Improvement of signal to noise ratio of ⁵⁷Mn in-beam Moessbauer spectroscopy by utilizing plastic scintillation counter

Parallel Plate Avalanche Counter (PPAC) Moessbauer resonance counter was used for 57XU of SPring-8 in Al metal at room temperature. A thin plastic scintillation counter was placed right in front of PPAC for β-ray detection. For 14 keV γ-ray, almost all γ-ray reached to PPAC. On the other hand, for β-ray, almost all β-ray detected by PPAC was also detected by the plastic detector, therefore β-ray derived noise was separated from PPAC signal by coincidence counting. Also, almost all β-ray derived noise can be removed by anticoincidence counting for the detector. It was clarified only 8.3% of counts at PPAC was Moessbauer resonant signal, and the rest of ∼92% was β-ray derived noise. By using anticoincidence counting, S/N ratio for Moessbauer resonant signal significantly improved from ∼10% to ∼200%. It was clarified that β-ray derived noise was one of the factors to reduce S/N ratio. (S.K.)