Energy response of X-rays under high flux conditions using a thin APD for the energy range of 6–33 keV

This paper reports on the demonstration of a high-rate energy measurement technique using a thin depletion layer silicon avalanche photodiode (Si-APD). A dedicated amplitude-to-time converter is developed to realize simultaneous energy and timing measurement in a high rate condition. The energy response of the system is systematically studied by using monochromatic X-ray beam with an incident energy ranging from 6 to 33 keV. The obtained energy spectra contain clear peaks and tail distributions. The peak fraction monotonously decreases as the incident photon energy increases. This phenomenon can be explained by considering the distribution of the energy deposit in silicon, which is investigated by using a Monte Carlo simulation

A scalable quantum computer with an ultranarrow optical transition of ultracold neutral atoms in an optical lattice

We propose a new quantum-computing scheme using ultracold neutral ytterbium atoms in an optical lattice. The nuclear Zeeman sublevels define a qubit. This choice avoids the natural phase evolution due to the magnetic dipole interaction between qubits. The Zeeman sublevels with large magnetic moments in the long-lived metastable state are also exploited to address individual atoms and to construct a controlled-multiqubit gate. Estimated parameters required for this scheme show that this proposal is scalable and experimentally feasible.Comment: 6 pages, 6 figure

Extra centrosomes and/or chromosomes prolong mitosis in human cells

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Cell Biology 10 (2008): 748-751, doi:10.1038/ncb1738.Using laser microsurgery and cell fusion we have explored how additional centrosomes and/or chromosomes influence the duration of mitosis in human cells. We find that doubling the chromosome number adds ~10 minutes to a 20 minute division while doubling the number of centrosomes adds ~30 minutes more, and extra centrosomes and/or chromosomes prolong mitosis by delaying satisfaction of the spindle assembly checkpoint. Thus mitosis can be prolonged by non genetic means and extra chromosomes and centrosomes likely contribute to the elevated mitotic index seen in many tumors.This work was supported by National Institutes of General Medical Sciences grants 40198 (to C.L.R.) and 59363 (to A.K.)

SiPM module for the ACME III electron EDM search

This report shows the design and the performance of a large area Silicon Photomultiplier (SiPM) module developed detection of fluorescent light emitted from a 10 cm scale volume. The module was optimized for the planned ACME III electron electric dipole moment (eEDM) search, which will be a powerful probe for the existence of physics beyond the Standard Model of particle physics. The ACME experiment searched for the eEDM with the world's highest sensitivity using cold ThO polar molecules (ACME II). In ACME III, SiPMs will be used for detection of fluorescent photons (the fundamental signal of the experiment) instead of PMTs, which were used in the previous measurement. We have developed an optimized SiPM module, based on a 16-channel SiPM array. Key operational parameters are characterized, including gain and noise. The SiPM dark count rate, background light sensitivity, and optical crosstalk are found to all be well suppressed and more than sufficient for the ACME III application.Comment: 10 pages, 6 figures, proceedings for NDIP2

Ice Nucleating Particle Connections to Regional Argentinian Land Surface Emissions and Weather During the Cloud, Aerosol, and Complex Terrain Interactions Experiment

Here, we present a multi-season study of ice-nucleating particles (INPs) active via the immersion freezing mechanism, which took place in north-central Argentina, a worldwide hotspot for mesoscale convective storms. INPs were measured untreated, after heating to 95°C, and after hydrogen peroxide digestion. No seasonal cycle of INP concentrations was observed. Heat labile INPs, which we define as “biological” herein, dominated the population active at −5 to −20°C, while non-heat-labile organic INPs (decomposed by peroxide) dominated at lower temperatures, from −20 to −28°C. Inorganic INPs (remaining after peroxide digestion), were minor contributors to the overall INP activity. Biological INP concentration active around −12°C peaked during rain events and under high relative humidity, reflecting emission mechanisms independent of the background aerosol concentration. The ratio of non-heat-labile organic and inorganic INPs was generally constant, suggesting they originated from the same source, presumably from regional arable topsoil based on air mass histories. Single particle mass spectrometry showed that soil particles aerosolized from a regionally common agricultural topsoil contained known mineral INP sources (K-feldspar and illite) as well as a significant organic component. The INP activity observed in this study correlates well with agricultural soil INP activities from this and other regions of the world, suggesting that the observed INP spectra might be typical of many arable landscapes. These results demonstrate the strong influence of regional continental landscapes, emitting INPs of types that are not yet well represented in global models

Fast x-ray detector system with simultaneous measurement of timing and energy for a single photon

We developed a fast X-ray detector system for nuclear resonant scattering (NRS) experiments. Our system employs silicon avalanche photo-diode (Si-APD) as a fast X-ray sensor. The system is able to acquire both timing and energy of a single X-ray photon simultaneously in a high rate condition, 106 counts per second for one Si-APD. The performance of the system was investigated in SPring-8, a synchrotron radiation facility in Japan. Good time resolution of 120 ps (FWHM) was achieved with a slight tail distribution in the time spectrum by a level of 10-9 at 1 ns apart from the peak. Using this system, we successfully observed the NRS from the 26.27-keV level of mercury-201, which has a half-life of 630(50) ps. We also demonstrated the reduction of background events caused by radioactive decays in a radioactive sample by discriminating photon energy