共查询到20条相似文献,搜索用时 156 毫秒
1.
A. V. Tsvyashchenko A. V. Nikolaev A. I. Velichkov A. V. Salamatin L. N. Fomicheva G. K. Ryasny A. A. Sorokin O. I. Kochetov M. Budzynski 《Journal of Experimental and Theoretical Physics》2010,111(4):627-634
We use the time-differential perturbed angular correlation technique to study nuclear electric quadupole hyperfine interactions
of probe 111Cd nuclei in cerium lattice sites at room temperature under pressures up to 8 GPa. We have found that the well known γ → α
phase transition in cerium is not isostructural. In α-Ce, the probe 111Cd nuclei reveal a quadrupole electron charge density component that is absent in γ-Ce. The hidden spacial structure of electronic
quadrupoles in α-Ce is triple-q antiferroquadrupolar, as was suggested in [14]. We relate our findings to the current understanding
of the γ → α phase transition and also report on nuclear quadrupole interactions in other high-pressure phases of cerium:
α″ (C2/m space symmetry) and α′ (α-U structure). 相似文献
2.
The hyperfine interaction of111Cd probes in preoxidized and α-irradiated Ag0.94Cd0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were
distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen
and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature
and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of111Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very
similar to the ones observed after α-irradiation. 相似文献
3.
A. A. Sorokin E. N. Shirani L. G. Shpinkova Z. Z. Akselrod B. A. Komissarova G. K. Ryasny S. I. Semyonov G. A. Denisenko I. P. Zibrov A. R. Buev 《Hyperfine Interactions》1992,73(3-4):337-346
The electric quadrupole interaction of181Ta in Y2O3, CuO, and in the YBa2Cu3O7−δ high temperature superconductors, doped with181Hf, has been studied by the time-differential perturbed angular correlation method (TDPAC). In Y2O3, two distinct fractions of the probe nuclei were detected, which were attributed to the substitutional positions at the two
cation sites in the lattice. In CuO, and in the ceramic samples, broad distributions of quadrupole frequencies were observed.
Possible configurations of the probe nuclei in these substances are discussed. 相似文献
4.
A. L. Lapolli A. W. Carbonari R. N. Saxena J. Mestnik-Filho 《Hyperfine Interactions》2004,158(1-4):157-161
Perturbed gamma–gamma angular correlation technique was used to measure the hyperfine interactions in the compound GdNiIn
using the 111InCd → and 140La140Ce probe nuclei at the In and Gd sites, respectively. A unique quadrupole frequency with asymmetry parameter η = 0.78 was observed for 111Cd probe at In sites for the measurements above Curie temperature. Below T
C
, the spectra for 111Cd show combined magnetic dipole and electric quadrupole interaction. Below 85 K, a unique magnetic interaction is observed
at 140Ce. A linear relationship between the saturated magnetic hyperfine field and the magnetic transition temperature was observed
for both probes, indicating that the main contribution to the mhf comes from the conduction electron polarization. 相似文献
5.
Excitation functions for the production of68Ga,67Ga,66Ga,65Ga +65Zn and61Cu fromα-induced reactions in natural copper have been measured in the energy range ≈ 10–40 MeV using the stacked foil technique.
A stack of nine copper foils was irradiated by a 40 MeVα-beam. Theγ-rays emitted from the irradiated samples were recorded. Excitation functions have also been calculated theoretically using
a statistical model with and without the inclusion of pre-equilibrium emission of particles. Pre-equilibrium component simulated
by exciton model shows that the inclusion of pre-equilibrium emission gives better agreement between experimental and theoretical
excitation functions. Pre-equilibrium fraction depends on the incident energy and the target mass number. 相似文献
6.
The proton motion in bulk and highly drawn fiber polyamide-6 has been studied by field cycling relaxometry and proton line
shape measurements. The dips in theT
1 dispersion allowed for the determination of the14N quadrupole coupling tensor. The fact that only one set of14N nuclear quadrupole resonance lines, has been found shows that all N-H groups in nylon-6 are H-bonded. A striking difference
in the main line width transition and the low-frequency molecular dynamics has been observed between a slowly cooled “bulk”
polyamide-6 sample and a rapidly cooled and highly drawn “fiber” sample by wide line proton nuclear magnetic resonance line
shape and spin-lattice relaxation time measurements. This result is consistent with the picture that shearing melt processing
procedures, such as spinning, plant stable and long-lived crystallization nuclei into the amorphous phase which impose additional
motional constraints on the surroundings and inhibit the self-diffusion process. 相似文献
7.
G. Lévai J. Cseh P. Van Isacker 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):305-308
A supersymmetry scheme is proposed for nuclear cluster systems. The bosonic sector of the superalgebra describes the relative
motion of the clusters, while its fermionic sector is associated with their internal structure. An example of core + α configurations
is discussed in which the core is a p-shell nucleus and the underlying superalgebra is U(4|12). The α-cluster states of the nuclei 20Ne and 19F are analyzed and correlations between their spectra, electric quadrupole transitions, and one-nucleon transfer reactions
are interpreted in terms of U(4|12) supersymmetry.
Received: 14 September 2001 / Accepted: 26 October 2001 相似文献
8.
Rais A. Yousif A. A. Gismelseed A. Elzain M. E. Al Rawas A. Al-Omari I. A. 《Hyperfine Interactions》2004,158(1-4):229-233
PAC measurements on 111In(111Cd) implanted and thermally treated α-Fe have shown an indication for a cubic defect with the 111Cd probe in the centre of it. The measured room temperature (R. T.) magnetic hyperfine fields are B
hf1 = −38.4(8) T for substitution and B
hf2 = +11.5(3) T for the cubic defect. Additionally, probes with pure quadrupole frequency distributions were observed, which
are incorporated in surface contaminations. 相似文献
9.
A. A. Sorokin G. K. Ryasny B. A. Komissarova L. N. Fomicheva A. V. Tsvyashchenko S. M. Nikitin 《Hyperfine Interactions》2006,171(1-3):269-275
The perturbed angular correlation (PAC) measurements with the 111In-111Cd nuclear probe embedded into the lattice of the cubic (C15) Laves compound ZrZn2 showed that 111Cd nuclei experienced an axially symmetric electric quadrupole interaction with a frequency ν
Q
= 132.4 MHz at room temperature. The samples were synthesized and doped with the probe at a pressure 8 GPa. The temperature
dependence of ν
Q
was shown to be linear: ν
Q
(T) = 147(1 − 0.033 T) MHz. Since the value of ν
Q
is very close to that known for 111Cd in the lattice of Zn, we have checked if it could be assigned to residual Zn metal in the sample. For the Zn sample melted
and doped with 111In at 8 GPa we have obtained ν
Q
= 117.3 MHz at 300 K and 127 MHz at 80 K – both values considerably lower than that for 111In doped Zn samples prepared at an ambient pressure. These data, and the fact that ν
Q
(T) in Zn is known to follow the T
3/2 law, allow to attribute the ν
Q
value quoted above to 111Cd nuclei at the substitutional sites with tetrahedral symmetry in the Zn sublattice of ZrZn2. 相似文献
10.
Gary L. Catchen 《Hyperfine Interactions》1989,52(1):65-78
Calculations and formulae are presented for the purpose of understanding and analyzing Perturbed Angular Correlation (PAC)
experiments that use spin-two and spin-three probe nuclei. For electric quadrupole interactions of probe nuclei in a polycrystalline
source with non-axially symmetric electric field gradients, the interaction frequencies and perturbation functions for spin-two
and spin-three nuclei differ qualitatively and quantitatively from those for spin-five-halves nuclei. These differences result
primarily because them-states of integral-spin nuclei are nondegenerate in an asymmetric electric field gradient. To help the experimenter deal
with the added complexity of the integral-spin casesI=2 and 3, closed-form expressions are provided for the energy eigenvalues and the eigenvectors as a function of the asymmetry
parameter η. To deal with the problem of calculating the perturbation functionsG
kk
(t) for η>0, the summation overm-state quantum numbers is formulated in terms ofa
n′,n
(k)
-coefficients. These coefficients are analogous to theS
kn
-coefficients used in the case for η=0. To illustrate the differences between the half-integral-spin caseI=5/2 and the integral-spin casesI=2 and 3, energy difference diagrams anda
n′,n′
(2)
diagrams are presented and discussed. 相似文献
11.
Stacked foil activation technique and Ge(Li) gamma ray spectroscopy have been used for the measurement of excitation functions
of197Au(α,xn) (x=1−3),197Au(α,2pn) and197Au(α,αn) reactions up to 50 MeV. The experimental cross-sections were compared with the predictions of pre-equilibrium hybrid model,
as well as with the more recent index model. A general agreement was found in all reactions using initial exciton numbern
0=4(4p0h) except for197Au(α,n) reaction, where index model gives fairly good agreement withn
0=5(5p0h). 相似文献
12.
J. Kesten 《Hyperfine Interactions》1989,52(1):17-27
Radioactive111In+ ions were implanted into an α-Al2O3 single crystal. The hyperfine parameters of111Cd at substitutional Al lattice sites were identified by measuring the perturbed angular correlation for different sample
orientations. The electric field gradientV
zz
=1.04(17)·1022V/m2 was obtained from the quadrupole coupling constant. This result is compared with the efg values of27Al in α-alumina and111Cd in α-Fe2O3, which also has the corundum structure. Two additional fractions with broad frequency distributions were observed, one of
which is attributed to111Cd atoms in a strongly distorted Al2O3-lattice. 相似文献
13.
Shengyun Zhu Shennan Zheng Anli Li Hangchen Huang Hongshan Du Honglin Din Donghong Li 《Hyperfine Interactions》1990,62(3):213-218
HighT
c superconductivity in the YBaCuO superconductor has been investigated through the quadrupole interaction of the probe nuclei99Tc. The quadrupole interactions were measured by the TDPAC method from 77 to 296 K. The probe nuclei99Tc were introduced into the YBaCuO superconducting specimen by diffusion. The derived electric quadrupole interaction parameters
show that the probe nuclei are subject to a unique EFG interaction and occupy a substitutional lattice site in the YBaCuO
superconductor. A strong EFG of 1019 V/cm2 was observed. The temperature dependence of the EFG exhibits a linear decrease with temperature increase. Anomalies of both
EFG and ν were found in the superconducting transition temperature region. The role of the oxygen vacancies in the Cu−O chains
is discussed. 相似文献
14.
F. P. Heßberger S. Antalic B. Streicher S. Hofmann D. Ackermann B. Kindler I. Kojouharov P. Kuusiniemi M. Leino B. Lommel R. Mann K. Nishio S. Saro B. Sulignano 《The European Physical Journal A - Hadrons and Nuclei》2005,26(2):233-239
The decay of odd-mass mendelevium isotopes ( A = 247-255) has been studied by means of α-γ spectroscopy. Strong evidence for a small α branch in the decay of 253Md was found. γ lines in coincidence with α-decays of 247, 249, 251, 253Md have been observed for the first time. Levels in the einsteinium daughter nuclei were assigned on the basis of α-γ coincidence
measurements. An energy systematics of the 7/2-[514] Nilsson level could be established, showing a correlation with the deformation parameter β2 of the corresponding nuclei. The results are compared with theoretical predictions 相似文献
15.
W. von Oertzen 《The European Physical Journal A - Hadrons and Nuclei》2006,29(2):133-139
The systematics for binding energies per α-particle in N = Z nuclei, E
Bα/N
α, are studied up to 164Pb. It is shown that, although a geometrical model can be used to explain the systematics for light nuclei, the binding energy
per α-particle exhibits structures which are due to the well-known shells of the mean field of nucleons in nuclei. The overall
dependence of E
Bα/N
α on N
α in N = Z nuclei (for the ground-state masses) can be described in a liquid-drop model of α-particles. Conditions for a phase change
with the formation of an α-particle condensate, a dilute Bose gas in excited compound nuclei are discussed for E
Bα/N
α = 0, at the thresholds. This is achieved when the binding energy per nucleon in nuclei is equal to or smaller than in the
α-cluster. At somewhat smaller excitation energies the appearance of a Bose gas with a closed-shell core (N = Z, e.g. of 40Ca) is proposed within the same concept. The experimental observation of the decay of such condensed α-particle states is
proposed with the coherent emission of several correlated α-particles not described by the Hauser-Feshbach approach for compound-nucleus
decay. This decay will be observed by the emission of unbound resonances in the form of 8Be and 12C * (0+
2) clusters. 相似文献
16.
M. Hunyadi A. M. van den Berg B. Davids M. N. Harakeh M. A. de Huu H. J. Wörtche M. Csatlós J. Gulyás A. Krasznahorkay D. Sohler U. Garg M. Fujiwara N. Blasi 《Physics of Atomic Nuclei》2007,70(8):1407-1414
The direct and statistical neutron decay of the isoscalar giant dipole resonance has been studied in 90Zr, 116Sn, and 208Pb using the (α, α’ n) reaction at a bombarding energy of 200 MeV. The spectra of fast decay neutrons populating valence hole states of the Z, N − 1 nuclei were analyzed, and estimates for the branching ratios were determined. The observation of the nucleon-direct-decay
channels helped to select giant-resonance strengths and suppress the underlying background and continuum, which led to an
indication of the existence of a new mode with L = 2 character, presumably the overtone of the isoscalar giant quadrupole resonance.
The text was submitted by the authors in English. 相似文献
17.
A. A. Ogloblin S. A. Goncharov T. L. Belyaeva A. S. Demyanova 《Physics of Atomic Nuclei》2006,69(7):1149-1154
Recently, it was supposed the nα light nuclei may have structures resembling the diluted gas of α particles which could be considered as Bose-Einstein condensate (αBEC) in nuclear systems. At the present time, the only more or less definite candidate for an αBEC state predicted by theory is the second 0+ state of 12C (E = 7.65 MeV) located near the threshold 12C → 3α. We discuss several possible experimental approaches to study the properties of interest of the 7.65-MeV level of 12C. Among them are shift of the positions of the rainbow minima in the inelastic scattering to this level, extraction of the
empirical inelastic form factor from the α and 3He scattering and its comparison with theoretical predictions, and getting information on the 8Be transfer reaction form factor. The conclusion was drawn that new measurements of 12C(α, α′) 12C(7.65) inelastic scattering at ∼120 MeV in the full angular range would be most adequate to solving the problem. The possibility
of observation of αBEC effects in heavier nα nuclei is also discussed. In particular, 112Ba is of great interest owing to possible existence of an α-particle “halo” outside the Z = N = 50 core.
The text was submitted by the authors in English. 相似文献
18.
S. Connell K. Bharuth-Ram H. Appel J. P. F. Sellschop M. Stemmet 《Hyperfine Interactions》1987,36(3-4):185-200
19F has been used to probe the structure of the diamond lattice. The measurements were performed via the time differential perturbed
angular distribution (TDPAD) technique applied to the 197 keV state (τ=128 ns,Q=0.10 b) of19F. The nuclei were excited and recoil implanted into an oriented diamond using a (p,p′γ) reaction initiated by a pulsed 4
MeV proton beam. Model functions simulating a variety of residence sites for the probe ions in a single crystal were developed
for the analysis of the data. The data implies the formation of two molecular types, or sites within the lattice, with possibly
a third radiation damage component. 相似文献
19.
F.P. Heßberger S. Hofmann D. Ackermann 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):365-370
Radium isotopes with mass numbers from 209 to 212 have been produced by heavy-ion fusion reactions 204Pb( 12C, xn) 216-Ra. Radioactive decay properties were investigated by means of α- and α-γ-spectroscopy after in-flight separation of the evaporation
residues from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si detector.
For the even-even nuclei 210,212Ra we identified α transitions into the first-excited 2+-state of the daughter nuclei 206,208Rn. Weak α transitions into excited levels of the odd-A daughter nuclei 205,207Rn were also observed.
Received: 19 August 2002 / Accepted: 6 November 2002 / Published online: 18 February 2003
RID="a"
ID="a"e-mail: f.p.hessberger@gsi.de
Communicated by D. Guerreau 相似文献
20.
Summary Capacitance-voltage measurements have been carried out onp-type ɛ-GaSe single crystal ∥c in the temperature range 300 to 360 K, with applied voltages of -1, 0 and +1 V. TheC-V measurements in this temperature range have shown a shift in capacitanceC and conductanceG to the higher values with an increase in temperature. The depletion layer widthW, the Debye length LD and the doping densityN
α
have been worked out and plots ofN
α
vs. W have shown a decrease inW with an increase in temperature. The plots of LD
vs. N
α
vary as 1/Nα1/2, which gives NαLD ⋍ 3.3 × 1011 charges/m2 for doping density of 1016m−3. The values ofG at different temperatures have been used to obtain the activation energies, which are found to be ΔE ⋍ 0.11 eV for -1 and
+1 V applied voltages, and ΔE ⋍ 0.06 eV for zero volt.
The authors of this paper have agreed to not receive the proofs for correction. 相似文献