Synchrotron-Radiation-Based Mössbauer Spectroscopy

We have developed a new method that yields Mössbauer absorption spectra using synchrotron radiation (SR); this method is applicable for almost all Mössbauer nuclides including those that cannot be measured by previous methods using radioisotope (RI) sources. The Mössbauer spectrum of the 68.752 keV excited state of ${}^{73}\mathrm{Ge}$, which cannot be measured using a RI source, was measured using SR. Our results show that this method can be used to perform advanced Mössbauer spectroscopy measurements owing to the excellent features of SR.

Figure 1

Schematic drawing of experimental setup. A double-crystal Si(333) premonochromator was used to handle the high heat load of undulator radiation, and 68.752 keV radiation was obtained using a Si(111) monochromator, which removes the undesirable first harmonic radiation. The transmitter and scatterer were cooled in a cryostat, and the scatterer was moved in the triangle mode using a velocity transducer. The glancing angle of the incident radiation with respect to the surface of the scatterer is approximately 5°, and delayed emission from the irradiated surface of the scatterer was measured using a multielement Si-APD detector ($4\times 2$ APDs, each with a detection area of $3\times 5{\mathrm{mm}}^2$).

Figure 2

Mössbauer spectrum of ${}^{57}\mathrm{Fe}$ observed at 298 K using SR. A powder sample of $\alpha \mathrm{\text{−}}{\mathrm{Fe}}_2{\mathrm{O}}_3$ was used as the transmitter, and a Pd metal foil containing ${}^{57}\mathrm{Fe}$ (2%) was used as the scatterer. The solid line shows the fitted spectrum with Lorentz line shapes.

Figure 3

Time distribution of nuclear resonance scattering of SR by ${}^{73}\mathrm{Ge}$ in ${\mathrm{GeO}}_2$. The upward and downward triangles show measurement results obtained under resonance and off-resonance conditions, respectively. The measured resonance spectrum was fitted with an exponential function in the time interval of 8–19 ns in order to avoid the strong influence of prompt pulses.

Figure 4

Mössbauer spectrum of ${}^{73}\mathrm{Ge}$ measured using SR. A powder sample of ${\mathrm{Li}}_2{\mathrm{GeO}}_3$ was used as the transmitter, and a powder sample of ${\mathrm{GeO}}_2$ was used as the scatterer. The solid line shows the fitted spectrum described in the text.