Remarkable improvement of the signal-to-noise ratio of 57Mn/57Fe in-beam Mossbauer spectroscopy

In-beam Mossbauer spectroscopy utilizing unstable Mn-57 beams is a powerful method to extract physical and chemical properties at the atomic scale. A parallel plate avalanche counter (PPAC), optimized to detect conversion electrons generated by the Mossbauer effect, can be employed to suppress higher-energy background gamma rays. However, beta rays are emitted by the Mn-57 parent nuclei of Fe-57, which can significantly degrade the spectrum quality. In the present work, we have developed a new anti-coincidence-detection system with a thin plastic scintillation counter (0.5 mmt), which can be used to detect beta rays and reject them from the recorded PPAC events. To demonstrate the anti-coincidence system, we carried out Mossbauer spectroscopy utilizing Mn-57 nuclei that were implanted into a non-magnetic aluminum metal plate at room temperature. Using the anti-coincidence method, we obtained a typical Mossbauer spectrum of high quality, despite a very low number of implanted Mn-57 atoms, of similar to 5 x 10(9). The signal to noise ratio of the obtained spectrum was increased remarkably, and the relative peak height above the baseline increased from 10% to 220% using the anti-coincidence method. The developed detection system is applicable to investigation of in situ properties, and avoids the potentially problematic agglomeration of probes in a sample. (C) 2010 Elsevier B.V. All rights reserved.