Interference parameters inγ-ray optics

Abstract

Calculations are given for the interference (or "screening") parameters $(LX) arising in low-energy y-ray optics. In y-ray emission, these parameters arise from the interaction of the emitted photon with the surrounding electron cloud of the atom, giving a phase shift to the emitted photon which depends on the multipolarity of the nuclear transition. In y-ray absorption experiments, the parameters specify the effects of the interference between photoelectron and internal-conversion electron absorption, and the interference betweeen nonresonant scattering from the atomic electrons and resonant scattering from the nucleus. These interference effects give rise to a dispersion term in the total cross section, thereby producing a small asymmety in the absorption spectrum and slightly shifting the center of the absorption line. These effects can be very important in determining precise isomer shifts and in analyzing Mossbauer tests of time-reversal invariance. We present calculated screening parameters for E1, M1, and E2 y-ray transitions, and we examine their dependences on the nuclear charge and the y-ray energy. We compare the results with the available experimental determinations.

Accurate Mössbauer line-shape measurements including interference inW182,Wagoner1, Mullen2, Schupp3 1993Phys. Rev. C7010View full textAdd to dashboardCite

“…The two theoretical interferenee values were -0.0117 [1] and -0.0122 [2], which are in agreement with our measured values to within experimental error. B. Iridium TABI E II.…”

“…The value for the interference parameter of -0.0071 (8) (2) is in good agreement with the theoretical values of -0.0071 [1] and -0.0069 [2], but has a large relative error of 11%,making it unsuitable for deciding on questions about the magnitude of interference efFects in TI experiments [4 -6].…”

“…All the Mossbauer thickness number t = f opn, , where f is the absorber recoilless fraction, e0 is the maximum resonant absorption cross section, and n is the number of Mossbauer isotopes per area in the absorber. The transmission interference parameter P is the value of primary concern to us and can be written as [1,3] p= pa+ pR, where Pc arises from interference between resonant p-ray absorption followed by internal conversion and inner-shell photoelectric absorption, and P~a rises from interference dioactive sources used were prepared at the University of Missouri Research Reactor facility, at a nominal fIux of 3 x 10 neutrons/(cm s). All the sources used were kept at =77 K throughout the duration of the experiments.…”

“…We were particularly interested in the Mossbauer interference parameter for transmission experiments, P, which appears in the resonance absorption cross section and introduces an asymmetry to the otherwise symmetric Mossbauer line shape [Eq. (1)]. The interference parameter arises from final state interference between nuclear and inner electron shell interactions [1 -3].…”

“…What is actually measured, however, is ri+PT, where PT is the TI interference parameter, and no means have yet been found to measure either g or PT independently. The practice has been to use theoretical values of PT [1,2], which come from the same theories from which the Mossbauer transmission interference parameter P is derived. Accordingly, measurements of P allow a means of testing the theories used to calculate PT, allowing one means of assessing the degree of confidence which should be placed on the PT values and hence on the TI experiments of which they are an integral part.…”