Measurement of the double K-shell vacancy creation probability in the electron-capture decay of 55Fe with active-pixel detectors

AbstraktAbstract

Background: In electron-capture decay, a second K-shell vacancy is eventually created with a small probability. Measurements of the double-vacancy creation probability per K-shell electron capture PKK of various nuclei undergoing electron-capture decays have already been performed, but the statistical accuracy of PKK of several nuclides is still not satisfying. Purpose: The purpose of this experiment was to improve the statistical error of PKK in the decay of Fe-55 and to demonstrate the possibility of detecting double-vacancy creation events with position resolving pixel detectors. This enables angle resolved measurements. Method: For the first time, two active-pixel detectors (A,B) were used to detect satellite- and hypersatellite-line photons in coincidence either both in two clusters of triggered pixels in only one detector (A,B) or in both detectors (A∧B). PKK was determined for the two detectors regarded as one single, larger detector (PKK), for each detector separately (single-sided analysis: PKK,A⊻B), and for both detectors in coincidence (double-sided analysis: PKK,A∧B). Results: The result of the experiment is PKK=(1.531±0.079)×10−4 with a systematic error of ±0.023×10−4. This value is in agreement with the value previously measured by Campbell et al. of PKK=(1.3±0.2)×10−4. The asymmetry between the result of the single-sided analysis and the double-sided analysis is consistent with zero: (PKK,A⊻B−PKK,A∧B)/(PKK,A⊻B+PKK,A∧B)=−0.003±0.051. This supports the assumption that angular correlations between the two photons are negligible within the achieved level of statistical accuracy for the given angular acceptance of our detectors. Conclusion: One can conclude that hybrid photon counting pixel detectors can be used to measure angular correlations between the directions of emission of satellite and hypersatellite photons.

Background: In electron-capture decay, a second K-shell vacancy is eventually created with a small probability. Measurements of the double-vacancy creation probability per K-shell electron capture PKK of various nuclei undergoing electron-capture decays have already been performed, but the statistical accuracy of PKK of several nuclides is still not satisfying. Purpose: The purpose of this experiment was to improve the statistical error of PKK in the decay of Fe-55 and to demonstrate the possibility of detecting double-vacancy creation events with position resolving pixel detectors. This enables angle resolved measurements. Method: For the first time, two active-pixel detectors (A,B) were used to detect satellite- and hypersatellite-line photons in coincidence either both in two clusters of triggered pixels in only one detector (A,B) or in both detectors (A∧B). PKK was determined for the two detectors regarded as one single, larger detector (PKK), for each detector separately (single-sided analysis: PKK,A⊻B), and for both detectors in coincidence (double-sided analysis: PKK,A∧B). Results: The result of the experiment is PKK=(1.531±0.079)×10−4 with a systematic error of ±0.023×10−4. This value is in agreement with the value previously measured by Campbell et al. of PKK=(1.3±0.2)×10−4. The asymmetry between the result of the single-sided analysis and the double-sided analysis is consistent with zero: (PKK,A⊻B−PKK,A∧B)/(PKK,A⊻B+PKK,A∧B)=−0.003±0.051. This supports the assumption that angular correlations between the two photons are negligible within the achieved level of statistical accuracy for the given angular acceptance of our detectors. Conclusion: One can conclude that hybrid photon counting pixel detectors can be used to measure angular correlations between the directions of emission of satellite and hypersatellite photons.