306 research outputs found
On the theory of resonant scattering of gamma rays by nuclei bound in crystals
An attempt is made in the present paper to give a
physical description of the process in which a gamma
quantum is resonantly scattered or absorbed by nuclei
bound in a crystal structure. The discussion includes
a description of the time development of these
processes as well as a critical study of the limits imposed
upon such a description by the laws of quantum
mechanics.(1
Quasi-Moessbauer effect in two dimensions
Expressions for the absorption spectrum of a nucleus in a three- and a
two-dimensional crystal respectively are obtained analytically at zero and at
finite temperature respectively. It is found that for finite temperature in two
dimensions the Moessbauer effect vanishes but is replaced by what we call a
Quasi-Moessbauer effect. Possibilities to identify two-dimensional elastic
behavior are discussed.Comment: 18 pages, 5 figures, notation simplifie
General aspects of nuclear hyperfine interactions in salts of the rare earths
Most of the experimental studies of recoilless nuclear resonance absorption performed until now have been using the 14.4-keV transition in Fe57. The low energy of this transition, the long lifetime of the relevant nuclear level, the long lifetime of the parent isotope, and, last but not least, the vast number of problems which could be tackled, made Fe57 the favorite isotope in the entire field covered by this conference. In increasing numbers, however, experimental and theoretical studies are progressing which involve nuclear isotopes other than Fe57
Electronic shielding by closed shells in salts of thulium
Electronic shielding by closed electron shells has been investigated in salts of trivalent thulium, by measuring the temperature dependence of the nuclear quadrupole splitting of the 8.42-keV gamma transition in Tm169. The measurements were performed by using the technique of recoilless nuclear resonance absorption. The nuclear quadrupole interaction was studied for Tm3+ ions in thulium ethyl sulfate, thulium oxide, and thulium trifluoride within a temperature range from 9.6 to 1970°K. The interpretation of the experimental data in terms of the contributions of distorted closed electron shells to the quadrupole interaction yields values for electronic shielding factors. The results lead to amounts of 10% or less for the atomic Sternheimer factor RQ. The experiments also reveal substantial shielding of the 4f electrons from the crystal electric field, expressed by the shielding factor σ2. Values of 250 and 130 are obtained for the ratio (1-γ∞)/(1-σ2) for thulium ethyl sulfate and thulium oxide, respectively, where γ∞ is the lattice Sternheimer factor
M\"ossbauer Antineutrinos: Recoilless Resonant Emission and Absorption of Electron Antineutrinos
Basic questions concerning phononless resonant capture of monoenergetic
electron antineutrinos (M\"ossbauer antineutrinos) emitted in bound-state
beta-decay in the 3H - 3He system are discussed. It is shown that lattice
expansion and contraction after the transformation of the nucleus will
drastically reduce the probability of phononless transitions and that various
solid-state effects will cause large line broadening. As a possible
alternative, the rare-earth system 163Ho - 163Dy is favoured.
M\"ossbauer-antineutrino experiments could be used to gain new and deep
insights into several basic problems in neutrino physics
Pseudoquadrupole shift of gamma resonance spectra
In most recoilless gamma-ray resonance experiments the magnetic-dipole and electric-quadrupole hyperfine interaction do not cause any shift of the center of gravity of the velocity spectrum. This is usually related to the fact that the trace of the hyperfine-interaction Hamiltonian is zero. Nevertheless a large shift can be caused under proper conditions by a magnetic hyperfine interaction in second order, the so-called "pseudoquadrupole" interaction.(1) This paper reports the first observation of the pseudoquadrupole shift of gamma lines.(2
Generation of Long-Lived Isomeric States via Bremsstrahlung Irradiation
A method to generate long-lived isomeric states effectively for Mossbauer
applications is reported. We demonstrate that this method is better and easier
to provide highly sensitive Mossbauer effect of long-lived isomers (>1ms) such
as 103Rh. Excitation of (gamma,gamma) process by synchrotron radiation is
painful due mainly to their limited linewidth. Instead,(gamma,gamma') process
of bremsstrahlung excitation is applied to create these long-lived isomers.
Isomers of 45Sc, 107Ag, 109Ag, and 103Rh have been generated from this method.
Among them, 103Rh is the only one that we have obtained the gravitational
effect at room temperature.Comment: ICAME 05 conference repor
Electronic shielding of the crystalline field in thulium ethyl sulfate
The method of recoilless nuclear resonance absorption of gamma radiation was employed in investigating the temperature dependence of the nuclear quadrupole interaction in the 8.4-keV level of Tm169 in thulium ethyl sulfate, Tm(C2H5SO4)3•9H2O. The experiment reveals a strong influence of electronic shielding resulting from the polarization induced in the closed electron shells by the crystalline electric field
Search for neutrino oscillations at a fission reactor
The energy spectrum of neutrinos from a fission reactor was studied with the aim of gaining information on neutrino oscillations. The well-shielded detector was set up at a fixed position of 8.76 m from the pointlike core of the Laue-Langevin reactor in an antineutrino flux of 9.8×10^11 cm^-2 s^-1. The target protons in the reaction ν̅ep→e+n were provided by liquid-scintillator counters (total volume of 377 l) which also served as positron detectors. The product neutrons moderated in the scintillator were detected by 3He wire chambers. A coincidence signature was required between the prompt positron and the delayed neutron events. The positron energy resolution was 18% full width at half maximum at 0.91 MeV. The signal-to-background ratio was better than 1: 1 between 2 and 6 MeV positron energy. At a counting rate of 1.58 counts per hour, 4890±180 neutrino-induced events were detected. The shape of the measured positron spectrum was analyzed in terms of the parameters Δ2 and sin22θ for two-neutrino oscillations. The experimental data are consistent with no oscillations. An upper limit of 0.15 eV2 (90% C.L.) for the mass-squared differences Δ2 of the neutrinos was obtained, assuming maximum mixing of the two-neutrino states. The ratio of the measured to the expected integral yield of positrons assuming no osciliations was determined to be ∫Yexp/∫Yth=0.955±0.035(statistical)±0.110(systematic)
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