Delayed avalanches in Multi-Pixel Photon Counters

Hamamatsu Photonics introduced a new generation of their Multi-Pixel Photon Counters in 2013 with significantly reduced after-pulsing rate. In this paper, we investigate the causes of after-pulsing by testing pre-2013 and post-2013 devices using laser light ranging from 405 to 820nm. Doing so we investigate the possibility that afterpulsing is also due to optical photons produced in the avalanche rather than to impurities trapping charged carriers produced in the avalanches and releasing them at a later time. For pre-2013 devices, we observe avalanches delayed by ns to several 100~ns at 637, 777nm and 820 nm demonstrating that holes created in the zero field region of the silicon bulk can diffuse back to the high field region triggering delayed avalanches. On the other hand post-2013 exhibit no delayed avalanches beyond 100~ns at 777nm. We also confirm that post-2013 devices exhibit about 25 times lower after-pulsing. Taken together, our measurements show that the absorption of photons from the avalanche in the bulk of the silicon and the subsequent hole diffusion back to the junction was a significant source of after-pulse for the pre-2013 devices. Hamamatsu appears to have fixed this problem in 2013 following the preliminary release of our results. We also show that even at short wavelength the timing distribution exhibit tails in the sub-nanosecond range that may impair the MPPC timing performances.Comment: Submitted to JINST, 14 pages, 16 figure

保育者効力感と親からの自立

保育者効力感と親からの自立の関係を調べるために、保育者効力感尺度に手を加えて、指導力感と援助力感の2因子を得た。親からの自立に関しては、評定尺度、自由記述、自立に関連する日常生活の行動などを調査した。調査対象は、保育科の学生である。保育者効力感尺度の回答をみると、子どもの状況に応じて、臨機応変に対応することには、自信がないようである。また、親からの自立に関しては、自立していないと評定している者が多い。日常行動においても、かなり親に依存して生活しているようである。指導力感と親からの自立の評定に関しては、プラスの相関が見られた。また、指導力感の高いほうが、低いほうに比べて、食事を作る、嫌いなものでも食べるなどの割合が高く、アルバイトの収入と時間、自宅学習時間などが多い傾向が見られた。これらから、保育者養成に日常生活の訓練が必要なことを考察した