JournalTOCs

Hyperfine Interactions

[4 followers] Follow
Full-text available via subscription

Subscription journal
ISSN (Print) 1572-9540 - ISSN (Online) 0304-3843
Published by Springer-Verlag

[2216 journals]

An IGISOL portrait
- PubDate: 2013-05-16
The IGISOL technique—three decades of developments
- Abstract: Abstract The Ion Guide Isotope Separator On-Line (IGISOL) technique, conceived in the early 1980s as a novel variation to the helium-jet method, has been used to provide radioactive ion beams of short-lived exotic nuclei for fundamental nuclear structure research and applications for three decades. This direct on-line mass separation of primary recoil ions from nuclear reactions has achieved similar extraction efficiencies for both volatile and non-volatile elements throughout the periodic table. The evolution of the ion guide has been driven by the pursuit of physics research on both sides of the valley of beta stability. The gradual improvement in the primary beam intensities of light ions, as well as the ever increasing availability of a range of heavy ions has been matched with the development of novel ion manipulation techniques in order to maximise the output of the IGISOL facility. In this article we describe the continual development of the facility to match the needs of the scientific programme, a relationship which has proceeded hand-in-hand over the years. We will show that this strategy has been and continues to be very important for the huge success of the ion guide method for radioactive ion beam production.
  PubDate: 2013-05-02
Free-ion hyperfine fields and magnetic-moment measurements on radioactive beams: progress and outlook
- Abstract: Abstract Hyperfine fields of highly-charged heavy ions carrying many electrons are discussed in view of their utility for magnetic-moment measurements on radioactive beams by the recoil in vacuum (RIV) technique. An overview of progress is given along with a review of the foundations for ab initio calculations of the relevant free-ion hyperfine interactions.
  PubDate: 2013-05-01
Inhomogeneous broadening of PAC spectra with V _zz and η joint probability distribution functions
- Abstract: Abstract The perturbed angular correlation (PAC) spectrum, G 2(t), is broadened by the presence of randomly distributed defects in crystals due to a distribution of electric field gradients (EFGs) experienced by probe nuclei. Heuristic approaches to fitting spectra that exhibit such inhomogeneous broadening (ihb) consider only the distribution of EFG magnitudes V zz , but the physical effect actually depends on the joint probability distribution function (pdf) of V zz and EFG asymmetry parameter η. The difficulty in determining the joint pdf leads us to more appropriate representations of the EFG coordinates, and to express the joint pdf as the product of two approximately independent pdfs describing each coordinate separately. We have pursued this case in detail using as an initial illustration of the method a simple point defect model with nuclear spin I = 5/2 in several cubic lattices, where G 2(t) is primarily induced by a defect trapped in the first neighbor shell of a probe and broadening is due to defects distributed at random outside the first neighbor shell. Effects such as lattice relaxation are ignored in this simple test of the method. The simplicity of our model is suitable for gaining insight into ihb with more than V zz alone. We simulate ihb in this simple case by averaging the net EFGs of 20,000 random defect arrangements, resulting in a broadened average G 2(t). The 20,000 random cases provide a distribution of EFG components which are first transformed to Czjzek coordinates and then further into the full Czjzek half plane by conformal mapping. The topology of this transformed space yields an approximately separable joint pdf for the EFG components. We then fit the nearly independent pdfs and reconstruct G 2(t) as a function of defect concentration. We report results for distributions of defects on simple cubic, face-centered cubic, and body-centered cubic lattices. The method explored here for analyzing ihb is applicable to more realistic cases.
  PubDate: 2013-05-01
Momentum dependence of spin polarization for beta emitting nuclei produced through charge exchange reaction at intermediate energy
- Abstract: Abstract In order to investigate the polarization process in charge exchange reactions, we observed the momentum and angular distribution as well as the nuclear polarization of a proton-rich beta-emitting nucleus, 28P (I π = 3 + , T 1/2 = 270 msec), produced through the reaction 28Si+ 9Be at E = 100 MeV/u, by selecting the momentum and the ejection angle. An analysis by using double Gaussian functions resolved the observed momentum distribution into two reaction components, nucleon knockout and pick-up abrasion reactions, as suggested in a previous study. The behavior of the observed angular distribution and nuclear polarization implies the influence of those two components. The momentum dependence of the observed nuclear polarization of 28P could be consistently reproduced by a simple model, in which two reaction components are considered. The present study also shows that the charge exchange reaction at intermediate energy is a useful method to produce polarized beta-emitting nuclei, especially for proton-rich nuclei.
  PubDate: 2013-05-01
A simple digital TDPAC spectrometer
- Abstract: Abstract We present a simplified digital time differential perturbed γ − γ angular correlation (TDPAC) spectrometer that demonstrates that such instruments can be built using primarily commercial components and with relatively modest coding effort. The system handles data rates of 70 kcps/detector with a timing resolution of better than 500 ps, and has been used with both 111In and 181Hf.
  PubDate: 2013-05-01
Applications of low temperature nuclear orientation
- Abstract: Abstract The techniques of low temperature nuclear orientation (LTNO) and nuclear magnetic resonance on oriented nuclei (NMRON) are versatile tools used across a range of applications. Such applications include nuclear moment and hyperfine field measurements and testing of nuclear decay models, as well as condensed matter studies, particularly applied to magnetism. Following the tradition of such presentations, the techniques LTNO and NMRON, are briefly outlined along with the principal applications with a focus on some recent works.
  PubDate: 2013-05-01
NMR studies of magnetic properties in Heusler-type Mn₃Si
- Abstract: Abstract In order to microscopically investigate the magnetic properties of both paramagnetic and antiferromagnetic phases in Mn3Si (T N = 23 K), the 55Mn NMR has been carried out at temperatures between 2.2 K and 300 K. The temperature dependences of the spectrum, Knight shift (or resonance frequency shift) and spin-lattice relaxation time T 1 of 55Mn NMR have been measured. In the paramagnetic phase, only one resonance spectrum can be obtained. The observed spectrum is identified to be a signal corresponding to the Mn(II) site. In the antiferromagnetic phase, two different spectra corresponding to the Mn(I) and Mn(II) sites are found at the resonance frequencies of 145 and 6 MHz, respectively, by the zero field NMR at 4.2 K. From these results, the internal magnetic fields on the 55Mn(I) and 55Mn(II) nuclei are found to be 13.6 and 0.6 T, respectively. According to the NMR results, the helical structure in incommensurate Mn spin states is better explained compared with the transverse sinusoidal structure.
  PubDate: 2013-05-01
Realistic models of stochastically varying hyperfine interactions caused by vacancy diffusion in L1₂-structured compounds
- Abstract: Abstract Perturbed angular correlation spectroscopy (PAC) is an attractive method for fundamental studies of diffusion because of the possibility to observe directly atomic scale defects involved in a diffusion process. Previous work investigated under what experimental conditions one could observe a contribution to a PAC spectrum that clearly could be attributed to a vacancy in L12-structured compounds for the special case of self-diffusion. This has since been extended in the present work to consider the case of impurity diffusion and to explore whether or not distant vacancies or configurations with multiple vacancies affect PAC spectra significantly.
  PubDate: 2013-05-01
Evidence of magnetic broadening in Mössbauer spectra of superconducting FeTe_0.8S_0.2
- Abstract: Abstract Magnetic properties of the FeTe0.8S0.2 superconductor were studied by Mössbauer spectroscopy. Low-velocity Mössbauer spectra that were recorded in the temperature range from 5.7 K up to 300 K show a paramagnetic doublet with a broadening at temperatures below 77 K. The broadening can be explained by the appearance of a distribution of hyperfine magnetic fields due to the magnetic ordering of a part of the sample. The magnetically ordered fraction starts to decrease at temperatures below 20 K indicating a possible competition with the onsetting superconductive state.
  PubDate: 2013-05-01
Production of nuclear polarization of unstable nuclei via polarization transfer reactions
- Abstract: Abstract The polarized 20F(I π = 2 + , T 1/2 = 11.163 s), 24m Al(I π = 1 + , T 1/2 = 131.3 ms), 29P(I π = 1/2 + , T 1/2 = 4.142 s) and 41Sc(I π = 7/2−, T 1/2 = 596.3 ms) isotopes were produced by nuclear-polarization transfer reactions with polarized proton or deuteron beams. In the case of 29P isotope, we have produced the polarization by two reactions; 29Si( $\overrightarrow{p}$ ,n)29P and 28Si( $\overrightarrow{d}$ ,n)29P. The degree of nuclear polarization of those nuclei have been measured using the β-ray detected nuclear magnetic resonance method.
  PubDate: 2013-05-01
Whither HFI/NQI'
- Abstract: Abstract A brief review is given of the Hyperfine Interactions Conference series and, in particular, of the Joint meetings of the Hyperfine Interactions and Nuclear Quadrupole Interaction (HFI/NQI) Conferences, with respect to number of participants, contributed papers and participant countries. Trends are traced and recommendations are offered to attract a wider participation at future HFI/NQI conferences.
  PubDate: 2013-05-01
Preface
- PubDate: 2013-05-01
Conference organization
- PubDate: 2013-05-01
In memoriam Robert Blinc (1933–2011)
- PubDate: 2013-05-01
In memoriam Romain Coussement (1935–2012)
- PubDate: 2013-05-01
Study of hyperfine interactions in the tetragonal GdRh₂Si₂ using PAC spectroscopy
- Abstract: Abstract Hyperfine interactions were studied in the intermetallic compound GdRh2Si2 by perturbed angular correlation (PAC) technique using 181Hf(181Ta) probe nuclei. The measurements were performed in the temperature range 15–285 K. The PAC spectra above the antiferromagnetic ordering temperature of the GdRh2Si2 compound (T N ∼ 106 K), were analyzed using a model that included only electric quadrupole interactions. The observed major fraction was assigned to the 181Hf(181Ta) probe substituting the Gd atoms. The PAC spectra below Néel temperature were analyzed using combined electric quadrupole and magnetic dipole interactions. The Bhf value at Gd, measured at 15 K was found to be 1.4(1) T which, is smaller, when compared with the values obtained in this compound using other nuclear probes, 155Gd (Bhf ∼ 30 T) and 140Ce (Bhf ∼ 26 T). The present result using 181Hf(181Ta) probe is quite interesting since it shows that the contribution to Bhf at Gd due the host is smaller than other components which contribute to the hyperfine field. The temperature dependence of Bhf shows an anomalous behavior.
  PubDate: 2013-05-01
Magnetism of Fe in SrFe₂As₂: Local investigation by time differential perturbed angular distribution (TDPAD) spectroscopy
- Abstract: Abstract Employing the γ-ray perturbed angular distribution technique, we have measured the magnetic hyperfine field of 54Fe in tetragonal and orthorhombic structural phases of SrFe2As2. In the tetragonal phase, the magnetic response of 54Fe shows Curie-Weiss type local susceptibility, indicating the presence of localized moment on Fe. The temperature dependence of the hyperfine field of 54Fe reflects quasi-two dimensional first order magnetic transition at 200 K. Our data indicate that Fe moments in the magnetically ordered phase of SrFe2As2 may be canted out of the ab-plane.
  PubDate: 2013-05-01
TDPAC measurements in pure and Fe-doped In₂O₃
- Abstract: Abstract Measurements of the electric quadrupole interactions were used to characterize pure and Fe-doped In2O3 samples using perturbed γ-γ angular correlation (PAC) technique with 111In-111Cd radioactive probe. The samples of pure as well as 1 % and 5 % Fe-doped In2O3 were prepared by sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). The PAC measurements were carried out with a conventional fast-slow coincidence set-up using four BaF2 detectors as a function of temperature from 295 K to 1073 K. The powder XRD spectra analyzed with Rietveld method as well as SEM and EDS results showed that Fe-doped samples are homogeneous without any secondary iron oxide phases. The PAC spectra of pure and 1 % Fe-doped In2O3 show well-known characteristic quadrupole frequencies for the two non-equivalent sites in the bixbyte structure. The hyperfine parameters in these cases change little with temperature. For the 5 % Fe-doped sample however the PAC spectra changed significantly and a third frequency with large η appears.
  PubDate: 2013-05-01
Production of spin polarized ¹²N through heavy ion reactions
- Abstract: Abstract Production of spin polarized short-lived nucleus 12N (I π = 1 + , T 1/2 = 11 ms) using heavy ion reactions at intermediate energies has been performed. Typical polarization of about −25 % and +10 % through the projectile fragmentation Be(14N, 12N)X and the charge exchange CH2(12C, 12N)X processes, respectively, was obtained. The present study proved that the combination of a 12C beam and a proton target provides a fairly good quality of polarized 12N beam in terms of intensity and energy uniformity, and is promising for materials science use of 12N as a nuclear probe.
  PubDate: 2013-04-17