ABSTRACT
Crystals of metal hexachlorides Cs2MCl6 (M = Hf or Zr) have recently emerged as promising materials for scintillation applications due to their excellent energy resolution. In this work, we investigated the crystal structure and scintillation properties of Cs2HfCl6 and Cs2ZrCl6 crystals in the broad temperature range from 9 to 300 K. X-ray diffraction data confirmed the same cubic structure (space group Fm3m) for Cs2HfCl6 and Cs2ZrCl6 over the entire examined temperature range. The room temperature scintillation light yield of Cs2HfCl6 excited with a 137Cs γ-source is measured to be 24 800 photons per MeV, while Cs2ZrCl6 exhibits 33 900 photons per MeV resulting in energy resolutions of 5.3% and 4.5%, respectively. The alpha-to-beta ratio determined at room temperature for 5.5 MeV α-particles from an 241Am source is equal to 0.39 for Cs2HfCl6 and 0.35 for Cs2ZrCl6. The measurements of scintillation decay curves revealed complex kinetics due to delayed recombination processes. A tangible enhancement of the scintillation yield with heating is observed in the 125-150 K range. This effect is a manifestation of negative thermal quenching explained by thermal activation of trapped carriers. A model of the emission centre is proposed that consistently explains the observed changes of emission intensity with temperature in the crystals under study.
ABSTRACT
OBJECTIVE: Both heart rate (HR) monitoring and detection and description of fetal movements provide essential information of the integrity of in utero development and fetal wellbeing. Our previously described method to identify movements from multichannel magnetocardiographic (MCG) recordings lacks of reliability in some cases. This work is aimed at the improvement of fetal movement detection by means of an advanced signal processing and validation strategy. APPROACH: The previously proposed methodology of fetal body movement detection from MCG recordings using single space angle (SSA), min-max amplitude (MMA) and a measure of the overall signal strength across (RSS) was extended by moving correlation coefficient (MCC). The methodology was developed with respect to the discrimination between active and quiet sleep, validated by testing its coupling with HR accelerations in a total of 137 recordings lasting 30 min from 98 fetuses aged 34-38 weeks of gestation (WGA) of normal pregnancy. MAIN RESULTS: The developed algorithm improves the reliable automatic detection of fetal body movements independent of the fetal sleep states and their changes in the individual MCG recordings. In the fetuses aged 34-38 WGA 94% of 15 × 15 HR accelerations were coupled with detected movements. The visual inspection of the movement graphs of 30 fetuses aged 20-32 WGA supports the transferability of the movement detector to this age. In four subjects MCG-based movement detection and maternal report on percepted fetal movements were consistent. SIGNIFICANCE: The presented methodology allows the parallel automatic acquisition of precise fetal heart rate variability (HRV) indices based on subsequent beat intervals and of fetal body movements from MCG recordings during late 2nd and 3rd trimester. Potential advantages of parallel monitoring of fetal HRV and movements using MCG compared to established ultrasound technology should be investigated in subsequent studies with respect to the identification of fetuses at risk.
Subject(s)
Fetus/physiology , Magnetocardiography , Movement , Signal Processing, Computer-Assisted , Automation , Female , Humans , Mothers , PregnancyABSTRACT
A new reaction mechanism of violent reseparation of a heavy nucleus-nucleus system, 197Au + 197Au, into three or four massive fragments in collisions at 15 MeV/nucleon has been observed. After reseparation, the fragments are almost exactly aligned, thus showing a very short time scale of the reseparation process, of about 70-80 fm/c.