Precision measurements of recoil-free fraction and interference with hundred Curie sources

Wagoner, R. A.; Bullard, B. R.; Mullen, J. G.; Schupp, G.

doi:10.1007/bf02320300

Cited by 6 publications

(3 citation statements)

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“…The thickness of the absorber and the SRSA were taken as known values from previous high-precision measurements. 11,12 Additionally, we have shown that, provided the actual absorber thickness and SRSA are constant, the elastic scattering fraction does not change for small inaccuracies in the thickness number of the absorber or the source. That is, using a slightly inaccurate value for one of these parameters will affect the recoilless fraction measured in both the before and after positions, but the elastic scattering fraction will be unaffected.…”

Section: Experimental Methods and Apparatusmentioning

confidence: 84%

“…We oscillated a resonant absorber, a natural tungsten foil 2 mils thick, between the sample crystal and the detector. A line shape analysis of each Mössbauer spectrum, based on an analytic expansion of the transmission integral, [8][9][10][11][12] determined the recoilless fraction of the photon beam after scattering from the sample. The Mössbauer line shape depends on the thickness of the absorber, the SRSA in the source, the recoilless fraction of the source, the width of the transition, and the number of counts collected.…”

Section: Experimental Methods and Apparatusmentioning

confidence: 99%

“…7 In addition, it allows us to fit our spectra to the true line shape of the transition, rather than assuming a Lorentzian shape, which leads to errors in the measured elastic scattering fraction in on-and off-resonance measurements and even erroneous Debye temperatures. [8][9][10][11][12][13][14] As a source decays, absorber nuclei build up in the source, and source resonance self-absorption ͑SRSA͒ begins to distort the shape of the observed Mössbauer line. We used sources for only 1 week, during which SRSA is negligible.…”

Section: Introductionmentioning

confidence: 99%

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Debye-Waller factors of alkali halides

1998

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Using very-high-intensity (ϳ70 Ci͒ 183 Ta Mössbauer sources, we have measured the Debye-Waller factors ͑DWF's͒ of sodium chloride, potassium chloride, and potassium bromide single crystals for several of the (h00) and (nnn) Bragg reflections. We have used an approach which properly accounts for thermal expansion over the temperature range of our experiment, from 90 K to 900 K, about 100 K below the melting point of our crystals. We have found that a procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and our procedure does not require empirical parameters to account for the effects of thermal expansion. Additionally, we find three items of significance. Contrary to earlier results, we observe that the cations and the anions have identical DWF's in NaCl and also in KBr. We observe terms in the expansion of the DWF exponential which are quartic in the scattering wave vector Q ជ in NaCl and KCl, with some evidence for a Q 4 term in KBr. The size of the Q 4 contribution is reported and varies with the direction of momentum transfer. We also observe that the Debye temperature and the coefficient of the anharmonic Q 2 term also vary with the direction of momentum transfer. We believe our data are the definitive evidence for a nonspherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the ͓h00͔ direction than in the ͓nnn͔ direction, contrary to the commonly held view of crystallographers that the most general form of the mean-square thermal motion is of an ellipsoid shape.

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Section: Experimental Methods and Apparatusmentioning

confidence: 84%