A 62-cm active optics telescope model with a Shack-Hartmann wavefront analyzer was used to measure the mirror seeing effect. The degradation of the imaging quality due to the generation of microthermal convection was quantitatively evaluated from diurnal monitoring measurements over 90 days and nights. The dependence of mirror seeing on the temperature difference between the mirror and the ambient air and the effect of flushing flow to blow away the microthermal turbulence were measured.

No abstract

No abstract

Positron annihilation lifetime measurements were performed on polyethylene films [low-density polyethylene and ultra-high molecular weight polyethylene (UHMWPE)] with a thickness of 15–2000 μm using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long-lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

When analyzing positron annihilation lifetime spectra with multiple components using an exponential function with a single component, there is a difference between the experimental data and the fitted spectrum. Compensating for this difference causes a shift in the starting time (T 0) in the fitted spectrum. Previously, we applied single-component analysis to the positron lifetime spectrum of a defect-containing metal and confirmed the effectiveness of the shift in T 0 (ΔT 0) for defect analysis. To optimally use the T 0 variation for defect analysis, however, it is necessary to minimize the drift in the positron lifetime spectrum due to the temporal instability of the photomultiplier tube and high-voltage power supply. In this study, we report significant suppression of the drift by using dual start/stop data acquisition (dual acquisition), which employs each of the two γ-ray detectors to acquire start and stop signals.