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

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

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

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

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

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

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)

Neutrino-oscillation experiments at the Gösgen nuclear power reactor

A search for neutrino oscillations has been conducted at the 2800-MW (thermal) nuclear power reactor in Gösgen (Switzerland), providing 5×10^20 electron antineutrinos per second. The energy spectrum of the antineutrinos was measured at three distances, 37.9, 45.9, and 64.7 m, from the reactor core. The detection of the neutrinos is based on the reaction ν¯e+p→e++n. Roughly 10^4 antineutrinos were registered at each of the three measuring positions. The measured spectra are analyzed in terms of a two-neutrino oscillation model and the results are represented as exclusion plots for the oscillation parameters Δm^2 and sin^2(2theta). Two analyses are performed: Analysis A relies exclusively on the data measured at the three different distances; analysis B combines the measured data with additional information, in particular with the reactor antineutrino spectrum as derived from independent β-spectroscopic measurements. Both analyses show that the data are consistent with the absence of neutrino oscillations, and rule out large regions of parameters (Δm2,theta). The resulting limits on the oscillation parameters are Δm^25 eV^2