstract In the singlet ground state system CsFeBr 3 the temperature and magnetic field dependence of the magnetic dispersion curves have been measured by inelastic neutron scattering. At a field of 4.1 T magnetic Bragg peaks appear at (⅓ ⅓ 1) and (⅔ ⅔ 1). The correlation lengths were derived from the experimental data by integrating the constant Q -scans over the energy transfer. The Q -dependence was fitted to Lorentzians and correlations lengths were extracted for different directions in the lattice. These correlation lengths decrease with increasing temperature and increase with increasing field. Above the phase transition the correlation lengths decrease again.

Temperature and magnetic field dependent correlations in the singlet ground state system CsFeBr3

The magnetic excitations in CsFeBr3 have been measured with inelastic scattering of cold neutrons to high precision at 80 mK. The fact that the lowest frequency mode softens with decreasing temperature but stabilizes at 0.11 THz below 2.5 K is the indication that CsFeBr3 remains a SGS system forT→0. From dispersion curves measured earlier in a magnetic field along the chain axis experimental intensities were derived and in turn correlation lengths. Correlation lengths were also calculated using the new parameters for exchange and anisotropy. The experimental results and the calculations both show that the correlation lengths increase for increasing magnetic field, flatten off around the pha…

Half-Life of the Doubly Magicr-Process NucleusN78i

Nuclei with magic numbers serve as important benchmarks in nuclear theory. In addition, neutron-rich nuclei play an important role in the astrophysical rapid neutron-capture process (r process). 78Ni is the only doubly magic nucleus that is also an important waiting point in the r process, and serves as a major bottleneck in the synthesis of heavier elements. The half-life of 78Ni has been experimentally deduced for the first time at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University, and was found to be 110(+100)(-60) ms. In the same experiment, a first half-life was deduced for 77Ni of 128(+27)(-33) ms, and more precise half-li…